Hierarchical Transmission Optimization for Massively Dense Distributed Antenna Systems

In a massively dense distributed antenna system (md-DAS), forming user-centric virtual cells (VCs) is an effective way to reduce the implementation complexity. However, the general transmission scheme design for multiple interfering VCs still remains largely open. In this letter, we present an efficient coordinated beamforming scheme to solve this problem in a hierarchical manner, i.e., making different transmission parameters hierarchically adapt to the channel information with different accuracy. Particularly, the direction of the beams is designed by optimizing the achievable rate of each VC, and the strength of the beams is contrived via joint multi-VC interference coordination. Simulation results show that the proposed scheme, although may not be globally optimal, can provide a significant performance gain over the existing methods.