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Title: Performance analysis of cooperative cognitive spectrum sharing systems over fading channels
Authors: Sharma, Pankaj Kumar
Keywords: Electrical Engineering
Issue Date: 16-Feb-2017
Publisher: Discipline Electrical Engineering, IIT Indore
Series/Report no.: TH60;
Abstract: Cognitive radio has emerged as a promising technology to improve the spectrum utilization e ciency in wireless networks. Typically, in cognitive radio systems, the secondary users (SUs) are allowed to share the spectrum licensed to the primary users (PUs), subject to satisfying certain quality of service (QoS) for PUs. To promote dynamic spectrum sharing, cognitive radio relies on the sophisticated transmission and signal processing mechanisms. The potential cooperative communication technology can enhance the performance of cognitive radio networks under the transmission restrictions imposed by the PUs. Hence, it is viable to integrate cooperative and cognitive technology for high reliability and spectrum utilization e ciency in futuristic high data rate networks. In this thesis, we aim to analyze cognitive spectrum sharing systems with cooperative relaying techniques over general fading channels to draw useful insights for the design of such systems.This thesis presents on the performance evaluation of two classes of cognitive radio systems, viz., underlay and overlay, coupled with cooperative communication techniques. For underlay systems, we rst investigate a cognitive amplify-and-forward relay network (CAFRN) with opportunistic relaying utilizing a direct link in the presence of multiple primary receivers. Herein, we develop uni ed analytical framework to evaluate outage probability of CAFRN with maximal ratio combining (MRC) and selection combining (SC) schemes. We further study a decode-and-forward (DF) based cognitive two-way relay network (CTWRN) with direct link utilization. We derive closed-form outage probability expressions for the CTWRN under Nakagami-m fading. Our analysis for these systems leads to various interesting insights into achievable performance gains. We further delve into the performance of the direct link enabled CAFRN with RF transceiver hardware impairments. Speci cally, we conduct outage performance analysis for both the partial relay selection (PRS) and opportunistic relay selection (ORS) schemes over Rayleigh channels. Moreover, we examine the performance of a cognitive DF relay network (CDFRN) taking into account the combined impact of hardware impairments and the channel estimation errors (CEE). Our ndings disclosed that the hardware impairments may invoke a relay cooperation ceiling (RCC) phenomenonwhich makes relaying infeasible under high-rate requirements. Although the CEE do not have impact on RCC, they can degrade the system performance by inducing oors. Next, we turn our focus on the performance of two-way relaying (TWR) based overlay systems aiming higher spectral e ciency. We rst investigate the performance of a three-phase cooperative spectrum sharing (3PCSS) scheme for two-way overlay multi-user multi-relay networks. For this system, we propose a distributed scheduling scheme for PUs and SUs, so that one-end PU communicates bidirectionally with one of the best selected other end-PUs with the cooperation of the best selected SU based on time-division broadcast (TDBC) protocol. By considering bidirectional tra c ows jointly with correlation, we present outage performance analysis for both primary and secondary systems under Nakagami-m fading channels. We also manifest the feasible region for the placement of SUs to access the spectrum. Further, we analyze the performance of a TDBC-based 3PCSS scheme for multiuser TWR networks with optimal PU scheduling. More speci cally, one-end PU communicates with an Nth best selected other-end PU with the cooperation of a SU in three transmission phases. As such, this scheduling policy takes into account the joint impact of the direct and the relay links for PU selection. Considering Nth order statistics with correlation, we present the uni- ed closed-form outage probability expressions for both primary and secondary systems over general fading channels. We further compare the proposed 3PCSS scheme with other competitive schemes in terms of spectrum sharing requirements and achievable throughput. Based on our results, we illustrate that the 3PCSS scheme can achieve spectral e ciency at par with the two-phase direct transmissions of primary system. To emulate practical scenario, we further analyze the performance of an overlay TWR network with co-channel interference (CCI) under Nakagami-m fading. For this complicated set-up, we derive tight closed-form expressions for the outage probability for both primary and secondary systems. We illustrate that the primary and secondary systems can achieve full diversity subject to the low levels of CCI. In addition, we depict that the CCI has critical impact on the spectrum sharing factor.Above all, the theoretical ndings in this thesis provide useful insights and guidelines for the design of reliable cognitive radio systems.
Appears in Collections:Discipline of Electrical Engineering

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