An iterative optimization method for unitary beamforming in MIMO broadcast channels is proposed, based on successive optimization of Givens rotations. Under the assumption of perfect channel state information at the transmitter (CSIT) and for practical average SNR values, the proposed technique provides higher sum rates than zero forcing (ZF) beamforming while performing close to minimum mean squared error (MMSE) beamforming. Moreover, it is shown to achieve linear sum-rate growth with the number of transmit antennas. Interestingly, the proposed unitary beamforming approach proves to be very robust to channel estimation errors, providing better sum rates than ZF beamforming and even MMSE beamforming as the variance of the estimation error increases. In addition, the proposed technique is presented as a performance reference for evaluation of existing reduced-complexity unitary beamforming techniques, providing numerical results in systems with multiuser scheduling.
An iterative optimization method for unitary beamforming in MIMO broadcast channels
ALLERTON 2007, 45th Annual Allerton Conference on Communications, Systems, and Computing, September 26-28, 2007, Urbana-Champaign, USA
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