Robust Transmit Multiuser Beamforming Using Worst Case Performance Optimization

We address the problem of transmit beamforming under channel uncertainties for a multiuser MIMO system, where both the transmitter and the receiver are equipped with multiple antennas. In transmit beamforming multi-user multiplexing is performed using spatial diversity techniques so that a base station could serve multiple users in the same frequency band enabling a substantial saving in bandwidth utilization. However, such techniques require nearly perfect knowledge of the channel state information at the transmitter, which is generally not available in practise. In this paper, we propose robust spatial multiplexing schemes based on a worst case performance optimization by incorporating imperfect channel state information. In the simulation, we have examined two scenarios. In the first the channel state information is assumed to have Gaussian distribution errors. In the second scenario, we analyze the performance for errors introduced due to a partial channel state information feedback scheme. In both scenarios, the proposed robust scheme outperforms the conventional scheme.