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Cricket chirping provides voice for interior GPS

What do knowing where to install an electrical outlet, locating your colleague or making a move in a virtual reality game have in common?

They are all potential applications for Cricket, an indoor location system developed by Professor Hari Balakrishnan and colleagues at MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL). Cricket is part of CSAIL's five-year Project Oxygen, a research initiative that aims to bring "abundant computation and communication, as pervasive and free as air, naturally into people's lives," say the researchers.

Cricket provides fine-grained location information to applications running on handhelds, laptops and sensor nodes. This data can range from location identifiers to position coordinates to compass-like orientation. Cricket is intended for use indoors or in urban areas where the Global Positioning System (GPS) does not work well.

While the Cricket project began in 1999, the second major version of the software was released in July 2004; it is the first to be commercially available. Early adopters include research groups at universities, corporations and hospitals; one chemical sensor company is experimenting with Cricket to help monitor chemical and gas leaks.

Cricket uses a combination of radio frequency (RF) and ultrasound technologies. Wall- and ceiling-mounted beacons placed throughout a building publish information on an RF channel. With each RF "chirp," the beacon sends a concurrent ultrasonic pulse. Receivers attached to mobile devices listen for RF signals and after receiving the first few bits, listen for the corresponding ultrasonic pulse. Cricket calculates distances between the handheld devices and beacons by running algorithms based on the difference in propagation speeds between RF (light) and ultrasound (sound). Even in the presence of competing beacons, Cricket quickly achieves good precision--usually within 1 to 5 centimeters.

Cricket's software--both the code embedded in sensors and the higher-layer software that runs on laptops and handhelds--is open source. It's also flexible, making it easy for others to code location-aware applications.

Balakrishnan foresees three broad areas of use for Cricket 10 years from now.

-- Robot and human navigation and discovery. Cricket could enable teams of robots to navigate the floor of a busy manufacturing plant and perform various tasks or help people make their way around large, unfamiliar places.

-- Monitoring and controlling environments through sensor networks. Applications could range from equipment and environmental monitoring to activating heating, ventilation and air conditioning (HVAC) systems.

-- Games and entertainment. With improved fast tracking of moving objects, Cricket-based virtual reality games have potential. In these games, physical movements made in special rooms in the real world appear in a computer-simulated world shared by others, who can make their own moves in response.

Cricket is funded by the MIT Project Oxygen partnership, the National Science Foundation, Intel Corporation and the Sloan Foundation.

A version of this article appeared in MIT Tech Talk on October 27, 2004 (download PDF).

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