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In this paper, we address the design of an optimally unbiased moving average (MA) filter for time error online estimating and synchronization in Global Positioning System (GPS)-based timekeeping. We proceed from the slowly changing nature of a time error generated by a local clock, assuming its function to be linear for N points in the average. Employing the inherent property of a simple MA to produce the lowest noise for the given averaging interval and using linear regression as a proper stochastic approximation to evaluate the bias, we find the optimal weighting coefficients. The designed optimally unbiased MA filter and its improved modification produce two times more noise than a simple MA when N /spl Gt/ 1. Both the numerical simulation and the filtering of the real GPS-based time error processes are provided and discussed in detail.
Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on (Volume:49 , Issue: 6 )
Date of Publication: June 2002