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UBC Theses and Dissertations

Cooperative beamforming for cognitive radio systems in presence of asynchronous interference Hassan, Mai Mohamed


Cognitive radio (CR) is considered a key enabling technology to exploit the underutilized and non-utilized radio spectrum bands. On the other hand, cooperative communication among nodes in CR networks, can improve the overall performance of CR systems, in terms of increasing data rates, attainable coverage range and overall energy efficiency, providing some diversity against shadow fading, and having low deployment costs. In a CR network, cooperative transmit beamforming can be achieved via a number of single antenna-based CR nodes organizing themselves in a virtual antenna array and focusing their transmission in the direction of intended CR receiver. However, deploying the beamforming in such a cooperative manner faces several implementation challenges. Therefore, in this thesis, we tackle some of these critical challenges facing the design and implementation of cooperative CR networks. The first challenge is referred to as asynchronous interference, that results from asynchronous arrival of the same signal from the set of cooperating CR nodes at primary receivers. Next, we address the problem of feedback overhead needed for cooperative beamforming. Specifically, each cooperating CR node requires knowing global information including other nodes' locations, in addition to accurate and instantaneous knowledge of their channel state information (CSI). We also tackle the problem of imperfect CSI estimation. Another important aspect of implementing cooperative CR networks is studied in this thesis, which is described as follows. Since the cooperating nodes can be located in different locations, they contribute differently to received signals at the CR receivers, as well as to interference signals at the primary receivers. Therefore, we propose different cooperating CR node selection strategies, to be applied in conjunction with cooperative beamforming. Finally, we study different participation decision making strategies that enable each CR user to independently decide whether to participate in the cooperative transmission or not, based on an offered incentive for cooperation and estimated cost of participation in cooperative transmission represented in transmit power. At the end of each chapter, we present some numerical examples to show the implications of ignoring different implementation challenges in the design of cooperative CR networks, and to assess the performance of the proposed solutions.

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Attribution-NonCommercial-NoDerivs 2.5 Canada