Implementation and Outdoor Test Results for GPS and Pseudolite System

S. Jeon, H. So, G. Kim, C. Kim, H. Song, T. Lee, K. Kwon

Abstract:	This paper presents the implementation and outdoor field test results of vector-based signal tracking algorithm designed for GPS and pseudolite (PL) navigation system. Using the GPS-PL system, the number of line-of-sight (LOS) satellites increases enough to calculate navigation solution in GPS shadow area. In addition, the geometry of LOS satellite vector is also improved because of relatively lower elevation angle of the PL position. To implement the GPS-PL system, however, there are some problems. One of the most severe problems is the near-far problem. The near-far problem of the PL system is a condition in which a strong PL signal saturates the auto gain controller of RF front end making it hard for the receiver to track weaker GPS or other PL signals. Because of this problem, the effective working area of the GPS-PL system is restricted. There have been lots of researches to mitigate the near-far problem, such as pulsing technique, different RF frequency, and robust tracking loop and so on. Among them, this paper focuses on the research field of receiver tracking loop. If the vector-based tracking loop, known as Vector Delay/Frequency Lock Loop (VDFLL) algorithm, is applied to GPS-PL system, the near-far problem could be reduced because the tracking performances for low and instantaneous low C/N0 signal are enhanced. In the similar vein, the effective working area of the GPS-PL system would be widened. We implemented VFLL and VDLL designed for the GPS-PL system on a software receiver. The Doppler frequency and code phase for each satellite and PL are predicted based on the position and velocity states of the Extended Kalman Filter (EKF). The outdoor field test was performed using GPS live signal and asynchronous pseudolite navigation system constructed in GNSS laboratory in Seoul National University. To analyze the tracking performance, we have accomplished two test scenarios. One is the analysis of the tracking and navigation performance improvement in GPS shadow area. Because of the PL augmentation and the vector based tracking loop, the availability and accuracy of user position increased. The other is the working area test. In the test that user is getting far from a certain PL, i.e. a user moves away to the far zone, the receiver could not keep tracking PL signal in conventional independent tracking loop. In VDFLL, however, successfully estimates the signal and succeeded to track weak PL signal. In addition to the far zone test, we tested the near zone tracking performance. When a user comes into the near zone, the majority of GPS and other PL signals are disrupted by relatively strong PL signal. In this situation, the implemented VDFLL could have tracked the majority signals continuously. Therefore the coverage of the GPS-PL system with VDFLL implementation became wide, compared with the conventional independent tracking loop. We expect these test results can show the possibility of the use of PL system in bad signal condition like urban canyon for real our lives.
Published in:	Proceedings of the 2012 International Technical Meeting of The Institute of Navigation January 30 - 1, 2012 Marriott Newport Beach Hotel & Spa Newport Beach, CA
Pages:	1098 - 1106
Cite this article:	Jeon, S., So, H., Kim, G., Kim, C., Song, H., Lee, T., Kwon, K., "Implementation and Outdoor Test Results for GPS and Pseudolite System," Proceedings of the 2012 International Technical Meeting of The Institute of Navigation, Newport Beach, CA, January 2012, pp. 1098-1106.
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