Optimizing Transmitter-Receiver Collaborative-Relay Beamforming with Perfect CSI

This letter studies a three-hop channel constructed by collaborative relaying terminals at both the transmitter and receiver ends. Our objective is to optimize the complex amplify-and-forward (AF) weights of the relaying terminals if the channel state information (CSI) is exploited. A near-optimal numerical solution for the collaborative-relay beamforming (CRBF) weights is first found from solving an unconstrained multi-variant minimization problem. Using the concept of subspace averaging, a near-optimal closed-form CRBF solution is then proposed.