Friday, May 26, 2006

Smart Antennas – Enabling Coopers Law

Wireless systems have come a long way in the last ten years due to the penetration of mobile telephony. The antenna is one aspect of a wireless system that is seeing emerging technologies under active development. Traditional antennas broadcast a signal in all directions spreading the power of the signal over a wide area. One way to improve the performance of the antenna is to create a series of cells with an antenna at the center of each cell. This strategy is used by the mobile phone industry. The second strategy places two antennas near to each other and then switches back and forth to get the best signal. This helps eliminate problems caused by multipath fading. Finally, there are smart antennas which use a series of antennas and DSP algorithms to create a more efficient transmission/reception of signals. Smart antennas are also called adaptive array or switched beam.

In this tutorial on smart antennas the author uses the analogy of how one uses hearing to detect the direction of a sound. Smart antennas use multiple antennas to determine the direction of an incoming signal and then transmit back in the same direction; thus providing more efficient reception and transmission.

One type of smart antenna is the MIMO which stands for Multiple Input Multiple Output, which was first investigated by Jack Winters at Bell Labs in 1984. Instead of fighting the problem of multipath fading, MIMO takes advantage of it. Multipath fading is caused by a radio signal bouncing off structures and topographies creating multiple signals which reach the antenna at different times and from various angles.

The Wireless Networking and Communications group at the University of Texas is one example of research in the area of Smart Antennas. Brian Evans researches the use of digital signal processing algorithms to improve the performance of the communication signal. Time equalization shortens the duration of the transmission while frequency equalization mitigates magnitude and phase distortions.

Smart antenna technology is not only under development in the University, but is also deployed by industry. One company on the forefront of Smart Antennas is ArrayComm. Their president, Martin Cooper, articulated “Cooper’s Law” which states that the number of conversations (both voice and data) has doubled every 2.5 years since radio waves were first used for transmission – that’s 104 years ago. This increase is due to several technology improvements including frequency division, modulation techniques, spatial division, and the increase in usable spectrum and now smart antennas.

Lyrtech makes FPGA and DSP-based platforms for smart antenna development which is all about providing higher data rates and higher capacities on the wireless network. Bandspeed is an Austin company that applied Spatial Division Multiplexing to WLAN applications, which adjusts the transmit power and sectorizes the physical coverage of the RF signal.

As wireless becomes increasingly important to our communications infrastructure, the need for bandwidth will grow. Smart antennas are an important technology in this area.

Best regards,
Hall T.