Title: On Optimum Power Control with Mean Channel Gains for Cooperative Relaying Protocols
Authors: Ramesh Annavajjala, Pamela C. Cosman, Laurence B. Milstein (Poster II, 2)

ABSTRACT

In this work, we are concerned with the transmit power optimization problem in a wireless relaying network with various cooperation protocols. With perfect channel state information at the receivers, we derive the optimal power allocation that minimizes the outage probability of the mutual information (MI) with amplify-and-forward (AF), decode-and-forward (DF) and distributed space-time coded (DSTC) relaying protocols operating over the Rayleigh fading channel. At high signal-to-noise ratio, we show that the MI outage probability expressions are convex, and the nature of the optimal power allocation depends on whether or not a direct link between the source and the destination exists. Additionally, for AF and DF protocols, this allocation depends only on the ratio of mean power gains (i.e., the source-to-relay gain to the relay-to-destination gain), whereas with a DSTC protocol this allocation also depends on the transmission rate when a direct link exists. Interestingly, our results without a direct link show that both the DF and DSTC protocols have identical optimal power allocation and the asymptotic coding gain ratio (i.e., the ratio of coding gain with optimal power allocation to the coding gain with equal power allocation). In addition to the immediate benefits of improved outage behavior, our results show that optimal power allocation brings in impressive coding gains over equal power allocation. Furthermore, our analysis reveals that the coding gain gap between the AF and DF protocols can also be bridged by the optimal power allocation.