Outage Analysis and Power Savings for Independent and Coherent Decode-Forward Relaying

In this paper, we consider a composite independent and coherent decode-forward (DF) relaying scheme and analytically evaluate its outage performance over Rayleigh fading channels. We examine the link-state regimes in which the optimal strategy is either direct transmission, independent DF (IDF), or coherent DF (CDF), depending on the relation among the links. Outage probabilities at both the relay and destination are determined in order to analytically derive the overall outage performance. With full channel state information (CSI), the relay can save power without affecting the overall outage performance. Specifically, by using only a portion of its maximum power for transmission, the relay conserves power in the IDF regime while still achieving the maximum transmission rate. Even with just statistical CSI, the relay can employ these link regime results to reduce transmit power significantly while maintaining the same outage performance as that of using full power.