Recommendations for Enhancement of RTCM-104 Differential Standard and Its Derivatives

Patrick Y. Hwang

Abstract:	The RTCM standard has been widely adopted for DGPS implementations. It has also spawned derivative formats which have adopted its well-designed system structure. From user experience obtained from full-constellation operation, it has been found that performance improvements can be obtained in two areas of the RTCM standard, both pertaining to system accuracy issues. The method recommended by the RTCM standard to linearly extrapolate differential corrections from the reference time of the last correction update is not the best way of handling data latencies, particularly since the time- correlation structure of selective availability is fairly well understood. Linear extrapolation is good enough if data latencies are small. However, in systems that deal with large data latencies, the inefficiency of linear extrapolation becomes quite evident. By taking advantage of knowledge of the SA temporal structure, the differential range error can be improved by 13% (0.7 m) after 30 seconds of latency, or 24% (4 m) after 60 seconds of latency. A second area recommended for improvement is an issue related to the interpretation of User Differential Range Error or UDRE. The reference station’s estimation of differential corrections often produces a very tight correlation between the corrections because of the effects of a common clock error - due to the reference station receiver. Technically, a specification of range error should include the common clock error. However, this common clock error has little effect on the position solution generated in the differential receiver unless very high clock stability in the latter was assumed in the processing of that solution. Analysis of the importance of this assumption will be presented.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	1501 - 1508
Cite this article:	Hwang, Patrick Y., "Recommendations for Enhancement of RTCM-104 Differential Standard and Its Derivatives," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 1501-1508.
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