Xuhai Yang

The method of time synchronization based on the combination of COMPASS GEO pseudo-range and two-way data

This paper presents a time synchronization method based on the COMPASS code measurements in combination with two-way transfer ranging, which results the clock offset between COMPASS GEO satellite and the ground station. The clock offset of COMPASS G3 satellite on board is computed by using the data observed on October 2010. In order to verify the accuracy of this method, the results are compared with the results, which are determined only by pseudo-range observation. By comparison and analysis, the following facts can be drawn. ○1 The precision of navigation satellite clock bias is better than 10 ns, when the clock bias is calculated by the new method. There is no systematic error between our results and clock bias deduced from precise satellite orbit. ○2 The new method can separate satellite orbit and clock bias, it is beneficial to researching satellite clock bias.

Global Navigation Satellite System Multipath Mitigation Using a Wave-Absorbing Shield

Code multipath is an unmanaged error source in precise global navigation satellite system (GNSS) observation processing that limits GNSS positioning accuracy. A new technique for mitigating multipath by installing a wave-absorbing shield is presented in this paper. The wave-absorbing shield was designed according to a GNSS requirement of received signals and collected measurements to achieve good performance. The wave-absorbing shield was installed at the KUN1 and SHA1 sites of the international GNSS Monitoring and Assessment System (iGMAS). Code and carrier phase measurements of three constellations were collected on the dates of the respective installations plus and minus one week. Experiments were performed in which the multipath of the measurements obtained at different elevations was mitigated to different extents after applying the wave-absorbing shield. The results of an analysis and comparison show that the multipath was mitigated by approximately 17%–36% on all available frequencies of BeiDou Navigation Satellite System (BDS), Global Positioning System (GPS), and Global Navigation Satellite System (GLONASS) satellites. The three-dimensional accuracies of BDS, GPS, and GLONASS single-point positioning (SPP) were, respectively, improved by 1.07, 0.63 and 0.49 m for the KUN1 site, and by 0.72, 0.79 and 0.73 m for the SHA1 site. Results indicate that the multipath of the original observations was mitigated by using the wave-absorbing shield.

Common-View time transfer experiment based on COMPASS-M1 satellite

The COMPASS Common-View time transfer experiment was done between National Time Service Center (NTSC) and Shanghai Observation (SHAO) via COMPASS-M1 satellite (MEO) in December in 2007 for the first time. NTSC is about 2000 km away from SHAO, and Cs atomic clock is equipped at each station. Our data processing method is as follows. The troposphere delay is calculated based on meteorological data, and the ionosphere delay is calculated based on IGS TEC Map. The satellite orbit obtained is about 10m accuracy, and then the clock difference between NTSC and SHAO is calculated with Common-View method. After that, the clock difference from Common-View is compared with that from Two-Way Satellite Time and Frequency Transfer (TWSTFT). The experiment result and analysis indicate that the accuracy of Common-View time transfer via COMPASS-M1 satellite is better than 10 nanoseconds.

High-Precision Ionosphere Monitoring Using Continuous Measurements from BDS GEO Satellites

The current constellation of the BeiDou Navigation Satellite System (BDS) consists of five geostationary earth orbit (GEO) satellites, five inclined geosynchronous satellite orbit (IGSO) satellites, and four medium earth orbit (MEO) satellites. The advantage of using GEO satellites to monitor the ionosphereis the almost motionless ionospheric pierce point (IPP), which is analyzed in comparison with the MEO and IGSO satellites. The results from the analysis of the observations using eight tracking sites indicate that the ionospheric total electron content (TEC) sequence derived from each GEO satellite at their respective fixed IPPs is always continuous. The precision of calculated vertical TEC (VTEC) using BDS B1/B2, B1/B3, and B2/B3 dual-frequency combinationsis compared and analyzed. The VTEC12 precision based on the B1/B2 dual-frequency measurements using the smoothed code and the raw code combination is 0.69 and 5.54 TECU, respectively, which is slightly higher than VTEC13 and much higher than VTEC23. Furthermore, the ionospheric monitoring results of site JFNG in the northern hemisphere, and CUT0 in the southern hemisphere during the period from 1 January to 31 December 2015 are presented and discussed briefly.

Use of NTRIP for optimizing the decoding algorithm for real-time data streams.

As a network transmission protocol, Networked Transport of RTCM via Internet Protocol (NTRIP) is widely used in GPS and Global Orbiting Navigational Satellite System (GLONASS) Augmentation systems, such as Continuous Operational Reference System (CORS), Wide Area Augmentation System (WAAS) and Satellite Based Augmentation Systems (SBAS). With the deployment of BeiDou Navigation Satellite system (BDS) to serve the Asia-Pacific region, there are increasing needs for ground monitoring of the BeiDou Navigation Satellite system and the development of the high-precision real-time BeiDou products. This paper aims to optimize the decoding algorithm of NTRIP Client data streams and the user authentication strategies of the NTRIP Caster based on NTRIP. The proposed method greatly enhances the handling efficiency and significantly reduces the data transmission delay compared with the Federal Agency for Cartography and Geodesy (BKG) NTRIP. Meanwhile, a transcoding method is proposed to facilitate the data transformation from the BINary EXchange (BINEX) format to the RTCM format. The transformation scheme thus solves the problem of handing real-time data streams from Trimble receivers in the BeiDou Navigation Satellite System indigenously developed by China.

Time Transfer Analysis of GPS- and BDS-Precise Point Positioning Based on iGMAS Products

International time transfer experiment based on GPS- and BDS-precise point positioning (PPP) technique is carried out using final (ISC) and rapid (ISR) precise satellite clock products provided by iGMAS (international GNSS continuous Monitoring and Assessment System). As a comparison, the same processing is conducted by using COD products provided by the Center for Orbit Determination in Europe (CODE). Experimental data come from observation of seven stations from Multi-GNSS-Experiment (MGEX) and two stations including PT11 (PTB) and BRUX (ROB) from time keeping laboratory in 70 days from 5 August to 15 October 2017. With PTB as the center node, the solutions of 8 time-links are formed. In order to verify the type A uncertainty (uA) of time transfer based on GPS- and BDS-PPP by using iGMAS products, this paper compares the differences between GPS- and BDS-PPP results and GPS PPP results using IGR products. The experimental results demonstrate that uA of time transfer based on GPS- and BDS-PPP using iGMAS products are roughly equal to CODE products. For the results of time-links based on GPS- and BDS-PPP, the STD of one-day arc solutions can reach better than 0.1 and 0.8 ns for all of processing, while 0.1 and 1 ns were achieved for ten-day arc solutions, respectively. Since uA of GPS- and BDS-PPP time transfer using iGMAS products was up to sub nanosecond, therefore, the experiments can provide a reference for BIPM to use BDS PPP based on iGMAS products for International UTC/TAI comparison. Moreover, this also illustrates iGMAS products is reliable.

Satellite clock offset estimation and analysis based on arc-wise observation files

In order to meet the demand of GPS real/near real time (RT/NRT) application, it is proposed that a clock estimation algorithm with high reliability and adequate accuracy, which is based on arc-wise observation data gained by merging hourly files or 15-min files offered by IGS. It is analyzed emphatically that the critical influence factors of the algorithm, and account the efficacy of the algorithm. Test indicates that lengths of the observation arc, precision of the obit, ERP and station number are all the important influence factors of the novel algorithm. When the observation arc is set as 24h, 12h, 6h, 3h, 1h, 0.5h and the station number is 120, STD of the clock offset is 0.05ns, 0.11ns, 0.19ns, 0.22ns, 0.27ns, 0.29ns, while the STD of the clock offset decreases by 100%, 73%, 47%, 48%, 52%, 58% when the station number is reduced by half, whats more the STD of the clocks decreases by 120%, 27%, 5%, 4%, 4%, 7% as the precision of orbit decreases.

The method on determining invisible satellite-ground clock difference with inter-satellite-link

Usually, satellite-ground clock difference of invisible arc is obtained by predicting. This paper proposes determining satellite-ground clock difference of invisible arc by way of inter-satellite link, using target satellite connecting station with relay satellite. Target satellite and station consists of satellite-ground link, target satellite and relay satellite consists of inter-satellite link. It analyzes relay-satellite angle. When more relay-satellites exist, clock difference of invisible arc is determined with weight. The result shows: time-synchronization precision of satellite-ground is less than 0.3ns, std is less than 0.3ns.

The method of determination of GEO satellite precise clock bias during maneuvering

This paper aims to research and determine GEO satellite clock bias during maneuvering. By analyzing of GEO satellite clock bias data, quadratic polynomials, cubic spline and Lagrange are chose as interpolation methods. The result of the test in this paper shows that in most cases, cubic spline interpolation is the best one of the three interpolation methods. And the accuracy of cubic spline interpolation is at the level of 0.08ns~0.38ns which can meet the actual demand; besides the stability of cubic spline interpolation is obviously better than that of quadratic polynomials and Lagrange interpolations.

GPS/BDS One-Step Combined Precise Orbit Determination Based on Double-Differenced Mode

In order to improve the precision of BDS precise ephemeris, GPS/BDS one-step combined precise orbit determination based on double-differenced mode was testified in this contribution. And double-differenced data was not formed between GPS and BDS, which eliminates the effect of inter system bias (ISB) on the precision of BeiDou precise orbit. Not only GPS and BDS orbit parameters are estimated, earth rotation parameter (ERP) and station coordinates are also estimated. Data of 114 tracking stations from MGEX are processed. The analysis shows that: Compared with IGS final orbit, the precision of GPS orbit is 5 cm, the precision of Xp, Yp, length of day (LOD) is 0.06, 0.10 mas, 21.6 μs. Validating the BDS orbit using SLR observation shows that the radial precision of BDS IGSO and MEO satellites is better than 6 cm, while that of GEO satellite is about 0.37 m.