Multiuser MIMO in distributed antenna systems

Distributed antenna systems (DAS) add remote radio units with one or more antennas to enhance coverage and capacity in cellular systems. DAS works by connecting the remote radio units to the base station via a high bandwidth and low latency link. This paper analyzes multiuser multiple input multiple output (MIMO) DAS and compares it with multiuser MIMO communication without DAS in terms of per-user throughput and area spectral efficiency. Zero-forcing transmit beamforming is used at the transmitter. To facilitate rapid simulation and design space exploration, approximations of the ergodic rate are proposed for each technique assuming path-loss, small-scale Rayleigh fading, and out-of-cell interference. Treating all the remote radio units as a super MIMO transmitter gives the best performance even accounting for out-of-cell interference, though gains diminish for higher numbers of active users.