title: Design and performance evaluation of sensing algorithms and cooperative relay selection protocols for multichannel cognitive radio networks            

Creators: name: Θεοδωρου Μαρια
Publisher: name: Technical University of Crete
Year: 2015

description: Recent years have witnessed a dramatic increase in the demand for radio spectrum. This is partly due to the increasing interest of consumers in wireless services, which in turn is driving the evolution of wireless networks toward high-speed data networks. Cognitive radio has been proposed as a promising technology to improve the spectral efficiency of radio spectrum, and is achieved by allowing unlicensed secondary users (SUs) to coexist with licensed primary users (PUs) in the same spectrum. The primary network owns the spectrum, and has performance guarantees. The secondary network(s) can access the spectrum if no significant degradation on the primary communication is caused. 
In this Thesis we start in Chapter 2 by proposing four new transmission algorithms for multichannel homogeneous cognitive radio networks (CRNs). We examine two cases: (i) the case where the network’s channels are not assigned to the SUs by a centralized entity and (ii) the case where a centralized entity exists and assigns the network’s channels to the SUs. Our event-driven simulations results demonstrate that the new transmission algorithms we have introduced improve (i) the normalized average throughput of SUs, (ii) reduce the dropping probability and (iii) increase the number of successful transmissions occurring during the system operation, when compared with a popular algorithm proposed in recent work in this area. 

Chapter 3 of the Thesis studies new transmission algorithms for multichannel heterogeneous CRNs. As in the first part we examine two cases: (i) a distributed CRN and (ii) a centralized CRN. For each case and for the same network topology, as in the first part of the work, we propose a new algorithm. Our event-driven simulations results demonstrate that the new transmission algorithms we have introduced considerably improve the average number of Mbits of secondary user traffic transmitted in each time slot, when compared with the corresponding results of the “γ-persistent strategy” recently introduced in the literature.

In Chapter 4 of the Thesis the “Distributed algorithm” proposed in Chapter 3, in which the SUs select their network’s channels in a distributed way without coordination by a centralized entity, is used and evaluated in the case of homogeneous multichannel CRNs. Our simulation results demonstrate that the “Distributed algorithm” achieves results close to those achieved by the algorithms proposed in Chapter 2 of the Thesis in which it has been assumed that a centralized entity exists and assigns the network’s channels to the SUs.

Finally, in Chapter 5 of the Thesis new cooperative communication protocols are proposed for cognitive radio networks, in which one primary user and multiple SUs cooperate for mutual benefit. We proposed and evaluate two new protocols, the Best Relay Selection Protocol (BRSP) and the Stopping Criterion Protocol (SCP) which allow cooperation between the PU and the SUs. Our simulation results demonstrate that the proposed protocols decrease the total primary packet transmission time, compared with the time required for direct packet transmission by the PU.