Performance analysis of an asymmetric two-hop amplify-and-forward relaying RF–FSO system in a cognitive radio with partial relay selection

In this paper a performance analysis is presented for an asymmetric two-hop amplify-and-forward (AF) relaying system with multiple relays in an underlay cognitive radio network (CRN), where a partial relay selection (PRS) is used to select the best relay for the signal transmission. In the considered system, the two hops employed are hybrid and asymmetric, which include the source-to-relay (SR) and the relay-to-destination (RD) links. The first hop (SR link) is a radio frequency (RF) channel and the second hop (RD link) is a free space optical (FSO) channel. The RF and FSO channels follow Rayleigh, and Gamma–Gamma distribution, respectively, where some practical concerns such as atmospheric turbulence and pointing errors are taken into consideration. To start the performance evaluation and analysis, the cumulative-distribution-function (CDF) of the received signal-to-noise-ratio (SNR) at the destination side is mathematically derived. Then, by means of the derived CDF, closed-form expressions are derived for the outage performance, average BER and the average channel capacity of the underlying system. Finally, the numerically evaluated results, validated by computer simulations, provide insights about system performance under various parameters and practical situations.