Accounting BDS3–BDS2 inter-system biases for precise time transfer

Abstract

The rapid development of BDS not only brings opportunities but also new problems. This article has been verified that the biases exist between BDS-2 and BDS-3 precise point positioning time transfer. We defined internal biases of BDS as Time Delay Bias (TDB) for a distinguish with inter system biases (ISB) exists in different systems. Motivated by the bias, we make comprehensive analysis for determining the characteristics of TDB referring to all the receivers capable of BDS-2 along with BDS-3 signals, furtherly, three kinds of TDB stochastic model are designed for parameter estimation. Later, the influence on time transfer with different TDB estimation strategy is compared in the end. We have some findings: (1) It is confirmed that TDB indeed exists in JAVAD TRE_3, CETC-54-GMR-4016, GNSS GGR and UB4B0-13478 receivers. Without external frequency source, the characteristics of TDB is related to the receiver itself. With the same external frequency source, TDB tendency of two receivers show the same evolution. (2) It is concluded that the STD (Standard Deviation) and stability of TDB estimated with random walk model and constant model is superior to white noise model because of strong correlation among TDB time series. (3) It is verified that the stability of time transfer estimated as random walk model and constant model is smaller than that of white noise model, what is more, when the two sides were receivers of different brands, the significant deviation exists in the clock offset with TDB estimation and without TDB estimation. When the two sides are receiver of the same brand, marginal deviation exists in the clock offset with TDB estimation and without TDB estimation.