Enhanced MU-MIMO Downlink Transmission in the FDD-Based Distributed Antennas System

The multi-user multiple input multiple output (MU-MIMO) downlink (DL) transmission solutions based on the frequency division duplex (FDD) mode, which is widely investigated in 3GPP Long Term Evolution-Advanced (LTE-A), has been found to fail in improving the throughput with the distributed antennas in previous work. After clarifying the reason for the throughput deterioration by taking insight into the users´ experienced channel vectors distribution in the complex hypersphere, the way of constructing the optimized codebook is designed. Then the new DL transmission strategy utilizing the reciprocity between uplink (UL) and DL in the sense of large scale fading is proposed for throughput improvement but without the great modification on the existing system in the context of LTE-A. The simulation results show that our proposal outperforms the existing methods by 600% at most in the environment where the antennas of base station are dispersedly located.