An Optimal Multiuser Beamforming Scheme Based on the Worst SNR in Cellular Systems

In the future cellular communication systems, multiple relay nodes can be used for distributed virtual multiple-input multiple-output (MIMO) beamforming to improve the performance of downlink transmissions. In this paper, we study a distributed relay scheme in cellular systems which consists of a base station (BS), multiple amplify-and-forward (AF) relay nodes, and multiple users. We propose an optimal distributed relay beamforming scheme that maximizes the worst-case received signal-to-noise ratio (SNR) under two different types of power constraints, which are the total relay transmit power constraint and individual relay transmit power constraints. We show that the distributed relay beamforming solution for multiusers can be obtained optimally by solving second-order cone programming (SOCP) problems. Numerical results validate our theoretical analysis and demonstrate an effective gain of the proposed scheme over other conventional schemes.