Detection of Anomalies in the Behavior of Atomic Clocks

Identifying Nonstationary Clock Noises in Navigation Systems

“…We have also validated our method with experimental data, proving that it is possible to understand the nonstationarities of a clock by directly inspecting the DAVAR surface. This means that it is possible to design anomaly detection methods directly in the dynamic Allan variance domain (a free Matlab implementation of the DAVAR can be found at www.ien.it/tf/ts/clock behavior.shtml) [5].…”

“…By using the dynamic Allan variance we are classifying the typical nonstationarities of atomic clocks that operate on board a satellite. The final goal is to identify the clock anomalies directly from the DAVAR, which can reveal variations in the stability that cannot be tracked with other methods [5]. In this way, proper warnings can be generated so that the integrity of the clock and of the satellite signal can be monitored continuously in time.…”

The Use of the GLRT for Revealing Faults in Atomic Frequency Standards

“…Moreover, an anomalous behavior of the clock is defined as a change in the frequency size and/or dynamic range. As a consequence, the anomaly, when and if it occurs, can be modeled as a change in the mean and/or in the standard deviation of the statistical model (D. W. Allan, 1987); (E. Nunzi et al, 2007); (E. Nunzi et al, 2007); (IEEEstd, 1999 …”

“…If this hypothesis is not satisfied, the accuracy and reliability of the classical fault detection techniques, and therefore of the whole system where the devices are inserted, are compromised (Vioarsson et al, 2000); (Bruce et al, 2000). In this context, this book chapter collects and summarizes the last years proposals about the use of Generalized Likelihood Ratio test (GLRT) as a fault detection technique, complementary to the classical ones, for revealing faults from frequency data (E. Nunzi et al, 2007); (E. Nunzi et al, 2007); ; ; (E. Nunzi & D. D'Ippolito, 2009); ). In particular, the GLRT (S. M. , following the Neyman-Pearson (NP) approach is presented and its effectiveness is demonstrated when clock frequency data are subjected to jumps in the mean and/or in the dynamic range.…”

An Approach for GPS Clock Jump Detection Using Carrier Phase Measurements in Real-Time

“…In addition, sudden anomalies such as phase jumps, frequency jumps, frequency increasing, etc., may also occur. Many studies have been conducted in order to detect these anomalies, observed in atomic clocks in ground station, which might be unlike behavior from what we intend to identify [7][8][9][10][11]. For example, Czopek applied a method that takes the average values of clock drifts in order to detect jumps that cause the average values to go out of a certain range, as in [7].…”