Improving Tracking Performance of PLL in High Dynamics Applications

Ping Lian, Gérard Lachapelle and ChangLin Ma

Abstract:	The Phase-Locked Loop (PLL) is used in GPS receivers to track an incoming signal and to provide accurate carrier phase measurement. However, the PLL tracking performance and measurement accuracy are affected by a number of factors, such as the signal-to-noise ratio, dynamic stress, the GPS receiver’s jitter caused by vibration and the Allan deviation. Among these factors, the thermal noise and dynamic stress are the most common present and have a large influence on the design of the PLL. In high dynamic situations, the confliction between improving PLL tracking performance and the ability to track the signal necessitates some compromises in PLL design. This paper investigates the strategies to resolve this confliction. Three methods are investigated to improve PLL tracking performance in high dynamic applications: a Kalman filter-based tracking algorithm, application of a wavelet de-noising technique in the PLL, and an adaptive bandwidth algorithm. The Kalman filter-based tracking algorithm makes use of a carrier phase dynamic model and a measurement from the output of the discriminator to estimate the phase difference between the incoming signal and the output of Numerical Controlled Oscillator (NCO), Doppler frequency and the change rate of Doppler frequency. The wavelet de-noising technique effectively decreases the noise level and allows broaden the PLL bandwidth to track high dynamics signals. The adaptive bandwidth PLL algorithm adapts the bandwidth of the PLL according to the estimation of the incoming signal dynamics and noise level. The performance is evaluated in terms of signal-to-noise ratios and dynamic variations using simulating signals. The results show that those methods outperform the ordinary PLL in the high dynamic tracking performance. The carrier phase measurement is more accurate.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	1042 - 1052
Cite this article:	Lian, Ping, Lachapelle, Gérard, Ma, ChangLin, "Improving Tracking Performance of PLL in High Dynamics Applications," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 1042-1052.
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