Survey of Cognitive Radio Techniques in Wireless Network
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paper_title: Radiometric detection of spreadspectrum signals in noise of uncertain power

paper_content:

The standard analysis of the radiometric detectability of a spread-spectrum signal assumes a background of stationary, white Gaussian noise whose power spectral density can be measured very accurately. This assumption yields a fairly high probability of interception, even for signals of short duration. By explicitly considering the effect of uncertain knowledge of the noise power density, it is demonstrated that detection of these signals by a wideband radiometer can be considerably more difficult in practice than is indicated by the standard result. Worst-case performance bounds are provided as a function of input signal-to-noise ratio (SNR), time-bandwidth (TW) product and peak-to-peak noise uncertainty. The results are illustrated graphically for a number of situations of interest. It is also shown that asymptotically, as the TW product becomes large, the SNR required for detection becomes a function of noise uncertainty only and is independent of the detection parameters and the observation interval. >
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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: Spectrum Sensing Measurements of Pilot, Energy, and Collaborative Detection

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In this paper we present an experimental study that comprehensively evaluates the performance of three different detection methods proposed for sensing of primary user signals in cognitive radios. For pilot and energy detection, our measurement results confirmed the theoretical expectations on sensing time performance. However, a physical implementation of these detectors in the presence of real noise uncertainties, analog impairments and interference allowed us to establish practical bounds on the detectable signal levels. In the case of collaborative detection, our analysis of experimental data collected in indoor environments identified the design parameters that can significantly improve the sensing gain: adaptive threshold, spatial separation and multiple antennas.
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paper_title: Subsection-average cyclostationary feature detection in cognitive radio

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Spectrum sensing plays an important role in cognitive radios because the secondary users need to continuously monitor the spectrum for the presence of primary user. In this paper, we mainly investigated the cyclostationary feature spectrum detection in cognitive radios. Our analysis shows that cyclostationary feature detection requires partial information of the primary user and high computation cost although it is robust to interference in low SNR. We propose a novel strategy for spectrum sensing based on cyclostationary feature detection. Our new approach can effectively decrease the computational complexity and improve the performance of the inhibition of noise interference. At last, numerical results are provided in order to illustrate the advantages of our new technique.
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paper_title: Markov-chain modeling for multicast signaling delay analysis

paper_content:

Feedback signaling plays a key role in flow control because the traffic source relies on the signaling information to make correct and timely flow-control decisions. However, it is difficult to design an efficient signaling algorithm since a signaling message can tolerate neither error nor latency. Multicast flow-control signaling imposes two additional challenges: scalability and feedback synchronization. Previous research on multicast signaling has mainly focused on the development of algorithms without analyzing their delay performance. To remedy this deficiency, we have previously developed a binary-tree model and an independent-marking statistical model for multicast-signaling delay analysis. This paper considers a general scenario where the congestion markings at different links are dependent - a more accurate but complex case. Specifically, we develop a Markov-chain model defined by the link-marking state on each path in the multicast tree. The Markov chain can not only capture link-marking dependencies, but also yield a tractable analytical model. We also develop a Markov-chain dependency-degree model to evaluate all possible Markov-chain dependency degrees without any prior knowledge of them. Using the above two models, we derive the general probability distributions of each path becoming the multicast-tree bottleneck. Also derived are the first and second moments of multicast signaling delays. The proposed Markov chain is also shown to asymptotically reach an equilibrium, and its limiting distribution converges to the marginal link-marking probabilities when the Markov chain is irreducible. Applying the two models, we analyze and contrast the delay scalability of two representative multicast signaling protocols: Soft-Synchronization Protocol (SSP) and Hop-By-Hop (HBH) algorithms.
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paper_title: CREAM-MAC: An efficient Cognitive Radio-enAbled Multi-Channel MAC protocol for wireless networks

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Cognitive radio technology has emerged as the novel and effective approach to improve the utilization of precious radio spectrum. Employing the cognitive radio technology, secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that constrains the level of interference to the primary (licensed) users. However, there are many new challenges associated with cognitive radio based wireless networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability is different 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 spectrum sensing at physical layer and packet scheduling at MAC layer, over the wireless networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. 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. In addition, we develop the analytical models to quantitatively analyze our proposed CREAM-MAC protocol in the saturated network case. We also conduct simulation experiments to validate our developed analytical models.
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paper_title: Opportunistic MAC Protocols for Cognitive Radio Based Wireless Networks

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Recently, cognitive radio technology has attracted more and more attention since it is a novel and effective approach to improve the utilization of the precious radio spectrum. We propose MAC protocols for the cognitive radio based wireless networks. Specifically, the cognitive MAC protocols allow secondary users to identify and use the available frequency spectrum in a way that constrains the level of interference to the primary users. In our schemes, each secondary user is equipped with two transceivers. One of the transceivers is tuned to a dedicated control channel, while the other is used as a cognitive radio that can periodically sense and dynamically use an identified available channels. Our proposed schemes integrate the spectrum sensing at the PHY layer and packet scheduling at the MAC layer. Our schemes smoothly coordinate the two transceivers of the secondary users to enable them to collaboratively sense and dynamically utilize the available frequency spectrum.
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paper_title: Cross-layer resource allocation over wireless relay networks for quality of service provisioning

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The authors propose a physical-datalink cross-layer resource allocation scheme over wireless relay networks for quality-of-service (QoS) guarantees. By integrating information theory with the concept of effective capacity, the proposed scheme aims at maximizing the relay network throughput subject to a given delay QoS constraint. This delay constraint is characterized by the so-called QoS exponent thetas, which is the only requested information exchanged between the physical layer and the datalink layer in our cross-layer design based scheme. Over both amplify-and-forwards (AF) and decode-and-forward (DF) relay networks; the authors develop the associated dynamic resource allocation algorithms for wireless multimedia communications. Over DF relay network, the authors also study a fixed power allocation scheme to provide QoS guarantees. The simulations and numerical results verify that our proposed cross-layer resource allocation can efficiently support diverse QoS requirements over wireless relay networks. Both AF and DF relays show significant superiorities over direct transmissions when the delay QoS constraints are stringent. On the other hand, the results demonstrate the importance of deploying the dynamic resource allocation for stringent delay QoS guarantees.
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paper_title: Performance of power detector sensors of DTV signals in IEEE 802.22 WRANs

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Sensing is the most important component in any cognitive radio system. The IEEE 802.22 Working Group (WG) is formulating the first worldwide standard for cognitive radios to operate in the television (TV) bands. In order for this standard to succeed, it is imperative that IEEE 802.22 systems employ an effective sensing mechanism to detect the presence of television signals so that it can opportunistically access those bands that are not currently used by TV transmitters. In this paper we highlight the simulation methodology used in the IEEE 802.22 WG and study the performance of the power detector.
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Title: Survey of Cognitive Radio Techniques in Wireless Network

Section 1: Introduction
Description 1: Introduction to cognitive radio and its necessity in addressing the limitation of the fixed radio spectrum.

Section 2: Background
Description 2: Overview of the fixed frequency allocation policies and the challenges they pose.

Section 3: Cognitive Radio Overview
Description 3: Explanation of cognitive radio technology and how it facilitates opportunistic spectrum usage.

Section 4: Spectrum Sensing Techniques
Description 4: Detailed discussion on various spectrum sensing methods, including matched filtering, feature detection, and energy detection.

Section 5: Matched Filtering Approach
Description 5: In-depth analysis of the matched filtering method, its advantages, and limitations.

Section 6: Feature Detection Approach
Description 6: Examination of the feature detection approach and its reliance on signal cyclostationarity.

Section 7: Energy Detection Approach
Description 7: Exploration of the energy detection method, its operation without signal information, and issues related to noise and signal fluctuation.

Section 8: Comparative Analysis
Description 8: Comparison of the different spectrum sensing techniques, highlighting their pros and cons in various scenarios.

Section 9: Conclusion
Description 9: Summary of findings and potential future directions for cognitive radio technology in wireless networks.