Remote Performance Evaluation of High-Precision Timekeeping Systems Based on BDS Real-Time PPP

Remote real-time performance evaluation of standard time and frequency is critical for full-scope time traceability and quantity unification. Conventional time and frequency calibration schemes predominantly adopt on-site accompanying calibration or laboratory submission, which are hampered by bulky equipment, high operational costs and poor flexibility, rendering them incompatible with continuous real-time monitoring and evaluation scenarios. While GNSS common-view and all-in-view techniques are available for remote performance evaluation, their limited precision cannot satisfy the demands of high-precision timekeeping systems with a frequency stability at the 10-15 level. This paper constructs a remote real-time performance evaluation system based on self-developed BDS real-time PPP (RTPPP) receivers. Two validation experiments are carried out: a 43 km short-baseline link between Lintong and Hangtian campus of the National Time Service Center (NTSC) referenced to an optical-fibre time transfer link, and a 1150 km long-baseline link between Lintong and Anhui referenced to a GNSS IPPP link. Experimental results indicate that the frequency stability of the BDS RTPPP link is better than 8 × 10-15 at an averaging time of one day. For the single hydrogen-maser timekeeping system located at Hangtian, the average frequency deviation and frequency stability measured via BDS RTPPP reach 1.93 × 10-15 and 2.07 × 10-15/1 d, respectively, showing close agreement with the independently calibrated optical-fibre reference. For the Anhui timekeeping system, the one-day average frequency deviation is 8.90 × 10-15 and frequency stability reaches 7.95 × 10-15 after one day of averaging, which are in close agreement with the GNSS IPPP reference results. The overall findings verify that BDS RTPPP based on PPP-B2b service is qualified for remote real-time performance evaluation and monitoring of high-precision timekeeping systems.