Robust Transmit Beamforming for Collaborative MIMO-OFDM Systems

We present a robust beamforming scheme for collaborative multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless systems. Optimum collaborative transmit beamforming requires knowledge of channel state information (CSI) at the transmitters (collaborative nodes). In practice, however, exact knowledge of CSI is not available at the transmitters. To mitigate the effects of the channel mismatch, we consider a max- min beamforming design approach for collaborative transmission by maximizing the minimum (worst-case) received signal-to-noise ratio (SNR) within a predefined uncertainty region at each OFDM subcarrier. In addition, several subcarrier power allocation strategies are investigated to further improve the performance of collaborative systems.