Linear Precoding for Multi-User Multiple Antenna TDD Systems

Traditional approaches in the analysis of downlink systems decouple the precoding and channel estimation problems. However, in cellular systems with mobile users, these two problems are in fact tightly coupled. In this paper, this coupling is explicitly studied by accounting for channel training overhead and estimation error while determining the overall system throughput. The paper studies the problem of utilizing imperfect channel estimates for efficient linear precoding and scheduling. We present a precoding method that takes into account the degree of channel estimation error in conjunction with the number of users. Next, we optimize the training period, which is an important operational parameter for these systems. Finally, we present lower and upper bounds of the achievable throughput. In typical scenarios, these bounds are close.