Cooperative Spectrum Sensing (CSS) allows Cognitive Radio Networks (CRNs) to locate vacant spectrum channels and to protect active Primary Users (PUs). However, the achieved detection accuracy is proportional to the duration of the CSS process which, unfortunately, reduces the time of useful communication as well as increases the Co-Channel Interference (CCI) perceived by an active PU. To overcome this, this thesis proposes three CSS strategies, namely the Dual-Threshold CSS (DTCSS), the Maximum CSS (MCSS), and the Max-Min CSS (MMCSS). These strategies reduce the number of reporting terminals while maintaining reliable performance and minimal CCI e ect. The performance of these three methods is analyzed, and the numerical and simulations results illustrate the accuracy of the derived results as well as the achieved performance gains. The second part of this thesis studies the impact of CCI on the performance of a number of transmission techniques used by CRNs. These are Chase combining Hybrid Automatic Repeat Request (HAQR), Fixed Relaying (FR), Selective Relaying (SR), Incremental Relaying (IR), and Selective Incremental Relaying (SIR). The performance of these techniques is studied in terms of the average spectral e ciency, the outage probability, and the error probability. To obtain closed forms for the error probabilities, this thesis proposes a novel accurate approximation of the exponential integral function using a sum of exponentials. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-02-05 13:39:22.35

Zhu, Qiang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 67-70). / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Technology overview --- p.4 / Chapter 2.1 --- Associate background --- p.4 / Chapter 2.2 --- Physical layer --- p.6 / Chapter 2.2.1 --- Signal specification --- p.6 / Chapter 2.2.2 --- Spectrum sensing --- p.7 / Chapter 2.2.3 --- Cooperative sensing --- p.10 / Chapter 2.2.4 --- Interference temperature --- p.13 / Chapter 2.3 --- MAC layer --- p.14 / Chapter 2.3.1 --- Cooperative spectrum sharing --- p.14 / Chapter 2.3.2 --- Non-cooperative spectrum sharing --- p.16 / Chapter 2.3.3 --- Inter-network spectrum sharing --- p.16 / Chapter 2.3.4 --- Interference mitigation --- p.19 / Chapter 3 --- Power Regulation Protocol --- p.21 / Chapter 3.1 --- Introduction --- p.21 / Chapter 3.2 --- Unlicensed user coexistence --- p.24 / Chapter 3.3 --- Protection of licensed user --- p.30 / Chapter 3.4 --- Mobility issues --- p.33 / Chapter 3.5 --- Conclusion --- p.36 / Chapter 4 --- Wireless fading channels --- p.40 / Chapter 4.1 --- Model and assumption --- p.40 / Chapter 4.2 --- Outage probability upper bound --- p.43 / Chapter 4.3 --- Conclusion --- p.49 / Chapter 5 --- Simulation and numerical results --- p.51 / Chapter 5.1 --- Greedy algorithm --- p.51 / Chapter 5.2 --- Detection threshold tradeoff --- p.55 / Chapter 5.3 --- System performance analysis --- p.56 / Chapter 6 --- Conclusion and future work --- p.63 / Chapter 6.1 --- Conclusion --- p.63 / Chapter 6.2 --- Future work --- p.64 / Bibliography --- p.67

In this thesis, we study the cognitive algorithm in digital television (DTV) bands for Wireless Regional Area Network (WRAN) signals. The WRAN standards are specified by the IEEE 802.22 Working Group. The principle of the proposed algorithm in this thesis is to recognize the band state by analyzing the transmitted signals in DTV bands. The received signals could be 4 possible options: 1.Noise 2.ATSC signal plus noise 3.WRAN signal plus noise 4.ATSC signal plus WRAN signal and noise. This thesis proposed an algorithm to cognize the WRAN signals, and the proposed schedule is 1.Cognitive algorithm for sensing ATSC signal 2.Cognitive algorithm for sensing WRAN signal. According to the result of this schedule, we will get the information of the band status. Later, WRAN will make use of cognitive radio technology we developed in the thesis, together with other cognitive information (such as channel capacity, system parameters, etc.), to sustain the WRAN signal transmission by making some adjustments of system parameters or the required bandwidth.

Cognitive radio network is discussing how to enhance frequency reuse by allowing the unlicensed users to utilize the frequency bands of licensed users when these bands are not currently being used. Generally speaking, we called these unlicensed users as secondary users and these licensed users as primary users. In order to enhance frequency reuse, the secondary users need to monitor the spectrum continuously to avoid possible interference with the primary users, and once the primary users are found to be active, the secondary users are required to vacate the frequency bands. Therefore, spectrum sensing plays a significant important role in cognitive radio network. There are two probability values associated with spectrum sensing: probability of detection and probability of false alarm. The higher the probability of detection means the better theprimary users are protected. However, from the secondary users¡¦ perspective, the lower the probability of false alarm, the more chances the frequency bands can be reused when it is available, thus the higher the achievable throughput for the secondary network. In this thesis, we study the problem of designing the sensing duration to maximize the achievable throughput for the secondary network under the constraint that the primary user is sufficiently protected. We formulate the sensing-throughput tradeoff problem mathematically, and use energy detection ¡]ED¡^[4] sensing scheme to prove that the formulated problem indeed has oneoptimal sensing time that yields the highest throughput for the secondary network. We also discuss the case of two secondary users with the concept of cooperative systems.

Cognitive radio networks have recently been proposed as a promising approach to overcome the serious problem of spectrum scarcity. Other emerging concept for innovative spectrum utilization is femtocells. Femtocells are low-power and short-range wireless access points installed by the end-user in residential or enterprise environments. A common feature of cognitive radio and femtocells is their two-tier nature involving primary and secondary users (PUs, SUs). While this new paradigm enables innovative alternatives to conventional spectrum management and utilization, it also brings its own technical challenges. A main challenge in cognitive radio is the design of efficient resource (spectrum) trading methods. Game and microeconomics theories provide tools for studying the strategic interactions through rationality and economic benefits between PUs and SUs for effective resource allocation. In this thesis, we investigate some efficient game theoretic and microeconomic approaches to address spectrum trading in cognitive networks. We propose two auction frameworks for shared and exclusive use models. In the first auction mechanism, we consider the shared used model in cognitive radio networks and design a spectrum trading method to maximize the total satisfaction of the SUs and revenue of the Wireless Service Provider (WSP). In the second auction mechanism, we investigate spectrum trading via auction approach for exclusive usage spectrum access model in cognitive radio networks. We consider a realistic valuation function and propose an efficient concurrent Vickrey-Clarke-Grove (VCG) mechanism for non-identical channel allocation among r-minded bidders in two different cases. The realization of cognitive radio networks in practice requires the development of effective spectrum sensing methods. A fundamental question is how much time to allocate for sensing purposes. In the literature on cognitive radio, it is commonly assumed that fixed time durations are assigned for spectrum sensing and data transmission. It is however possible to improve the network performance by finding the best tradeoff between sensing time and throughput. In this thesis, we derive an expression for the total average throughput of the SUs over time-varying fading channels. Then we maximize the total average throughput in terms of sensing time and the number of SUs assigned to cooperatively sense each channel. For practical implementation, we propose a dynamical programming algorithm for joint optimization of sensing time and the number of cooperating SUs for sensing purpose. Simulation results demonstrate that significant improvement in the throughput of SUs is achieved in the case of joint optimization. In the last part of the thesis, we further address the challenge of pricing in oligopoly market for open access femtocell networks. We propose dynamic pricing schemes based on microeconomic and game theoretic approaches such as market equilibrium, Bertrand game, multiple-leader-multiple-follower Stackelberg game. Based on our approaches, the per unit price of spectrum can be determined dynamically and mobile service providers can gain more revenue than fixed pricing scheme. Our proposed methods also provide residential customers more incentives and satisfaction to participate in open access model.

Cognitive radio has recently been proposed as a promising approach for efficient utilization of radio spectrum. However, there are several challenges to be addressed across all layers of a cognitive radio system design, from application to hardware implementation. From the physical layer point-of-view, two key challenges are spectrum sensing and an appropriate signaling scheme for data transmission. The modulation techniques used in cognitive radio not only should be efficient and flexible but also must not cause (harmful) interference to the primary (licensed) users. Among all the proposed signaling schemes for cognitive radio, orthogonal frequency division multiplexing (OFDM) has emerged as a promising one due to its robustness against multipath fading, high spectral efficiency, and capacity for dynamic spectrum use. However, OFDM suffers from high out-of-band radiation which is due to high sidelobes of subcarriers. In this thesis, we consider spectral shaping in OFDM-based cognitive radio systems with focus on reducing interference to primary users created by by out-of-band radiation of secondary users' OFDM signal. In the first part of this research, we first study the trade-o between time-based and frequency-based methods proposed for sidelobe suppression in OFDM. To this end, two recently proposed techniques, active interference cancellation (AIC) and adaptive symbol transition (AST), are considered and a new joint time-frequency scheme is developed for both single-antenna and multi-antenna systems. Furthermore, knowledge of wireless channel is used in the setting of the proposed joint scheme to better minimize interference to the primary user. This scheme enables us to evaluate the trade-o between the degrees of freedom provided by each of the two aforementioned methods. In the second part of this research, a novel low-complexity technique for reducing out-of-band radiation power of OFDM subcarriers for both single-antenna and multi-antenna systems is proposed. In the new technique, referred to as a phase adjustment technique, each OFDM symbol is rotated in the complex plane by an optimal phase such that the interference to primary users is minimized. It is shown that the phase adjustment technique neither reduces the system throughput, nor does increase the bit-error-rate of the system. Moreover, the performance of the technique in interference reduction is evaluated analytically in some special cases and is verified using numerical simulations. Due to high sensitivity of OFDM systems to time and frequency synchronization errors, performance of spectral shaping techniques in OFDM is significantly affected by timing jitter in practical systems. In the last part of this research, we investigate the impact of timing jitter on sidelobe suppression techniques. Considering AIC as the base method of sidelobe suppression, we first propose a mathematical model for OFDM spectrum in presence of timing jitter and evaluate the performance degradation to AIC due to timing jitter. Then, a precautionary scheme based on a minimax approach is proposed to make the technique robust against random timing jitter.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Akyildiz, Ian; Committee Member: Ammar, Mostafa; Committee Member: Laskar, Joy; Committee Member: Li, Ye; Committee Member: Sivakumar, Raghupathy. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Cognitive Radio (CR) system is an adaptive, reconfigurable communication system that can intuitively adjust its parameters to meet users or network demands. The major objective of CR is to provide a platform for the Secondary User (SU) to fully utilize the available spectrum resource by sensing the existence of spectrum holes without causing interference to the Primary User (PU). However, PU detection has been one of the main challenges in CR technology. In comparison to traditional wireless communication systems, due to the Cross-Channel Interference (CCI) from the adjacent channels used by SU to PU, CR system now poses new challenges to Resource Allocation (RA) problems. Past efforts have been focussed on Orthogonal Frequency Division Multiplexing (OFDM) based CR systems. However, OFDM technique show various limitations in CR application due to its enormous spectrum leakage. Filter Bank based Multicarrier (FBMC) has been proposed as a promising Multicarrier Modulation (MCM) candidate that has numerous advantages over OFDM. In this dissertation, a critical analysis of the performance of FBMC over OFDM was studied, and CR system was used as the testing platform. Firstly, the problem of spectrum sensing of OFDM based CR systems in contrast to FBMC based were surveyed from literature point of view, then the performance of the two schemes was analysed and compared from the spectral efficiency point of view. A resource allocation algorithm was proposed where much attention was focused on interference and power constraint. The proposed algorithms have been verified using MATLAB simulations, however, numerical results show that FBMC can attain higher spectrum efficiency and attractive benefit in terms of spectrum sensing as opposed to OFDM. The contributions of this dissertation have heightened the interest in more research and findings on how FBMC can be improved for future application CR systems.

One of the problems facing wireless network planners is a perceived scarcity of spectrum. A technology that addresses this problem is cognitive radio (CR). A critical function of a CR network is spectrum sensing (SS). A secondary user (SU) in a CR network will perform SS to gather information about the radio environment within which it wishes to operate and then make decisions based on that information. While SS by individual SUs is very useful it has been found in the literature that a cooperative approach, where SUs share their individual results, may provide more accurate information about the radio environment. It has also been shown that it is beneficial for SUs to be able to make proactive decisions about spectrum resource allocation. To be able to make these proactive decisions, a SU will need to be able to make predictions about the future behaviour of other users of the same spectrum. This research project was divided into two parts. Firstly, a measurement campaign was performed to characterise spectrum scarcity in the South African context. Detailed information, about the occupancy of various commercially utilised South African frequency bands, was collected from spectrum measurement campaigns carried at the Hatfield campus of the University of Pretoria and at Pinmill Farm in Johannesburg. These bands included the television broadcast and mobile cellular bands. On average, the television broadcast bands were found to be underutilised highlighting the existence of a number of opportunities for television white space devices. However, the mobile cellular bands were found to be much more heavily occupied, particularly for the bands around 900 MHz, suggesting that mobile operators are currently in need of additional spectrum resources. The second part of this thesis followed a more theoretical approach and was based on the need for proactive decision making in CR networks. A single SU prediction method, of relatively cheap computational complexity, was proposed and tested under various traffic conditions. The premise that collaboration between SUs may improve the accuracy of single SU traffic predictions was then explored. Pre-fusion and post-fusion approaches to cooperative prediction were compared with the single SU prediction scenario. The prediction error for the cooperative approaches was found to be lower than for the single SU case, especially for the pre-fusion scenario. For example, for a signal-to-noise ratio of 8 dB and individual forecast probability of 0.9, the pre-fusion prediction error was found to be approximately 2% compared with 26% for single SU prediction error. The cost of this improvement, however, was added algorithm complexity. It was then demonstrated that primary user traffic prediction could be used to improve the energy consumption associated with cooperative SS in a CR network. Combined with an optimal scheduling algorithm, this approach was shown to prolong the lifetime of a group of twenty cooperating SUs by 21.2 time samples for a uniformly distributed group of SUs when predictions were made ten time samples into the future. / Thesis (PhD)--University of Pretoria, 2016. / The Sentech Chair in Broadband Wireless Multimedia Communication / The National Research Foundation / The Independent Communications Authority of South Africa / Electrical, Electronic and Computer Engineering / PhD / Unrestricted

Dans des systèmes de communication sans fil modernes, la demande de débit de transmission des données par utilisateur est en croissance constante. Pour soutenir la forte demande de débit de données des utilisateurs une solution possible est de rapprocher l'utilisateur de la station de base émettrice et donc déployer une infrastructure réseau très dense. Dans cette configuration nous obtenons de fortes interférences. L’interférence a été souvent identifiée comme le principal obstacle des systèmes modernes de communications sans fil cellulaires. Cette considération a conduit à d'intenses activités de recherche qui a récemment poussé les opérateurs de réseaux et les fabricants à inclure de manière plus proactive et efficace pour supprimer/contrôler les interférences. D'un point de vue théorie de l'information, ce problème peut être mathématiquement étudié comme, ce qui est appelé, un canal d'interférence. Dans la première partie de cette thèse, nous concentrons notre attention à la conception de l'émetteur pour le canal d'interférence avec des terminaux avec antennes multiples. Nous proposons l'optimisation conjointe de l'émetteur et du récepteur en fonction de deux critères: l'alignement des interférences et la maximisation la somme pondérée des débits. La deuxième partie de la thèse est consacrée au problème de conception de l'émetteur dans le scénario de la radio cognitive. Nous commençons à considérer un scénario Underlay, ensuite, nous passons au scénario Interweave. L'objectif est de concevoir les émetteurs et les récepteurs, au niveau du réseau secondaire, telle que l'interférence, générée à chaque récepteur principal, est égal à zéro. / In modern wireless communication systems, the per-user data rate demand is constantly growing. To sustain the heavy user data rate demand, network operators try to deploy cellular system with more cells and applying more efficient spectrum reuse techniques. One possible solution to increase system throughput is to get the user closer to the transmitting base station and hence deploy very dense network infrastructure. In this setup strong interference situations will result. Interference has been identified as the main bottleneck of modern wireless cellular communication systems. With small dense cells this is more the case. This consideration has led to intense research activities that has recently pushed network operators and manufacturers to include more proactive and efficient way to suppress/control interference. From an information theoretic point of view this problem can be mathematically studied as an interference channel. In the first part of this thesis, we focus our attention on the beamforming design for the interference channel with particular focus on the MIMO case. There we propose the joint optimization of linear transmitter and receiver according to two criteria : Interference Alignment and weighted sum rate maximization. The second part of the thesis is devoted to the beamforming design problem in cognitive radio settings. We start considering an underlay scenario where the secondary network is modeled as a MISO interference channel. Then we move to the MIMO interweave cognitive radio. There the objective is to design the transmitters and receivers, at the secondary network, such that the interference, generated at each primary receiver, is zero.