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Senior Editor

The battle for wireless antennae

Aug 04, 20042 mins
Cellular NetworksNetwork SecurityWi-Fi

* A look at the emerging antenna technology known as Multiple Input Multiple Output, or MIMO

The promise of doubling the throughput and range of wireless LANs could ensure the success of an emerging antenna technology known as Multiple Input Multiple Output. MIMO algorithms in a radio chipset send information out over two or more antennas. The radio signals reflect off objects, creating multiple paths that in conventional radios cause interference and fading. But MIMO uses these paths to carry more information, which is recombined on the receiving side by the MIMO algorithms.

Many WLAN vendors expect that some form of MIMO will be the basis of work just starting in the IEEE 802.11n Task Group, which is creating a specification for WLANs having at least 100M bit/sec throughput. The 3rd Generation Partnership Project, a collaboration of telecom standards groups, also is evaluating MIMO techniques for use in cellular networks.

According to a recent Technology Update by ( MIMO is one technology being considered for 802.11n, a standard for next-generation 802.11 that boosts throughput to 100M bit/sec per 20-MHz channel. In the meantime, proprietary MIMO technology is available that improves performance of existing 802.11a/b/g networks.

Keep in mind however that MIMO is just one form of smart antenna. Motia has designed its Javelin 2.4-GHz chipset, coupled with a four-antenna adaptive array, as an add-on for existing 802.11 radio transceivers. The chipset combines signals to shape an optimal radio beam, and like MIMO uses the multipath method. Wireless vendor Vivato Networks uses another smart antenna technique, called phased array. This approach packs a lot of individual antennas, each with a slightly different directional pattern, into a single panel. Algorithms steer the radio beam to the appropriate antenna elements for a given WLAN client. The result is a big increase in range, though this technique has been most successful in outdoor applications.

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