Submitted to IEEE Journal on Selected Areas in Communications, Nov. 2007.
In this paper, we propose a novel joint optimization of linear transmit beamformers and receive combining vectors for the multiple-input multiple-output (MIMO) broadcast channel. We consider the specific case of transmission of a single information stream to multiple users with one on more receive antennas. Unlike past work in which an iterative algorithm is required to design the beamformers, we provide a simple closed-form expression for the jointly optimized transmit beamformers which works for any number of receive antennas. We derive a specific formulation for the two transmit antenna case and provide a good extension to multiple antennas via the generalized eigenvalue decomposition for two active users. To enable practical implementation, a new limited feedback algorithm is proposed that exploits the structure of the algorithm to avoid full channel quantization, and is independent of the number of receive antennas. Monte Carlo simulations are used to evaluate the bit error rate and the sum rate performances of the proposed algorithm. Simulation results show that the proposed method performs close to the sum capacity of the MIMO broadcast channel even with limited feedback.
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