Performance evaluation on dynamic dual layer beamforming transmission in TDD LTE system

In TDD LTE system, beamforming technology is feasible with dynamic switch between single-layer beamforming and dual-layer beamforming for data transmission. However, in a heavy-loaded system, dense flash-light effects will significantly impact cell performance. In this paper, we review the basic downlink Radio Resource Management (RRM) functions and propose to combat flash-light effects by explicitly shielding off flash-light impacts in rank determination. Compared to original scheme using Outer Loop Link Adaptation (OLLA) to compensate all link quality variations, the proposed scheme shows average 8% cell throughput gain in simulation. We also analyze the system behavior with finite traffic model and different rank adaptation working points. Finally, we compare the 8-pipe radio based dynamic beamforming transmission with 2-pipe based dynamic closed-loop MIMO transmission. Simulation results show that, TDD beamforming system has 22% gain in average cell throughput but quite limited gain (+3%) per UE cell edge against TDD 2×2 system.