MAC capacity under distributed scheduling of multiple users and linear decorrelation

Consider the problem of a multiple-antenna Multiple-Access Channel at the limit of large number of users. Clearly, in practical scenarios, only a small subset of the users can be scheduled to utilize the channel simultaneously. Thus, a problem of user selection arises. Since solutions which collect Channel State Information (CSI) from all users and decide on the best subset to transmit in each slot do not scale when the number of users is large, distributed algorithms for user selection are advantageous. In this paper, we suggest distributed user selection algorithms which select a group of users to transmit without coordinating between all users and without all users sending CSI to the base station. These threshold-based algorithms are analyzed, and their expected capacity in the limit of large number of users is investigated. It is shown that for large number of users a distributed algorithm can achieve the same scaling laws as the optimal centralized scheme.