Rethinking the Computer

Continued from page 3

By Lisa Scanlon

01/01/2001

Location, Location, Location

Some Oxygen researchers created new hardware devices and even processors to help realize the pervasive-computing dream. Associate professor Hari Balakrishnan built beacons and receivers that work together to pinpoint a user's location. Called Cricket, his system uses wall- and ceiling-mounted beacons that simultaneously send out radio and ultrasound signals. When the radio signal-which travels faster than the ultrasound signal-reaches a receiver installed in a badge or handheld device, it starts a timer that runs until the ultrasound signal catches up. The receiver then calculates the distance between the beacon and itself. When the receiver determines the distance to three beacons, it can pinpoint its location (and the user's) to within a couple centimeters.

When Balakrishnan started working on the project in 1999, he thought it would be useful for handheld applications. Four years later, his research has taken a different turn. Now he thinks that its "killer application" may be in wireless sensor networks. "If you put a sensor out and it starts telling you something about the environment, unless it tells you where it's coming from, it's useless," he says. A second version of the system, which combines Cricket with sensors that run on a special operating system, will be commercially available later this year.

Another new piece of hardware can separate and amplify a speaker's voice from within a crowd of chattering people. The one-by-two-meter array of more than 1,000 microphones delays the signal from each of the microphones depending on how far it is from the speaker, then combines all the signals so that only the waves from one particular point in the room are amplified. At the same time, the waveforms from other noise in the room cancel each other out and are dampened. The system now works only with a stationary speaker, but the researchers plan to integrate it with vision technology, allowing it to track a professor and amplify his voice as he moves around an auditorium.

The array runs on a processor, designed by Agarwal and known as the Raw chip, that can reconfigure itself to suit many applications. Traditionally, hardware manufacturers will hand-design a chip wire by wire to make sure that signals get to the right place at the right time, depending on how the chip is to be used. For computers to reach their processing potential, they often need special add-on cards designed for specific applications. The Raw chip allows software to control the paths signals take on the wires, so it can customize itself to handle many different tasks. A handheld device powered by the Raw chip can just as easily run graphics software as make a cellular-phone call; such versatility would previously have required two separate chips, increasing costs and taking up valuable real estate on small devices.