Sensor-laden robots capable of vital search and rescue missions at disaster sites are no figment of a science fiction writers imagination.  Prototypes and commercial models of Urban Search and Rescue (US&R) robots will soon begin to work rubble piles across the United Stated.  Too many of these lifesaving robots, however, could be too much of a good thing, according to researchers at the National Institute of Standards and Techn-ology (NIST), who report that the radio transm-issions of multiple robots can interfere with each other and degrade search and rescue performance.

A NIST analysis of 2,006 wireless radio field trials for US&R robots found that 10 out of the 14 robots tested experienced communication problems due to radio interference from other systems.  Engineers carried out tests on the robots last August at a US&R robot standards development gathering in Gaithersburg, Md., the U.S. sponsored by the Depar tment of Hom- eland Security.

The researchers found that neither use of Industrial, Scientific, and Medical (ISM) frequency bands nor adherence to protocols designed to minimize interference between sys- tems in the bands could guarantee flawless commu- nication between a robot and its human operator.  Radio interference could happen whenever the ISM frequency bands became crowded or when one user had a much higher output power than the others.  An example of the latter problem occurred during the tests when transmitters in the 1760 MHz band knocked out video links in the 2.4 GHz frequency band.  In another case, a robot using an 802.11b signal in the 2.4 GHz band overwhelmed and cut off a robot that had been transmitting an analog video link at 2.414 GHz.

The NIST paper lists a number of ways to improve urban search and rescue wireless commu-nications.  Options, some of which are currently being investigated by robot manufacturers, incl-ude changes in frequ-ency coordination, trans-mission protocols, power output, access priority, and using relay transformers to increase the range of wireless transmissions (a technique known as multi-hop com-

mu nications).  The paper also suggests establishing new access schemes or software-defined radios that allow interoperable commu-nications.