A low-complexity relaying protocols for incremental DF relay systems with co-channel interference

In this paper, we evaluate the interference effect on the performance of incremental decode-and-forward (DF) relay systems with a low-complexity relaying protocols and interference at the relays and destination. These protocols are based on the switch-and-examine diversity combining (SEC) and switch-and-examine diversity combining with post-examining selection (SECps) techniques. Based on the relaying criterion, the first checked relay whose second hop signal-to-noise ratio (SNR) satisfies a predetermined switching threshold is asked to forward the source message to destination only if the direct link is in outage. Closed-form expression is derived for the end-to-end (e2e) outage probability assuming Rayleigh fading channels. Also, the system performance is studied at high SNR regime for the two relaying protocols where the diversity order and coding gain are derived and analyzed. We assume that maximal-ratio combining (MRC) is used at the destination to combine the signal through the relay with that on the direct link. Monte-Carlo simulations are provided to validate the achieved analytical results. Findings illustrate that despite the presence of interference, the system still achieves performance gain and that the outage probability decreases when the number of relays increases, especially, in the range of SNR values that are comparable to switching threshold. Also, results show the effectiveness of the SEC and SECps relaying protocols in reducing the system complexity compared to the existing protocols as the opportunistic relaying.