Very Precise Synchronization of a Group of Pseudolites

Werner R. Lange

Abstract:	Pseudolites are GNSS transmitters that have a fixed position on the ground and transmit original satellite signals. Very often pseudolites are used around airports and harbors to ease the navigation and increase integrity and availability of satellite navigation systems. Pseudolites are also used in the European “Gate”-Projects. “GATE” is the name of a Galileo test bed where several pseudolites are located around a valley in southeast Bavaria transmitting Galileo signals so that receivers are able to use Galileo signals for testing purpose in “real life” before the satellites are in the sky. Besides this first Gate project, a number of similar pseudolite projects have been established. One of these projects is named “aviation gate” and is located at the research airport of Braunschweig. This project shall show the use of Galileo signals in aviation – from approach to landing to taxiing. It is extremely important to synchronize the pseudolites as well as possible to minimize the navigation errors. The system in Braunschweig consists of nine pseudolites and a reference station. The pseudolites are mounted in an inner circle of five systems around the airport and four systems in distances between 30 and 60 km. In the present stage of the project, the inner circle is working, and the outer circle is under construction. The paper describes the basics and goals of the project and includes the results of the first phase of the project – five free-running GPS receivers are synchronizing five pseudolites. The results look very promising – the five receivers are far better synchronized than anticipated;they are working in a range of about ±2ns. To enhance the accuracy of the timing receivers into the sub-nanosecond range, the receivers have a remote adjustment capability: The reference station continuously measures the range of the pseudolites and is able to adjust the phase of the GPS receivers’ 10 MHz output with a resolution of 25 ps over a WLAN link. This type of receiver is ideally suited at locations where independent stations require a very high degree of synchronization.
Published in:	Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting November 15 - 18, 2010 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	381 - 388
Cite this article:	Lange, Werner R., "Very Precise Synchronization of a Group of Pseudolites," Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, November 2010, pp. 381-388.
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