We consider a multiuser system where a single transmitter equipped withmultiple antennas (the base station) communicates with multiple users each witha single antenna. Regularized channel inversion is employed as the precodingstrategy at the base station. Within this scenario we are interested in theproblems of power allocation and user admission control so as to maximize thesystem throughput, i.e., which users should we communicate with and what powershould we use for each of the admitted users so as to get the highest sum rate.This is in general a very difficult problem but we do two things to allow someprogress to be made. Firstly we consider the large system regime where thenumber of antennas at the base station is large along with the number of users.Secondly we cluster the downlink path gains of users into a finite number ofgroups. By doing this we are able to show that the optimal power allocationunder an average transmit power constraint follows the well-known water fillingscheme. We also investigate the user admission problem which reduces in thelarge system regime to optimization of the user loading in the system.
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