Fast Forward: Gasping for Air

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Last month, I talked about the growing need for radio-frequency (RF) spectrum to support Internet services on smartphones and other mobile computing devices. Some experts say we’ll need 700–800MHz of additional spectrum—none of which is available now.

We can’t manufacture RF spectrum. It’s a finite resource, and only some of it has the range and penetration required to blanket a region. Data compression conserves spectrum, but there’s a mathematical limit (Shannon’s law) that prevents further compression without losing data integrity. Today’s communications standards already approach the limit.

The telecommunications industry wants to grab more spectrum from TV broadcasters, who surrendered a big chunk of airspace in the recent transition from analog to digital TV. The telecoms want UHF channels 40 to 51, or even 20 to 51. Some people want to end terrestrial TV broadcasting altogether—which would still free less than half the spectrum we supposedly need.

Another solution is to use the “white space” between TV channels. White space is unused spectrum that keeps TV signals from interfering with each other. Unfortunately, recent experiments suggest it doesn’t work well in urban areas, the very places where demand for wireless Internet coverage is highest. And it won’t provide nearly enough spectrum when everyone has a smartphone.

Yet another proposal is to replace today’s powerful, regional TV broadcasting with lots of weaker signals. Their reduced range would allow different TV stations to use the same channels in the same region. But this proposal has technical problems and would free only 100–180MHz.

What’s left? Femtocells. A femtocell is a tiny cellular network, usually confined to a home or office. It’s like cellular Wi-Fi. Cellular traffic hops a short distance to the nearest femtocell router, which connects to the Internet over a landline. We can always lay more landline wire, cable, and fiber.

To make this solution universal, femtocells should allow public access, which means they must be secure. Also, millions of femtocell routers must be installed in homes and businesses, which will probably bear the cost of this infrastructure. Despite the drawbacks, femtocells seem the best way to keep us from running out of air.

Tom Halfhill was formerly a senior editor for
Byte magazine and is now an analyst for Microprocessor Report .

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