Orthogonalization techniques for single group multicasting in cooperative amplify-and-forward networks

We consider the problem of distributed beamforming in amplify-and-forward (AF) relay networks for single-group multicasting, where a single transmitter sends common information symbols to a group of users via cooperating relays. The objective is to design a computationally efficient beamforming scheme to minimize the total transmitted power at the relays subject to quality-of-service (QoS) constraints of all users. We extend the simple orthogonalization techniques, originally developed in the context of conventional broadcasting systems with instantaneous channel state information (CSI) to solve the present problem in the case when second-order statistics of the channel are available. Simulation results show that our technique outperforms the popular SDR-based technique and provides an excellent performance to complexity trade-off over a large range of QoS constraint thresholds.