GNSS Receiver Tracking Loss and Cycle Slip Detection Using Frequency Lock Loop Phase Acceleration and Jerk Estimation

Taehwan Kim, Hyungmin So, Su Jin, Choi, and Changdon Kee

Abstract:	The on-line detection of carrier cycle slip and loss remains a challenge in high-end GNSS receiver design. Costas and conventional Phase Lock Loops (PLLs) are both sensitive to dynamic stress and frequency error while providing more accurate velocity measurements than either a Delay Lock Loop (DLL) or a Frequency Lock Loop (FLL). For high-precision differential RTK receivers, it is important to detect cycle slips quickly to resolve cycle ambiguities. For safety-of-life GNSS receivers, it is advantageous to distinguish harmful PLL cycle losses from cycle slips because PLL cycle losses mislead the carrier-aided code tracking beyond the recoverable DLL correlation limit. Upon detecting a PLL cycle loss, the carrier-aided code tracking should stop and another available estimate of carefully calibrated external carrier estimate needs to aid the PLL before the carrier phase tracking can resume. DLLs usually have more than 3-dB higher tracking thresholds than PLLs such that DLLs can maintain a lock through carrier cycle slips unless a channel is in a very low signal-to-noise ratio (SNR) condition. In this paper, a robust on-line detection algorithm for carrier cycle slip and loss from double-time-differenced FLL statistics is presented. When FLL is synchronized and sampled at the same integrate-and-dump rate with PLL in 10 Hz loop bandwidth to accommodate dynamics, the moving average of double-time-differenced FLL provides robust statistics for frequency error acceleration rate under slow fading such as ionospheric scintillation and diffusion multipath. Using the Monte-Carlo simulation, it is also shown that the probability of cycle slip detection remains robust when minimum operational performance standard aviation dynamics are added to a simulated strong scintillation. However, if PLL noisebandwidth is reduced to 3 Hz for a ground based receiver mode, the PLL cycle slip detection through FLL becomes less robust at the typical Costas PLL’s operational SNR threshold of 26 dB-Hz. A hardware-oriented two threshold detection of PLL cycle slip and loss is developed using the moving average and the Cumulative Sum (CUSUM) statistics of timedifferenced FLL frequency errors. The effectiveness of the FLL-based carrier phase estimate as an inexpensive external carrier aiding source is investigated in not only opening but also closing a divergent PLL in slow signal fading conditions. The trade-off relationship between the PLL loop noise bandwidth versus the robustness of FLLbased cycle slip detection is also discussed.
Published in:	Proceedings of the 2007 National Technical Meeting of The Institute of Navigation January 22 - 24, 2007 The Catamaran Resort Hotel San Diego, CA
Pages:	585 - 593
Cite this article:	Kim, Taehwan, So, Hyungmin, Jin, Su, Choi,, Kee, Changdon, "GNSS Receiver Tracking Loss and Cycle Slip Detection Using Frequency Lock Loop Phase Acceleration and Jerk Estimation," Proceedings of the 2007 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2007, pp. 585-593.
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