Mobile working Toolkit

The long and winding road to Wi-Fi 2.0

Matthew Broersma ZDNet.co.uk

Published: 17 Oct 2005 15:30 BST

...big business and promising to reveal an enterprise-grade licensee this year. The company says larger companies are "very open" to the technology, now that a number of competing chipmakers have jumped aboard the MIMO bandwagon. Trapeze Networks says it will begin selling MIMO Wi-Fi products to enterprises for specialised applications such as wireless videoconferencing.

How it works
MIMO's main benefits are all to do with using its multiple antennas — which can be internal or external — to process signals.

One of these techniques, used by most MIMO chips, is the ability to resolve multiple signal paths, known more technically as multipath signals. These are the echoes and fragments of signals that arrive after the main line-of-sight signal, such as the reflections off of buildings in a built-up environment. Traditional 802.11 gear sees these signals as distortion, but MIMO is able to use them to reinforce the main signal. That means clearer signals, longer-range signals or a bit of both.

A related feature, pioneered by Airgo, is spatial division multiplexing (SDM), which transmits multiple independent data streams within a single channel of bandwidth. This can increase throughput as the number of data streams is increased. Multipath processing can work with a conventional transmitter at the other end, but spatial multiplexing requires an antenna pair at each end of the transmission for each data stream — in other words, it won't give any benefits unless MIMO hardware is in use on both ends of the signal.

MIMO antennas each need dedicated processing hardware, which means manufacturing costs are unavoidably higher than current standard Wi-Fi kit.

Routers from Linksys and Belkin are currently using Airgo's True MIMO technology, with multipath and spatial multiplexing. The RangeMax Wireless Router from Netgear uses BeamFlex from Ruckus Wireless, formerly known as Video54. This MIMO variant has seven antennas and uses a technique called beamforming instead of spatial multiplexing.

Beamforming transmits multiple identical data streams, instead of independent streams, but the results are similar. D-Link's Super-G with MIMO wireless router uses a four-antenna Atheros Communications chipset, which also uses beamforming instead of spatial multiplexing.

MIMO hardware generally shows only slight...

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