A Phase-locked Loop Design with External Aiding Based on Kalman Filter

S. Zhao, M. Lu, Z. Feng

Abstract:	Tracking loops play an important part in GPS receivers, however under dynamics or in weak signal conditions, it cannot provide satisfying performance. When designing a tracking loop, there is a dilemma. Take a phase-locked loop (PLL) as an example, in some dynamic environments, PLL should increase its bandwidth to keep tracking while more thermal noise is introduced. To enhance the ability of GPS receivers, the idea of aiding the tracking loop with external information from sensors such as INS was proposed by some researchers, and the ultra-tight GPS/INS integration concept and its implementation are widely studied in recent years[1-3]. With external sensor aiding (e.g. INS), a traditional PLL can effectively reduce its bandwidth when suffering dynamic stresses because most of the dynamics are compensated by external aiding. In this paper, the author provides a novel tracking loop design which utilizes external velocity aiding information based on Kalman filter. In the first part, how to transform a second order PLL into a Kalman filter (referred to as “Kalman PLL” hereafter) is discussed. The relationship between Kalman gains and loop gains is derived and their performances are also compared via some analysis and simulations. Next, due to inaccurate external velocity aiding information, the structure of Kalman PLL is modified and the means to estimate the external aiding errors is proposed (This modified Kalman PLL is referred to as “Kalman PLL with error estimator” hereafter). Finally, simulations with dynamics and low SNR are carried out to examine the performance of the Kalman PLL with external aiding and validate the “Kalman PLL with error estimator” ability of estimating external aiding errors. Results demonstrate that the Kalman PLL with external aiding achieves smaller tracking errors and works under lower SNR than PLLs without aiding. Also the Kalman PLL with error estimator can provide satisfying estimates of external aiding errors. Meanwhile, it also has better tracking performance than the Kalman PLL with external aiding only.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	3096 - 3100
Cite this article:	Zhao, S., Lu, M., Feng, Z., "A Phase-locked Loop Design with External Aiding Based on Kalman Filter," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 3096-3100.
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