Quality Monitoring for Multipath Affected GPS Signals

Maurizio Fantino, Fabio Dovis, Jinling Wang

Politecnico di Torino, Electronics Department , c.so Duca degli Abruzzi 24 10129 Torino Italy.
School of Surveying & Spatial Information Systems, University of New South Wales Sydney Australia.

DOI:                 

Abstract

The ability to monitor and detect any disturbances on the PRN code signals transmitted from the navigation satellite constellation is of primary importance. It is known that the tracking performance of a navigation receiver stems from the correlation property of the PRN code signals transmitted. These anomalies can be detected in several different ways, either observing the outputs of navigation user receivers, or processing the received signal within the receiver. Quality control is the process that defines how well the solution of a problem is known and in the context of navigation, it consists of assuring an agreed level of accuracy, reliability and robustness for the measurements. In this work a modified version of the conventional tracking scheme will be proposed with the aim of monitoring the quality of the measurements at the signal processing level. The proposed tracking scheme is able to give a measure of the distortion of the correlation function and consequently, of the reliability of the signal tracked. In particular the problem of multipath distortion is considered The amplitude and multipath delay can be estimated with an extension of the linear Kalman Filter which can be implemented inside the traditional DLL architecture. Simulations show that due to its prediction capability, Kalman Filter enhances the robustness of the system when weak signals are present or there is loss of lock on the signals, trading off the performance improvement with an increase in complexity of the new architecture. The recognition of a multipath corrupted signal estimating the amplitude and delay of the reflection can be used to select the more reliable pseudo-range measurements for the evaluation of the positioning equations. Mitigation of the multipath effects may be performed where the number of tracked signals is not sufficient.

Keywords

GPS, Multipath, Kalman Filter, Quality Control, Monitoring.

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Braasch M. (2001): Performance Comparison of Multipath Mitigation Receiver Architectures, IEEE Proceedings of Aerospace conference, 3, 1309-1315.
[2]	Enge P. (1999): Local Area Augmentation of GPS for the precision approach of aircraft, Proc. IEEE, 87, 111-132.
[3]	Hewitson S. (2003): GNSS Receiver Autonomous Integrity Monitoring: A separability Analysis, 16th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. Of Navigation, Portland, OR, 9-12 September, 1502-1509.
[4]	Hewitson S.; Hung K.; Wang J. (2004): Localizability Analysis for GPS/Galileo Receiver Autonomous Integrity Monitoring, The journal of Navigation, 57, 245-259.
[5]	Jee G.; Kim H.; Lee Y.; Park C. (2002): A GPS C/A Code Tracking Loop Based on Extended Kalman Filter with Multipath Mitigation, 15th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation, Portland, OR, 24-27 September, 446-452.
[6]	Kaplan ED. (1996): Understanding GPS: Principles and Aplications, Artech, Boston Massachusetts.
[7]	Leick A. (2004): GPS Satellite Surveying – Third Edition, John Wiley & Sons, Inc.
[8]	Macabiau C. (2000): Impact of Evil Waveforms on GBAS Performance, IEEE Position Location and Navigation Symposium, San Diego, 22-29.
[9]	Mitelman P.; Phelts P.; Akos D.; Pullen S.; Enge P. (2000): A Real-Time Signal Quality Monitor For GPS Augmentation Systems, Institute of Navigation's GPS conference, Salt Lake City, UT, 177-84.
[10]	Norgaard M.; Poulsen NK.; Ravn O. (2000): Advances in Derivative-Free State Estimation for Nonlinear Systems, Technical University of Denmark, Technical report: IMMREP-1998-15.
[11]	Phelts P.; Akos D.; Enge P. (2000): Robust Signal Quality Monitoring and Detection of Evil Waverforms. 13th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. Of Navigation, Salt Lake City, Utah, 19-22 September, 1180-1190.
[12]	Psiaki ML.; Hee J. (2002): Extended Kalman Filter Methods for Tracking Weak GPS Signals, 15th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation, Portland, OR, 24-27 September, 2359-2553.
[13]	Ronald A. (1990): Joint Estimation of PN Code Delay and Multipath Using the Extended Kalman Filter, IEEE Trans. Commun, 38, 1677-1685.
[14]	Shloss P.; Phelts RE.; Walter T.; Enge P. (2002): A Simple Method of Signal Quality Monitoring for WAAS LNAV/VNAV, 15th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation, Portland, OR, 24-27 September, 800-809.
[15]	Wang J.; Chen Y. (1999): Outlier Detection and Reliability Measures for Singular Adjustment Models, Geomatic Research Australasia, No. 71, 57-72.