Buffer-aided max-sum relay selection and energy efficiency analysis in OFDM relay systems

In this paper, we analyze the energy efficiency (EE) and outage performance in buffer-aided orthogonal frequency division multiplexing (OFDM) relay systems. All the relays adopt the amplify-and-forward (AF) protocol and the transmission from the source to destination on orthogonal subcarriers. We propose the max-sum relay selection scheme, which fully exploits the flexibility offered by both OFDM subcarriers and buffer-aided relays. The max-sum scheme always chooses the strongest available relay which dynamically switching between reception and transmission while. The exact expressions for the EE and the stationary state probability are derived. We adopt a novel joint time-frequency subchannel pairing (TPFP) strategy based on channel quality that obtains both the two gains bring by time pairing and frequency pairing of channels respectively. Numerical results show that the max-sum scheme provides significant improvement on EE and outage performance in buffer-aided OFDM relay system. Furthermore, the performance of the TPFP strategy is shown optimal compared with that of conventional no subchannel pairing systems.