### Low Complexity User Selection Algorithms

### for Multiuser MIMO Systems with Block Diagonalization

### Authors:

Zukang Shen, Runhua Chen, Jeffrey G. Andrews, Robert W. Heath, Jr., and Brian L. Evans

### Reference:

In Proc. *IEEE Asilomar
Conf. on Signals, Systems, and Computers*, Oct. 30-Nov. 2, 2005, Pacific
Grove, CA.

### Abstract:

Block diagonalization
(BD) is a precoding technique that eliminates
inter-user interference in downlink multiuser
multiple-input multiple-output (MIMO) systems. With the assumptions that all
users have the same number of receive antennas and utilize all receive antennas
when scheduled for transmission, the number of simultaneously supportable users
with BD is limited by the ratio of the number of basestation
transmit antennas to the number of user receive antennas. In a downlink MIMO
system with a large number of users, the basestation
may select a subset of users to serve in order to maximize the total
throughput. The brute-force search for the optimal user set, however, is
computationally prohibitive. We propose two low-complexity suboptimal user
selection algorithms for multiuser MIMO systems with
BD. Both algorithms aim to select a subset of users such that the total
throughput is nearly maximized. The first user selection algorithm greedily
maximizes the total throughput, whereas the criterion of the second algorithm
is based on the channel energy. We show that both algorithms have linear
complexity in the total number of users and achieve around 95% of the total throughput of the complete search method in simulations.

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