Abstract
BeiDou global navigation satellite system (BDS) began to provide positioning, navigation, and timing (PNT) services to global users officially on 31 July, 2020. BDS constellations consist of regional (BDS-2) and global navigation satellites (BDS-3). Due to the difference of modulations and characteristics for the BDS-2 and BDS-3 default civil service signals (B1I/B3I) and the increase of new signals (B1C/B2a) for BDS-3, a systemically bias exists in the receiver-end when receiving and processing BDS-2 and BDS-3 signals, which leads to the inter-system bias (ISB) between BDS-2 and BDS-3 on the receiver side. To fully utilize BDS, the BDS-2 and BDS-3 combined precise time and frequency transfer are investigated considering the effect of the ISB. Four kinds of ISB stochastic models are presented, which are ignoring ISB (ISBNO), estimating ISB as random constant (ISBCV), random walk process (ISBRW), and white noise process (ISBWN). The results demonstrate that the datum of receiver clock offsets can be unified and the ISB deduced datum confusion can be avoided by estimating the ISB. The ISBCV and ISBRW models are superior to ISBWN. For the BDS-2 and BDS-3 combined precise time and frequency transfer using ISBNO, ISBCV, ISBRW, and ISBWN, the stability of clock differences of old signals can be enhanced by 20.18%, 23.89%, 23.96%, and 11.46% over BDS-2-only, respectively. For new signals, the enhancements are −50.77%, 20.22%, 17.53%, and −3.69%, respectively. Moreover, ISBCV and ISBRW models have the better frequency transfer stability. Consequently, we recommended the optimal ISBCV or suboptimal ISBRW model for BDS-2 and BDS-3 combined precise time and frequency transfer when processing the old as well as the new signals.
Highlights
As the third navigation satellite system recognized by International Maritime Organization (IMO), the development and construction of BeiDou navigation satellite system (BDS) has experienced three stages: The demonstration system (BDS-1), the regional system (BDS-2), and the global system (BDS-3) [1,2,3]
We present four kinds of inter-system bias (ISB) stochastic models called ignoring ISB (ISBNO ), ISBCV, ISBRW, and ISBWN to explore the influence of ISB on BeiDou global navigation satellite system (BDS)-2 and BDS-3 combined precise time and frequency transfer
We first prove that the ISB exists between BDS-2 and BDS-3 for both new signals (B1C/B2a) and old signals (B1I/B3I) by comparing the receiver clock offsets of BDS-2-only and BDS-3-only
Summary
As the third navigation satellite system recognized by International Maritime Organization (IMO), the development and construction of BeiDou navigation satellite system (BDS) has experienced three stages: The demonstration system (BDS-1), the regional system (BDS-2), and the global system (BDS-3) [1,2,3]. The common view (CV) and all-in view (AV) techniques are utilized for GNSS time and frequency transfer [5,6,7]. The CV technique, by observing the same satellites to remove the common satellites errors, can achieve 1 to 10 ns accuracy of time transfer [8]. Due to the limitation of the baseline length, the CV technique is difficult to realize global time transfer. Thanks to the development of precise orbit and clock products in terms of precision and timeliness, precise point positioning (PPP) as a typical AV technique is of great interest in the time and frequency field, which can obtain the sub-nanosecond to nanosecond accuracy [9]. Zhang, et al [12] got similar conclusions
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