Analysis of BDS Satellite Clock in Orbit with ODTS and TWTT Satellite Clock Data

Abstract

Two Way Time Transfer (TWTT) is used in BDS to synchronize the time between satellite and ground system. Therefore, both Orbit Determination and Time Synchronization (ODTS) and TWTT can obtain BDS satellite clocks. For ODTS, satellite clock is estimated with satellite orbit, and the consistency of them is better, but estimation error of them cannot be separated. Compared with ODTS, satellite clock estimated by TWTT is less impacted by satellite orbit, because of the difference between uplink and downlink pseudo-ranges in TWTT processing. Consistency of ODTS satellite clock and TWTT satellite clock is of importance for the performance analysis of BDS satellite clock in orbit. Based on the satellite clocks estimated by ODTS and TWTT respectively, this paper analyzes the systematic, periodical and stochastic characteristics of BDS satellite clock, taking into account the characteristics of satellite clock data. The result can provide reference for BDS service performance optimization. It is shown that the performance of BDS satellite clock is approximately 5 × 10⁻¹² τ^−0.5 (WHFM, 10³ s ≤ τ ≤ 10⁴ s) + 4 × 10⁻¹⁴ (FLFM, τ > 10⁵ s), while during the 10⁴–10⁵ s period, the orbital-period characteristics is notable.