GPS C/A Code Self-Interference: Error Detection Using Existing GBAS Monitors

Jessica A. Belzer, Frank van Graas

Peer Reviewed

Abstract:	GPS self-interference has been identified as a source of error for many years. Cross correlation between two satellites was found to cause C/A pseudorange errors in 1978 [1]. An overview of the concerns of C/A code cross-correlation in the context of precision approaches and landings is given by Zhu and van Graas [2]. This paper focuses on the effects of GPS C/A code self-interference on integrity in Ground Based Augmentation System (GBAS) Approach Service Type D (GAST-D) operations for landings in Category III minima. A worst-case scenario of cross correlation occurrence between two satellites with a slow doppler fading frequency and relatively high elevation angle was identified. This scenario was simulated on a Spirent STRS4760 GPS Simulator, and data was collected using a USRP N210 software defined radio with processing completed using the ChameleonChips Software Defined Radio (SDR) toolkit [3]. The ability of three existing GBAS monitors: the Code Carrier Divergence (CCD) monitor, the Dual Smoothing Ionospheric Gradient Monitoring Algorithm (DSIGMA), and the Bias-Value (B-Value) monitor to detect cross-correlation errors was investigated. The received signal power offset between the two simulated satellites was 10 dB. The expected maximum pseudorange errors were approximately 0.6 m and 6.1 m for the stronger and weaker satellites respectively. All three of the tested monitors can detect C/A code cross-correlation. The B-Value monitor is the most effective. The B-Value monitor allows for full imaging of the cross-correlation error, while the DSIGMA monitor detects large cross-correlation errors (>5 m), and the CCD monitor will detect small errors (0.6 m) but does not guarantee detection. In conclusion, the feasibility of applying the B-Value monitor for detection of C/A code cross-correlation error in a GBAS GAST-D environment has been shown.
Published in:	Proceedings of the ION 2019 Pacific PNT Meeting April 8 - 11, 2019 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	997 - 1012
Cite this article:	Belzer, Jessica A., van Graas, Frank, "GPS C/A Code Self-Interference: Error Detection Using Existing GBAS Monitors," Proceedings of the ION 2019 Pacific PNT Meeting, Honolulu, Hawaii, April 2019, pp. 997-1012. https://doi.org/10.33012/2019.16781
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