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.Comment: Submitted to Transactions on Information Theory, December 2006. 34 pages, 4 figures. Correction, March 26, 2007. Revision, September 13, 2007: Revised text and provided additional proofs regarding diversity-multiplexing tradeoffs and delay-limited rates with optimal long-term power contro

Practical Costa precoding for the multiple antenna broadcast channel

Abstract — For a multiple antenna broadcast channel, the sumrate capacity achieving transmit strategy requires the centralized transmitter to simultaneously communicate with multiple receivers. The objective of this paper is to design an implementable sum-rate capacity achieving transmit strategy that uses a combination of beamforming and coding for known interference. For a two-user Gaussian broadcast channel, results indicate that in the context of typical QAM constellations, with Mt = 2 and Mr = 1, there is significant gain in sum-rate capacity over an approach that uses only beamforming. 1 I