DGPS/Radiobeacon Field Trials, Which Compare Type 1 & Type 9 Messaging

Per Enge, David Young, Leonid Sheynblat and Brian Westfall

Abstract:	A medium frequency (MF) radio system is being deployed worldwide for the broadcast of differential corrections to users of the Global Positioning System (GPS). This system adds a digitally modulated subcarrier to transmissions from some of the marine radio beacons, which currently operate in the 283.5 to 325 kHz band. These “DGPS/radiobeacons” use groundwave propagation to carry the DGPS correction well beyond the “radio horizon” where the DGPS data is still valid. Improvements in the DGPS/radiobeacon receiver design or messaging protocol which reduce the required signal to noise ratio (SNR) are important, because they can significantly increase the range or availability of the DGPS/radiobeacon service. Such an improvement is being pioneered by the U.S. Coast Guard, and this innovation calls for the transmission of three satellite corrections per message rather than the transmission of all corrections in every message. In other words, DGPS/radiobeacons will broadcast a string of Type 9 messages as defined by the RTCM broadcast standard for DGPS rather than the normal string of Type 1 messages. If a lightning burst corrupts a message, then only three corrections are lost rather than the corrections for all satellites in view of the reference station. This paper contains an analysis and field results, which show that the improvement made possible by Type 9 messaging is significant.
Published in:	Proceedings of the 49th Annual Meeting of The Institute of Navigation (1993) June 21 - 23, 1993 Royal Sonesta Hotel Cambridge, MA
Pages:	671 - 680
Cite this article:	Enge, Per, Young, David, Sheynblat, Leonid, Westfall, Brian, "DGPS/Radiobeacon Field Trials, Which Compare Type 1 & Type 9 Messaging," Proceedings of the 49th Annual Meeting of The Institute of Navigation (1993), Cambridge, MA, June 1993, pp. 671-680.
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