Identifying Nonstationary Clock Noises in Navigation Systems

Abstract

The stability of the atomic clocks on board the satellites of a navigation system should remain constant with time. In reality, there are numerous physical phenomena that make the behavior of the clocks a function of time, and for this reason we have recently introduced the dynamic Allan variance (DAVAR), a measure of the time-varying stability of an atomic clock. In this paper, we discuss the dynamic Allan variance for phase and frequency jumps, two common nonstationarities of atomic clocks. The analysis of both numerical simulations and experimental data proves that the dynamic Allan variance is an effective way of characterizing nonstationary behaviors of atomic clocks.

Detection and identification of atomic clock anomalies

“…In figure 6 we show the dynamic Allan deviation of the frequency jump shown in figure 1. In [4] we have discussed in detail this type of anomaly. The increase in variance, localized about the anomaly time n a , is typical of this anomaly.…”

“…When an anomaly occurs, the clock stability changes with time. To represent the variations with time of the stability we use the dynamic Allan variance, or DAVAR, defined as [4]…”

“…In this paper we develop a method for the detection and identification of three typical anomalies of atomic clocks, namely, the frequency jump, the increase in variance, and the presence of sinusoidal components [3]. The method is based on the dynamic Allan variance, or DAVAR, a representation of the time-varying stability of an atomic clock [4][5][6]. An anomaly produces in fact a variation of the clock stability, which can be identified in the DAVAR representation.…”

Failure detection and correction for clock ensemble in space

“…These frequency values are considered outliers, since they are numerically distant from the rest of the data which should be removed in the preprocessing of data. The phase jump can be modeled as a spike in frequency data as [8]: y[n] = f[n]+cδ[n-n 0 ], where f[n] contributes for the combination of White Frequency Noise and Random Walk Frequency, c is an arbitrary constant and n 0 is the discrete-time at which delta function is located. Simulation results show that smaller phase jumps as shown in Figure 10 with less than 0.2° can be automatically compensated by the composite clock itself within the Kalman filter without any degradation in ADEV performance.…”