Comparative Investigation on Spatial Multiuser Diversity for Downlink MIMO in TDD System

MIMO can enhance the performance of wireless system greatly. However, the limited battery life and terminal size of the UE in a cellular system put a constraint on the performance enhancement by MIMO. Especially when the transmitter has more antenna than the receiver in downlink, the conventional MIMO schemes can only exploit partial spatial multiplexing gain and diversity gain. For different users' independent locations lead to independent spatial fading one another, the spatial multiuser diversity is proposed to achieve the tradeoff between the multiplexing gain and spatial diversity gain available. In this paper, the enhanced MIMO schemes with multiuser diversity for this scenario are compared, zero forcing beamforming (ZFB), dual space time block coding (DSTBC), singular value decomposition (SVD) and vertical Bell labs layered spatial time code plus antenna selection (VBLAST-AS). From the simulation results, the ZFB has achieved the best spectrum efficiency, and the gain over the VBLATS-AS and DSTBC is more than 50%.