Downlink Power Allocation for Distributed Antenna Systems in a Multi-Cell Environment

In this paper, the downlink performance of distributed antenna systems (DAS) in a multi-cell environment is investigated. The individual power constraints (IPC) for the distributed antennas and the total power constraint (TPC) for all the distributed antennas are proposed to characterize the inter-cell interference power limits and the total transmit power consumption, respectively. When the large-scale channel state information is available at the transmitter, the problem of power allocation among distributed antennas with the target of downlink ergodic capacity maximization is formulated with consideration of IPC and TPC. Based on system scale-up, an approximation of the objective function is derived, which is further proved to be concave on the transmit powers of the distributed antennas. Consequently, a simple sub-optimal power allocation scheme is proposed by substituting the approximation for the objective function. The system capacity with the suboptimal power allocation is illustrated to be quite close to the optimal one obtained by numerical optimizations.