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 a low-complexity relay selection schemes in the presence of interference at the relays and destination. The schemes are mainly based on the switch-and-examine diversity combining (SEC) and SEC with post-examine selection (SECps) techniques in which a relay whose second hop signal-to-noise ratio (SNR) satisfies a predetermined switching threshold is selected instead of the best relay to forward the source message to destination. 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 for the e2e outage probability. We assume that maximal-ratio combining (MRC) is used at the destination to combine the signals of relay and the direct link. Furthermore, to get more about system insights, the outage performance is studied at high SNR regime. Monte-Carlo simulations are provided to validate the derived analytical and asymptotic expressions. Main results illustrate that when the interference power does not scale with SNR, the system can still achieve diversity gain, especially, at SNR values that are comparable to the switching threshold. Asymptotic results show that at high SNR values, the system with the SEC and SECps relaying schemes has a diversity order of 2 and approximately the same coding gain.