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Wednesday, 17 January, 2001, 19:16 GMT
Driving data to new highs
London skyline BBC
Buildings can be a pain and boon to data transmission
By BBC News Online internet reporter Mark Ward

US scientists have found a neat way to boost the data-carrying abilities of wireless networks.

By taking advantage of the way that radio signals get scattered in built-up areas, a team from Harvard and Bell Labs has produced a six-fold increase in the amount of data these systems can support.

The research could be a boon to mobile phone companies who sometimes struggle to serve subscribers living in densely populated urban areas.

It could also help them improve the return on the huge sums of money some network operators spent to buy licences for future networks.

Day-to-day data

Mobile phone companies face all kinds of problems when setting up services in urban areas, where the high concentration of buildings of different heights can scatter signals.

Mobile phone
The technology should boost reception
Sometimes this can be a benefit because the signals bouncing off buildings reach phones that would otherwise get no reception. But just as often, the cityscapes can create spots where reception is poor or non-existent.

Some innovative wireless network operators have been using the scattering to boost the amount of data that can be shipped around the network.

Often, signals sent from a particular antenna have a scatter or echo signature that reflects the sometimes tortuous journey a signal takes from one batch of aerials to another.

Signal processing software in the receivers can separate the radio streams by echo signature and boost the data carrying capacity of the whole network.

Scattering techniques

Operators are keen to boost the amount of data passing over their networks because many experts believe mobile information services will be one of the ways that phone firms recoup some of the cash they spent to buy licences for future networks. Already data services such as SMS, or text messaging, are proving hugely popular.

The disadvantage of this approach is that the receivers have to be set a certain distance apart from each other to be able to distinguish between the separate signals.

This means that the technique cannot be used to boost the data-receiving abilities of handsets or handheld gadgets because the separate antenna cannot be set far enough apart.

Now, though, the journal Nature reports that Michael Andrews and Partha Mitra, from Bell Labs (Lucent Technologies) in New Jersey, US, working with Robert deCarvalho from Harvard, have found a way to improve the data-boosting abilities of this scattering technique.

Right angles

Andrews and his colleagues have done this by discovering that when signals are scattered, their polarisation states change.

Typically the electric and magnetic fields that make up an electromagnetic wave, such as a light beam or a radio wave, are at right angles to one another and the direction that the wave is travelling. As such, they have two polarisation states.

Andrews and his co-workers have discovered that when signals are scattered the number of these polarisation, or direction, states increases.

By using three antennas at right angles to each other, each one tuned to use a different part of the three-dimensional polarisation field, the trio found they could produce a six-fold improvement in a networks data-carrying capacity.

Because the receiving antennae sit together, the technique could be adopted by mobile phone companies who want to get high data rates out of their networks without spending money installing huge numbers of base stations.

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