Precise disciplining of a chip-scale atomic clock using PPP with broadcast ephemerides

Over the last decade, chip-scale atomic clocks (CSACs) have emerged as stable time and frequency references with small size, weight, and power (SWaP). While the short-term stability of these devices clearly outperforms other oscillators with similar power consumption, their stability over longer time intervals is notably limited by frequency noise. Such long-term deviations can effectively be compensated by disciplining the clock with respect to a stable time and frequency reference such as Coordinated Universal Time (UTC) or a time scale based on GNSS observations. In view of the limited accuracy of GPS pseudorange observations and broadcast ephemerides, the performance of GNSS-disciplined atomic clocks is commonly limited to the few-nanosecond level. For further improvement, this study combines the use of carrier phase-based precise-point-positioning (PPP) techniques and high-performance broadcast ephemerides to discipline the phase of a CSAC with respect to GNSS broadcast time. Making use of a dual-frequency, dual-constellation GPS/Galileo receiver, a sub-nanosecond time interval error with respect to a national UTC timing laboratory is demonstrated over time intervals from 1 s to several days.