Joint MIMO Beamforming and Power Adaptation at Base Station and Broadcasting Relay Transmitters with Quality-of-Service (QoS) Constraints

We propose a broadcasting relay scheme in which the source-to-relay link is a multiple input multiple output (MIMO) channel and the relay-to-destination link is a broadcast channel. The operation for relay station consists of receive beamforming, amplifying and transmit beamforming (R-A-T). We study joint MIMO beamforming and power adaptation to transmit parallel data streams to multiple users with different quality-of-service (QoS) constraints. We derive the optimal solution for the beamforming weights and power adaptation at the base station and the relay station transmitters for the R-A-T scheme, and propose iterative algorithms for joint beamforming weights and power adaption. Simulation results are presented to show that the proposed iterative algorithms achieve the respective target signal-to-interference-plus-noise ratio (SINR) of mobile receivers.