Network coding gain of cooperative diversity

Cooperative diversity allows a collection of radio terminals that relay signals for each other to emulate an antenna array and exploit spatial diversity in wireless fading channels. Analysis of performance in terms of information-theoretic outage probability leads to two key parameters for these systems, namely, network diversity order and network coding gain, corresponding to the slope and intercept, respectively, in a plot of log-outage versus signal-to-noise ratio (SNR) in decibels (dB). This paper examines the network coding gains of various cooperative diversity protocols, studying the impact of transmission rate and network geometry on this important parameter. In particular, we observe that amplify-and-forward generally outperforms repetition decode-and-forward except when all the relays are much closer to the source than to the destination. Coding gains for amplify-and-forward relative to repetition decode-and-forward are determined and shown to match simulation results.