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. The technique used in AAS is known as beamforming or beamsteering or beamshaping. It works by adjusting the width and the angle of the antenna radiation pattern (a.k.a. the beam).
Figure. WiMAX BS with AAS beamforming capability
The main lobe is directed toward a subscriber station (SS).
Combined with multiple antennas in the Base Station (BS), AAS can be used to serve multiple Subscriber Stations (SSs) with higher throughput. A technique known as SDMA (Space Division Multiple Access) is employed here where multiple SSs that are separated (in space) can transmit and receive at the same time over the same sub-channel.
Figure. WiMAX BS with multiple antennas and AAS
AAS and multiple antennas combined in the BS can increase per user data rate.
AAS also eliminates interference to and from other SSs and other sources by steering the nulls to the direction of interferers. AAS is an optional feature in WiMAX and not included in WiMAX certification. But due to its effectiveness in improving performance and coverage especially in Mobile WiMAX case, many vendors integrate AAS capability into their products.
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