Opportunistic Spatial Multiuser Diversity when Transmitter has More Antennas in Downlink

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 from 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, adaptive spatial and temporal scheduling can be developed to exploit the spatial multiuser diversity and achieve the tradeoff between multiplexing gain and spatial diversity gain available. In this paper, the enhanced MIMO schemes with greedy multiuser diversity are compared when Node B has more antenna than UE, e.g. 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 exceeds VBLATS-AS and DSTBC more than 50%