Aircraft Surveillance Based on GPS Position Broadcasts from Mode S Beacon Transponders

Edward Bayliss, Robert Boisvert, Michael Burrows, and William Harman

Abstract: Flight testing of a new air surveillance concept, GPS-Squitter, began during the past year. It integrates GPS receivers with the existing secondary surveillance radar beacon equipment carried by most aircraft. Simple, inexpensive, non-scanning ground stations listen for GPS position reports broadcast by the Mode S beacon transponders on the aircraft and send them on to air traffic control facilities. In addition to its surveillance application, GPS-Squitter presents opportunities for enhancing other important functions such as collision avoidance systems and data link services. System tradeoff studies are comparing range and altitude coverage with the. cost and number of stations needed. Other issues are data link interference, multipath, total aircraft capacity, and unambiguous reporting range. The baseline system uses commercial off-the-shelf components such as TCAS (Traffic Alert and Collision Avoidance System) avionics units, omni- directional DME (Distance Measuring Equipment) antennas, and computer workstations in order to ensure low production costs. The cost/performance tradeoff of of minimum modifications such as the addition of a 6 sector antenna, multiple receive channels, or higher transmit power, are being evaluated. The omni- directional baseline system is designed for a range of 50 nmi while the 6-sector system is designed for 100 nmi range. Two aircraft have been equipped with Mode S beacon transponders modified to broadcast (i.e., “squitter”) their GPS position twice each second. The numerous test flights have accumulated a significant data base including a demonstration of coverage out to over 100 nmi range. Data have been collected to analyze a number of issues: received power margins, performance of bottom versus top aircraft antenna, ground bounce multipath, propagation over water, and parallel runway approach monitoring. In addition, standard squitter data from commercial aircraft have been recorded and correlated with Mode S tracking to show link margins experienced in practice from aircraft in operational service. More tests are planned, including a demonstration of GPS-Squitter air surveillance in the Gulf of Mexico.
Published in: Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994)
September 20 - 23, 1994
Salt Palace Convention Center
Salt Lake City, UT
Pages: 939 - 950
Cite this article: Bayliss, Edward, Boisvert, Robert, Burrows, Michael, Harman, William, "Aircraft Surveillance Based on GPS Position Broadcasts from Mode S Beacon Transponders," Proceedings of the 7th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1994), Salt Lake City, UT, September 1994, pp. 939-950.
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