GPS Comes Inside, Courtesy of Television Signals

If you've ever used GPS, you know that it can be difficult to get a signal. Try driving through New York City, for example. Drive down a street lined with tall buildings, and suddenly you're signal is gone. Go inside, and forget it. The technology simply doesn't work if the GPS receiver doesn't have a direct line of sight to the sky. A new startup company, Rosum, is hoping to change that, however. By making GPS work anywhere, whole new possibilities open up, among them a huge expansion of the GPS capabilities of cell phones, and a whole new generation of indoor tracking products.

GPS, essentially, works by sending out a signal from a network of 24 satellites, in geosynchronous Earth orbit. The GPS receiver, by picking up signals from three or more satellites, can then use trig to calculate its exact location, to within about 50 feet. In addition to providing information on location, it can also provide elevation, and an extremely accurate reading of the time. This technology, originally designed to guide missiles, is now widely used for civilian navigational purposes, as well as for purposes of exact timing. However, the signal sent from the satellites is extremely weak, and is not strong enough to come inside. TV signals, however, are much stronger, reasoned Rosum cofounder James Spilker. If you could make TV signals, 10 million times more powerful than GPS signals, work the way GPS signals do, you could combine the two technologies to make a GPS receiver that could get a signal almost anywhere. And, using a piece of experimental equipment that had been assembled for about $1,000, Spilker did just that.