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 (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.

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.

No description available.

The radio frequency (RF) spectrum is a scarce natural resource, currently regulated by government agencies. With the explosive emergence of wireless applications, the demands for the RF spectrum are constantly increasing. On the other hand, it has been reported that localised temporal and geographic spectrum utilisation efficiency is extremely low. Cognitive radio is an innovative technology designed to improve spectrum utilisation by exploiting those spectrum opportunities. This ability is dependent upon spectrum sensing, which is one of most critical components in a cognitive radio system. A significant challenge is to sense the whole RF spectrum at a particular physical location in a short observation time. Otherwise, performance degrades with longer observation times since the lagging response to spectrum holes implies low spectrum utilisation efficiency. Hence, developing an efficient wideband spectrum sensing technique is prime important. In this thesis, a multirate asynchronous sub-Nyquist sampling (MASS) system that employs multiple low-rate analog-to-digital converters (ADCs) is developed that implements wideband spectrum sensing. The key features of the MASS system are, 1) low implementation complexity, 2) energy-efficiency for sharing spectrum sensing data, and 3) robustness against the lack of time synchronisation. The conditions under which recovery of the full spectrum is unique are presented using compressive sensing (CS) analysis. The MASS system is applied to both centralised and distributed cognitive radio networks. When the spectra of the cognitive radio nodes have a common spectral support, using one low-rate ADC in each cognitive radio node can successfully recover the full spectrum. This is obtained by applying a hybrid matching pursuit (HMP) algorithm - a synthesis of distributed compressive sensing simultaneous orthogonal matching pursuit (DCS-SOMP) and compressive sampling matching pursuit (CoSaMP). Moreover, a multirate spectrum detection (MSD) system is introduced to detect the primary users from a small number of measurements without ever reconstructing the full spectrum. To achieve a better detection performance, a data fusion strategy is developed for combining sensing data from all cognitive radio nodes. Theoretical bounds on detection performance are derived for distributed cognitive radio nodes suffering from additive white Gaussian noise (AWGN), Rayleigh fading, and log-normal fading channels. In conclusion, MASS and MSD both have a low implementation complexity, high energy efficiency, good data compression capability, and are applicable to distributed cognitive radio networks.

We study a dynamic channel selection framework for cognitive radio networks (CRNs) which support both delay sensitive and best effort services. Unlike existing works in the literature, we consider the effect of heterogeneous radio frequency characteristics and heterogeneous primary user activities on channel selection in multi-channel CRNs. Optimal spectrum decision policies are obtained to achieve minimum delay using dynamic programming techniques, such as Markov decision process (MDP) and reinforcement learning, under different assumptions. To address the computational complexity issue in the MDP solutions, a myopic scheme is proposed based on the estimated packet sojourn time. / October 2016

In a CR network, the maximum SUs throughput is desired generally. In this thesis, We investigate and formulate the problem of the secondary users¡¦ throughput maximization in cognitive radio systems under channel capacity constrain. By using KKT theorem, an objec- tive function is developed to obtain an optimal solution for the SU throughput maximization problem. An numerical example is also presented for illustration. The most important results revealed in the example show that the maximum SU throughput is achieved by cooperating an optimal number of SU pairs instead of cooperating all the SU pairs.

There has been a growing demand for wireless communication services in the past few years. Recent reports reveal that the demand will not only increase in the number of subscribers but also in more diverse applications such as Machine-to-Machine (M2M) communications and the Internet of Things. With such demand for capacity increase, there is a necessity to shift from today’s Static Frequency Allocation (SFA) to Dynamic Spectrum Access (DSA). The change will make efficient use of spectrum by utilizing the unused parts in different times, frequencies and spaces. With this regard, cognitive radio (CR) is a powerful potential candidate for the spectrum scarcity problem. This work addresses the two main current discussions in Cognitive Radio Networks (CRN), spectral efficiency and interference mitigation problem. There are two main spectrum sharing techniques in CRN, overlay and underlay, which have been thoroughly investigated in the literature. Unlike the relative works which separate the use of overlay and underlay, this works considers the joint overlay and underlay as a hybrid system to enhance the spectral efficiency and Bit Error Rate (BER) performance in CRNs. MC-CDMA is proposed for underlay transmission for two main advantages. Firstly, for low power spectral density due to spreading. Secondly, for its capability to mitigate high interference. Two hybrid MC-CDMA schemes are proposed in this work. The first scheme spreads the underlay signal through the whole bandwidth to mitigate PU interference and benefit from the frequency diversity. To maximize data rate, overlay utilizes the available bands while keeping orthogonality with underlay using Orthogonal Variable Spreading Factor (OVSF) codes. To further increase capacity, an overload MC-CDMA system is proposed. In this scheme, overlay utilizes the full signal dimension, while underlay overloads the system. Two layered spreading is applied to differentiate overlay and underlay users. In order to detect the underlay signal, the overlay signal is detected first and is cancelled from the received signal. The underlay data is then detected from this modified signal. The framework is then extended to a multi-user underlay scenario. A code allocation algorithm is proposed in order to achieve low cross-correlation between the overlay and underlay users. The results show that the proposed overload system maintains good performance even in high PU interference level. Furthermore, the proposed hybrid capacities are optimized and compared with the two available hybrid systems in the literature. The proposed overload system showed to increase capacity significantly, both in AWGN and fading environment, in compared with the existing methods.

Cognitive radio is an important technology which aims to improve the spectrum resource utilization and allows a cognitive radio transceiver to detect and sense spectrum holes without causing interference to the primary users (PUs). As a result of the development of cognitive radio technology, the concept of cognitive radio ad hoc networks (CRAHNs) has recently been proposed in the literature, which aims to apply the cognitive radio to traditional ad hoc networks. However, this new network paradigm creates more research challenges than those in classical cognitive radio networks (CRNs). These research challenges in CRAHNs are due to the variable radio environments caused by spectrum-dependent communication links, hop-by-hop transmission, and changing topology. This study will focus on important research topics in spectrum management in scalable CRAHNs driven by local control, such as spectrum sharing, allocation, and mobility. To conduct this study, a local control approach is proposed to enable system-level analysis and protocol-level design with distributed protocols for spectrum sharing. In the local control approach, we can evaluate the system dynamics caused by either protocol-specific parameters or application-specific parameters in CRAHNs, which is hard to explore using existing methods. Moreover, combining the previous evaluations and scaling law analysis based on local control concept, we can design new distributed protocols based on the features of the medium access control (MAC) layer and the physical layer. In this study, the proposed research themes and related research issues surrounding spectrum sharing are discussed. Moreover, justification of the research has been made by experimental and analytical results. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2013-02-04 14:37:45.883