Contrary to what may be reported, MIMO is *not* antenna diversity, beam forming etc. There are many pseudo-MIMO products out there in WLAN but not a real MIMO yet.
MIMO takes advantage of fading. It doesn't try to 'fix' it. A 2x2 MIMO system for example outputs different data at the same frequency (one data stream for each antenna) which is coded in such a way so that at the receiver the fading is used to merge and decode the data successfully.
Read the following:
h**p://www.datacommresearch.com/whitepapers/Downloads/MIMO_Research_Alert.pdf [/b]