A survey on dynamic spectrum access protocols for distributed cognitive wireless networks
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paper_title: Cognitive radio: making software radios more personal

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Software radios are emerging as platforms for multiband multimode personal communications systems. Radio etiquette is the set of RF bands, air interfaces, protocols, and spatial and temporal patterns that moderate the use of the radio spectrum. Cognitive radio extends the software radio with radio-domain model-based reasoning about such etiquettes. Cognitive radio enhances the flexibility of personal services through a radio knowledge representation language. This language represents knowledge of radio etiquette, devices, software modules, propagation, networks, user needs, and application scenarios in a way that supports automated reasoning about the needs of the user. This empowers software radios to conduct expressive negotiations among peers about the use of radio spectrum across fluents of space, time, and user context. With RKRL, cognitive radio agents may actively manipulate the protocol stack to adapt known etiquettes to better satisfy the user's needs. This transforms radio nodes from blind executors of predefined protocols to radio-domain-aware intelligent agents that search out ways to deliver the services the user wants even if that user does not know how to obtain them. Software radio provides an ideal platform for the realization of cognitive radio.
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paper_title: Dynamic spectrum management for cognitive radio: an overview

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The currently in use spectrum management policies are responsible for the poor utilization of the electromagnetic radio spectrum. By performing dynamic spectrum management (DSM), cognitive radio (CR) has the potential to increase the radio spectrum efficiency significantly and has gained a lot of attention recently. In this paper, we present an overview of the DSM problem in CR. After describing the CR briefly, the DSM is explained. In order to increase the spectrum utilization efficiency, CR tries to share the spectrum with primary users. We discuss two methods for spectrum-sharing, namely price-based spectrum-sharing and opportunistic spectrum-sharing. After introducing necessary mathematical definitions, the formulation of the DSM problem is presented. We show that the DSM problem is equivalent to a well-known graph-coloring problem (GCP) called list-coloring. Finding the exact solution for this problem is computationally intensive and various approximate algorithms have been proposed to obtain suboptimum solutions. Finally, we discuss two approaches for solving the DSM problem: centralized approach and decentralized approach. Decentralized approach, although has complicated design and may not achieve the global optimum solution, is more suitable for CR due to scalability and lower complexity. Copyright © 2009 John Wiley & Sons, Ltd.
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paper_title: CRAHNs : Cognitive radio ad hoc networks

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Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications. CR networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality-of-service (QoS) requirements. Specifically, in cognitive radio ad hoc networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, intrinsic properties and current research challenges of the CRAHNs are presented. First, novel spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. A particular emphasis is given to distributed coordination between CR users through the establishment of a common control channel. Moreover, the influence of these functions on the performance of the upper layer protocols, such as the network layer, and transport layer protocols are investigated and open research issues in these areas are also outlined. Finally, a new direction called the commons model is explained, where CRAHN users may independently regulate their own operation based on pre-decided spectrum etiquette.
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paper_title: Channel access protocols for multihop opportunistic networks: challenges and recent developments

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Heavy traffic over the unlicensed portion of the spectrum along with inefficient usage of the licensed spectrum gave impetus for a new spectrum allocation policy, the main purpose of which is to improve spectrum efficiency through opportunistic spectrum access. Cognitive radios have been proposed as a key enabling technology for such an opportunistic policy. One of the key challenges to enabling multihop CR communications is how to perform opportunistic medium access control while limiting the interference imposed on licensed users. In this article we highlight the unique characteristics of multihop cognitive radio networks, discuss key MAC design challenges specific to such networks, and present some of the work that has been done on MAC design for CRNs.
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paper_title: A survey on MAC protocols for cognitive radio networks

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In cognitive radio (CR) networks, identifying the available spectrum resource through spectrum sensing, deciding on the optimal sensing and transmission times, and coordinating with the other users for spectrum access are the important functions of the medium access control (MAC) protocols. In this survey, the characteristic features, advantages, and the limiting factors of the existing CR MAC protocols are thoroughly investigated for both infrastructure-based and ad hoc networks. First, an overview of the spectrum sensing is given, as it ensures that the channel access does not result in interference to the licensed users of the spectrum. Next, a detailed classification of the MAC protocols is presented while considering the infrastructure support, integration of spectrum sensing functionalities, the need for time synchronization, and the number of radio transceivers. The main challenges and future research directions are presented, while highlighting the close coupling of the MAC protocol design with the other layers of the protocol stack.
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paper_title: Comparison of Multichannel MAC Protocols

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This paper compares, through analysis and simulation, a number of multichannel MAC protocols. We first classify these protocols into four categories based on their principles of operation: dedicated control channel, common hopping, split phase, and parallel rendezvous protocols. We then examine the effects of the number of channels and devices, channel switching times, and traffic patterns on the throughput and delay of the protocols. Here are some of the conclusions of our study: (1) parallel rendezvous protocols generally perform better than single rendezvous protocols, (2) the dedicated control channel protocol can be a good approach with its simplicity when the number of channels is high and the packets are long, and (3) the split phase protocol is very sensitive to the durations of the control and data phases. Our study focuses on a single collision domain.
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paper_title: First Cognitive Radio Networking Standard for Personal/Portable Devices in TV White Spaces

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Recent FCC rules allowing unlicensed use on a secondary basis of the Television White Spaces (TVWS) promise a whole new set of possible applications. The first step towards realizing these applications is the creation and adoption of industry standards. In this paper we present the first such standard for personal/portable devices in the TVWS that complies fully with the existing FCC rules while retaining flexibility for use with other regulatory domains. We describe the physical (PHY) and medium access control (MAC) layers specified in the standard and present performance results to demonstrate the robustness and spectral efficiency of the proposed protocols.
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paper_title: Wireless medium access control protocols

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Technological advances, coupled with the flexibility and mobility of wireless systems, are the driving force behind the Anyone, Anywhere, Anytime paradigm of networking. At the same time, we see a convergence of the telephone, cable and data networks into a unified network that supports multimedia and real-time applications like voice and video in addition to data. Medium access control protocols define rules for orderly access to the shared medium and play a crucial role in the efficient and fair sharing of scarce wireless bandwidth. The nature of the wireless channel brings new issues like location-dependent carrier sensing, time varying channel and burst errors. Low power requirements and half duplex operation of the wireless systems add to the challenge. Wireless MAC protocols have been heavily researched and a plethora of protocols have been proposed. Protocols have been devised for different types of architectures, different applications and different media. This survey discusses the challenges in the design of wireless MAC protocols, classifies them based on architecture and mode of operation, and describes their relative performance and application domains in which they are best deployed.
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paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

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In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
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paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

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A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
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paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

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Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
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paper_title: A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Networks

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A cognitive radio (CR) network should be able to sense its environment and adapt communication to utilize the unused licensed spectrum without interfering with licensed users. In this paper, we look at CR-enabled networks with distributed control. As CR nodes need to hop from channel to channel to make the most use of the spectrum opportunities, we believe distributed multichannel medium access control (MAC) protocols to be key enablers for these networks. In addition to the spectrum scarcity, energy is rapidly becoming one of the major bottlenecks of wireless operations and has to be considered as a key design criterion. We present here an energy-efficient distributed multichannel MAC protocol for CR networks (MMAC-CR). Simulation results show that the proposed protocol significantly improves performance by borrowing the licensed spectrum and protects primary users (PUs) from interference, even in hidden terminal situations. Sensing costs are evaluated and shown to contribute only 5% to the total energy cost.
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paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

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We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
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paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

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Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
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paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

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The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
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paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

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We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
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paper_title: Eigenvalue-based spectrum sensing algorithms for cognitive radio

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Spectrum sensing is a fundamental component in a cognitive radio. In this paper, we propose new sensing methods based on the eigenvalues of the covariance matrix of signals received at the secondary users. In particular, two sensing algorithms are suggested, one is based on the ratio of the maximum eigenvalue to minimum eigenvalue; the other is based on the ratio of the average eigenvalue to minimum eigenvalue. Using some latest random matrix theories (RMT), we quantify the distributions of these ratios and derive the probabilities of false alarm and probabilities of detection for the proposed algorithms. We also find the thresholds of the methods for a given probability of false alarm. The proposed methods overcome the noise uncertainty problem, and can even perform better than the ideal energy detection when the signals to be detected are highly correlated. The methods can be used for various signal detection applications without requiring the knowledge of signal, channel and noise power. Simulations based on randomly generated signals, wireless microphone signals and captured ATSC DTV signals are presented to verify the effectiveness of the proposed methods.
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paper_title: Distributed Spectrum Sensing and Access in Cognitive Radio Networks With Energy Constraint

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We design distributed spectrum sensing and access strategies for opportunistic spectrum access (OSA) under an energy constraint on secondary users. Both the continuous and the bursty traffic models are considered for different applications of the secondary network. In each slot, a secondary user sequentially decides whether to sense, where in the spectrum to sense, and whether to access. By casting this sequential decision-making problem in the framework of partially observable Markov decision processes, we obtain stationary optimal spectrum sensing and access policies that maximize the throughput of the secondary user during its battery lifetime. We also establish threshold structures of the optimal policies and study the fundamental tradeoffs involved in the energy-constrained OSA design. Numerical results are provided to investigate the impact of the secondary user's residual energy on the optimal spectrum sensing and access decisions.
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paper_title: Optimal spectrum sensing framework for cognitive radio networks

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Spectrum sensing is the key enabling technology for cognitive radio networks. The main objective of spectrum sensing is to provide more spectrum access opportunities to cognitive radio users without interfering with the operations of the licensed network. Hence, recent research has been focused on the interference avoidance problem. Moreover, current radio frequency (RF) front-ends cannot perform sensing and transmission at the same time, which inevitably decreases their transmission opportunities, leading to the so-called sensing efficiency problem. In this paper, in order to solve both the interference avoidance and the spectrum efficiency problem, an optimal spectrum sensing framework is developed. More specifically, first a theoretical framework is developed to optimize the sensing parameters in such a way as to maximize the sensing efficiency subject to interference avoidance constraints. Second, in order to exploit multiple spectrum bands, spectrum selection and scheduling methods are proposed where the best spectrum bands for sensing are selected to maximize the sensing capacity. Finally, an adaptive and cooperative spectrum sensing method is proposed where the sensing parameters are optimized adaptively to the number of cooperating users. Simulation results show that the proposed sensing framework can achieve maximum sensing efficiency and opportunities in multi-user/multi-spectrum environments, satisfying interference constraints.
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paper_title: Multi-antenna based spectrum sensing for cognitive radios: A GLRT approach

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In this letter, we propose multi-antenna based spectrum sensing methods for cognitive radios (CRs) using the generalized likelihood ratio test (GLRT) paradigm. The proposed methods utilize the eigenvalues of the sample covariance matrix of the received signal vector from multiple antennas, taking advantage of the fact that in practice, the primary user signals to be detected will either occupy a subspace of dimension strictly smaller than the dimension of the observation space, or have a non-white spatial spectrum. These methods do not require prior knowledge of the primary user signals, or the channels from the primary users to the CR. By making different assumptions on the availability of the white noise power value at the CR receiver, we derive two algorithms that are shown to outperform the standard energy detector.
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paper_title: Joint Design and Separation Principle for Opportunistic Spectrum Access in the Presence of Sensing Errors

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Opportunistic spectrum access (OSA) that allows secondary users to independently search for and exploit instantaneous spectrum availability is considered. The design objective is to maximize the throughput of a secondary user while limiting the probability of colliding with primary users. Integrated in the joint design are three basic components: a spectrum sensor that identifies spectrum opportunities, a sensing strategy that determines which channels in the spectrum to sense, and an access strategy that decides whether to access based on potentially erroneous sensing outcomes. This joint design is formulated as a constrained partially observable Markov decision process (POMDP), and a separation principle is established. The separation principle reveals the optimality of myopic policies for the design of the spectrum sensor and the access strategy, leading to closed-form optimal solutions. Furthermore, it decouples the design of the sensing strategy from that of the spectrum sensor and the access strategy, and reduces the constrained POMDP to an unconstrained one. Numerical examples are provided to study the tradeoff between sensing time and transmission time, the interaction between the physical layer spectrum sensor and the MAC layer sensing and access strategies, and the robustness of the ensuing design to model mismatch.
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paper_title: Spectrum-Sensing Algorithms for Cognitive Radio Based on Statistical Covariances

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Spectrum sensing, i.e., detecting the presence of primary users in a licensed spectrum, is a fundamental problem in cognitive radio. Since the statistical covariances of the received signal and noise are usually different, they can be used to differentiate the case where the primary user's signal is present from the case where there is only noise. In this paper, spectrum-sensing algorithms are proposed based on the sample covariance matrix calculated from a limited number of received signal samples. Two test statistics are then extracted from the sample covariance matrix. A decision on the signal presence is made by comparing the two test statistics. Theoretical analysis for the proposed algorithms is given. Detection probability and the associated threshold are found based on the statistical theory. The methods do not need any information about the signal, channel, and noise power a priori. In addition, no synchronization is needed. Simulations based on narrow-band signals, captured digital television (DTV) signals, and multiple antenna signals are presented to verify the methods.
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paper_title: Opportunistic Spectrum Access for Energy-Constrained Cognitive Radios

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We consider a scenario in which a secondary user makes opportunistic use of a channel allocated to a primary network. The primary network operates in a time-slotted manner and switches between idle and active states according to a stationary Markovian process. At the beginning of each time slot, the secondary user can choose to stay idle or to carry out spectrum sensing to check if the primary network is idle or active. If the primary network is detected as idle, the secondary user can carry out data transmission. Spectrum sensing consumes energy and introduces false alarms and mis-detections. Given the delay cost associated with staying idle, the energy cost associated with spectrum sensing and data transmission, and the throughput gain associated with successful transmissions, the objective is to find an optimal sequence of idle/sensing actions, together with the optimal spectrum sensing durations, to maximize the expected net reward for the secondary user. We formulate this problem as a partially observable Markov decision process (POMDP) and obtain optimal control policies. Heuristic control policies that can be obtained at low complexity are also proposed.
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paper_title: On Myopic Sensing for Multi-Channel Opportunistic Access: Structure, Optimality, and Performance

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The invention relates to confectionery moulding apparatus through which moulds, each containing at least one mould cavity having minute holes in its base, are traversed successively by a conveyor. After filling with confectionery and subsequently cooling the moulds pass in inverted relation beneath a demoulding unit which blows air through the holes in the bases of the mould cavities to eject the confectionery from the cavities. To reduce the force required for demoulding each mould has a backing plate spaced from the perforated base of the mould cavity or each mould cavity to define an air chamber and the demoulding unit includes an air pipe which is brought into sealing engagement with a hole in the backing plate of each mould to deliver air into the chamber and so effect demoulding.
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paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

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The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
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paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

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A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
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paper_title: Polarization-Based Long-Range Communication Directional MAC Protocol for Cognitive Ad Hoc Networks

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Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.
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paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

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In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
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paper_title: Power control in cognitive radio networks: how to cross a multi-lane highway

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We consider power control in cognitive radio networks where secondary users identify and exploit instantaneous and local spectrum opportunities without causing unacceptable interference to primary users. We qualitatively characterize the impact of the transmission power of secondary users on the occurrence of spectrum opportunities and the reliability of opportunity detection. Based on a Poisson model of the primary network, we quantify these impacts by showing that (i) the probability of spectrum opportunity decreases exponentially with respect to the transmission power of secondary users, where the exponential decay constant is given by the traffic load of primary users; (ii) reliable opportunity detection is achieved in the two extreme regimes in terms of the ratio between the transmission power of secondary users and that of primary users. Such analytical characterizations allow us to study power control for optimal transport throughput under constraints on the interference to primary users. Furthermore, we reveal the difference between detecting primary signals and detecting spectrum opportunities, and demonstrate the complex relationship between physical layer spectrum sensing and MAC layer throughput. The dependency of this PHY-MAC interaction on the application type and the use of handshake signaling such as RTS/CTS is illustrated.
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paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

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Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
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paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

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In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
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paper_title: Stochastic Medium Access for Cognitive Radio Ad Hoc Networks

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In ad hoc cognitive radio (CR) networks, medium access control (MAC) design has been raised as a major challenge due to its highly dynamic nature and strong user diversity, particularly in situations where a dedicated control channel is not reserved among the distributed CR nodes. In this paper, we propose a novel Stochastic Medium Access (SMA) scheme that takes interference constraints into account to improve spectrum sharing efficiency. Specifically, the proposed SMA scheme is developed to serve in a CR network without dedicated control channels, such that the probability of successful channel accesses can be maximized. The formulated optimization problem is then solved by using a dynamic Markov-Chain Monte-Carlo scheme. Moreover, the paper introduces a suite of mechanisms for implementation of the proposed SMA scheme, including segmentation of long packets and contention resolution, which is working on top of power controlled Request-to-Send (RTS) and Clear-to-Send (CTS) exchanges in a multichannel environment. An analytical model is developed on the proposed SMA scheme using an absorbing Markov chain model to evaluate throughput of the secondary user network. Extensive simulation is conducted to study the impact of some important factors on the proposed SMA scheme, such as channel conditions and secondary traffic loads.
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paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: OS-MAC: An Efficient MAC Protocol for Spectrum-Agile Wireless Networks

paper_content:

Wireless networks and devices have been rapidly gaining popularity over their wired counterparts. This popularity, in turn, has been generating an explosive and ever-increasing demand for, and hence creating a shortage of, the radio spectrum. Existing studies indicate that this foreseen spectrum shortage is not so much due to the scarcity of the radio spectrum, but due to the inefficiency of current spectrum access methods, thus leaving spectrum opportunities along both the time and the frequency dimensions that wireless devices can exploit. Fortunately, recent technological advances have made it possible to build software-defined radios (SDRs) which, unlike traditional radios, can switch from one frequency band to another at little or no cost. We propose a MAC protocol, called Opportunistic Spectrum MAC (OS-MAC), for wireless networks equipped with cognitive radios like SDRs. OS-MAC (1) adaptively and dynamically seeks and exploits opportunities in both licensed and unlicensed spectra and along both the time and the frequency dimensions; (2) accesses and shares spectrum among different unlicensed and licensed users; and (3) coordinates with other unlicensed users for better spectrum utilization. Using extensive simulation, OS-MAC is shown to be far more effective than current access protocols from both the network's and the user's perspectives. By comparing its performance with an Ideal-MAC protocol, OS-MAC is also shown to not only outperform current access protocols, but also achieve performance very close to that obtainable under the Ideal-MAC protocol.
---
paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

paper_content:

In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: On designing MAC protocols for wireless networks using directional antennas

paper_content:

We investigate the possibility of using directional antennas for medium access control in wireless ad hoc networks. Previous research in ad hoc networks typically assumes the use of omnidirectional antennas at all nodes. With omnidirectional antennas, while two nodes are communicating using a given channel, MAC protocols such as IEEE 802.11 require all other nodes in the vicinity to remain silent. With directional antennas, two pairs of nodes located in each other's vicinity may potentially communicate simultaneously, increasing spatial reuse of the wireless channel. Range extension due to higher gain of directional antennas can also be useful in discovering fewer hop routes. However, new problems arise when using directional beams that simple modifications to 802.11 may not be able to mitigate. This paper identifies these problems and evaluates the tradeoffs associated with them. We also design a directional MAC protocol (MMAC) that uses multihop RTSs to establish links between distant nodes and then transmits CTS, DATA, and ACK over a single hop. While MMAC does not address all the problems identified with directional communication, it is an attempt to exploit the primary benefits of beamforming in the presence of some of these problems. Results show that MMAC can perform better than IEEE 802.11, although we find that the performance is dependent on the topology and flow patterns in the system.
---
paper_title: Polarization-Based Long-Range Communication Directional MAC Protocol for Cognitive Ad Hoc Networks

paper_content:

Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
---
paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

paper_content:

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

paper_content:

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: Cognitive radio: brain-empowered wireless communications

paper_content:

Cognitive radio is viewed as a novel approach for improving the utilization of a precious natural resource: the radio electromagnetic spectrum. The cognitive radio, built on a software-defined radio, is defined as an intelligent wireless communication system that is aware of its environment and uses the methodology of understanding-by-building to learn from the environment and adapt to statistical variations in the input stimuli, with two primary objectives in mind: /spl middot/ highly reliable communication whenever and wherever needed; /spl middot/ efficient utilization of the radio spectrum. Following the discussion of interference temperature as a new metric for the quantification and management of interference, the paper addresses three fundamental cognitive tasks. 1) Radio-scene analysis. 2) Channel-state estimation and predictive modeling. 3) Transmit-power control and dynamic spectrum management. This work also discusses the emergent behavior of cognitive radio.
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: Efficient multi-channel MAC protocol and channel allocation schemes for TDMA based cognitive radio networks

paper_content:

We propose a cross-layer based multi-channel Medium Access Control (MAC) protocol to maximize the utilization of the leftover spectrum of primary user channels in cognitive radio networks. This protocol integrates the spectrum sensing at Physical layer and the packet scheduling at the MAC layer for mobile ad-hoc networks. With a TDMA-based control channel, we have a scheme to handle collision. Moreover, our scheme is suitable for heterogeneous network with different device capabilities. We formulate the channel allocation problem as a constrained optimization problem and propose strategies to handle channel allocation based on graph theoretic principles, specifically using Weighted Bipartite Graph Matching technique. We name our proposed modeling as Weighted Bipartite Multi-Vertex Matching (WBMM) and describes three different schemes based on this model. We conduct extensive simulation studies to analyze and compare the performance of the proposed strategies.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

paper_content:

In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
---
paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

paper_content:

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Networks

paper_content:

A cognitive radio (CR) network should be able to sense its environment and adapt communication to utilize the unused licensed spectrum without interfering with licensed users. In this paper, we look at CR-enabled networks with distributed control. As CR nodes need to hop from channel to channel to make the most use of the spectrum opportunities, we believe distributed multichannel medium access control (MAC) protocols to be key enablers for these networks. In addition to the spectrum scarcity, energy is rapidly becoming one of the major bottlenecks of wireless operations and has to be considered as a key design criterion. We present here an energy-efficient distributed multichannel MAC protocol for CR networks (MMAC-CR). Simulation results show that the proposed protocol significantly improves performance by borrowing the licensed spectrum and protects primary users (PUs) from interference, even in hidden terminal situations. Sensing costs are evaluated and shown to contribute only 5% to the total energy cost.
---
paper_title: Polarization-Based Long-Range Communication Directional MAC Protocol for Cognitive Ad Hoc Networks

paper_content:

Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.
---
paper_title: Efficient multi-channel MAC protocol and channel allocation schemes for TDMA based cognitive radio networks

paper_content:

We propose a cross-layer based multi-channel Medium Access Control (MAC) protocol to maximize the utilization of the leftover spectrum of primary user channels in cognitive radio networks. This protocol integrates the spectrum sensing at Physical layer and the packet scheduling at the MAC layer for mobile ad-hoc networks. With a TDMA-based control channel, we have a scheme to handle collision. Moreover, our scheme is suitable for heterogeneous network with different device capabilities. We formulate the channel allocation problem as a constrained optimization problem and propose strategies to handle channel allocation based on graph theoretic principles, specifically using Weighted Bipartite Graph Matching technique. We name our proposed modeling as Weighted Bipartite Multi-Vertex Matching (WBMM) and describes three different schemes based on this model. We conduct extensive simulation studies to analyze and compare the performance of the proposed strategies.
---
paper_title: CRAHNs : Cognitive radio ad hoc networks

paper_content:

Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications. CR networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality-of-service (QoS) requirements. Specifically, in cognitive radio ad hoc networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, intrinsic properties and current research challenges of the CRAHNs are presented. First, novel spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. A particular emphasis is given to distributed coordination between CR users through the establishment of a common control channel. Moreover, the influence of these functions on the performance of the upper layer protocols, such as the network layer, and transport layer protocols are investigated and open research issues in these areas are also outlined. Finally, a new direction called the commons model is explained, where CRAHN users may independently regulate their own operation based on pre-decided spectrum etiquette.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: A survey on MAC protocols for cognitive radio networks

paper_content:

In cognitive radio (CR) networks, identifying the available spectrum resource through spectrum sensing, deciding on the optimal sensing and transmission times, and coordinating with the other users for spectrum access are the important functions of the medium access control (MAC) protocols. In this survey, the characteristic features, advantages, and the limiting factors of the existing CR MAC protocols are thoroughly investigated for both infrastructure-based and ad hoc networks. First, an overview of the spectrum sensing is given, as it ensures that the channel access does not result in interference to the licensed users of the spectrum. Next, a detailed classification of the MAC protocols is presented while considering the infrastructure support, integration of spectrum sensing functionalities, the need for time synchronization, and the number of radio transceivers. The main challenges and future research directions are presented, while highlighting the close coupling of the MAC protocol design with the other layers of the protocol stack.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

paper_content:

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
---
paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

paper_content:

In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

paper_content:

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: Stochastic Medium Access for Cognitive Radio Ad Hoc Networks

paper_content:

In ad hoc cognitive radio (CR) networks, medium access control (MAC) design has been raised as a major challenge due to its highly dynamic nature and strong user diversity, particularly in situations where a dedicated control channel is not reserved among the distributed CR nodes. In this paper, we propose a novel Stochastic Medium Access (SMA) scheme that takes interference constraints into account to improve spectrum sharing efficiency. Specifically, the proposed SMA scheme is developed to serve in a CR network without dedicated control channels, such that the probability of successful channel accesses can be maximized. The formulated optimization problem is then solved by using a dynamic Markov-Chain Monte-Carlo scheme. Moreover, the paper introduces a suite of mechanisms for implementation of the proposed SMA scheme, including segmentation of long packets and contention resolution, which is working on top of power controlled Request-to-Send (RTS) and Clear-to-Send (CTS) exchanges in a multichannel environment. An analytical model is developed on the proposed SMA scheme using an absorbing Markov chain model to evaluate throughput of the secondary user network. Extensive simulation is conducted to study the impact of some important factors on the proposed SMA scheme, such as channel conditions and secondary traffic loads.
---
paper_title: Prediction-Based Throughput Optimization for Dynamic Spectrum Access

paper_content:

Cognitive radio (CR) for dynamic spectrum sensing and access has been a hot research topic in recent years. To avoid collision with the primary users, secondary users need to sense the channels before transmitting on them, which is referred to as sensing time overhead. Our previous work shows that the spectral correlations between the channels within the same service are sufficiently high for accurate prediction, which can further be used to reduce the sensing time. With such motivation, in this paper, we propose a new definition, i.e., channel availability vector (CAV), to characterize the state information of a group of licensed channels by introducing spectrum prediction while focusing on the scenario of a single secondary user with multiple channels and leverage it by formulating the throughput optimization problem as a Markov decision process, which is further solved by our optimal sensing scheme and verified with the real spectrum measurement data. The results show that our prediction-based sensing scheme outperforms one existing work.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: Random Access Protocols for Collaborative Spectrum Sensing in Multi-Band Cognitive Radio Networks

paper_content:

In this paper, collaborative sensing and distributed detection are addressed in the context of multi-band cognitive radios. In a cognitive radio network, all the nodes may sense the spectrum simultaneously. They should then exchange their sensing results in order to improve the reliability of the detection. This exchange of information has to be done effectively to improve the bandwidth efficiency of the network. We propose a generalized medium access control (MAC) signaling protocol based on random access and study its performance through a thorough theoretical analysis. We begin with a nonadaptive protocol with fixed parameters. The numerical results obtained from analysis reveals that the fixed parameter protocol is not robust to the variation of the network conditions which, in general, are unknown a priori. We thus extend the proposed protocol to an adaptive one. Analysis of this adaptive protocol reveals its much superior performance. Our analysis covers a wide range of network conditions, including the case where some spectral activities may be hidden from a few of cognitive nodes and the case when a cognitive node senses only a subset of spectral bands. All theoretical results are corroborated through computer simulations.
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
---
paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

paper_content:

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: Stochastic Medium Access for Cognitive Radio Ad Hoc Networks

paper_content:

In ad hoc cognitive radio (CR) networks, medium access control (MAC) design has been raised as a major challenge due to its highly dynamic nature and strong user diversity, particularly in situations where a dedicated control channel is not reserved among the distributed CR nodes. In this paper, we propose a novel Stochastic Medium Access (SMA) scheme that takes interference constraints into account to improve spectrum sharing efficiency. Specifically, the proposed SMA scheme is developed to serve in a CR network without dedicated control channels, such that the probability of successful channel accesses can be maximized. The formulated optimization problem is then solved by using a dynamic Markov-Chain Monte-Carlo scheme. Moreover, the paper introduces a suite of mechanisms for implementation of the proposed SMA scheme, including segmentation of long packets and contention resolution, which is working on top of power controlled Request-to-Send (RTS) and Clear-to-Send (CTS) exchanges in a multichannel environment. An analytical model is developed on the proposed SMA scheme using an absorbing Markov chain model to evaluate throughput of the secondary user network. Extensive simulation is conducted to study the impact of some important factors on the proposed SMA scheme, such as channel conditions and secondary traffic loads.
---
paper_title: A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Networks

paper_content:

A cognitive radio (CR) network should be able to sense its environment and adapt communication to utilize the unused licensed spectrum without interfering with licensed users. In this paper, we look at CR-enabled networks with distributed control. As CR nodes need to hop from channel to channel to make the most use of the spectrum opportunities, we believe distributed multichannel medium access control (MAC) protocols to be key enablers for these networks. In addition to the spectrum scarcity, energy is rapidly becoming one of the major bottlenecks of wireless operations and has to be considered as a key design criterion. We present here an energy-efficient distributed multichannel MAC protocol for CR networks (MMAC-CR). Simulation results show that the proposed protocol significantly improves performance by borrowing the licensed spectrum and protects primary users (PUs) from interference, even in hidden terminal situations. Sensing costs are evaluated and shown to contribute only 5% to the total energy cost.
---
paper_title: Efficient multi-channel MAC protocol and channel allocation schemes for TDMA based cognitive radio networks

paper_content:

We propose a cross-layer based multi-channel Medium Access Control (MAC) protocol to maximize the utilization of the leftover spectrum of primary user channels in cognitive radio networks. This protocol integrates the spectrum sensing at Physical layer and the packet scheduling at the MAC layer for mobile ad-hoc networks. With a TDMA-based control channel, we have a scheme to handle collision. Moreover, our scheme is suitable for heterogeneous network with different device capabilities. We formulate the channel allocation problem as a constrained optimization problem and propose strategies to handle channel allocation based on graph theoretic principles, specifically using Weighted Bipartite Graph Matching technique. We name our proposed modeling as Weighted Bipartite Multi-Vertex Matching (WBMM) and describes three different schemes based on this model. We conduct extensive simulation studies to analyze and compare the performance of the proposed strategies.
---
paper_title: Prediction-Based Throughput Optimization for Dynamic Spectrum Access

paper_content:

Cognitive radio (CR) for dynamic spectrum sensing and access has been a hot research topic in recent years. To avoid collision with the primary users, secondary users need to sense the channels before transmitting on them, which is referred to as sensing time overhead. Our previous work shows that the spectral correlations between the channels within the same service are sufficiently high for accurate prediction, which can further be used to reduce the sensing time. With such motivation, in this paper, we propose a new definition, i.e., channel availability vector (CAV), to characterize the state information of a group of licensed channels by introducing spectrum prediction while focusing on the scenario of a single secondary user with multiple channels and leverage it by formulating the throughput optimization problem as a Markov decision process, which is further solved by our optimal sensing scheme and verified with the real spectrum measurement data. The results show that our prediction-based sensing scheme outperforms one existing work.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: Random Access Protocols for Collaborative Spectrum Sensing in Multi-Band Cognitive Radio Networks

paper_content:

In this paper, collaborative sensing and distributed detection are addressed in the context of multi-band cognitive radios. In a cognitive radio network, all the nodes may sense the spectrum simultaneously. They should then exchange their sensing results in order to improve the reliability of the detection. This exchange of information has to be done effectively to improve the bandwidth efficiency of the network. We propose a generalized medium access control (MAC) signaling protocol based on random access and study its performance through a thorough theoretical analysis. We begin with a nonadaptive protocol with fixed parameters. The numerical results obtained from analysis reveals that the fixed parameter protocol is not robust to the variation of the network conditions which, in general, are unknown a priori. We thus extend the proposed protocol to an adaptive one. Analysis of this adaptive protocol reveals its much superior performance. Our analysis covers a wide range of network conditions, including the case where some spectral activities may be hidden from a few of cognitive nodes and the case when a cognitive node senses only a subset of spectral bands. All theoretical results are corroborated through computer simulations.
---
paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

paper_content:

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: Stochastic Medium Access for Cognitive Radio Ad Hoc Networks

paper_content:

In ad hoc cognitive radio (CR) networks, medium access control (MAC) design has been raised as a major challenge due to its highly dynamic nature and strong user diversity, particularly in situations where a dedicated control channel is not reserved among the distributed CR nodes. In this paper, we propose a novel Stochastic Medium Access (SMA) scheme that takes interference constraints into account to improve spectrum sharing efficiency. Specifically, the proposed SMA scheme is developed to serve in a CR network without dedicated control channels, such that the probability of successful channel accesses can be maximized. The formulated optimization problem is then solved by using a dynamic Markov-Chain Monte-Carlo scheme. Moreover, the paper introduces a suite of mechanisms for implementation of the proposed SMA scheme, including segmentation of long packets and contention resolution, which is working on top of power controlled Request-to-Send (RTS) and Clear-to-Send (CTS) exchanges in a multichannel environment. An analytical model is developed on the proposed SMA scheme using an absorbing Markov chain model to evaluate throughput of the secondary user network. Extensive simulation is conducted to study the impact of some important factors on the proposed SMA scheme, such as channel conditions and secondary traffic loads.
---
paper_title: Efficient multi-channel MAC protocol and channel allocation schemes for TDMA based cognitive radio networks

paper_content:

We propose a cross-layer based multi-channel Medium Access Control (MAC) protocol to maximize the utilization of the leftover spectrum of primary user channels in cognitive radio networks. This protocol integrates the spectrum sensing at Physical layer and the packet scheduling at the MAC layer for mobile ad-hoc networks. With a TDMA-based control channel, we have a scheme to handle collision. Moreover, our scheme is suitable for heterogeneous network with different device capabilities. We formulate the channel allocation problem as a constrained optimization problem and propose strategies to handle channel allocation based on graph theoretic principles, specifically using Weighted Bipartite Graph Matching technique. We name our proposed modeling as Weighted Bipartite Multi-Vertex Matching (WBMM) and describes three different schemes based on this model. We conduct extensive simulation studies to analyze and compare the performance of the proposed strategies.
---
paper_title: Prediction-Based Throughput Optimization for Dynamic Spectrum Access

paper_content:

Cognitive radio (CR) for dynamic spectrum sensing and access has been a hot research topic in recent years. To avoid collision with the primary users, secondary users need to sense the channels before transmitting on them, which is referred to as sensing time overhead. Our previous work shows that the spectral correlations between the channels within the same service are sufficiently high for accurate prediction, which can further be used to reduce the sensing time. With such motivation, in this paper, we propose a new definition, i.e., channel availability vector (CAV), to characterize the state information of a group of licensed channels by introducing spectrum prediction while focusing on the scenario of a single secondary user with multiple channels and leverage it by formulating the throughput optimization problem as a Markov decision process, which is further solved by our optimal sensing scheme and verified with the real spectrum measurement data. The results show that our prediction-based sensing scheme outperforms one existing work.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

paper_content:

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
---
paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

paper_content:

In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

paper_content:

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Networks

paper_content:

A cognitive radio (CR) network should be able to sense its environment and adapt communication to utilize the unused licensed spectrum without interfering with licensed users. In this paper, we look at CR-enabled networks with distributed control. As CR nodes need to hop from channel to channel to make the most use of the spectrum opportunities, we believe distributed multichannel medium access control (MAC) protocols to be key enablers for these networks. In addition to the spectrum scarcity, energy is rapidly becoming one of the major bottlenecks of wireless operations and has to be considered as a key design criterion. We present here an energy-efficient distributed multichannel MAC protocol for CR networks (MMAC-CR). Simulation results show that the proposed protocol significantly improves performance by borrowing the licensed spectrum and protects primary users (PUs) from interference, even in hidden terminal situations. Sensing costs are evaluated and shown to contribute only 5% to the total energy cost.
---
paper_title: Prediction-Based Throughput Optimization for Dynamic Spectrum Access

paper_content:

Cognitive radio (CR) for dynamic spectrum sensing and access has been a hot research topic in recent years. To avoid collision with the primary users, secondary users need to sense the channels before transmitting on them, which is referred to as sensing time overhead. Our previous work shows that the spectral correlations between the channels within the same service are sufficiently high for accurate prediction, which can further be used to reduce the sensing time. With such motivation, in this paper, we propose a new definition, i.e., channel availability vector (CAV), to characterize the state information of a group of licensed channels by introducing spectrum prediction while focusing on the scenario of a single secondary user with multiple channels and leverage it by formulating the throughput optimization problem as a Markov decision process, which is further solved by our optimal sensing scheme and verified with the real spectrum measurement data. The results show that our prediction-based sensing scheme outperforms one existing work.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: Random Access Protocols for Collaborative Spectrum Sensing in Multi-Band Cognitive Radio Networks

paper_content:

In this paper, collaborative sensing and distributed detection are addressed in the context of multi-band cognitive radios. In a cognitive radio network, all the nodes may sense the spectrum simultaneously. They should then exchange their sensing results in order to improve the reliability of the detection. This exchange of information has to be done effectively to improve the bandwidth efficiency of the network. We propose a generalized medium access control (MAC) signaling protocol based on random access and study its performance through a thorough theoretical analysis. We begin with a nonadaptive protocol with fixed parameters. The numerical results obtained from analysis reveals that the fixed parameter protocol is not robust to the variation of the network conditions which, in general, are unknown a priori. We thus extend the proposed protocol to an adaptive one. Analysis of this adaptive protocol reveals its much superior performance. Our analysis covers a wide range of network conditions, including the case where some spectral activities may be hidden from a few of cognitive nodes and the case when a cognitive node senses only a subset of spectral bands. All theoretical results are corroborated through computer simulations.
---
paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

paper_content:

In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
---
paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

paper_content:

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: Stochastic Medium Access for Cognitive Radio Ad Hoc Networks

paper_content:

In ad hoc cognitive radio (CR) networks, medium access control (MAC) design has been raised as a major challenge due to its highly dynamic nature and strong user diversity, particularly in situations where a dedicated control channel is not reserved among the distributed CR nodes. In this paper, we propose a novel Stochastic Medium Access (SMA) scheme that takes interference constraints into account to improve spectrum sharing efficiency. Specifically, the proposed SMA scheme is developed to serve in a CR network without dedicated control channels, such that the probability of successful channel accesses can be maximized. The formulated optimization problem is then solved by using a dynamic Markov-Chain Monte-Carlo scheme. Moreover, the paper introduces a suite of mechanisms for implementation of the proposed SMA scheme, including segmentation of long packets and contention resolution, which is working on top of power controlled Request-to-Send (RTS) and Clear-to-Send (CTS) exchanges in a multichannel environment. An analytical model is developed on the proposed SMA scheme using an absorbing Markov chain model to evaluate throughput of the secondary user network. Extensive simulation is conducted to study the impact of some important factors on the proposed SMA scheme, such as channel conditions and secondary traffic loads.
---
paper_title: A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Networks

paper_content:

A cognitive radio (CR) network should be able to sense its environment and adapt communication to utilize the unused licensed spectrum without interfering with licensed users. In this paper, we look at CR-enabled networks with distributed control. As CR nodes need to hop from channel to channel to make the most use of the spectrum opportunities, we believe distributed multichannel medium access control (MAC) protocols to be key enablers for these networks. In addition to the spectrum scarcity, energy is rapidly becoming one of the major bottlenecks of wireless operations and has to be considered as a key design criterion. We present here an energy-efficient distributed multichannel MAC protocol for CR networks (MMAC-CR). Simulation results show that the proposed protocol significantly improves performance by borrowing the licensed spectrum and protects primary users (PUs) from interference, even in hidden terminal situations. Sensing costs are evaluated and shown to contribute only 5% to the total energy cost.
---
paper_title: Polarization-Based Long-Range Communication Directional MAC Protocol for Cognitive Ad Hoc Networks

paper_content:

Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.
---
paper_title: Efficient multi-channel MAC protocol and channel allocation schemes for TDMA based cognitive radio networks

paper_content:

We propose a cross-layer based multi-channel Medium Access Control (MAC) protocol to maximize the utilization of the leftover spectrum of primary user channels in cognitive radio networks. This protocol integrates the spectrum sensing at Physical layer and the packet scheduling at the MAC layer for mobile ad-hoc networks. With a TDMA-based control channel, we have a scheme to handle collision. Moreover, our scheme is suitable for heterogeneous network with different device capabilities. We formulate the channel allocation problem as a constrained optimization problem and propose strategies to handle channel allocation based on graph theoretic principles, specifically using Weighted Bipartite Graph Matching technique. We name our proposed modeling as Weighted Bipartite Multi-Vertex Matching (WBMM) and describes three different schemes based on this model. We conduct extensive simulation studies to analyze and compare the performance of the proposed strategies.
---
paper_title: Prediction-Based Throughput Optimization for Dynamic Spectrum Access

paper_content:

Cognitive radio (CR) for dynamic spectrum sensing and access has been a hot research topic in recent years. To avoid collision with the primary users, secondary users need to sense the channels before transmitting on them, which is referred to as sensing time overhead. Our previous work shows that the spectral correlations between the channels within the same service are sufficiently high for accurate prediction, which can further be used to reduce the sensing time. With such motivation, in this paper, we propose a new definition, i.e., channel availability vector (CAV), to characterize the state information of a group of licensed channels by introducing spectrum prediction while focusing on the scenario of a single secondary user with multiple channels and leverage it by formulating the throughput optimization problem as a Markov decision process, which is further solved by our optimal sensing scheme and verified with the real spectrum measurement data. The results show that our prediction-based sensing scheme outperforms one existing work.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
---
paper_title: Random Access Protocols for Collaborative Spectrum Sensing in Multi-Band Cognitive Radio Networks

paper_content:

In this paper, collaborative sensing and distributed detection are addressed in the context of multi-band cognitive radios. In a cognitive radio network, all the nodes may sense the spectrum simultaneously. They should then exchange their sensing results in order to improve the reliability of the detection. This exchange of information has to be done effectively to improve the bandwidth efficiency of the network. We propose a generalized medium access control (MAC) signaling protocol based on random access and study its performance through a thorough theoretical analysis. We begin with a nonadaptive protocol with fixed parameters. The numerical results obtained from analysis reveals that the fixed parameter protocol is not robust to the variation of the network conditions which, in general, are unknown a priori. We thus extend the proposed protocol to an adaptive one. Analysis of this adaptive protocol reveals its much superior performance. Our analysis covers a wide range of network conditions, including the case where some spectral activities may be hidden from a few of cognitive nodes and the case when a cognitive node senses only a subset of spectral bands. All theoretical results are corroborated through computer simulations.
---
paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

paper_content:

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

Cognitive radios (CRs) have a great potential to improve spectrum utilization by enabling users to access the spectrum dynamically without disturbing licensed primary radios (PRs). A key challenge in operating these radios as a network is how to implement an efficient medium access control (MAC) mechanism that can adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most existing works address this issue via suboptimal heuristic approaches or centralized solutions. In this paper, we propose a novel joint power/channel allocation scheme that improves the performance through a distributed pricing approach. In this scheme, the spectrum allocation problem is modeled as a noncooperative game, with each CR pair acting as a player. A price-based iterative water-filling (PIWF) algorithm is proposed, which enables CR users to reach a good Nash equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved through pricing. Depending on the different orders according to which CRs take actions, we study sequential and parallel versions of the PIWF algorithm. We show that the parallel version converges faster than the sequential version. We then propose a corresponding MAC protocol to implement our resource management schemes. The proposed MAC allows multiple CR pairs to be first involved in an admission phase, then iteratively negotiate their transmission powers and spectrum via control-packet exchanges. Following the negotiation phase, CRs proceed concurrently with their data transmissions. Simulations are used to study the performance of our protocol and demonstrate its effectiveness in terms of improving the overall network throughput and reducing the average power consumption.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
---
paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
---
paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
---
paper_title: Stochastic Medium Access for Cognitive Radio Ad Hoc Networks

paper_content:

In ad hoc cognitive radio (CR) networks, medium access control (MAC) design has been raised as a major challenge due to its highly dynamic nature and strong user diversity, particularly in situations where a dedicated control channel is not reserved among the distributed CR nodes. In this paper, we propose a novel Stochastic Medium Access (SMA) scheme that takes interference constraints into account to improve spectrum sharing efficiency. Specifically, the proposed SMA scheme is developed to serve in a CR network without dedicated control channels, such that the probability of successful channel accesses can be maximized. The formulated optimization problem is then solved by using a dynamic Markov-Chain Monte-Carlo scheme. Moreover, the paper introduces a suite of mechanisms for implementation of the proposed SMA scheme, including segmentation of long packets and contention resolution, which is working on top of power controlled Request-to-Send (RTS) and Clear-to-Send (CTS) exchanges in a multichannel environment. An analytical model is developed on the proposed SMA scheme using an absorbing Markov chain model to evaluate throughput of the secondary user network. Extensive simulation is conducted to study the impact of some important factors on the proposed SMA scheme, such as channel conditions and secondary traffic loads.
---
paper_title: A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Networks

paper_content:

A cognitive radio (CR) network should be able to sense its environment and adapt communication to utilize the unused licensed spectrum without interfering with licensed users. In this paper, we look at CR-enabled networks with distributed control. As CR nodes need to hop from channel to channel to make the most use of the spectrum opportunities, we believe distributed multichannel medium access control (MAC) protocols to be key enablers for these networks. In addition to the spectrum scarcity, energy is rapidly becoming one of the major bottlenecks of wireless operations and has to be considered as a key design criterion. We present here an energy-efficient distributed multichannel MAC protocol for CR networks (MMAC-CR). Simulation results show that the proposed protocol significantly improves performance by borrowing the licensed spectrum and protects primary users (PUs) from interference, even in hidden terminal situations. Sensing costs are evaluated and shown to contribute only 5% to the total energy cost.
---
paper_title: Prediction-Based Throughput Optimization for Dynamic Spectrum Access

paper_content:

Cognitive radio (CR) for dynamic spectrum sensing and access has been a hot research topic in recent years. To avoid collision with the primary users, secondary users need to sense the channels before transmitting on them, which is referred to as sensing time overhead. Our previous work shows that the spectral correlations between the channels within the same service are sufficiently high for accurate prediction, which can further be used to reduce the sensing time. With such motivation, in this paper, we propose a new definition, i.e., channel availability vector (CAV), to characterize the state information of a group of licensed channels by introducing spectrum prediction while focusing on the scenario of a single secondary user with multiple channels and leverage it by formulating the throughput optimization problem as a Markov decision process, which is further solved by our optimal sensing scheme and verified with the real spectrum measurement data. The results show that our prediction-based sensing scheme outperforms one existing work.
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paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
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paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
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paper_title: Random Access Protocols for Collaborative Spectrum Sensing in Multi-Band Cognitive Radio Networks

paper_content:

In this paper, collaborative sensing and distributed detection are addressed in the context of multi-band cognitive radios. In a cognitive radio network, all the nodes may sense the spectrum simultaneously. They should then exchange their sensing results in order to improve the reliability of the detection. This exchange of information has to be done effectively to improve the bandwidth efficiency of the network. We propose a generalized medium access control (MAC) signaling protocol based on random access and study its performance through a thorough theoretical analysis. We begin with a nonadaptive protocol with fixed parameters. The numerical results obtained from analysis reveals that the fixed parameter protocol is not robust to the variation of the network conditions which, in general, are unknown a priori. We thus extend the proposed protocol to an adaptive one. Analysis of this adaptive protocol reveals its much superior performance. Our analysis covers a wide range of network conditions, including the case where some spectral activities may be hidden from a few of cognitive nodes and the case when a cognitive node senses only a subset of spectral bands. All theoretical results are corroborated through computer simulations.
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paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

paper_content:

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
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paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
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paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
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paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

paper_content:

In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
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paper_title: Decentralized cognitive MAC for opportunistic spectrum access in ad hoc networks: A POMDP framework

paper_content:

We propose decentralized cognitive MAC protocols that allow secondary users to independently search for spectrum opportunities without a central coordinator or a dedicated communication channel. Recognizing hardware and energy constraints, we assume that a secondary user may not be able to perform full-spectrum sensing or may not be willing to monitor the spectrum when it has no data to transmit. We develop an analytical framework for opportunistic spectrum access based on the theory of partially observable Markov decision process (POMDP). This decision-theoretic approach integrates the design of spectrum access protocols at the MAC layer with spectrum sensing at the physical layer and traffic statistics determined by the application layer of the primary network. It also allows easy incorporation of spectrum sensing error and constraint on the probability of colliding with the primary users. Under this POMDP framework, we propose cognitive MAC protocols that optimize the performance of secondary users while limiting the interference perceived by primary users. A suboptimal strategy with reduced complexity yet comparable performance is developed. Without additional control message exchange between the secondary transmitter and receiver, the proposed decentralized protocols ensure synchronous hopping in the spectrum between the transmitter and the receiver in the presence of collisions and spectrum sensing errors
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paper_title: Optimality of Myopic Sensing in Multi-Channel Opportunistic Access

paper_content:

We consider opportunistic communications over multiple channels where the state ("good" or "bad") of each channel evolves as independent and identically distributed Markov processes. A user, with limited sensing and access capability, chooses one channel to sense and subsequently access (based on the sensed channel state) in each time slot. A reward is obtained when the user senses and accesses a "good" channel. The objective is to design the optimal channel selection policy that maximizes the expected reward accrued over time. This problem can be generally formulated as a Partially Observable Markov Decision Process (POMDP) or a restless multi-armed bandit process, to which optimal solutions are often intractable. We show in this paper that the myopic policy, with a simple and robust structure, achieves optimality under certain conditions. This result finds applications in opportunistic communications in fading environment, cognitive radio networks for spectrum overlay, and resource-constrained jamming and anti-jamming.
---
paper_title: Polarization-Based Long-Range Communication Directional MAC Protocol for Cognitive Ad Hoc Networks

paper_content:

Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.
---
paper_title: Efficient multi-channel MAC protocol and channel allocation schemes for TDMA based cognitive radio networks

paper_content:

We propose a cross-layer based multi-channel Medium Access Control (MAC) protocol to maximize the utilization of the leftover spectrum of primary user channels in cognitive radio networks. This protocol integrates the spectrum sensing at Physical layer and the packet scheduling at the MAC layer for mobile ad-hoc networks. With a TDMA-based control channel, we have a scheme to handle collision. Moreover, our scheme is suitable for heterogeneous network with different device capabilities. We formulate the channel allocation problem as a constrained optimization problem and propose strategies to handle channel allocation based on graph theoretic principles, specifically using Weighted Bipartite Graph Matching technique. We name our proposed modeling as Weighted Bipartite Multi-Vertex Matching (WBMM) and describes three different schemes based on this model. We conduct extensive simulation studies to analyze and compare the performance of the proposed strategies.
---
paper_title: Distributed Spectrum Sensing and Access in Cognitive Radio Networks With Energy Constraint

paper_content:

We design distributed spectrum sensing and access strategies for opportunistic spectrum access (OSA) under an energy constraint on secondary users. Both the continuous and the bursty traffic models are considered for different applications of the secondary network. In each slot, a secondary user sequentially decides whether to sense, where in the spectrum to sense, and whether to access. By casting this sequential decision-making problem in the framework of partially observable Markov decision processes, we obtain stationary optimal spectrum sensing and access policies that maximize the throughput of the secondary user during its battery lifetime. We also establish threshold structures of the optimal policies and study the fundamental tradeoffs involved in the energy-constrained OSA design. Numerical results are provided to investigate the impact of the secondary user's residual energy on the optimal spectrum sensing and access decisions.
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paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: Joint Design and Separation Principle for Opportunistic Spectrum Access in the Presence of Sensing Errors

paper_content:

Opportunistic spectrum access (OSA) that allows secondary users to independently search for and exploit instantaneous spectrum availability is considered. The design objective is to maximize the throughput of a secondary user while limiting the probability of colliding with primary users. Integrated in the joint design are three basic components: a spectrum sensor that identifies spectrum opportunities, a sensing strategy that determines which channels in the spectrum to sense, and an access strategy that decides whether to access based on potentially erroneous sensing outcomes. This joint design is formulated as a constrained partially observable Markov decision process (POMDP), and a separation principle is established. The separation principle reveals the optimality of myopic policies for the design of the spectrum sensor and the access strategy, leading to closed-form optimal solutions. Furthermore, it decouples the design of the sensing strategy from that of the spectrum sensor and the access strategy, and reduces the constrained POMDP to an unconstrained one. Numerical examples are provided to study the tradeoff between sensing time and transmission time, the interaction between the physical layer spectrum sensor and the MAC layer sensing and access strategies, and the robustness of the ensuing design to model mismatch.
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paper_title: Opportunistic Spectrum Access for Energy-Constrained Cognitive Radios

paper_content:

We consider a scenario in which a secondary user makes opportunistic use of a channel allocated to a primary network. The primary network operates in a time-slotted manner and switches between idle and active states according to a stationary Markovian process. At the beginning of each time slot, the secondary user can choose to stay idle or to carry out spectrum sensing to check if the primary network is idle or active. If the primary network is detected as idle, the secondary user can carry out data transmission. Spectrum sensing consumes energy and introduces false alarms and mis-detections. Given the delay cost associated with staying idle, the energy cost associated with spectrum sensing and data transmission, and the throughput gain associated with successful transmissions, the objective is to find an optimal sequence of idle/sensing actions, together with the optimal spectrum sensing durations, to maximize the expected net reward for the secondary user. We formulate this problem as a partially observable Markov decision process (POMDP) and obtain optimal control policies. Heuristic control policies that can be obtained at low complexity are also proposed.
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paper_title: On Myopic Sensing for Multi-Channel Opportunistic Access: Structure, Optimality, and Performance

paper_content:

The invention relates to confectionery moulding apparatus through which moulds, each containing at least one mould cavity having minute holes in its base, are traversed successively by a conveyor. After filling with confectionery and subsequently cooling the moulds pass in inverted relation beneath a demoulding unit which blows air through the holes in the bases of the mould cavities to eject the confectionery from the cavities. To reduce the force required for demoulding each mould has a backing plate spaced from the perforated base of the mould cavity or each mould cavity to define an air chamber and the demoulding unit includes an air pipe which is brought into sealing engagement with a hole in the backing plate of each mould to deliver air into the chamber and so effect demoulding.
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paper_title: DH-MAC: A Dynamic Channel Hopping MAC Protocol for Cognitive Radio Networks

paper_content:

In this paper, we propose a channel-hopping MAC protocol called dynamic hopping MAC (DH-MAC) to improve the utilization of spectrum in cognitive radio networks. In DH-MAC, each secondary user (SU) switches its operation channel with a channel-hopping sequence which is adaptive to the activity of primary users (PUs). Our proposed DH-MAC mechanism enjoys the following merits. 1) It needs no dedicated common control channel for operation. 2) It supports multiple rendezvous for multiple simultaneous transmission pairs of SUs within the interfering range. 3) The rendezvous channel of two SUs will not be blocked by PUs for a long time. 4) It allows SUs a higher probability to operate on available channels as compared with existing schemes. 5) One cognitive radio transceiver is sufficient. The simulation results show that DH-MAC outperforms existing schemes in terms of higher aggregate throughput and more robustness to the disturbance of PUs.
---
paper_title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks

paper_content:

A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.
---
paper_title: Cooperative Adaptive Spectrum Sharing in Cognitive Radio Networks

paper_content:

The cognitive radio (CR) paradigm calls for open spectrum access according to a predetermined etiquette. Under this paradigm, CR nodes access the spectrum opportunistically by continuously monitoring the operating channels. A key challenge in this domain is how the nodes in a CR network (CRN) cooperate to access the medium in order to maximize the CRN throughput. Typical multichannel MAC protocols assume that frequency channels are adjacent and that there are no constraints on the transmission power. However, a CRN may operate over a wide range of frequencies, and a power mask is often enforced on the transmission of a CR user to avoid corrupting the transmissions of spectrum-licensed primary-radio (PR) users. To avoid unnecessary blocking of CR transmissions, we propose a novel distance-dependent MAC protocol for CRNs. Our protocol, called DDMAC, attempts to maximize the CRN throughput. It uses a novel probabilistic channel assignment mechanism that exploits the dependence between the signal's attenuation model and the transmission distance while considering the traffic profile. DDMAC allows a pair of CR users to communicate on a channel that may not be optimal from one user's perspective, but that allows more concurrent transmissions to take place, especially under moderate and high traffic loads. Simulation results indicate that, compared to typical multichannel CSMA-based protocols, DDMAC reduces the blocking rate of CR requests by up to 30%, which consequently improves the network throughput.
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paper_title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management

paper_content:

Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.
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paper_title: Price-Based Spectrum Management in Cognitive Radio Networks

paper_content:

A key challenge in operating cognitive radios (CRs) in a self-organizing (ad hoc) network is how to adaptively and efficiently allocate transmission powers and spectrum among CRs according to the surrounding environment. Most previous works address this issue via heuristic approaches or using centralized solutions. In this paper, we present a novel joint power/channel allocation scheme that uses a distributed pricing strategy to improve the network's performance. In this scheme, the spectrum allocation problem is modelled as a non-cooperative game. A price-based iterative water-filling (PIWF) algorithm is proposed, which allows users to converge to the Nash Equilibrium (NE). This PIWF algorithm can be implemented distributively with CRs repeatedly negotiating their best transmission powers and spectrum. Simulation results show that the social optimality of the NE solution is dramatically improved with our price-based strategy. Based on the orders by which CRs take actions, we study sequential and parallel versions of the algorithm. We show that the parallel version converges faster than the sequential version.
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paper_title: Stochastic Medium Access for Cognitive Radio Ad Hoc Networks

paper_content:

In ad hoc cognitive radio (CR) networks, medium access control (MAC) design has been raised as a major challenge due to its highly dynamic nature and strong user diversity, particularly in situations where a dedicated control channel is not reserved among the distributed CR nodes. In this paper, we propose a novel Stochastic Medium Access (SMA) scheme that takes interference constraints into account to improve spectrum sharing efficiency. Specifically, the proposed SMA scheme is developed to serve in a CR network without dedicated control channels, such that the probability of successful channel accesses can be maximized. The formulated optimization problem is then solved by using a dynamic Markov-Chain Monte-Carlo scheme. Moreover, the paper introduces a suite of mechanisms for implementation of the proposed SMA scheme, including segmentation of long packets and contention resolution, which is working on top of power controlled Request-to-Send (RTS) and Clear-to-Send (CTS) exchanges in a multichannel environment. An analytical model is developed on the proposed SMA scheme using an absorbing Markov chain model to evaluate throughput of the secondary user network. Extensive simulation is conducted to study the impact of some important factors on the proposed SMA scheme, such as channel conditions and secondary traffic loads.
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paper_title: A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Networks

paper_content:

A cognitive radio (CR) network should be able to sense its environment and adapt communication to utilize the unused licensed spectrum without interfering with licensed users. In this paper, we look at CR-enabled networks with distributed control. As CR nodes need to hop from channel to channel to make the most use of the spectrum opportunities, we believe distributed multichannel medium access control (MAC) protocols to be key enablers for these networks. In addition to the spectrum scarcity, energy is rapidly becoming one of the major bottlenecks of wireless operations and has to be considered as a key design criterion. We present here an energy-efficient distributed multichannel MAC protocol for CR networks (MMAC-CR). Simulation results show that the proposed protocol significantly improves performance by borrowing the licensed spectrum and protects primary users (PUs) from interference, even in hidden terminal situations. Sensing costs are evaluated and shown to contribute only 5% to the total energy cost.
---
paper_title: Polarization-Based Long-Range Communication Directional MAC Protocol for Cognitive Ad Hoc Networks

paper_content:

Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.
---
paper_title: Efficient multi-channel MAC protocol and channel allocation schemes for TDMA based cognitive radio networks

paper_content:

We propose a cross-layer based multi-channel Medium Access Control (MAC) protocol to maximize the utilization of the leftover spectrum of primary user channels in cognitive radio networks. This protocol integrates the spectrum sensing at Physical layer and the packet scheduling at the MAC layer for mobile ad-hoc networks. With a TDMA-based control channel, we have a scheme to handle collision. Moreover, our scheme is suitable for heterogeneous network with different device capabilities. We formulate the channel allocation problem as a constrained optimization problem and propose strategies to handle channel allocation based on graph theoretic principles, specifically using Weighted Bipartite Graph Matching technique. We name our proposed modeling as Weighted Bipartite Multi-Vertex Matching (WBMM) and describes three different schemes based on this model. We conduct extensive simulation studies to analyze and compare the performance of the proposed strategies.
---
paper_title: Cross-Layer Based Opportunistic MAC Protocols for QoS Provisionings Over Cognitive Radio Wireless Networks

paper_content:

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
---
paper_title: CREAM-MAC: Cognitive Radio-EnAbled Multi-Channel MAC Protocol Over Dynamic Spectrum Access Networks

paper_content:

As the novel and effective approach to improving the utilization of the precious radio spectrum, cognitive radio technology is the key to realize the dynamic spectrum access (DSA) networks, where the secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that confines the level of interference to the range the primary (licensed) users can tolerate. However, there are many new challenges associated with cognitive-radio-based DSA networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability differs for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the cooperative sequential spectrum sensing at physical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential spectrum sensing scheme improves the accuracy of spectrum sensing and further protects the primary users. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. We develop the Markov chain model and M/GY/1 queueing model to rigorously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conduct extensive simulations to validate our developed protocol and analytical models.
---
paper_title: A Throughput-Aimed MAC Protocol with QoS Provision for Cognitive Ad Hoc Networks

paper_content:

In this letter, we propose a Throughput-aimed MAC Protocol with Quality of Service (QoS) provision (T-MAC) for cognitive Ad Hoc networks. This protocol operates based on the Time Division Multiple Access (TDMA) slot assignments and the power control mechanism, which can improve the QoS provision and network throughput. Our simulation results show that the T-MAC protocol can efficiently increase the network throughput and reduce the access delay.
---
paper_title: Synchronized MAC Protocol For Multi-Hop Cognitive Radio Networks

paper_content:

Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.
---
paper_title: DCR-MAC: distributed cognitive radio MAC protocol for wireless ad hoc networks

paper_content:

The MAC protocol for a cognitive radio network should allow access to unused spectrum holes without (or with minimal) interference to incumbent system devices. To achieve this main goal, in this paper a distributed cognitive radio MAC (DCR-MAC) protocol is proposed for wireless ad hoc networks that provides for the detection and protection of incumbent systems around the communication pair. DCR-MAC operates over a separate common control channel and multiple data channels; hence, it is able to deal with dynamics of resource availability effectively in cognitive networks. A new type of hidden node problem is introduced that focuses on possible signal collisions between incumbent devices and cognitive radio ad hoc devices. To this end, a simple and efficient sensing information exchange mechanism between neighbor nodes with little overhead is proposed. In DCR-MAC, each ad hoc node maintains a channel status table with explicit and implicit channel sensing methods. Before a data transmission, to select an optimal data channel, a reactive neighbor information exchange is carried out. Simulation results show that the proposed distributed cognitive radio MAC protocol can greatly reduce interference to the neighbor incumbent devices. A higher number of neighbor nodes leads to better protection of incumbent devices. Copyright © 2008 John Wiley & Sons, Ltd.
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paper_title: Random Access Protocols for Collaborative Spectrum Sensing in Multi-Band Cognitive Radio Networks

paper_content:

In this paper, collaborative sensing and distributed detection are addressed in the context of multi-band cognitive radios. In a cognitive radio network, all the nodes may sense the spectrum simultaneously. They should then exchange their sensing results in order to improve the reliability of the detection. This exchange of information has to be done effectively to improve the bandwidth efficiency of the network. We propose a generalized medium access control (MAC) signaling protocol based on random access and study its performance through a thorough theoretical analysis. We begin with a nonadaptive protocol with fixed parameters. The numerical results obtained from analysis reveals that the fixed parameter protocol is not robust to the variation of the network conditions which, in general, are unknown a priori. We thus extend the proposed protocol to an adaptive one. Analysis of this adaptive protocol reveals its much superior performance. Our analysis covers a wide range of network conditions, including the case where some spectral activities may be hidden from a few of cognitive nodes and the case when a cognitive node senses only a subset of spectral bands. All theoretical results are corroborated through computer simulations.
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paper_title: MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

paper_content:

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).
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paper_title: First Cognitive Radio Networking Standard for Personal/Portable Devices in TV White Spaces

paper_content:

Recent FCC rules allowing unlicensed use on a secondary basis of the Television White Spaces (TVWS) promise a whole new set of possible applications. The first step towards realizing these applications is the creation and adoption of industry standards. In this paper we present the first such standard for personal/portable devices in the TVWS that complies fully with the existing FCC rules while retaining flexibility for use with other regulatory domains. We describe the physical (PHY) and medium access control (MAC) layers specified in the standard and present performance results to demonstrate the robustness and spectral efficiency of the proposed protocols.
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Title: A Survey on Dynamic Spectrum Access Protocols for Distributed Cognitive Wireless Networks

Section 1: Introduction
Description 1: Introduce the motivation, background, and scope of the paper, including the significance of dynamic spectrum access (DSA) in cognitive radio (CR) technology and its impact on spectrum efficiency.

Section 2: Challenges for Distributed Dynamic Spectrum Access Protocols
Description 2: Discuss the key challenges faced in designing distributed DSA protocols, such as the common control channel problem, spectrum sensing scheduling, power control mechanisms, multi-channel hidden and exposed terminal problems, access coordination mechanisms, and mobility issues.

Section 3: Classifications for Distributed Dynamic Spectrum Access Protocols
Description 3: Present the classification of existing distributed DSA protocols based on various criteria, including spectrum sharing modes, spectrum allocation behaviors, spectrum access modes, the usage of a common control channel, spectrum usage strategies, the number of radios, and spectrum sensing techniques.

Section 4: Distributed Dynamic Spectrum Access Protocols
Description 4: Survey state-of-the-art distributed DSA protocols under different spectrum access modes, categorized into contention-based, slotted, and hybrid protocols. Discuss protocols' details, mechanisms, and comparative advantages.

Section 5: Cognitive Radio Standards
Description 5: Review ongoing standardization efforts related to CR technology, focusing on major standards like IEEE 802.22, Ecma 392, IEEE 802.11 AF, IEEE 802.19, and IEEE SCC 41, and their contributions to DSA protocols.

Section 6: Open Research Issues
Description 6: Explore open research issues and future directions in distributed DSA protocols, such as spectrum handoff mechanisms, spectrum prediction, adaptation of spectrum sharing modes, protocols based on cooperative spectrum sensing, and distributed collision avoidance mechanisms.

Section 7: Conclusions
Description 7: Summarize the key points discussed in the paper, including the current state of research, challenges, and future research directions in the field of distributed DSA protocols for cognitive wireless networks.