Cooperative Communications with Outage-Optimal Opportunistic Relaying

TLDR

The paper proposes simple opportunistic relaying using decode‑and‑forward and amplify‑and‑forward strategies under an aggregate power constraint. The authors employ distributed relay‑selection algorithms that rely solely on local channel knowledge to implement the opportunistic relaying. The study demonstrates that opportunistic decode‑and‑forward relaying achieves outage optimality equivalent to using all relays, while opportunistic amplify‑and‑forward relaying outperforms equal‑power multi‑relay schemes and shows that passive listening relays still provide diversity gains, with numerical results confirming the analysis.

Abstract

In this paper, we present simple opportunistic relaying with decode-and-forward (DaF) and amplify-and-forward (AaF) strategies under an aggregate power constraint. In particular, we consider distributed relay-selection algorithms requiring only local channel knowledge. We show that opportunistic DaF relaying is outage-optimal, that is, it is equivalent in outage behavior to the optimal DaF strategy that employs all potential relays. We further show that opportunistic AaF relaying is outage-optimal among single-relay selection methods and significantly outperforms an AaF strategy based on equal-power multiple-relay transmissions with local channel knowledge. These findings reveal that cooperation offers diversity benefits even when cooperative relays choose not to transmit but rather choose to cooperatively listen; they act as passive relays and give priority to the transmission of a single opportunistic relay. Numerical and simulation results are presented to verify our analysis.