Relay Power Savings through Independent Coding

We present a link-state based composite decode-forward (DF) scheme for the relay channel comprised of independent coding and coherent block Markov coding. Although it is believed that block Markov coding is the optimal DF technique whenever the source- to-relay link is stronger than the direct link, we show that under some link-state conditions, independent coding achieves the same rate but also results in power savings at the relay. We then apply this composite scheme in fading under a practical channel state information (CSI) assumption in which nodes have perfect receive CSI and long-term transmit CSI. Through simulation, we demonstrate that the throughput with practical CSI achieves a rate comparable to that of block Markov coding, but with less required relay power. Further, we expose a novel trade-off between consumed relay power and rate gain for relay placement. Specifically, the relay conserves the most power when closer to the destination but achieves the most rate gain when closer to the source.