Jointly optimized linear transmit beamforming and receive combining is a low complexity approach for communication in the multiuser MIMO (multiple input multiple output) broadcast channel. This paper proposes an iterative algorithm for jointly designing the beamforming and combining vectors, which enforces a zero interference requirement after combining. Since the optimization is performed at the base station with channel state information for all the users, the receive beamformers are quantized at the basestation and sent to the users via a lowrate feedforward control channel. Rate bounds are provided to estimate the impact of quantization loss on the achievable rate in Rayleigh channels is performed. Simulations show that the proposed approach using Grassmannian codebooks approaches the sum capacity of the MIMO broadcast channel.
This paper proposes non-iterative coordinated beamforming algorithms for a multiuser MIMO (multiple input multiple output) system with multiple antennas at the transmitter and multiple users, each with multiple receive antennas. The transmitter uses linear beamforming to convey information to each user, while each receiver uses a quantized combining vector, sent from the transmitter via a low-rate feedforward control channel. Two different algorithms for optimizing transmit beamformers and receive combining vectors are proposed: a joint optimization and a greedy search. Simulations show that the proposed methods using quantized codebooks approach the sum capacity of the MIMO broadcast channel.
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