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Boosting Wireless Bandwidth

Bandwidth for wireless communications doesn't come cheap, but scientists report today in Nature on a clever way to carve more channels from each available radio frequency. The new approach, developed by Michael Andrews and colleagues at Lucent Technologies, capitalizes on two facts to achieve a six-fold increase in the data-carrying capacity of radio signals: first they exploit the nature of radio signals themselves. The signals consist of oscillating electric and magnetic fields, running perpendicular to each other and to the signal's direction of travel. So the electric field, which alone determines the signal's polarization, can be in one of two states--each of which, in principle, can carry independent signals at the same frequency. As a result, using both polarization states doubles the frequency's capacity.

To better that increase by another factor of three, Andrews and company take advantage of scattering, which originally plagued cell phone signals in urban environments. They showed that a set of three perpendicular antennas can each transmit separate signals at the same frequency that are readily picked up and distinguished by another trio of antennas. In a test of the idea, the researchers transmitted signals encoding the color information for a Joan Miro painting. The signals--all sent at 880 megahertz--successfully traveled from three antennas across 25 meters and around a corner to the receiver.

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