Adaptive Power Allocation for Cooperative Relaying System in Fading Wireless Channel

Cooperative relaying technique is a promising technique to provide high rate data transmission. In this paper, optimal power adaptation which maximizes the capacity of relaying system in time-variant wireless channel is addressed. Different from the existing power adaptation methods, where the total instantaneous transmit power of the source terminal and the relay terminal is fixed, the total transmit power is allowed to vary with the channel fading state. We develop an equivalent channel gain model for both the amplify-and- forward and the decode-and-forward relaying mode, based on the optimal power adaptation between the source and the relay. Using the equivalent channel gain model, the relaying channel is modeled as an equivalent direct transmission channel. Then, the optimal power adaptation is found by the time domain water- filling approach. With the time-varying nature of wireless fading channel exploited, our approach is capable of achieving higher channel capacity than the existing power adaptation methods.