Transmit Diversity Method with User´s Power Constraint for Distributed Antenna System

In this paper, we consider single user transmit diversity problem in distributed antenna system. As known, maximum ratio transmission can maximize the received SNR under sum power constraint (SPC) (T. Lo, 1999). Multi user downlink beamforming problem with per-antenna power constraint (PAPC) is considered in papers ((F. Boccardi and H. Huang, 2006), (Wei Yu and Tian Lan, 2006)). In this paper, a general power constraint named user´s power constraint (UPC) is placed on each antenna in distributed antenna system, which limits antenna practical power for desired user not higher than the constraint. The optimum transmit weight designing problem is investigated under both sum power constraint (SPC) and user´s power constraint (UPC) in DAS. The weight designing problem under SPC and UPC is formulated as a nonlinear optimization problem, and we find the optimum weight vector have the same phase as MRT. After that, we transform the primal problem to a convex optimisation problem, and numerical method can be used to get the optimal solution. Furthermore, an algorithm named gradient-MRT is proposed to find the optimal solution