Linearized Robust Beamforming for Two-Way Relay Systems

In beamforming, channel state information (CSI) is used to design the beamforming vector (or matrix). Since in a practical system the CSI always needs to be estimated, channel estimation (CE) errors are inevitable, which could severely affect the performance of a beamforming scheme. In this paper, we present a novel beamforming method for two-way relay (TWR) systems that is robust against CE errors. The proposed method obtains a sub-optimal solution for the associated non-convex robust optimization problem by solving a set of closed-form linear equations. Simulations show a considerable performance gain over the rank-one relaxation-based semidefinite programming (SDP) solutions, especially for the cases where the relaxed problem becomes infeasible. In addition, there is significant reduction in complexity, making this method very attractive for practical implementation.