Opportunistic beamforming in a downlink distributed antenna system with linear receivers

Distributed antenna systems provide efficient utilization of the spatial degrees of freedom by processing signals on geographically separated remote radio units. In such systems, the heterogeneous large scale channel effects caused by the distributed located nature complicate the design of opportunistic scheduling schemes and the related issues of limited feedback and exploitation of multiuser diversity. In this paper, we propose and analyze opportunistic beamforming schemes with linear receiver design in a downlink distributed antenna system where the remote radio units serve as virtual transmit antenna array. When each user is equipped with one receive antenna, a single-beam scheme and a multi-beam scheme are proposed and the closed form sum rate is derived. When multiple receive antennas are available, we analyze the multi-beam opportunistic scheme jointly in conjunction with receiver design approaches such as selection combining and linear MMSE receiver. The asymptotic (in users) approximations of the sum rate with linear receivers are derived using asymptotic analysis.