Adaptive MIMO Beamforming Algorithm Based on Gradient Search of the Channel Capacity in OFDM-SDMA Systems

This letter proposes an adaptive beamforming algorithm for uplink access in broadband wireless networks employing orthogonal frequency-division multiplexing with space-division multiple access (OFDM-SDMA) technologies. The proposed algorithm seeks, iteratively, the optimal transmit weight vectors that directly maximize the OFDM-SDMA channel capacity for each user in the system, using gradient search of the channel capacity. The analysis and simulation show that the capacity of OFDM-SDMA systems with the transmit weights obtained using the proposed adaptive beamforming algorithm is substantially higher than the one based on conventional approaches such as eigen-beamforming.