Critical GPS-GLONASS Interoperability Issues

Gerald L. Cook

Abstract:	GLONASS has made significant gains over the past few years, and the introduction of new receivers has made its joint use with GPS feasible. However, GLONASS does not show the maturity of GPS in terms of continuity, integrity, and general support for the user. This could cause interoperability difficulties. After completing the constellation in early 1996, GLONASS had a number of satellite outages and failures, thus providing less than 40 days of full coverage. By the end of the year, the constellation was down to 21 useable satellites, while no replacement launches have been announced. In spite of GLONASS’ operational difficulties, evaluation of individual satellite performance, by time transfer analysis, shows that accuracy is good, comparable to GPS without Selective Availability. Because GLONASS lacks a world-wide control segment, satellites can go unnoticed for hours while transmitting erroneous data. The most common occurrence is message data dropout, but incorrect and corrupted data which cause range errors of kilometers have also been noted while the satellite at fault was marked healthy. In addition, some of the satellites demonstrate anomalies which cause smaller range errors. Because the transformation from GLONASS to GPS coordinates has not been formally specified, positioning results are presented horn our west-coast site. To circumvent receiver/satellite biases, single- satellite/multiple day solutions were obtained by use of a high performance cesium clock. Results were repeatable at about the one meter level, and show an equivalent GLONASS-relative-to-GPS rotation of -.33 arc seconds about the z-axis.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	183 - 193
Cite this article:	Cook, Gerald L., "Critical GPS-GLONASS Interoperability Issues," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 183-193.
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