Optimal Long-Term Power Adaption for Cooperative DF Relaying

This paper addresses the problem of relay power adaption in time for half-duplex decode and forward cooperative system with channel side information knowledge at the relay. We derive the optimal power distribution as a solution of a convex optimization problem that maximizes the long-term average end-to-end spectral efficiency while respecting a target long-term average power constraint. We also propose an efficient algorithm to obtain the exact optimal solution for the important case of discrete channel states. Numerical results show that long-term optimal relay power adaptation provides significant achievable spectral efficiency gains and relay power savings versus the fixed relay transmit power scheme.