Performance Comparisons Between FLL, PLL and a Novel FLL-Assisted-PLL Carrier Tracking Loop Under RF Interference Conditions

Phillip W. Ward

Abstract:	A well-designed frequency lock loop (FLL) will outperform a well-designed phase lock loop (PLL) tracking threshold under dynamic stress and RF interference (RFI) conditions. However, the PLL will significantly outperform the FLL measurement accuracy. This paper compares the FLL and the PLL tracking thresholds and measurement accuracy. The thresholds are compared under high dynamic stress on the carrier tracking loop and deteriorating signal conditions such as RFI. The comparisons are performed by analytical techniques and by Monte Carlo simulation techniques for several receiver design cases. The results demonstrate the performance advantages of using both the FLL and the PLL. An innovative carrier tracking loop design technique which integrates both the FLL and the PLL characteristics (called an FLL-assisted-PLL) is presented. The FLL-assisted-PLL solves the GPS receiver designer’s dilemma when faced with the need for both the dynamics robustness of FLL plus the accuracy performance of the PLL. The paper demonstrates that the best overall performance is obtained when the FLL is designed to provide better tracking threshold than the PLL under both high and low dynamic stress. Under RFI conditions, the measure of GPS receiver performance defined here is the tracking threshold under expected maximum line-of-sight dynamic stress conditions. The tracking threshold is then used to predict the jamming-to- signal power ratio (J/S) performance of the receiver. The paper also presents a novel approach to comparing dynamic tracking thresholds between the FLL and the PLL as well as comparing measurement accuracy. Analytical techniques are not as reliable as the more sophisticated Monte Carlo simulation techniques in predicting receiver performance, but are an excellent starting point since they require much less computational time and effort. FLL performance is particularly difficult to predict by analysis. The paper provides insight into “rule-of-thumb” assumptions that can be used with analytical techniques in order to more closely compare with the more reliable Monte Carlo simulator results.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	783 - 795
Cite this article:	Ward, Phillip W., "Performance Comparisons Between FLL, PLL and a Novel FLL-Assisted-PLL Carrier Tracking Loop Under RF Interference Conditions," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 783-795.
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