Ergodic capacity and power allocation in wireless relay channels [ad hoc networks]

This paper studies the ergodic capacity and power allocation for a three-node relay channel over Rayleigh fading. Assuming perfect channel side information (CSI) at the transmitters and the receivers, we find the upper bounds and lower bounds on the capacity by solving generalized "water-filling" power allocation problems. Our results reveal that the optimum relay channel signaling can significantly outperform direct transmissions and traditional multi-hop transmissions. We also characterize the power gain of using the optimum signaling in the high SNR regime and find the corresponding power allocation policies.