Time and Position Accuracy using Codeless GPS

C.E. Dunn, D.C. Jefferson, S.M. Lichten, J.B. Thomas, Y. Vigue, L.E. Young

Abstract:	The Global Positioning System has allowed scientists and engineers to make measurements having accuracy far beyond the original 15 meter goal of the system. Using global networks of P-Code capable receivers and extensive post-processing, geodesists have achieved baseline precision of a few parts per billion, and clock offsets have been measured at the nanosecond level over intercontinental distances. A cloud hangs over this picture, however. The Department of Defense plans to encrypt the P-Code (called Anti-Spoofing, or AS) in the fall of 1993. After this event, geodetic and time measurements will have to be made using codeless GPS receivers. There appears to a silver lining to the cloud, however. In response to the anticipated encryption of the P-Code, the geodetic and GPS receiver community has developed some remarkably effective means of coping with AS without classified information. We will discuss various codeless techniques currently available, and the data noise resulting from each. We will review some geodetic results obtained using only codeless data, and discuss the implications for time measurements. Finally, we will present the status of GPS research at JPL in relation to codeless clock measurements.
Published in:	Proceedings of the 25th Annual Precise Time and Time Interval Systems and Applications Meeting November 29 - 2, 1993 Ritz-Carlton Hotel Marina Del Rey, California
Pages:	169 - 182
Cite this article:	Dunn, C.E., Jefferson, D.C., Lichten, S.M., Thomas, J.B., Vigue, Y., Young, L.E., "Time and Position Accuracy using Codeless GPS," Proceedings of the 25th Annual Precise Time and Time Interval Systems and Applications Meeting, Marina Del Rey, California, November 1993, pp. 169-182.
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