Robust multi-cell joint transmission beamforming based on uplink-downlink duality

This paper considers robust beamforming design for coordinated multiple point joint transmission systems with imperfect channel state information at the base stations (BSs). A robust lower bound duality relation between the downlink max-min worst-case SINR optimization problem and the virtual uplink min-max worst-case SINR optimization problem is first revealed. Based on this, an iterative optimization method is then proposed using the subgradient theory to solve the virtual uplink problem, by which the solution to the downlink optimization problem is easily obtained. It is proved that the convergence of the proposed algorithm can be guaranteed with monotonic boundary sequence theorem and the subgradient theory. Numerical simulation verifies the effectiveness of the proposed method.