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Originally featured on BroadcastEngineering.com
Mar 7

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3/7/2012 12:33 PM  RssIcon

Using pasta as a model, a team of researchers has developed twisted spectrum that could allow a “potentially infinite” number of channels to be broadcast simultaneously. They claim the technique saves bandwidth by encoding several channels on the same frequency using “radio vorticity.”

Researchers at the University of Padova in Italy and associated institutions found that by forcing spectrum to rotate in a three-dimensional axis as it travels—in the shape of fusilli pasta as it moves forward—these twisted beams can be independently generated, propagated and detected even in the very same frequency band, behaving as independent communication channels that avoid interference.

The research team demonstrated the technique in Venice, transmitting two twisted radio waves, in the 2.4 GHz band, over a distance of 442 meters. But the researchers claim it would be easy to keep adding more and more twisted waves, to increase the number of signals that can be sent simultaneously.

By forcing spectrum to rotate as it travels, these twisted beams can behave as independent communication channels.

[Here’s a video demonstration of the technique]

In the “New Journal of Physics,” the researchers said they have shown experimentally, in a real-world setting, that it is possible to use two beams of incoherent radio waves, transmitted on the same frequency but encoded in two different orbital angular momentum states, to simultaneously transmit two independent radio channels.

According to those involved, this novel technique allows the implementation of, in principle, an infinite number of channels in a given, fixed bandwidth, even without using polarization, multiport or dense coding techniques. This paves the way for innovative techniques in radio science and entirely new paradigms in radio communication protocols that might offer a solution to the problem of radio-band congestion.

The group noted that all current radio communication services are based on various forms of phase, frequency and/or amplitude modulation of the EM radiation in the form of EM linear momentum (i.e. integrated Poynting vector or energy flux). In order that many different broadcasting stations were able to transmit simultaneously without overlapping their signals, Guglielmo Marconi suggested that the total available spectrum of frequencies be divided into many non-overlapping frequency subbands.

“Now, the wide use of wireless communication has unavoidably led to the saturation of all available frequency bands, even after the adoption of artificial techniques that increase band capacity. We have experimentally shown that by using helicoidal parabolic antennae, the use of OAM states might dramatically increase the capacity of any frequency band, allowing the use of dense coding techniques in each of these new vortex radio channels. This might represent a concrete proposal for a possible solution to the band saturation problem,” the researchers wrote in the New Journal of Physics.

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