Diversity Analysis of Multi-User Multi-Relay Networks

In this paper, we analyze the diversity order of opportunistic scheduling networks with arbitrary numbers of relays and users. We show that the opportunistic selection of the relay-user pair with the best end-to-end signal-to-noise ratio (SNR) among M relays and N users achieves a diversity order in the range of [M + N, MN + N] for amplify-and-forward (AF) relays and in the range of [N, MN + N] for decode-and-forward (DF) relays. Our analysis reveals that the achievable diversity order with AF relays depends on the relative strength of the source-relay (SR) and relay-destination (RD) links, while the achievable diversity order with DF relays depends on the SR link SNR. Based on our analysis, which is verified by simulation results, we show that, for AF relays, the maximum diversity order of MN + N is achieved if the SR link quality is better than the RD link quality, and, for DF relays, if the SR link is sufficiently strong such that the relays always succeed in decoding.