Development of a new data link for the GPS range system

The GPS (Global Positioning System) range data link is being developed for the primary purpose of supporting GPS position data collection and processing. The authors discuss the data-link message capacity required to support the generation and downlinking of GPS navigation solutions, using several range differential methods. They also discuss 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 include unprocessed receiver data and/or navigation solutions, plus receiver status data. The data link provides a nominal throughput of 200000 b/s, the greatest part being used for downlink data. To accommodate the largest GPS message blocks planned, data are transmitted in 736-b 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. 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