Guanwen Huang

GNSS Precise Point Positioning Algorithm Based on Parameter Equivalent Reduction Principle

The standard GNSS combined PPP algorithm cannot be used satisfactorily in the real-time and high frequency precise positioning because of its low compute efficiency. A new algorithm based on the parameter equivalent reduction principle is proposed. First, the observations equation and the normal equation which belong to the single navigation system can be solved independently. Second, the normal equations of overlapping parameters between the different systems can be obtained by using parameter equivalent reduction principle. At last, the combined PPP resolutions can be computed easily by using the Least Squares method. The proposed algorithm can improve the calculating efficiency immensely. In addition, an adaptively combined method which can automatically adjusts the contributed weight of different GNSS systems is also proposed in this paper. The numerical examples using the data set of three IGS stations, show that the PPP precisions and efficiencies based on the proposed model have been improved significantly compared with those of standard model. This proposed principle can also be applied in the GNSS precise satellite clock determination and the indifference baseline network adjustment plus the GNSS time offset monitoring.

A Real-Time Robust Method to Detect BeiDou GEO/IGSO Orbital Maneuvers

The frequent maneuvering of BeiDou Geostationary Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO) satellites affects the availability of real-time orbit, and decreases the accuracy and performance of positioning, navigation and time (PNT) services. BeiDou satellite maneuver information cannot be obtained by common users. BeiDou broadcast ephemeris is the only indicator of the health status of satellites, which are broadcast on an hourly basis, easily leading to ineffective observations. Sometimes, identification errors of satellite abnormity also appear in the broadcast ephemeris. This study presents a real-time robust detection method for a satellite orbital maneuver with high frequency and high reliability. By using the broadcast ephemeris and pseudo-range observations, the time discrimination factor and the satellite identification factor were defined and used for the real-time detection of start time and the pseudo-random noise code (PRN) of satellites was used for orbital maneuvers. Data from a Multi-GNSS Experiment (MGEX) was collected and analyzed. The results show that the start time and the PRN of the satellite orbital maneuver could be detected accurately in real time. In addition, abnormal start times and satellite abnormities caused by non-maneuver factors also could be detected using the proposed method. The new method not only improves the utilization of observations for users with the data effective for about 92 min, but also promotes the reliability of real-time PNT services.

Estimate DCB of BDS Satellites Based on the Observations of GPS/BDS

In single frequency precise point positioning, satellite’s DCBs is one of the main factors impacting the positioning accuracy. In the consideration of BDS navigation system has not completed and the limited distribution of regional monitoring network, these adverse condition make it is hard to estimate the DCBs accuracy. So put forward using GPS rice data to estimate the DCB of BDS satellite by make a global ionosphere model using the observations of GPS and BDS. In this paper the strategy of estimate the DCB of BDS satellite is discussed in detail. Further analysis showed that the stability of BDS satellite’s DCBs is about 0.15 ns at 1 month. In order to further validate the precision of DCB of BDS satellites from this strategy, used BDS single frequency observations to position with the correct of BDS satellite’s DCB or without it. Compared with no DCBs correction, single-frequency user’s positioning accuracy is improved from 47% to 63% by using DCBs correction from the algorithm.

The Analysis of the Characterization for GLONASS and GPS on-Board Satellite Clocks

With GLONASS and GPS satellite clocks aging and modernizing, their characteristics present corresponding changes and certain differences. For that reason, the paper puts forward a combined method of detecting gross, adopts the quadratic polynomial model to fit the satellite clock error model, calculates the phase, frequency, frequency drift and residual of GLONASS and GPS on-board satellite clocks, chooses Modified Total Variance and Hadamard Total Variance to calculate the stability of cesium (Cs) and rubidium (Rb) clock respectively, and then analyses the characterization of the on-board satellite clocks. From examples, finding out that the combined method of detecting gross is effective; revealing the variation law of the phase, frequency, drift and residual for GLONASS and GPS satellite clocks; discovering that the stability of GPS BLOCK IIF satellite clocks are the best, GPS BLOCK IIR-M&IIR Rb clocks and the newer GLONASS satellite clocks follow, and then there are GPS BLOCK IIA Cs clocks and the older GLONASS satellite clocks, but GPS BLOCK IIA Rb clocks are the worst. Meanwhile, there is a numerical relationship between the stability and residual of the satellite clocks.

An Optimized Method to Detect BDS Satellites’ Orbit Maneuvering and Anomalies in Real-Time

The orbital maneuvers of Global Navigation Satellite System (GNSS) Constellations will decrease the performance and accuracy of positioning, navigation, and timing (PNT). Because satellites in the Chinese BeiDou Navigation Satellite System (BDS) are in Geostationary Orbit (GEO) and Inclined Geosynchronous Orbit (IGSO), maneuvers occur more frequently. Also, the precise start moment of the BDS satellites’ orbit maneuvering cannot be obtained by common users. This paper presented an improved real-time detecting method for BDS satellites’ orbit maneuvering and anomalies with higher timeliness and higher accuracy. The main contributions to this improvement are as follows: (1) instead of the previous two-steps method, a new one-step method with higher accuracy is proposed to determine the start moment and the pseudo random noise code (PRN) of the satellite orbit maneuvering in that time; (2) BDS Medium Earth Orbit (MEO) orbital maneuvers are firstly detected according to the proposed selection strategy for the stations; and (3) the classified non-maneuvering anomalies are detected by a new median robust method using the weak anomaly detection factor and the strong anomaly detection factor. The data from the Multi-GNSS Experiment (MGEX) in 2017 was used for experimental analysis. The experimental results and analysis showed that the start moment of orbital maneuvers and the period of non-maneuver anomalies can be determined more accurately in real-time. When orbital maneuvers and anomalies occur, the proposed method improved the data utilization for 91 and 95 min in 2017.

A New Azimuth-Dependent Elevation Weight (ADEW) Model for Real-Time Deformation Monitoring in Complex Environment by Multi-GNSS

Global navigation satellite systems (GNSS) have provided an excellent way to monitor micro-deformation in real-time. However, at local sites where landslides frequently occur, the environment can include complex surroundings with mountains, dense vegetation, and human settlements, which can severely degrade the accuracy of positioning with the GNSS technique. In this study, we propose an azimuth-dependent elevation weight (ADEW) model using an azimuth-dependent elevation mask (ADEM) to reduce the effects of multipath errors and improve the accuracy of real-time deformation monitoring in such environments. We developed an adaptive fixed-elevation mask to serve as the outlier of low precision observations at lower elevations for the ADEM, and then, we applied the weighted phase observations into the mitigation process for the effects of multipath errors. The real numerical results indicate that the ADEM model performs better than the conventional model, and the average improvements were 18.91% and 34.93% in the horizontal and vertical direction, respectively. The ADEW model further improved upon the ADEM model results by an additional 21.9% and 29.8% in the horizontal and vertical direction, respectively. Therefore, we propose that the ADEW model can significantly mitigate the effects of multipath errors and improve the accuracy of micro-deformation monitoring via GNSS receivers.

An Improved Predicted Model for BDS Ultra-Rapid Satellite Clock Offsets

The satellite clocks used in the BeiDou-2 satellite navigation System (BDS) are Chinese self-developed Rb atomic clocks, and their performances and stabilities are worse than GPS and Galileo satellite clocks. Due to special periodic noises and nonlinear system errors existing in the BDS clock offset series, the GPS ultra-rapid clock model, which uses a simple quadratic polynomial plus one periodic is not suitable for BDS. Therefore, an improved prediction model for BDS satellite clocks is proposed in order to enhance the precision of ultra-rapid predicted clock offsets. First, a basic quadratic polynomial model which is fit for the rubidium (Rb) clock is constructed for BDS. Second, the main cyclic terms are detected and identified by the Fast Fourier Transform (FFT) method according to every satellite clock offset series. The detected results show that most BDS clocks have special cyclic terms which are different from the orbit periods. Therefore, two main cyclic terms are added to absorb the periodic effects. Third, after the quadratic polynomial plus two periodic fitting, some evident nonlinear system errors also exist in the model residual, and the Back Propagation (BP) neural network model is chosen to compensate for these nonlinear system errors. The simulation results show that the performance and precision using the improved model are better than that of China iGMAS ultra-rapid prediction (ISU-P) products and the Deutsches GeoForschungsZentrum GFZ BDS ultra-rapid prediction (GBU-P) products. Comparing to ISU-P products, the average improvements using the proposed model in 3 h, 6 h, 12 h and 24 h are 23.1%, 21.3%, 20.2%, and 19.8%, respectively. Meanwhile the accuracy improvements of the proposed model are 9.9%, 13.9%, 17.3%, and 21.2% compared to GBU-P products. In addition, the kinematic Precise Point Positioning (PPP) example using 8 Multi-GNSS Experiment MGEX stations shows that the precision based on the proposed clock model has improved about 16%, 14%, and 38% in the North (N), East (E) and Height (H) components.

Application Performance Analysis of Three GNSS Precise Positioning Technology in Landslide Monitoring

In this paper, the accuracy and applicability of GNSS PPP (Precise Point Positioning), RTK (Real Time Kinematic) and static baseline positioning based on landslide monitoring are presented with compared the characteristics of different methods. The performance of BeiDou, GPS and BDS/GPS modes is demonstrated by using the real experiment data from a large loess landslide and simulated slow deformation test. It is show that for the integrated GPS/BeiDou, the precision of PPP, RTK, and Static baseline solutions are better than 6 cm, 6 and 3 mm respectively. The accuracy of those is significantly improved with the BeiDou/GPS case. These results reveal that the technology of RTK, PPP, and Static baseline can be used for the real-time monitoring, deformation datum recovery and periodic deformation monitoring respectively.

A Comparative Analysis of Relative Positioning Methods for BDS/GPS in Three Different Fields of Combination

In this contribution, we study the models of BDS/GPS combined in three different fields relative positioning, which contain field of coordinate estimates, field of normal equations and that of observation equations. The precision of coordinate solution, differences and similarities in different fields are discussed. On the condition of single epoch and static sequential Least-squares calculation, combination of normal equation field and that of observation equation field are with equivalence, while on the condition of dynamic calculation, the combination of observations equation field is more rigorous than that of normal equation field, and the Ratio rate of the integer ambiguity estimates is higher. Based on the data from measured short-baseline, we verify inference given in the contribution by experiment and analyze through calculation on single epoch, sequential Least-squares and dynamic.

An Enhanced Global Positioning Technology and Precision Verification of BDS

Precise point positioning (PPP) technology is a positioning enhancement technique that can cover a large area and reduce the cost of positioning. With the support of real-time precise orbit and clock offset products, the global real-time PPP can be realized, which greatly improves the effectiveness and availability of the results. First, in this paper, the global real-time precise orbit and clock offset can be calculated by the BeiDou global continuous tracking station. Then the BeiDou global-enhanced message is designed, the frequency and the type of broadcasting-enhanced message are analyzed. Finally, the real-time PPP accuracy of BDS is studied. The actually measured numerical example shows that the real-time PPP based on BDS can achieve decimeter-level position accuracy in the Asian-Pacific region.