Outage Probability-Based Power and Time Optimization for Relay Networks
Walid Hachem, Pascal Bianchi, Philippe Ciblat · IEEE Transactions on Signal Processing · 2008
In the context of cooperative wireless networks that convey data on slow fading channels, outage probabilityPois the relevant performance index from the point of view of information theory. Derivation and minimization of this probability with respect to the relaying protocol parameters is of central importance. However, it is often hard to derive its expression, let alone to find its exact minimum for all possible values of the signal-to-noise ratio (SNR). This problem can be simplified by studying the behavior ofPoin the asymptotic regime where the SNRrhoconverges to infinity. In this regime, usuallyrhoN+1Poconverges to a constantxiwhereNis the number of relays. In this paper, a simple and general method for deriving and minimizingxiwith respect to the power distribution between the source and the relays, and with respect to the durations of the slots specified by the relaying protocol, is developed. While the proposed approach is designed for the high SNR regime, simulations show that outage probability is reduced in a similar proportion at moderate SNR. The method applies to a general class of radio channels that includes the Rayleigh and the Rice channels as particular cases. Convexity ofxiwith respect to the design parameters is shown. Decode-and-forward, as well as amplify-and-forward protocols are considered in the half duplex mode.