Adaptive Antenna System

Hi,

Is there any document / link that explains the Adaptive Antenna System
(AAS) w.r.t WiMAX in detail . I did search , but got only high level
idea about Adaptive Antenna System.

- An Adaptive Antenna System (AAS) can focus its transmit energy to
the direction of a receiver. While receiving, it can focus to the
direction of the transmitting device.
Some of the techniques used
a) Beamforming or beamsteering or beamshaping.
b) SDMA (Space Division Multiple Access) for multiple SSs that are
separated (w.r.t space) to
transmit and receive at the same time over the same sub-channel.

But, i would liket to have more info regarding the techniques and its
implementation w.r.t WiMAX.
I do not find any elaborative tutorial/pdf/link/document w.r.t this in
internet.
Any links/pdfs ?

Thx in advans,
Karthik Balaguru