Experimental Results of Time Synchronization Between Two Aircraft Using GPS

William Webster, Stuart Nicholson, Philip Moser and Patricia Hasenfang

Abstract:	An experiment was conducted to test the feasibility of time synchronizing data collection systems on two widely separated airborne platforms using GPS. On each aircraft the 1 pulse per second (lpps) from the GPS receiver (C/A code only, SA was on) was time tagged, the resulting data streams differentially filtered and the statistics measured. The time tagging was performed by a quantizer with highly stable, independent oscillators. The platform positions were estimated by the same GPS receivers. The result was an absolute offset standard deviation of 3-5 nanoseconds depending on the filter integration time. Cesium beam standards were also included and their lpps signal also time tagged. Using the same filtering technique, the difference between the GPS lpps and Cesium beam lpps on each aircraft was estimated and the standard deviation was slightly less than 40 nanoseconds. This result agrees with the published total error for a coordinated time transfer using GPS with unknown positions as given in the “NAVSTAR GPS User Equipment Manual.” [l] From these results, it can be concluded that the random noise component in the timing estimation process between two widely separated (5 Nmi. to 20 Nmi.) moving platforms is highly correlated and most of its effects can be removed even without precise position knowledge of the two platforms. Removing the noise using differential filtering makes it now possible to conduct data collections requiring precise relative timing information between moving platforms using GPS as the common time standard. This paper presents an overview of the experiment, details the filtering used in processing the time tagged data, and discusses the results and conclusions.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	725 - 731
Cite this article:	Webster, William, Nicholson, Stuart, Moser, Philip, Hasenfang, Patricia, "Experimental Results of Time Synchronization Between Two Aircraft Using GPS," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 725-731.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In