Buffer-Aided Relaying with Mixed Rate Transmission

We investigate a simple three-node network consisting of a source, a half-duplex decode-and-forward relay with a buffer, and a destination. We assume that a direct source-destination link is not available and all links undergo fading. We consider the case where the source has no channel state information (CSI) and thus is forced to transmit with a fixed rate. On the other hand, the relay has full CSI and thus is able to adapt its rate to the underlaying channel. We propose a buffer-aided relaying protocol which allows the relay to choose its transmission and reception time slots adaptively and based on the quality of the source-relay and relay-destination links. For this system, we derive the maximum achievable throughput and the fraction of throughput lost due to outages. Our results reveal that compared to the conventional case when the relay always alternates between reception and transmission, a throughput gain of up to 100% is possible.