An Opportunistic Protocol Employing Independent Codebooks for Bidirectional Cooperative Networks

We propose an opportunistic source selection (OSS) protocol employing independent (channel) codebooks (OSS-IC), which outperforms any existing bidirectional-coded decode-and-forward (DF) protocols at high signal-to-noise ratios (SNRs). We derive the expressions of the mutual information, exact outage probability, and asymptotic outage probability for the OSS-IC protocol. We also derive a closed-form and tight approximation for the outage probability. Then, we show that the ideal relay location is the midpoint between two end-sources. Furthermore, we analytically prove that the OSS-IC protocol provides the best outage performance at high SNRs, compared with any known bidirectional-coded DF protocols, including time-division broadcast (TDBC) and physical-layer network coding (PNC). Finally, we quantify the gains of OSS-IC over those protocols at high SNRs.