Range Applications Joint Program Office GPS Range System Data Link

M. Birnbaum, R. F. Quick, Jr., K. S. Gilhousen, J. Blanda

Abstract:	The Range Applications Joint Program Office (RAJPO) Range System is being developed to provide an integrated system capable of functioning as the Time, Space, Position Information (TSPI) measurement instrumentation facility for test and training ranges of the Armed Services of the United States employing GPS range equipment. The Range System includes a GPS Range Pod Subsystem (RPS), a two-way Data link (DL) Subsystem, and a Reference Receiver/Processor (RR/P). Initial deployment is scheduled for August 1990. The GPS Range Data link is being developed for the primary purpose of supporting GPS position data collection and processing. This paper discusses the data link message capacity required to support the generation and downlinking of GPS navigation solutions, using range differential methods 1, 3, and 4. The paper also discusses data link networking, with emphasis on the features required to provide high reliability message transmission while downlinking data from highly dynamic aircraft. Support of GPS navigation in the test and training range environment requires the uplinking of receiver control messages and (for some solution methods) differential correction data. Downlink data includes unprocessed receiver data and/or navigation solutions, plus receiver status data. The RAJPO Data Link provides a nominal throughput of 200,000 bits per second, the greatest part being used for downlink data. To accommodate the largest GPS message blocks planned, data are transmitted in 736-bit packets. Packet transmission is governed by a time-division multiple-access protocol, using 330 packet slots per second, of which approximately 280 are available for GPS data uplink and downlink. Airborne users generally require from one to ten downlink messages per second. Data transmission takes place on an L-band link, requiring 1.6-MHz bandwidth. Reliable data collection is assured by several data link features. Parallel data reception by multiple ground stations provides spatial diversity. Optional use of two frequencies, on which each packet is transmitted during a single time slot, provides frequency diversity. Both types of diversity ensure robust performance in the presence of multipath and interference. The data link also employs a distributed message routing protocol, allowing up to five L-band relays from the GPS receiver to the ground data processing facility via intermediate data link transceivers. This feature assures maximum flexibility in network configuration, and provides a reliable downlink message path via relays even when ground stations are not in line of sight of the data link transceiver. Integration of the data link into range data processing and control facilities is discussed, along with data link features allowing cooperative interoperation among adjacent ranges.
Published in:	Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989) September 27 - 29, 1989 The Broadmoor Hotel Colorado Spring, CO
Pages:	103 - 108
Cite this article:	Birnbaum, M., Quick, R. F., Jr.,, Gilhousen, K. S., Blanda, J., "Range Applications Joint Program Office GPS Range System Data Link," Proceedings of the 2nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1989), Colorado Spring, CO, September 1989, pp. 103-108.
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