Distributed relay beamforming based on worst signalto-noise ratio constraints for multiple receivers

Recent studies suggest that relay communications can be a major application to extend the range of wireless communications by forwarding the signal from the sender to the receiver. Although fixed or robust distributed relay schemes for single receiver have been previously investigated, the distributed relay beamforming (DRBF) for multiple receivers is studied here. The authors propose an algorithm to design the DRBF weights for maximising the worst received signal-to-noise ratio subject to two different types of relay power constraints, which are the total relay power constraints and individual relay power constraints. The authors also prove that the proposed algorithm with relay power constraints results in a quadratic programming optimisation problem, which can be optimally solved by using semidefinite relaxation technology. The simulation results demonstrate an effective gain of the proposed optimal scheme over other intuition schemes.