The Characteristic and Effect of Code Bias Variations of BeiDou

Different from other navigation system, there is a divergence between code and phase observables of BeiDou Navigation Satellite System (BDS). In this paper, we analyze the characteristic of code bias variations and propose a polynomial correction model of GEO, IGSO and MEO satellites. Firstly, different stations and different receiver types observables of BeiDou Experiment Tracking Stations (BETS) of Wuhan University, Crustal Movement Observation Network of China (CMONOC) and Multi-GNSS Experiment campaign(MGEX) of IGS are used for analysis and verification. The results show that the code bias variations, which are dependent with satellite types and frequency and independent with receiver type, station position and observation time, vary with satellite elevations. Besides, the code bias variations of satellites may reach up to 1.5 m and can be divided into two groups (GEO/IGSO and MEO). Secondly, based on the analysis of code bias variations of BDS, we established a polynomial correction model of IGSO/MEO code bias variations. Besides, since the elevation of a GEO satellite remains unchanged, we propose to model the single-difference fractional cycle bias with wide-spread ground stations. Then, a correction model for code bias variations of GEO satellites is established by using the consistency of the fractional of wide-lane ambiguity of single-difference between satellites. Finally, the improvement brought by applying our correction model is validated by various strategies, e.g. residual distribution of pseudo-range is more close to normal distribution, and the positioning accuracy of dual-frequency single point positioning as well as single-frequency precise point positioning is improved.