Achieving Optimal Diversity Gain in Buffer-Aided Relay Networks with Small Buffer Size

This paper investigates the buffer-aided relay selection problem for a decode-and-forward cooperative wireless network with K relays. We propose a new relay selection scheme that incorporates the status of the relay buffers and the instantaneous strength of the wireless links. Specifically, each link is assigned with a weight related to the buffer status; then, the best relay is selected with the largest weight among all the qualified source-relay and relay-destination links. We derive the closed-form expression for the outage probability and the diversity gain by introducing several Markov chains (MCs) to model the evolution of the buffer status. The analysis shows that the proposed scheme can achieve the optimal diversity gain 2K for a small L (i.e., L ≥ 3), an improvement in comparison with the existing max-link scheme that achieves the optimal diversity gain only when L is sufficiently large, where L denotes the buffer size of each relay. The provided theoretical and numerical results confirm the performance gain of the proposed relay selection scheme over the existing max-link scheme.