Transmission strategies in downlink of multi-user multi-cell distributed antenna systems

The use of multiple-input multiple-output (MIMO) systems has been a central part of cellular systems for achieving higher capacity. Distributed antenna system (DAS) is a MIMO system with geographically distributed antennas that provide high coverage and capacity due to the spatial macro diversity. In a multi-user scenario, DAS provides better spatial separation among users. An optimal transmission strategy in a multiuser multi-cell DAS is unknown. We analyze and evaluate downlink capacity of three multiplexing strategies: orthogonal transmission, joint precoding, and space division multiplexing (SDM). Based on the evaluation we propose the most appropriate strategy. The sum-rate has been measured in different scenarios. Simulation results show that DAS has superior performance compared to co-located antennas systems (CAS). It is particularly shown that DAS with simple SDM can provide better capacity than joint transmission in addition to reduced complexity and less feedback overhead. This happens when the number of users increases and remote radio units have single antenna.