Flow-optimized Cooperative Transmission for the Relay Channel

This paper describes an approach for half-duplex cooperative transmission in a classical three-node relay channel. Assuming availability of channel state information at nodes, the approach makes use of this information to optimize distinct flows through the direct link from the source to the destination and the path via the relay, respectively. It is shown that such a design can effectively harness diversity advantage of the relay channel in both high-rate and low-rate scenarios. When the rate requirement is low, the proposed design gives a second-order outage diversity performance approaching that of full-duplex relaying. When the rate requirement becomes asymptotically large, the design still gives a close-to-second-order outage diversity performance. The design also achieves the best diversity-multiplexing tradeoff possible for the relay channel. With optimal long-term power control over the fading relay channel, the proposed design achieves a delay-limited rate performance that is only 3.0dB (5.4dB) worse than the capacity performance of the additive white Gaussian channel in low- (high-) rate scenarios.