Thursday, September 17, 2009

Adaptive Antenna System (AAS) | Technologies

An adaptive antenna system allows a transmitter to focus radio beams to increase the transmission range, reduce interference and increase signal quality. When an AAS system is used to allow multiple users to communicate with the same transceiver (multiple beams), it is called spatial division multiple access (SDMA). SDMA technology has been successfully used in satellite communications for several years. In some SDMA systems, radio beams may dynamically change with the location of the mobile radio.

The WiMAX system is designed with AAS capability. To support AAS, it is necessary to supplement the medium access control (MAC) protocol with additional commands so that base stations can better monitor subscriber stations which may be operating in a narrow focused beam area. If the subscriber station were to move out of the focused beam area, the system could loose control of the subscriber station.

Figure 1 shows an example of a WiMAX adaptive antenna system (AAS). The cell site can focus radio signals using the same frequency to multiple devices within the same cell site. Focusing of the radio signal allows for an increase in the distance that a cell site can have when communicating with devices. Using AAS technology, the system can adapt the direction of the focused beam to a specific device as it moves throughout the coverage area.

Figure 1: WiMax Adaptive Antenna System
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