Range of Achievable Diversity Order in Multiple Relay Networks with Multiple Users

In this paper, we investigate the range of the achievable diversity order of opportunistic relay selection with M amplify-and-forward (AF) relays and N users. We show that the opportunistic selection of the relay-user pair with the best end-to-end signal-to-noise ratio (SNR) achieves a diversity order between M+N and MN+N. Our analysis reveals that the achievable diversity order depends on the SNR values of the source-relay (SR) and relay-destination (RD) links. Based on our analysis, which is verified by simulation results, we show that the achievable diversity order converges to the upper bound MN+N when the SR link SNR is greater than the RD link SNR; when the SR link quality is poorer than the RD link quality, the diversity order approaches the lower bound M+N.