Cooperative beamforming in multi-source multi-destination relay systems with SINR constraints

The paper investigates linear beamforming techniques in relay networks with multiple independent sources, destinations and relay(s). The goal is to determine the beamforming matrix to minimize the sum transmit power at the relays while meeting signal-to-interference (SINR) requirements at the destinations. Two scenarios are considered: one is the case of single relay with multiple antennas in which the beamforming matrix can be of any form, while the other is the case of distributed single antenna relays, where the beamforming matrix is diagonal. An interference zero-forcing criterion is applied for the design of the beamforming matrix at the relays assuming that perfect channel state information is available. It is shown that the former problem is a constrained least square problem and the latter one can be solved by SemiDefinite Programming (SDP) with relaxation. Simulation results show that the proposed beamforming schemes can reliably support multiple parallel data streams with SINR requirements in multiuser relay systems.