The Life Cycle of the Rendezvous Problem of Cognitive Radio Ad Hoc Networks: A Survey
---
paper_title: NeXt generation/dynamic spectrum access/cognitive Radio Wireless Networks: A Survey

paper_content:

Today's wireless networks are characterized by a fixed spectrum assignment policy. However, a large portion of the assigned spectrum is used sporadically and geographical variations in the utilization of assigned spectrum ranges from 15% to 85% with a high variance in time. The limited available spectrum and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum opportunistically. This new networking paradigm is referred to as NeXt Generation (xG) Networks as well as Dynamic Spectrum Access (DSA) and cognitive radio networks. The term xG networks is used throughout the paper. The novel functionalities and current research challenges of the xG networks are explained in detail. More specifically, a brief overview of the cognitive radio technology is provided and the xG network architecture is introduced. Moreover, the xG network functions such as spectrum management, spectrum mobility and spectrum sharing are explained in detail. The influence of these functions on the performance of the upper layer protocols such as routing and transport are investigated and open research issues in these areas are also outlined. Finally, the cross-layer design challenges in xG networks are discussed.
---
paper_title: An IEEE 802.11p-Based Multichannel MAC Scheme With Channel Coordination for Vehicular Ad Hoc Networks

paper_content:

In recent years, governments, standardization bodies, automobile manufacturers, and academia are working together to develop vehicular ad hoc network (VANET)-based communication technologies. VANETs apply multiple channels, i.e., control channel (CCH) and service channels (SCHs), to provide open public road safety services and the improve comfort and efficiency of driving. Based on the latest standard draft IEEE 802.11p and IEEE 1609.4, this paper proposes a variable CCH interval (VCI) multichannel medium access control (MAC) scheme, which can dynamically adjust the length ratio between CCH and SCHs. The scheme also introduces a multichannel coordination mechanism to provide contention-free access of SCHs. Markov modeling is conducted to optimize the intervals based on the traffic condition. Theoretical analysis and simulation results show that the proposed scheme is able to help IEEE 1609.4 MAC significantly enhance the saturated throughput of SCHs and reduce the transmission delay of service packets while maintaining the prioritized transmission of critical safety information on CCH.
---
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: 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: OSA-MAC: A MAC Protocol for Opportunistic Spectrum Access in Cognitive Radio Networks

paper_content:

We present a MAC protocol for opportunistic spec- trum access (OSA-MAC) in cognitive wireless networks. The proposed MAC protocol works in a multi-channel environment which is capable of performing channel sensing to discover spectrum opportunities. For this MAC protocol, two channel selection methods are considered which trade the implementation complexity with throughput improvement. We then analyze the saturation throughput performance of the proposed MAC protocol under scenarios where the probabilities for each channel to be available to different secondary flows are the same or different. We then derive analytically the probability of col- lision of secondary users with primary users due to sensing errors. This analysis can be used, for example, to determine the requirement of sensing accuracy for secondary users, and to design an admission control method. We present numerical results to demonstrate the throughput performance of the OSA- MAC protocol and applications of the proposed analytical model.
---
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: Efficient Recovery Control Channel Design in Cognitive Radio Ad Hoc Networks

paper_content:

A constantly available control channel facilitates control message exchange and spectrum coordination in cognitive radio (CR) ad hoc networks. When a dedicated control channel is unavailable, a control channel must be dynamically allocated in licensed channels and vacated for the presence of primary users (PUs). As a result, the establishment of such a control channel is a challenge. In this paper, an efficient recovery control channel (ERCC) design is proposed to address this challenge. This heuristic and distributed design approach is essentially based on the observed spectrum homogeneity in a neighborhood. By adaptively updating a list of channels commonly available to neighbors, each secondary user is able to efficiently establish new control channels among neighbors in response to PU activity changes. Therefore, a virtually “always on” control channel robust to PU activity can be realized by the proposed method. The contributions are summarized as follows: 1) The proposed method efficiently recovers control channels from PU activity changes and maintains network connectivity. 2) It extends the control channel coverage to facilitate broadcast and reduce control overhead and delay. 3) It minimizes the interference with PUs. Simulation results show that the proposed solution outperforms the classic group- and sequence-based solutions in the responsiveness to rapidly changing PU activity and the maintenance of connectivity. Furthermore, the increase in control channel coverage and the allocation of the highest quality channels to control channels can be well balanced with reliability and scalability in various network scenarios.
---
paper_title: Dynamic open spectrum sharing MAC protocol for wireless ad hoc networks

paper_content:

In legacy wireless communication systems, spectrum allocation is static, resulting in extremely low spectrum utilization. On the other hand, there is little spectrum left for allocation to an increasing number of emerging wireless applications. A promising approach to solving this paradox is opening up most of the spectrum for unlicensed spectrum users in ways that co-exist with legacy users. Following this direction, this paper proposes the dynamic open spectrum sharing (DOSS) MAC protocol. This protocol allows nodes to adaptively select an arbitrary spectrum for the incipient communication subject to spectrum availability. It offers real-time dynamic spectrum allocation and high spectrum utilization without relying on any infrastructure. It also coexists with legacy wireless applications, while avoiding the hidden and exposed terminal problems. We conduct theoretical analysis of the protocol, and study its performance via simulations. In addition, we covers the radio receiver design
---
paper_title: Thwarting Control-Channel Jamming Attacks from Inside Jammers

paper_content:

Coordination of network functions in wireless networks requires frequent exchange of control messages among participating nodes. Typically, such messages are transmitted over a universally known communication channel referred to as the control channel. Due to its critical role, this channel can become a prime target of Denial-of-Service (DoS) attacks. In this paper, we address the problem of preventing control-channel DoS attacks manifested in the form of jamming. We consider a sophisticated adversary who has knowledge of the protocol specifics and of the cryptographic quantities used to secure network operations. This type of adversary cannot be prevented by antijamming techniques that rely on shared secrets, such as spread spectrum. We propose new security metrics to quantify the ability of the adversary to deny access to the control channel, and introduce a randomized distributed scheme that allows nodes to establish and maintain the control channel in the presence of the jammer. Our method is applicable to networks with static or dynamically allocated spectrum. Furthermore, we propose two algorithms for unique identification of the set of compromised nodes, one for independently acting nodes and one for colluding nodes. Detailed theoretical evaluation of the security metrics and extensive simulation results are provided to demonstrate the efficiency of our methods in mitigating jamming and identifying compromised nodes.
---
paper_title: A frequency rendezvous approach for decentralized dynamic spectrum access networks

paper_content:

In this paper, we propose a transmission frequency rendezvous approach for secondary users deployed in decentralized dynamic spectrum access networks. Frequency rendezvous is a critical step in bootstrapping a wireless network that does not possess centralized control. Current techniques for enabling frequency rendezvous in decentralized dynamic spectrum access networks either require pre-existing infrastructure or use one of several simplifying assumptions regarding the architecture, such as the use of regularly spaced frequency channels for communications. Our proposed approach is designed to be operated in a strictly decentralized wireless networking environment, where no centralized control is present and the spectrum does not possess pre-defined channels. This is accomplished via a combination of receiver pilot tones, a tone scanning protocol, and transmitter/receiver handshaking process. In our proposed rendezvous algorithm, the most important step is pilot tone detection and receiver query. In order to realize a shortest search time for the target receiver, an efficient scanning rule should be employed. In this paper, three scanning rules are proposed and evaluated, namely: frequency sequence scanning, pilot tone strength scanning, and cluster scanning. To validate our result, we test our scanning rules with actual paging band spectrum measurements.
---
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: Rendezvous for Cognitive Radios

paper_content:

Cognitive radios have been touted as a solution to communicating in a Dynamic Spectrum Access environment. This paper examines how cognitive radios initially find one another among the expanse of ever-changing open spectrum, termed the rendezvous problem. Specifically, it addresses the problem of rendezvous under varying levels of system capabilities, spectrum policies, and environmental conditions. The focus is on rendezvous when there are are no control channels or centralized controllers, which we term the blind rendezvous problem. Under these conditions, a sequence-based and modular clock blind rendezvous algorithms are proposed, and it is shown that the performance of these algorithms compares favorably to that of a random blind rendezvous algorithm. Specifically, the sequence-based algorithm provides a bounded Time To Rendezvous (TTR) and the ability to prioritize channels where rendezvous is more likely to occur; the modular clock algorithm reduces the expected TTR, requires little precoordination among radios attempting to rendezvous, and is robust to radios sensing different sets of available channels.
---
paper_title: A distributed broadcast protocol in multi-hop cognitive radio ad hoc networks without a common control channel

paper_content:

Broadcast is an important operation in wireless ad hoc networks where control information is usually propagated as broadcasts for the realization of most networking protocols. In traditional ad hoc networks, since the spectrum availability is uniform, broadcasts are delivered via a common channel which can be heard by all users in a network. However, in cognitive radio (CR) ad hoc networks, different unlicensed users may acquire different available channel sets. This non-uniform spectrum availability imposes special design challenges for broadcasting in CR ad hoc networks. In this paper, a fully-distributed broadcast protocol in multi-hop CR ad hoc networks without a common control channel is proposed. In our design, we consider practical scenarios that each unlicensed user is not assumed to be aware of the global network topology, the spectrum availability information of other users, and time synchronization information. By intelligently downsizing the original available channel set and designing the broadcasting sequences and scheduling schemes, our proposed broadcast protocol can provide very high successful broadcast ratio while achieving the shortest average broadcast delay. It can also eliminate broadcast collisions. To the best of our knowledge, this is the first work that addresses the broadcasting challenges specifically in multi-hop CR ad hoc networks under practical scenarios.
---
paper_title: A Channel Rendezvous Scheme for Cognitive Radio Networks

paper_content:

Cognitive radio networks need to utilize available spectrum in a dynamic and opportunistic fashion without causing interference to co-located primary nodes. Before data transmission begins, secondary nodes must establish a link on a channel which is not occupied by primary nodes. Unfortunately, in cognitive radio networks, the set of available channels can be different for each node, since it is determined by the relative locations of nodes to primary nodes. We are the first to present a distributed channel rendezvous scheme which finds a commonly available channel between any two nodes in a bounded time without synchronization. Our scheme determines the order, in which two nodes visit channels to find a common channel, if any, within a bounded time.
---
paper_title: Parallel Link Rendezvous in Ad Hoc Cognitive Radio Networks

paper_content:

A Cognitive Radio (CR) network seeks to access and utilize the unused license spectrum portions. These portions have dynamic behavior that introduces challenge for the CR user to allocate and rendezvous on the same portion. In CR Ad-hoc Network (CRAHN), there is difficulty of maintaining a Common Control Channel (CCC); for that, CRAHN requires a protocol able to guarantee users rendezvous without CCC. This paper proposes a distributed Medium Access Control (MAC) protocol using the concept of Balanced Incomplete Block Design (BIBD) to achieve a rendezvous channel without a CCC or synchronization. If the channels of a network are assigned to the BIBD elements and the searching sequence to the BIBD block, there is a guarantee of a rendezvous in at least one channel for each searching sequence. Simulation results confirm that the protocols outperform other protocols with respect to Time to Rendezvous (TTR), channel utilization, network throughput, and percentage of collisions between the SU and the PU network. In addition, the protocols fairly distribute the network load on channels, and share the channels fairly among network nodes.
---
paper_title: NeXt generation/dynamic spectrum access/cognitive Radio Wireless Networks: A Survey

paper_content:

Today's wireless networks are characterized by a fixed spectrum assignment policy. However, a large portion of the assigned spectrum is used sporadically and geographical variations in the utilization of assigned spectrum ranges from 15% to 85% with a high variance in time. The limited available spectrum and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum opportunistically. This new networking paradigm is referred to as NeXt Generation (xG) Networks as well as Dynamic Spectrum Access (DSA) and cognitive radio networks. The term xG networks is used throughout the paper. The novel functionalities and current research challenges of the xG networks are explained in detail. More specifically, a brief overview of the cognitive radio technology is provided and the xG network architecture is introduced. Moreover, the xG network functions such as spectrum management, spectrum mobility and spectrum sharing are explained in detail. The influence of these functions on the performance of the upper layer protocols such as routing and transport are investigated and open research issues in these areas are also outlined. Finally, the cross-layer design challenges in xG networks are discussed.
---
paper_title: Sequence-Based Rendezvous for Dynamic Spectrum Access

paper_content:

In the context of dynamic spectrum access (DSA), rendezvous refers to the ability of two or more radios to meet and establish a link on a common channel. In decentralized networks, this is often accomplished by each radio visiting potential channels in random fashion, in a process that we call blind random rendezvous. In this work, we propose the use of sequences that determine the order with which radios visit potentially available channels. Through sequence-based rendezvous, it is possible to: (i) establish an upper bound to the time to rendezvous (TTR); (ii) establish a priority order for channels in which rendezvous occurs; (Hi) reduce the expected TTR as compared to random rendezvous. We provide an example of a family of sequences and derive the expected time-to- rendezvous using this method. We also describe how the method can be adopted when one or more primary users are detected in the channels of interest.
---
paper_title: Rendezvous for Cognitive Radios

paper_content:

Cognitive radios have been touted as a solution to communicating in a Dynamic Spectrum Access environment. This paper examines how cognitive radios initially find one another among the expanse of ever-changing open spectrum, termed the rendezvous problem. Specifically, it addresses the problem of rendezvous under varying levels of system capabilities, spectrum policies, and environmental conditions. The focus is on rendezvous when there are are no control channels or centralized controllers, which we term the blind rendezvous problem. Under these conditions, a sequence-based and modular clock blind rendezvous algorithms are proposed, and it is shown that the performance of these algorithms compares favorably to that of a random blind rendezvous algorithm. Specifically, the sequence-based algorithm provides a bounded Time To Rendezvous (TTR) and the ability to prioritize channels where rendezvous is more likely to occur; the modular clock algorithm reduces the expected TTR, requires little precoordination among radios attempting to rendezvous, and is robust to radios sensing different sets of available channels.
---
paper_title: Common control channel design for cognitive radio wireless ad hoc networks using adaptive frequency hopping

paper_content:

Cognitive radio (CR) technology enables the opportunistic use of the portions of the licensed spectrum by the CR users, while ensuring low interference to the primary user (PU) activity in the licensed bands. The spectrum is sensed locally by the CR users, and a specific channel that is acceptable to both the end nodes of the communication link is chosen. However, this necessitates a common control channel (CCC) for exchanging the sensing information and reserving the channel before actual data transfer. In this paper, a common control channel design for CR ad hoc networks is proposed, called as adaptive multiple rendezvous control channel (AMRCC) based on frequency hopping. Our scheme is scalable, and allows continuous connectivity between the CR users under dynamic PU activity. The contribution made in this paper is threefold: (i) a frequency hopping scheme is proposed that allows altering the hopping sequence based on the PU activity in the channels, (ii) a simple and low-overhead procedure is developed to aid new node-join and leave events, and (iii) a slot duration optimization is given that avoids a significant performance degradation with the number of available channels. Performance evaluation proves that our solution achieves better performance than the other classic CCC solutions in terms of time to rendezvous (TTR) and the resulting throughput, specifically in CR ad hoc networks.
---
paper_title: Control Channel Establishment in Cognitive Radio Networks using Channel Hopping

paper_content:

In decentralized cognitive radio (CR) networks, enabling the radios to establish a control channel (i.e., "rendezvous" to establish a link) is a challenging problem. The use of a dedicated common control channel simplifies the rendezvous process but may not be feasible in many opportunistic spectrum sharing scenarios due to the dynamically changing availability of all the channels, including the control channel. To address this problem, researchers have proposed the use of channel hopping protocols for enabling rendezvous in CR networks. Most, if not all, of the existing channel hopping schemes only provide ad hoc approaches for generating channel hopping sequences and evaluating their properties. In this paper, we present a systematic approach, based on quorum systems, for designing and analyzing channel hopping protocols for the purpose of control channel establishment. The proposed approach, called Quorum-based Channel Hopping (QCH) system, can be used for implementing rendezvous protocols in CR networks that are robust against link breakage caused by the appearance of incumbent user signals. We describe two synchronous QCH systems under the assumption of global clock synchronization, and two asynchronous channel hopping systems that do not require global clock synchronization. Our analytical and simulation results show that the proposed channel hopping schemes outperform existing schemes under various network conditions.
---
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: The Rendezvous Problem on Discrete Locations

paper_content:

Two friends have become separated in a building or shopping mall and and wish to meet as quickly as possible. There are n possible locations where they might meet. However, the locations are identical and there has been no prior agreement where to meet or how to search. Hence they must use identical strategies and must treat all locations in a symmetrical fashion. Suppose their search proceeds in discrete time. Since they wish to avoid the possibility of never meeting, they will wish to use some randomizing strategy. If each person searches one of the n locations at random at each step, then rendezvous will require n steps on average. It is possible to do better than this: although the optimal strategy is difficult to characterize for general n, there is a strategy with an expected time until rendezvous of less than 0.829 n for large enough n. For n = 2 and 3 the optimal strategy can be established and on average 2 and 8/3 steps are required respectively. There are many tantalizing variations on this problem, which we discuss with some conjectures. DYNAMIC PROGRAMMING; SEARCH PROBLEMS
---
paper_title: Jump-stay based channel-hopping algorithm with guaranteed rendezvous for cognitive radio networks

paper_content:

Cognitive radio networks (CRNs) have emerged as advanced and promising paradigm to exploit the existing wireless spectrum opportunistically. It is crucial for users in CRNs to search for neighbors via rendezvous process and thereby establish the communication links to exchange the information necessary for spectrum management and channel contention etc. This paper focuses on the design of algorithms for blind rendezvous, i.e., rendezvous without using any central controller and common control channel (CCC). We propose a jump-stay based channel-hopping (CH) algorithm for blind rendezvous. The basic idea is to generate CH sequence in rounds and each round consists of a jump-pattern and a stay-pattern. Users “jump” on available channels in the jump-pattern while “stay” on a specific channel in the stay-pattern. Compared with the existing CH algorithms, our algorithm achieves the following advances: i) guaranteed rendezvous without the need of time-synchronization; ii) applicability to rendezvous of multi-user and multi-hop scenarios. We derive the maximum time-to-rendezvous (TTR) and the upper-bound of expected TTR of our algorithm for both 2-user and multi-user scenarios (shown in Table I). Extensive simulations are further conducted to evaluate performance of our algorithm.
---
paper_title: Multi-channel mac for ad hoc networks: handling multi-channel hidden terminals using a single transceiver

paper_content:

This paper proposes a medium access control (MAC) protocol for ad hoc wireless networks that utilizes multiple channels dynamically to improve performance. The IEEE 802.11 standard allows for the use of multiple channels available at the physical layer, but its MAC protocol is designed only for a single channel. A single-channel MAC protocol does not work well in a multi-channel environment, because of the multi-channel hidden terminal problem . Our proposed protocol enables hosts to utilize multiple channels by switching hannels dynamically, thus increasing network throughput. The protocol requires only one transceiver per host, but solves the multi-channel hidden terminal problem using temporal synchronization. Our scheme improves network throughput signifiantly, especially when the network is highly congested. The simulation results show that our protocol successfully exploits multiple hannels to achieve higher throughput than IEEE 802.11. Also, the performance of our protocol is comparable to another multi-hannel MAC protocol that requires multiple transceivers per host. Since our protocol requires only one transceiver per host, it an be implemented with a hardware complexity comparable to IEEE 802.11.
---

Title: The Life Cycle of the Rendezvous Problem of Cognitive Radio Ad Hoc Networks: A Survey

Section 1: INTRODUCTION
Description 1: This section provides an overview of cognitive radio technology and introduces the rendezvous problem, emphasizing its importance and the challenges in CR ad hoc networks.

Section 2: SOLUTIONS FOR RENDEZVOUS PROBLEM
Description 2: This section categorizes and explains the two main approaches to solve the rendezvous problem: using a Common Control Channel (CCC) and employing the Channel Hopping approach.

Section 3: Common Control Channel Approach
Description 3: This section elaborates on the CCC approach to solving the rendezvous problem, highlighting its operation, advantages, and the major issues such as lack of availability, control channel saturation, and security vulnerability.

Section 4: Channel Hopping Approach
Description 4: This section discusses the Channel Hopping approach, its operational mechanism, benefits over the CCC approach, and the key challenges it faces like channel access delay, complexity, and lack of network status information.

Section 5: THE LIFE CYCLE
Description 5: This section illustrates the problem life cycle formed by the two rendezvous solutions, explaining how each approach compensates for the other's shortcomings, yet fails in specific scenarios.

Section 6: CONCLUSION
Description 6: This section summarizes the key points of the survey, acknowledging the unresolved nature of the rendezvous problem and the shortcomings of existing solutions.