IEEE 802.11 Performance Enhancement by MIMO Spatial Multiplexing

IEEE 802.11 wireless LANs are evolving into a high speed system by adopting MIMO technologies. Currently the standard deals with transmission for one user over a link. In this paper, we consider the MIMO technique of spatial multiplexing that enables multiple users to receive packets over the downlink simultaneously. It takes advantage of multiuser diversity in the space and time domains, supposing that each antenna independently performs link adaptation for each subchannel. Through analysis, we show that multiuser transmission has performance improvement over the single-user case. However, by using adaptive data splitting over spatial multiplexing, the performance of the single-user transmission is enhanced, and even better than that of multiuser case for small multiuser diversity. To exploit the multiuser diversity extensively, we apply a scheduling algorithm that considers channel condition of each subchannel. Simulation results show the multiuser transmission has higher link utilization than the single-user case for large multiuser diversity. To implement this, the system requires further considerations to modify ACK policy, and to mix conventional and MIMO-capable stations