An exact error probability analysis of incremental opportunistic decode-and-forward relaying with feedback delay

Incremental opportunistic relaying (IOR) has been proposed to increase the spectral efficiency of the two-phase cooperative transmissions by exploiting limited feedback from the destination node. Specifically, the relaying process is activated only if the source-destination channel is of insufficient quality. In this case, the feedback instructs the best relay to forward the source message to the destination in order to exploit the spatial diversity. In this work, we analyze the effect of feedback delay on the performance of IOR with decode-and-forward strategy. Particularly, we derive an exact expression for the average symbol error probability (SEP) of IOR with feedback delay over independent but not necessarily identically distributed Rayleigh fading channels. An approximate but tight closed-form expression for the SEP is also provided. Finally, we perform Monte Carlo simulations to verify the analytical results. The results show that IOR is robust to the feedback delay at sufficiently high signal-to-noise ratio.