Dynamic Beamforming for Time-varying Distributed Antenna System

This paper handles dynamic beamforming for distributed antenna system (DAS) by considering time varying of wireless channel. Most of existing results on optimal beamformer are established under the assumption that channel state information (CSI) is quasi-static or constant. We consider a more realistic scenario to minimize the sum power of all the antenna nodes while meeting the quality of service (QoS) requirements of all the mobile users (MUs) in time-varying DAS. Assuming the channel changes continuously, CSI is firstly modeled by employing stochastic differential equation (SDE). The considered dynamic beamforming problem is then transformed into stabilization for SDE using primal-dual interior point (PDIP) method for semidefinite program (SDP). By exploiting the theory of stochastic stability, the proposed method can be shown to be asymmetrically stable in the sense of probability. Our method can be extended to the scenario with outdated CSI by channel prediction. Simulation results show that the proposed method can save about 5dBm power, in contrast to the method using outdated CSI.