Clearing Cellular Gridlock With Software
CELLULAR PHONE CALLS MAY hop all over the place, but the networks themselves aren't very nimble. If lots of motorists in a traffic jam phone home at once, for example, half of them could get busy signals because there's no way to allocate more channels to the congested area. Someone sending a large data file can't order extra bandwidth. And U.S. cellular systems won't handle foreign modulation schemes, such as Europe's GSM.
The coming solution? "Software radio." Companies such as Analog Devices, Watkins-Johnson, AirNet Communications, and Raytheon intend to use software--rather than hard-wired tuners--to process radio signals. In the traffic jam, for instance, a cellular base station could reallocate channels that normally handle calls coming from other directions.
While an ordinary radio listens to only one channel at a time, a software radio grabs a swath of them, then uses special digital signal processing (DSP) chips to separate out the individual channels. This requires incredible speed. Take the chip introduced in October by Analog Devices Inc. in Norwood, Mass. The DSP chip samples the entire cellular band 50 million times a second, which generates enough data to fill a 1-gigabyte hard disk every 13 seconds. In the late 1980s, such frequency-gobbling systems raked in $10,000 each from U.S. intelligence agencies. Today the chip is $89.