Channel estimation in MIMO-OFDM

Wireless LAN Comes of Age:Understanding theIEEE 802.11n Amendment
by Thomas Paul and Tokunbo Ogunfunmi

published in IEEE circuits and systems magazine
Tutorial for WLAN design (including 802.11n, 802.11ac)

Check Section III. 2.5


Also, some tutorial on least square estimation techniques, which is used to derive the results in channel estimation.

http://www.stat.math.ethz.ch/~geer/bsa199_o.pdf