From Single to Precise Point Positioning: The Impact on Time Retrieval

The usage of Global Navigation Satellite System (GNSS) as a means to transfer time and for granting time, phase and frequency synchronization is widely adopted in both critical and non-critical infrastructures. GNSS-based Timing and Synchronization (TS) performance depends on several factors such as the type of receiver used, the environments where the device is placed and the processing strategy adopted for time retrieval. For the first two aspects, several works are available in the specialized literature, while for the impact of the processing strategy adopted by the receivers, no in-depth analysis is currently available. In order to fill this gap, in this work different positioning techniques have been implemented and tested: from standard single-frequency Single Point Positioning (SPP) (code-based) to the more complex dual-frequency Precise Point Positioning (PPP) (carrier-based). In addition, different ephemeris products from broadcast ephemerides to final International GNSS Service (IGS) products have been used. The combination of the selected different positioning strategies and ephemeris products leads to 15 configurations. The impact of each configuration on timing solution stability has been evaluated using the Allan Deviation (ADEV). The assessment has been performed using real data: about 60 hours of data were collected using a dedicated setup including a professional GNSS receiver and an external rubidium oscillator. The analysis shows a high consistency of the clock parameter estimates; SPP and PPP solutions have a similar behaviour in terms of stability. PPP with final IGS ephemerides is the configuration providing the higher stability. For code based strategies, the inclusion of a second frequency does not provide benefits in terms of stability but it increases the variance of a factor close to 2.4.