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See Inside October 2006

The New Age of Wireless

Technologies that turn broadcasting "bugs" into features that open radio spectrum to novel uses will be a boon for consumers
Andrew Lippman



WEBB CHAPPELL
Before 1968 no one in the U.S. could connect anything to the AT&T telephone system unless Western Electric, AT&T's manufacturing arm, provided it. The Federal Communication Commission's landmark "Carterfone" decision erased that policy and ignited an explosion of communications innovations, including faxes, fast modems, PBXs, burglar alarms, answering machines and phone mobility. Although AT&T no longer owned the whole pie, the slice that it kept became part of a far larger industry.

That same explosive growth is beginning in wireless mobile. Microprocessors are now so fast that they can synthesize and handle directly both sound-and-image data and radio signals. Meanwhile the emergence of agile, end-to-end networks is creating unprecedented opportunities in what for 100 years have been staid communications structures. No matter what you think of the wireless devices you have today, you ain't seen nothing yet. Radio is just getting interesting.

Mobile phones will become programs loaded into whatever physical "engine" is convenient or perhaps into many at once. Instead of a "family" phone service plan, you might someday have a "molecular" account that makes accessible any radio-accessible thing or data that you choose. You could decide whether to put your dog's view of the world online, whether to monitor your blood sugar level from afar or whether to talk to someone through your eyeglasses. Broadband will become the province of a person rather than a wire to a home.

The broadcast radio spectrum, which has typically been regarded as limited and interference-plagued, will become open and accessible everywhere by anything. Of course, some broadcasters and registered networks will still rely on keeping certain airwaves empty and silent, and they will be used by legacy devices that we are loath to discard, such as cell phones and AM radios. But grander possibilities await radios that cooperatively sense one another's proximity, use one another to economize on radiated energy and battery life, and turn ever more remote regions of the spectrum into fertile territory for personal use.


Spectrum need not be a finite resource.

Disparate demonstrations paint this new picture of wireless communications. For example, the multipath phenomenon, in which buildings and walls bounce multiple copies of a signal to a receiver, was once just the source of ghosts in television pictures. But in essence, those reflectors are also sending additional energy that would have been lost. Thus, they can also be regarded as independent transmitters. Multiple-input, multiple-output radios built to take advantage of that effect can improve communications.

Other work has built ad hoc networks of mobile radios that at each moment dynamically select for intermediate relays requiring the least energetic connections. One radio might momentarily be in a dead spot, but another will be in a hot spot for passing on a communication. As radios become cheaper than their batteries, adding transmitters becomes more efficient than adding power to make reliable systems. Even more important, the dichotomy between broadcasting and point-to-point connectivity disappears; the two work together by design.

A new discipline called network coding uses broadcasting to save bandwidth by coding and then relaying bits for more than one receiver. Decoding involves combining several transmissions, including your own. Using this principle, we have built a demonstration telephone system in which the default is that everyone can hear anyone--a wireless party line. We call it "push to listen" because you decide how loudly and in which ear you would like to place any speaker's voice. Stock traders, emergency workers and perhaps conference callers might find it particularly useful.

The broadcast nature of wireless is thus a feature rather than a bug: it can save energy, increase efficiency and nurture new ideas. And spectrum need not be regarded as a fixed and finite resource to be divided among users. Instead it can support more communication as more communicators use it. The theory has been in place for a few years, but now it is becoming real. The pie will soon start to grow, and there will be enough slices for all.

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