Joint Robust Design Of Beamforming For Downlink Of MU-MIMO Systems

Multiple-Input Multiple-Output technology can improve system's capacity and reliability without any more system band required. It also provides rich diversity gains, multiplexing gains and array gains. So, it is considered as one of the key technologies in future mobile communication systems. However, most of current researches on MIMO multi-user downlink systems are based on the assumption that transmitter could get perfect channel state information(CSI), which is actually very difficult to implement in practical communication systems. As a result, the performance of wireless communication systems based on these theories may be much worse than what we expected.In this paper, we propose a joint transmit and receive beamformer approach under the condition of imperfect channel state information (CSI) for the downlink of multi-user MIMO systems. This approach makes use of the assumption of the total transmit power constraint, the objective of our design is to minimize the system-level sum-MSE. According to this non-convex and non-linear optimization problem's optimum solution condition, we approximately obtain the original issue's optimum solution by computing each user's optimum solution iteratively. Simulation results indicate that this method can reduce system performance loss which induced by imperfect CSI effectively, compared to non-robust approaches. Finally, we expand our solution to broad band MIMO-OFDM systems and meet a good improvement of the system's performance.