Joint Power and Channel Resource Allocation for Two-User Orthogonal Amplify-and-Forward Cooperation

We consider the jointly optimal allocation of the radio resources for a two-user orthogonal amplify-and-forward (AF) cooperation scheme. In particular, we derive a simple efficient algorithm for determining the power and channel resource allocations required to operate at any point on the boundary of the achievable rate region. The algorithm is based on two results derived herein: a closed-form solution for the optimal power allocation for a given channel resource allocation; and the fact that the channel resource allocation problem is quasi-convex. The structure of the optimal power allocation reveals that at optimality at most one user acts as a relay, and hence a fraction of the channel resource will be idle. We propose a modified orthogonal AF cooperation scheme that uses the channel resources more efficiently and hence provides a larger achievable rate region.