Effective Cooperative ARQ Protocols with the Opportunistic Selective AF Relaying: The Perspectives of Outage versus Packet Error Probabilities

In contrast to the outage analysis, the packet error rates (PERs) of two types of cooperative automatic retransmission request (ARQ) protocols with opportunistic selective amplified-and-forward (OSAF) relaying are investigated from the perspective of the maximum likelihood sequence detection (MLSD). The results show that PERs with the threshold requirements derived from the outage analysis cannot benefit from the diversity via opportunistic retransmissions. Based on the PER analysis, effective threshold setting methods for the two types of ARQs are developed to avoid the diversity losses during ARQs, and verified via simulations using convolutional codes. In contrast to the ARQ protocols with the typical opportunistic AF relaying, the new threshold setting methods allow the OSAF ARQ protocols to provide for practical systems a spatial and temporal diversity comparable to what predicts with the outage analysis.