On Limits of Wireless Communications in a Fading Environment when UsingMultiple Antennas
Wireless Personal Communications: An International Journal
Sum power iterative water-filling for multi-antenna Gaussian broadcast channels
IEEE Transactions on Information Theory
An introduction to the multi-user MIMO downlink
IEEE Communications Magazine
On the optimality of multiantenna broadcast scheduling using zero-forcing beamforming
IEEE Journal on Selected Areas in Communications
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We propose a best zero-forcing (ZF) precoding methodology that utilizes best a multiple-input multiple-output broadcast (MIMO-BC) channel. To utilize best a ZF-precoded MIMO-BC channel, we would select the best subset of users for ZF-precoding within a given set of users, so that the maximum sum capacity could be achieved under the given set of users and associated channel condition. We also propose a simple and accurate best-user grouping algorithm that selects a proper subset of users for ZF-precoding without a noticeable loss in the sum capacity. The ZF-precoding methodology based on best-user grouping might improve significantly the sum capacity through pre-exemption of some poor and/or highly correlated users prior to ZF-precoding, rather than simple ZF-precoding followed by a simple water-filling power allocation to all the users considered. Simulation results show that the proposed methodology based on best-user grouping provides a much higher sum capacity than the original one does. The proposed best-user selection algorithm works quite well without noticeable complexity increase and provides the highest sum capacity for ZF-precoding in almost all cases. The performance improvement of the proposed methodology becomes more significant as the number of transmit antennas and associated number of users increases and/or the signal-to-noise ratio (SNR) gets low.