Performance Analysis of Partial Relay Selection in Cooperative Spectrum Sharing Systems

In recent years, cooperative diversity and cognitive radio have received considerable attention from the wireless communications community due to its performance gains and spectrum utilization improvements, respectively, when compared to the traditional communications techniques. In one hand, cooperative diversity combats the signal fading caused by the multipath propagation. On the other hand, cognitive radio offers an efficient way to enhance spectrum utilization. However, these two promising technologies have been usually studied apart. In this paper, motivated by the important benefits of cooperative communications, we introduce decode-and-forward relays in primary/secondary spectrum sharing systems with the aim to provide a higher performance for the secondary user. Our analysis considers a partial relay selection in the first-hop transmission, with the relay nodes pertaining to the selected cluster positioned relatively close together (location-based clustering). The end-to-end performance of the secondary communication is investigated for several number of fading channels, such as Generalized Gamma (or alpha - mu), Nakagami-m, and Rayleigh. In particular, considering Rayleigh fading channels, closed-form expressions for the average bit error rate and outage probability are derived. Illustrative numerical examples are provided and the influence of the number of relays, fading parameters, and noise power imbalance between the hops on system performance is discussed.