Subject: [NEXTEL-1] Multipath Interference Blessing in Disguise

From: [email-masked]
Date: Wed, 28 May 2003 09:04:04 -0400

Multipath Interference Blessing in Disguise

By Nick Helm, Electronics News Australia -- 5/23/2003
Electronic News

Victoria University of Technology researchers have developed a wireless
technique that not only combats, but actually takes
advantage of the multi-path fading channel that plagues many indoor Wi-Fi and
802.11 installations.

The university’s approach differs from the conventional set-up -- whereby a
transmitter sends a signal from an antenna, which is
received by a second matched antenna at the opposite end -- by using a
multiple-in multiple-out (MIMO) system consisting of a minimum of two
transmitter and receiver pairs. Although more than one antenna -- or active
transmission source -- is used
simultaneously, each pair uses exactly the same frequency band and delivers
power into same spectral channel as its neighbor.

According to the developers, the key the technique relies on “space
diversity”. This method allows transmitting (or receiving)
antennas to be in proximity (in some cases only a few centimeters apart), the
characteristics of the separate fading channels remain unique, or
uncorrelated. The MIMO system uses a deterministic training sequence to sample
the “distinguishing features” of each channel allowing the transmitting and
receiving antenna pairs to recognize each other.

Transmitted data is then divided into a number of sub-streams, split across
the narrow frequency range allocated to a particular
channel. The receiver recombines the sub-stream signals from each antenna
pair, and recreates the original, coherent information.

Potentially, the MIMO system allows a single fading frequency band to support
many individual data channels. More channels
 equals more bandwidth, leading to commercial advantages such as higher speeds
for Wi-Fi implementations.

The university researchers are working within the Australian
Telecommunications CRC’s Wireless Program, a funding initiative that targets
research projects with potential for commercial success. Interest levels were
high at Sydney’s recent CeBit tradeshow, where prototypes demonstrated the
technique. If audience interest is any indicator, we should see the technology
in cafés, offices and other wireless hotspots sometime soon.

http://www.e-insite.net/electronicnews/index.asp?layout=article&articleid=CA301074&spacedesc=news

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