Adaptive link selection in buffer-aided relaying with statistical QoS constraints

This paper considers a 3-node buffer-aided relaying network with statistical delay quality-of-service (QoS) constraints imposed at the source and relay. To exploit the relay buffering capability and link fading diversity, an adaptive link selection relaying scheme is proposed. In a time slot, the relay (R) can adaptively select to receive from the source (S) or to transmit to the destination (D) based on the instantaneous conditions of the S-R and R-D links. The selection scheme aims to maximize the constant supportable arrival rate to the source, i.e., the effective capacity in consideration of the link fading distributions and the average signal-to-noise power ratios (SNRs) as well as the QoS constraints. We compare the capacities of the adaptive relaying and the fixed relaying where the relay employs fixed transmission and reception schedule, demonstrating the gain of the former, especially under loose QoS constraints. The capacities of the buffer-aided relaying and non-buffer relaying under similar end-to-end delay QoS constraint are also compared, showing the benefits of using buffer-aided relaying to support delay-sensitive applications.