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ABSTRACT: In this paper, we discuss optimal synchronization of local clocks using Global Positioning System (GPS) one-pulse-per-second (1PPS) timing signals. To eliminate sawtooth errors that are peculiar to the 1PPS signals and optimally steer the clock errors each M seconds, we propose the use of a ramp-predictive finite-impulse-response (FIR) filter that is known to be optimal for clock models on large averaging horizons. A low-pass filter is used to smooth the hold filter output between the optimally predicted points. A GPS-locked crystal clock has been investigated in detail in terms of the time interval error, Allan deviation, and precision time protocol (PTP) variance. A high-efficiency implementation of the proposed synchronization algorithm is experimentally demonstrated.
IEEE Transactions on Instrumentation and Measurement 07/2009; · 1.21 Impact Factor
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IEEE Transactions on Instrumentation and Measurement 06/2009; 58(6):1833-1840. · 1.21 Impact Factor
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ABSTRACT: We discuss optimal synchronization of local clocks by the Global Positioning System (GPS) one pulse per second (1PPS) timing signals. To eliminate sawtooth errors peculiar to the 1PPS signals and optimally steer the clock errors each M seconds, we propose using a ramp predictive finite impulse response (FIR) filter that is known to be optimal for clock models on large averaging horizons. A low-pass filter is used to smooth the hold filter output between the optimally predicted points. A GPS locked crystal clock has been investigated in detail in terms of the time interval error, Allan deviation, and precision time protocol (PTP) variance. A high efficiency implementation of the proposed synchronization algorithm is demonstrated experimentally.
Frequency Control Symposium, 2009 Joint with the 22nd European Frequency and Time forum. IEEE International; 05/2009
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Digital Signal Processing 09/2008; 18(5):739-750. · 1.43 Impact Factor
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22nd European Frequency and Time Forum (EFTF'08), Toulouse, France; 04/2008
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22nd European Frequency and Time Forum (EFTF'08), Toulouse, France; 04/2008
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Sensors and Transducers. 05/2007; 79(5):1151-1156.
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ABSTRACT: The 3-state unbiased finite impulse response (FIR) filter and the 3-state Kalman filters are investigated for the time interval error (TIE) K-degree polynomial model of a local crystal clock in GPS-based timekeeping in presence of the sawtooth noise induced by the receiver. We show that both algorithms produce consistent estimates for the reference (rubidium) measurements. We also demonstrate that the unbiased FIR algorithm produces a lower error than the standard Kalman filter in presence of the sawtooth noise
Frequency Control Symposium and Exposition, 2005. Proceedings of the 2005 IEEE International; 09/2005
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ABSTRACT: In this paper, we show that recently designed the finite impulse response (FIR) filtering algorithm provides realtime estimation of the fractional frequency offset of a local clock with high accuracy via GPS-based measurements of the time interval error (TIE). Such a splendid property of the algorithm is due to small produced noise in the estimates of the TIE. It is also shown that the algorithm applied to sawtooth measurements serves as a nice estimator of the Allan deviation. The latter cannot be estimated via sawtooth-less measurements.
Frequency Control Symposium, 2007 Joint with the 21st European Frequency and Time Forum. IEEE International;
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ABSTRACT: In this paper, we address a theoretical analysis of errors of the l-degree unbiased finite impulse response (FIR) filter applied to the if-degree time interval error (TIE) model of a local clock. Emphasizing the fact that the TIE model originates from the slowly changing Brownian phase and thus cannot obligatorily be distinct on a horizon of N points, we investigate estimates for l ne K and derive optimal horizons N<sub>opt</sub>(T<sub>opt</sub>) as functions of the optimal time step T<sub>opt</sub>. Practical justification is provided based upon GPS-based sawtooth measurements of the TIE of a crystal clock imbedded to the Stanford Frequency Counter SR620 and using the SynPaQ III GPS Sensor and Symmetricom cesium standard of frequency as a reference source.
Frequency Control Symposium, 2007 Joint with the 21st European Frequency and Time Forum. IEEE International;
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ABSTRACT: We show that, owing to small noise and smoothed excursions, the unbiased FIR filtering algorithm produces more accurate estimates of the TIE model of a local clock than the sawtooth-less GPS-based measurements. The algorithm becomes much more efficient in estimating the fractional frequency offset and higher order states. For the algorithm to work with minimum errors, the optimal time step τ opt and number of the points in the average N opt must be ascertained in the sense of the minimum mean-square error (MSE) for each of the clock states. The relevant dependencies of N opt on τ opt are found experimentally for a crystal clock. The trade-off between the estimates and sawtooth-less measurements is illustrated graphically.
