Performance of Switch-and-Examine DF Relay Systems With CCI at the Relays and Destination Over Rayleigh Fading Channels

In this paper, we evaluate the outage performance of a decode-and-forward (DF) relay system with two low-complexity relay selection schemes and interference at the relays and the destination. The schemes are mainly based on the switch-and-examine diversity combining (SEC) and SEC postexamine selection (SECps) techniques in which a relay out of multiple relays is selected to forward the source message to the destination. The selection process is performed such that the signal-to-noise ratio (SNR) of the second hop of the selected relay satisfies a predetermined switching threshold. In this paper, we first derive the probability density function (pdf) of the SNR of the relay selection scheme and the conditional cumulative distribution function (cdf) of the end-to-end (e2e) signal-to-interference-plus-noise ratio (SINR), assuming Rayleigh fading channels. The derived statistics, along with the statistics of first-hop channels of the relays and the direct link, are then used to derive a closed-form expression of the e2e outage probability. Maximal-ratio combining (MRC) is used at the destination to combine the signals from the relay and the direct link. Furthermore, the outage performance is studied at the high-SNR regime where approximate expressions for the outage probability, diversity order, and coding gain are derived and analyzed. Monte Carlo simulations and some numerical examples are provided to illustrate the validity of the derived results and to show the effect of interference and other parameters on the system performance. Main results illustrate that when the interference power is fixed, the system can still achieve some performance gain when more relays are added, particularly at SNR values that are comparable with the switching threshold. Asymptotic results show that at a high SNR, the system with the SEC and SECps relaying schemes achieves a diversity order of 2 and approximately the same coding gain. Finally, findings illustrate that the interference at the destination is more severe on the system performance compared with that at the relays.