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As an essential national space-time infrastructure, the BeiDou navigation satellite system (BDS) comprehensively empowers the Internet of Things and enhances the development of the digital economy. Due to prominent issues, such as complex system engineering, inaccessible space environments, and obscure theoretical abstractions, it is difficult to understand intuitively the working mechanism of BDS. For the simulation and visualization of satellite navigation systems, the existing commercial software is characterized by high acquisition costs, strong professionalism, and complex operations that restrict improvements in practical and innovative abilities. Therefore, developing an open and shared visual simulation platform to help users intuitively understand BDS is an urgent task. This paper presents BeiDou visual simulation platform (BDViSim), an open-source web application platform for visual simulation, to intuitively demonstrate BDS's spatial structural characteristics, functional innovation features, and positioning performance advantages. BDViSim utilizes the flexible, convenient, and powerful platform provided by the Cesium virtual earth engine with the Browser/Server (B/S) architecture, which implements visual simulation functions such as orbit calculation, constellation simulation, and service performance. Users can easily access the platform on any browser, making it a convenient tool and platform for BDS visualization analysis. In addition, the open-source code provided by BDViSim can supply reference information for developers interested in building similar visual simulation web application platforms. [ABSTRACT FROM AUTHOR]

We statistically study 10 weak to moderate geomagnetic storms that occurred since the 25th solar activity cycle to evaluate the quality of satellite signal and positioning accuracy of Beidou Navigation Satellite System (BDS). The results show that the PAS (Percentage of Affected Satellites) index, which integrates three scenarios: satellite signal loss, satellite signal loss of lock, and carrier phase signal anomaly, appears significant anomaly changes during weak and moderate geomagnetic storms, and its changing trend is closely related to the geomagnetic storm Kp index and Dst index, the correlation coefficient is greater than 0.75. Based on the results of PAS signal quality evaluation, the effect of PAS on the positioning error of Precision Point Positioning (PPP) of BDS-2/BDS-3 systems is analyzed and verified in conjunction with PAS. The results show that there is a strong agreement between the time of PAS anomaly and the time of PPP positioning accuracy anomaly. The positioning error of PPP increases by 9 to 44 times compared to the quiet period. The statistical results indicate that the PAS index is useful for the signal quality evaluation of the Beidou Navigation Satellite System under different space weather conditions. [ABSTRACT FROM AUTHOR]

Pseudorange bias refers to the receiver-dependent and satellite-dependent constant bias in the pseudorange resulting from the nonideal characteristics of a signal. The impact of pseudorange bias on high-precision satellite navigation services has long been ignored. This paper proposes a pseudorange bias calibration method for two collocated receivers. Then, we calibrate pseudorange biases for two types of collocated receivers at a monitoring station within China and evaluate their impact on two high-precision services: BeiDou Navigation Satellite System 3 (BDS-3) dual-frequency pseudorange augmentation and precise point precision (PPP). Theoretical analysis reveals that the calibrated pseudorange biases contribute 17.2% and 7.7% to the user equivalent ranging error (UERE) of BDS-3 and Global Positioning System (GPS) dual-frequency pseudorange augmentation, respectively, and that the convergence time of the GPS static and kinematic PPP increases from 6 min and 26 min to 19 min and 58 min, respectively. The experimental results indicate that the calibrated pseudorange biases are consistent as the receiver location and time vary. The spatial distribution consistency is generally better than 0.1 m, and the temporal consistency is better than 0.15 m. The pseudorange biases for BDS-3 B1C and B2a are approximately 0.7 m and 0.1 m, respectively, whereas those for GPS L1C/A and L2P are both approximately 0.25 m. Furthermore, The results show that after correction of the pseudorange biases, the average convergence time for BDS-3/GPS static PPP decreases from 48.83/24.03 min to 38.54/21.12 min, respectively, a decrease of approximately 21%/12%. For BDS-3/GPS/BDS-3 + GPS kinematic PPP, the average convergence time decreases from 109.53/45.10/39.15 min to 62.99/40.83/22.94 min, respectively, a decrease of approximately 42%/41%/9%. Similarly, the three-dimensional positioning accuracy for BDS-3/GPS/BDS-3 + GPS dual-frequency pseudorange augmentation improves from 3.25/3.94/2.49 m to 2.65/3.69/2.16 m, respectively, increasing by approximately 6.3%, 18.5%, and 13.3%, respectively. The above analysis and experiments demonstrate that pseudorange bias is an important error source affecting both dual-frequency pseudorange augmentation and PPP services. [ABSTRACT FROM AUTHOR]

• An improved SICB correction model is proposed based on elevation and azimuth angles. • The parameters are estimated for each BDS frequency with node-separation of 1°. • The threshold of elevation for the new model is determined based on the statistics. • Weight-average algorithm with SNR is used to obtain the optimal MP deviations. The satellite-induced code bias (SICB) resulting in code-phase divergences of nearly 1.0 m has been observed in the code measurements of BeiDou navigation satellite system (BDS). Since the SICB is proved to be elevation- and frequency-dependent, several SICB correction models have been proposed to remove the systematic bias, but most of them only consider elevation angles, overlooking the influence of azimuth angles, which would limit the accuracy of the correction models, especially for Medium Earth Orbit (MEO) satellites. To deal with this problem, we proposed an improved SICB piecewise correction model as a function of elevation and azimuth angles and estimated parameters for each BDS un-GEO (Geostationary Earth Orbit) satellite and each available frequency with node-separation of 1°. The epoch-difference method is employed to remove the effect of stable terms, such as phase-ambiguities, receiver- and satellite-dependent hardware delays. Moreover, to reduce the effect of code noise and multipath at low-elevation conditions, the threshold of elevation angle for the improved model is determined based on the statistics of Multipath (MP) combinations. Besides, weight-average algorithm is used to obtain the optimal MP deviations and improve the accuracy of proposed correction model in consideration of signal-to-noise (SNR). The experiment results with real GNSS data show that the SICB models are more suitable for BDS-2 MEO satellites than Inclined Geosynchronous Orbit (IGSO) satellites. The code measurements on B1 signal are more susceptible to the SICB than that on B3 signal. After applying the improved SICB correction models, the RMS errors of MP series are significantly reduced for BDS-2 un-GEO satellites. However, for BDS-3 satellites, only centimeter-level SICB deviations can be detected for all frequency-bands, and the RMS of MP variations have slight changes after applying the SICB corrections, indicating that the systematic bias in MP combinations is not obvious, especially for BDS-3 MEO satellites. [ABSTRACT FROM AUTHOR]

Carrier Smoothing Code (CSC), as a low-pass filter, has been widely used in GNSS positioning processing to reduce pseudorange noise via carrier phases. However, current CSC methods do not consider the systematic bias between the code and carrier phase observation, also known as Satellite-induced Code Bias (SICB). SICB has been identified in the BDS-2 and the bias will reduce the accuracy or reliability of the CSC. To confront bias, an improved CSC algorithm is proposed by considering SICB for GEO, IGSO, and MEO satellites in BDS constellations. The correction model of SICB for IGSO/MEO satellites is established by using a 0.1-degree interval piecewise weighted least squares Third-order Curve Fitting Method (TOCFM). The Variational Mode Decomposition combined with Wavelet Transform (VMD-WT) is proposed to establish the correction model of SICB for the GEO satellite. To verify the proposed method, the SICB model was established by collecting 30 Multi-GNSS Experiment (MGEX) BDS stations in different seasons of a year, in which the BDS data of ALIC, KRGG, KOUR, GCGO, GAMG, and SGOC stations were selected for 11 consecutive days to verify the effectiveness of the algorithm. The results show that there is obvious SICB in the BDS-2 Multipath (MP) combination, but the SICB in the BDS-3 MP is smaller and can be ignored. Compared with the modeling in the references, TOCFM is more suitable for IGSO/MEO SICB modeling, especially for the SICB correction at low elevation angles. After the VMD-WT correction, the Root Mean Square Error (RMSE) of SICB of B1I, B2I, and B3I in GEO satellites is reduced by 53.35%, 63.50%, and 64.71% respectively. Moreover, we carried out ionosphere-free Single Point Positioning (IF SPP), Ionosphere-free CSC SPP (IF CSC SPP), CSC single point positioning with the IGSO/MEO SICB Correction based on the TOCFA Method (IGSO/MEO SICB CSC), and CSC single point positioning with the IGSO/MEO/GEO SICB correction based on VMD-WT and TOCFA (IGSO/MEO/GEO SICB CSC), respectively. Compared to IF SPP, the average improvement of the IGSO/MEO/GEO SICB CSC algorithm in the north, east, and up directions was 24.42%, 27.94%, and 24.98%, respectively, and the average reduction in 3D RMSE is 24.54%. Compared with IF CSC SPP, the average improvement of IGSO/MEO/GEO SICB CSC is 7.03%, 6.50%, and 10.48% in the north, east, and up directions, respectively, while the average reduction in 3D RMSE was 9.86%. IGSO/MEO SICB mainly improves the U direction positioning accuracy, and GEO SICB mainly improves the E and U direction positioning accuracy. After the IGSO/MEO/GEO SICB correction, the overall improvement was about 10% and positioning improved to a certain extent. [ABSTRACT FROM AUTHOR]

The Sarez Dam, currently recognized as the world's highest natural dam, holds immense economic significance, necessitating the reliable monitoring and early detection of potential deformations. This study utilizes the Beidou high-precision deformation monitoring system for the dam. Employing baseline network solutions, precise point positioning, and real-time kinematic positioning, the monitoring data from October 2021 to March 2023 were meticulously processed and comparatively analyzed. The results reveal varied degrees of displacement deformation at all sites, with horizontal deformation towards the lake center and vertical deformation showing subsidence. The three-dimensional vector average displacement is 29.1 mm, with an average monthly rate of 4.3 mm/month, and the maximum deformation is 41.4 mm. The cause of the horizontal deformation towards the lake center may be a slow collapse of the coastal soil and rock towards the lake center. Additionally, the monitoring detected a 7.2-magnitude earthquake on 23 February 2023, 52 km from the dam, causing an average displacement of 22.5 mm towards the south, which is 20 times the monthly deformation rate. In summary, deformation is present within the dam monitoring area, with a relatively stable deformation rate, warranting continued tracking and monitoring. Furthermore, earthquakes significantly impact dam deformation, necessitating heightened attention to the potential for seismic-induced dam damage in the future. [ABSTRACT FROM AUTHOR]

The BeiDou navigation satellite system (BDS) provides precise positioning, navigation, and timing (PNT) services in the Asia-Pacific Region, but the BDS-based structural health monitoring (SHM) approach (SHM) is rarely studied, especially in civil engineering. Moreover, how BDS can be applied to complete the tasks of SHM in a real project is also not fully investigated, especially working in conjunction with other techniques. This study aims to propose a BDS-based approach for SHM in civil engineering. The performance of the proposed approach is investigated through a case study—the Tianhan Grand Theater (TGT). A specific Tianhan system corresponding to BDS is proposed to complete the SHM tasks of TGT. Based on the collected data, the trusses with maximum displacement and stress are found by BDS to evaluate structural health in the construction stage. The results show that the maximum displacement and stress have certain safety reserves and meet the requirements of the specifications and regulations. Thus, BDS can satisfactorily complete the tasks of SHM for Long-span steel structures. This study gives a clear view to engineers and researchers that how to apply BDS in structural construction and provides a valuable real case for evaluating the performance of BDS in SHM. [ABSTRACT FROM AUTHOR]

Cycle slip detection and repair is a prerequisite to obtain high-precision positioning based on a carrier phase. Traditional triple-frequency pseudorange and phase combination algorithm are highly sensitive to the pseudorange observation accuracy. To solve the problem, a cycle slip detection and repair algorithm based on inertial aiding for a BeiDou navigation satellite system (BDS) triple-frequency signal is proposed. To enhance the robustness, the INS-aided cycle slip detection model with double-differenced observations is derived. Then, the geometry-free phase combination is united to detect the insensitive cycle slip, and the optimal coefficient combination is selected. Furthermore, the L2-norm minimum principle is used to search and confirm the cycle slip repair value. To correct the INS error accumulated over time, the extended Kalman filter based on the BDS/INS tightly coupled system is established. The vehicular experiment is conducted to evaluate the performance of the proposed algorithm from a few aspects. The results indicate that the proposed algorithm can reliably detect and repair all cycle slips that occur in one cycle, including the small and insensitive cycle slips as well as the intensive and continuous cycle slips. Additionally, in signal-challenged environments, the cycle slips occurring 14 s after a satellite signal outage can be correctly detected and repaired. [ABSTRACT FROM AUTHOR]

The BeiDou navigation satellite system (BDS) comprises geostationary earth orbit (GEO) satellites as well as inclined geosynchronous orbit (IGSO) and medium earth orbit (MEO) satellites. Owing to their special orbital characteristics, GEO satellites require frequent orbital maneuvers to ensure that they operate in a specific orbital window. The availability of the entire system is affected during the maneuver period because service cannot be provided before the ephemeris is restored. In this study, based on the conventional dynamic orbit determination method for navigation satellites, multiple sets of instantaneous velocity pulses parameters which belong to one of pseudo-stochastic parameters were used to simulate the orbital maneuver process in the orbital maneuver arc and establish the observed and predicted orbits of the maneuvered and non-maneuvered satellites of BeiDou regional navigation satellite system (BDS-2) and BeiDou global navigation satellite system (BDS-3). Finally, the single point positioning (SPP) technology was used to verify the accuracy of the observed and predicted orbits. The orbit determination accuracy of maneuvered satellites can be greatly improved by using the orbit determination method proposed in this paper. The overlapping orbit determination accuracy of maneuvered GEO satellites of BDS-2 and BDS-3 can improve 2–3 orders of magnitude. Among them, the radial orbit determination accuracy of each maneuvered satellite is basically better than 1 m. simultaneously, the combined orbit determination of the maneuvered and non-maneuvered satellites does not have a great impact on the orbit determination accuracy of the non-maneuvered satellites. Compared with the multi GNSS products (indicated by GBM) from the German Research Centre for Geosciences (GFZ), the impact of adding the maneuvered satellites on the orbit determination accuracy of BDS-2 satellites is less than 9 %. Furthermore, the orbital recovery time and the service availability period are significantly improved. When the node of the predicted orbit is traversed approximately 3 h after the maneuver, the accuracy of the predicted orbit of the maneuvered satellite can reach that of the observed orbit. The SPP results for the BDS reached a normal level when the node of the predicted orbit was 2 h after the maneuver. [ABSTRACT FROM AUTHOR]

As the Global Navigation Satellite System (GNSS) is widely used in all walks of life, the signal structure of satellite navigation is open, and the vulnerability to spoofing attacks is also becoming increasingly prominent, which will seriously affect the credibility of navigation, positioning, and timing (PNT) services. Satellite navigation signal authentication technology is an emerging technical means of improving civil signal anti-spoofing on the satellite navigation system side, and it is also an important development direction and research focus of the GNSS. China plans to carry out the design and development of the next-generation Beidou navigation satellite system (BDS), and one of its core goals is to provide more secure and credible PNT services. This paper first expounds on the principles and technical architecture of satellite navigation signal authentication, then clarifies the development history of satellite navigation signal authentication, and finally proposes the BDS authentication service system architecture. It will provide technical support for the construction and development of the follow-up Beidou authentication service. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new method to quantitatively evaluate the quality of the carrier phase observation signals of the BeiDou Navigation Satellite System (BDS) during weak and moderate geomagnetic storms. We take a moderate geomagnetic storm that occurred on 12 May 2021 during the 25th solar cycle as an example. The results show that the newly defined PAS (Percentage of Affected Satellites) index shows significant anomaly changes during the moderate geomagnetic storm. Its variation trend has good correlations with the geomagnetic storm Kp index and Dst index. The anomaly stations are mainly distributed in the equatorial region and auroral region in the northern and southern hemispheres. The proposed PAS index has a good indication for both BDS2 and BDS3 satellites. We further validated this index by calculating the Precise Point Position (PPP) positioning error. We found that the anomaly period of PAS has strong consistency with the abnormal period of PPP positioning accuracy. This study could provide methodological support for the evaluation of the signal quality and analysis of positioning accuracy for the BeiDou satellite navigation system under different space weather conditions. [ABSTRACT FROM AUTHOR]

This paper focuses on PPP-B2b, one of the featured services for BDS-3, which provides users around China with centimetre-level static positioning accuracy and decimetre-level kinematic positioning accuracy by broadcasting precise corrections for GPS/BDS-3 satellites. The GEO PPP-B2b signal broadcasted information types, including the PRN mask, orbit corrections, differential code bias corrections and clock corrections, are introduced, as well as a brief description of their usage. A new orbit determination strategy using regional L-band code/phase measurements and inter-satellite link measurements in combination and a real-time clock estimation strategy based on the Kalman filter for PPP-B2b precise correction generation are introduced in this contribution. Then, the accuracy of the orbit and clock corrections is assessed. The orbit user ranging error (URE) is 0.05 m for the BDS-3 MEO and GPS satellites. The orbit URE for BDS-3 IGSO satellites is worse, i.e., 0.15 m. The clock correction accuracy is 0.2 ns for BDS-3 and GPS satellites. Finally, the PPP-B2b performance is validated by both the static PPP process and simulated kinematic PPP process. BDS-3/GPS dual-system PPP offers faster convergence and better accuracy. The positioning accuracy achievable using PPP-B2b real-time products is at the same level as that using post-processed products. The RMS for BDS-3/GPS dual-system static positioning errors is less than 1.0 cm in east and north and about 3.0 cm in the up. The simulated kinematic positioning accuracy is better than 2.5 cm in the north, 3.5 cm in the east and 8.5 cm in the up directions after convergence. Highlights: A new determination strategy using regional L-band code/phase measurements and inter-satellite link measurements in combination and a real-time clock estimation strategy based on the Kalman filter for PPP-B2b precise correction generation are introduced. User ranging error (URE) is 0.05 m for the BDS-3 MEO and GPS satellites. The clock correction accuracy is 0.2 ns for BDS-3 and GPS satellites. The positioning accuracy achievable using PPP-B2b real-time products is at the same level as that using post-processed products. [ABSTRACT FROM AUTHOR]

A semi-analytical investigation on the dynamics of BeiDou IGSO is conducted in this paper. First, a semi-analytical propagator is constructed based on the mean element method. The comparison of results of semi-analytical propagation with reference orbits shows that all orbital elements except the semi-major axis agree well within six centuries. For some example orbits, the semi-analytical propagation of the semi-major axis is accurate only within several decades, which is related to the chaotic motion of the one-to-one tesseral resonance. Compared with the numerical ephemeris of Moon, an improvement of accuracy in the semi-analytical propagation is observed when a simple analytical ephemeris of Moon is adopted. This phenomenon agrees with the doubly averaging process of the third-body perturbation. Second, the dynamics of BeiDou IGSO are investigated using the Hamiltonian approach with simplified models. The transition between different resonance regions of one-to-one tesseral resonance is investigated by the computation of one-dimensional maximal Lyapunov characteristic exponent (1-mLCE). The secular resonance from the lunisolar perturbation modeled by a 2-DOF system is systematically investigated using the surface of section. The secondary resonance related to the precession of lunar node is identified by the computation of 1-mLCE. In the end, the reentry disposal for BeiDou IGSO is investigated as an optimization problem. With IGSO3 as an example of reentry orbit, the sensitivity analysis is conducted to study its stability and predictability. [ABSTRACT FROM AUTHOR]

Farmland area data is one of the important agricultural basic data, which provides parameter basis for the precise operation of agricultural equipment. In order to meet the technical needs of farmers and agricultural machinery operation service billing for acquiring basic information of farmland, this study proposes a farmland area measuring instrument based on the BeiDou Navigation Satellite System. Firstly, the overall design scheme of the measuring instrument, the hardware circuit design scheme and the algorithm design scheme are introduced, and the triangulation area measurement algorithm is emphatically analysed. Finally, the design of this research is applied. The farmland area measuring instrument measures the area of different shapes of farmland and verifies the measurement accuracy. The results show that the average relative error of the measuring instrument for measuring the area of irregularly shaped farmland is 0.7%, which realizes the rapid and high-precision measurement of the area of arbitrarily shaped farmland. It is hoped that this study can provide some reference for the research on the area measurement of farmland in my country. [ABSTRACT FROM AUTHOR]

Precise point positioning (PPP) technology is one of the core technologies in the field of GNSS high-precision positioning. It is used widely because it can realize centimeter-level positioning in outdoor environments by using only a single receiver. However, its convergence is time-consuming, particularly in urban areas where satellite occlusion is more severe. A combined BeiDou Navigation Satellite System (BDS) and fifth generation mobile communication technology (5G) PPP observation model is proposed, in which the two kinds of observations are combined and solved at the original observation level. The impact of different numbers and geometries of 5G base stations on the convergence time of PPP is analyzed from both static and dynamic perspectives. The results confirm that PPP technology combining BDS and 5G can effectively accelerate convergence while improving the accuracy of positioning. [ABSTRACT FROM AUTHOR]

This article describes the design, testing, and space qualification of a 150-W high-power and high-efficiency GaN solid-state amplifier (SSPA) used in the BeiDou Navigation Satellite System (BDS). The SSPA, based on 0.5-μm GaN technology, includes the radio frequency unit (RFU) and electronic power conditioner unit (EPC). The power amplifier solves the problems of high efficiency, reliability, stability, and high-power thermal design for 80-W GaN HEMT onboard applications. The RFU together with the EPC is accommodated in a different box with limited volume and mass. In continuous-wave operating mode, the SSPA delivers an output power higher than 150 W at less than 3 dB of gain compression in the whole B2-band (i.e., center frequency freq = 1.191 GHz, bandwidth BW = 80 MHz). Moreover, the demonstrated gain is higher than 52 dB and power added efficiency, including the power dissipated by the EPC, is above 50%. The SSPA has completed all space qualification tests and 10 000-h accelerated life test. The space qualification tests have been approved in 2013, and the first satellite employing this SSPA has been launched in 2015. The SSPA has been applied to more than 10 BeiDou Navigation Satellites. So far, the SSPA in the first satellite has worked successfully for more than 6 years and leads to a technology readiness level more than Level 8. The large-scale application of the high-power gallium nitride solid-state power amplifier in space is reported first in this article. [ABSTRACT FROM AUTHOR]

Precise point positioning (PPP) with ambiguity resolution (AR) has been proved to be an effective method to improve the positioning accuracy and shorten the convergence time, which plays an important role in geodetic and geodynamic applications. In this study, the performance achieved based on the BeiDou Navigation Satellite System (BDS-2 and BDS-3) joint PPP-AR with high rate data was considered and the validation of its application to seismic displacement and marine high-precision surveying was evaluated. First, the methods of uncalibrated phase delays (UPDs) estimation and PPP-AR were introduced. Next, the performance achieved based on BDS PPP-AR in both static and simulated real-time kinematic mode was evaluated with hourly data selected from 16 tracking stations over 3 days and data sampling rate of 1 s. After convergence, the positioning accuracies in the east, north, and up directions were 3.4 cm, 1.5 cm, and 5.5 cm, which were improved by 11.9%, 3.8% and 2.2% compared with the float solutions. Finally, a test of applying BDS PPP-AR to marine surveying was carried out with two hours data collected from two independent GNSS receivers installed on a boat sailing along the coast of Bohai Sea, China. The onboard two data set are processed in post-processing kinematic BDS PPP mode. The accuracies were improved from 2.4 cm, 3.5 cm and 4.0 cm to 2.2 cm, 3.1 cm and 3.1 cm in the east, north and up directions by ambiguity resolution, with improvements of 8.3%, 11.4% and 22.5% over the float solutions. The results validated the feasibility of the BDS PPP-AR for high-accuracy maritime applications. [ABSTRACT FROM AUTHOR]

In this article, we propose a new particle swarm optimization–based satellite selection algorithm for BeiDou Navigation Satellite System/Global Positioning System receiver, which aims to reduce the computational complexity of receivers under the multi-constellation Global Navigation Satellite System. The influences of the key parameters of the algorithm—such as the inertia weighting factor, acceleration coefficient, and population size—on the performance of the particle swarm optimization satellite selection algorithm are discussed herein. In addition, the algorithm is improved using the adaptive simulated annealing particle swarm optimization (ASAPSO) approach to prevent converging to a local minimum. The new approach takes advantage of the adaptive adjustment of the evolutionary parameters and particle velocity; thus, it improves the ability of the approach to escape local extrema. The theoretical derivations are discussed. The experiments are validated using 3-h real Global Navigation Satellite System observation data. The results show that in terms of the accuracy of the geometric dilution of precision error of the algorithm, the ASAPSO satellite selection algorithm is about 86% smaller than the greedy satellite selection algorithm, and about 80% is less than the geometric dilution of precision error of the particle swarm optimization satellite selection algorithm. In addition, the speed of selecting the minimum geometric dilution of precision value of satellites based on the ASAPSO algorithm is better than that of the traditional traversal algorithm and particle swarm optimization algorithm. Therefore, the proposed ASAPSO algorithm reduces the satellite selection time and improves the geometric dilution of precision using the selected satellite algorithm. [ABSTRACT FROM AUTHOR]

For aircrafts equipped with BeiDou Navigation Satellite System/Strapdown Inertial Navigation System integrated navigation system, BeiDou Navigation Satellite System information can be used to achieve autonomous alignment. However, due to the complex polar environment and multipath effect, BeiDou Navigation Satellite System measurement noise often exhibits a non-Gaussian distribution that will severely degrade the estimation accuracy of standard Kalman filter. To address this problem, a new polar alignment algorithm based on the Huber estimation filter is proposed in this article. Considering the special geographical conditions in the polar regions, the dynamic model and the measurement model of BeiDou Navigation Satellite System/Strapdown Inertial Navigation System integrated alignment system in the grid frame are derived in this article. The BeiDou Navigation Satellite System measurement noise characteristics in the polar regions are analyzed and heavy-tailed characteristics are simulated, respectively. Since the estimation accuracy of standard Kalman filter can be severely degraded under non-Gaussian noise, a Kalman filter based on the Huber estimation is designed combining grid navigation system and generalized maximum likelihood estimation. The simulation and experiment results demonstrate that the proposed algorithm has better robustness under non-Gaussian noise, and it is effective in the polar regions. By employing the proposed algorithm, the rapidity and accuracy of the alignment process can be improved. [ABSTRACT FROM AUTHOR]

The Autonomous Navigation (AutoNav) mode of a Global Navigation Satellite System (GNSS) utilizes Inter-Satellite Links (ISLs) to maintain satellite operations without the service from the ground control segment. The newly launched Beidou satellites are capable of conducting ISLs for orbit determination to improve their autonomy, integrity, reliability, and robustness. However, the satellite orbit errors can increase over time due to various force model errors, particularly that of Solar Radiation Pressure (SRP). Accelerometers aboard satellites can measure non-conservative forces directly and have been successfully used in satellite missions for gravity recovery and atmosphere study (i.e., GRACE, CHAMP, and GOCE). This study investigates the feasibility to use accelerometers aboard Beidou satellites to improve AutoNav accuracy and service span. The results show that in a simulated 180-day AutoNav period, the orbit accuracy with the aid of accelerometers is two times better than that of using ISL data only. • AutoNav performance has been significantly improved by using accelerometers. • The constellation rotation can be seen on orbital ellipse parameters. • Accelerometers of current gravity satellites may satisfy the requirements of BDS. [ABSTRACT FROM AUTHOR]

According to the problem of complex data processing caused by the correlation between stations and satellites in the double-difference network RTK(real-time kinematic), an algorithm of BDS un-difference network RTK with triple-frequency is proposed. Firstly, the integer linear relationship among extra-widelane, wide-lane and triple-frequency integer ambiguity is used to determine double-difference integer ambiguity between BDS network RTK reference stations. Then, according to the composition relationship between double-difference and un-difference integer ambiguity, un-difference integer ambiguity between reference stations is quickly determined at single epoch. On this basis, a high-precision region error correction model of BDS un-difference is established to realize the error correction and integer ambiguity fixing of use. This algorithm is tested by the measured triple-frequency data of BDS CORS(continuously operating reference stations) network. The results indicate that the algorithm of un-difference network RTK with triple-frequency can effectively overcome the correlation between station and satellite which is brought by the double-difference network RTK and make the operating type of the network RTK more flexible. [ABSTRACT FROM AUTHOR]

According to the requirements of port management system, all fishing vessels must stop fishing and return to their registry ports during the summer fishing moratorium. Fishing vessels are not allowed to dock at the non-registry port. In order to investigate the fishing vessels docking at other provinces or cities’ ports which are not their registry ports during the summer fishing moratorium, a method to extract the off-site docking information of offshore fishing vessels based on Beidou navigation satellite system position data was proposed in this paper. First of all, we need to find out the time periods during which the fishing boat stoped sailing, and then selected the longest time period and obtained the longitude and latitude of the location where the boat stoped during the longest time period. The reverse address query web service provided by Gaud map was used to obtain the provinces, cities and districts based on the longitude and latitude. Then compared the docking address with that of registry ports to determine whether the vessel was off-site docked. Taking Zhejiang Province of China as an example, the fishing vessels positions data of vessel monitoring systems based on Beidu Navigation Satellite System was used to extract the off-site docking information and conduct statistical analysis. The results showed that 2.75% of fishing vessels docked across provinces, 5.86% of fishing vessels docked across cities in the province and 15.6% of fishing vessels docked accross district in the city。This method can quickly extract and count off-site docking information of fishing vessels, and provided technical support for fishing vessel's management information during the fishing moratorium. [ABSTRACT FROM AUTHOR]

In the form of satellite ephemerides and clock parameters, the information of space datum and system time of one global navigation satellite system (GNSS) is transferred to users. With continuously updating of satellite payload such as high precision atomic clocks, monitoring and tracking techniques such as inter-satellite links, and data processing techniques, the accuracy and real-time performance of satellite ephemerides and clock products are steadily improved. Starting from December 27th, 2018, BeiDou Navigation System 3, or BDS-3 has been providing accurate and reliable basic positioning, navigation, and timing (PNT) services to users in the countries within the "one belt and one road". This paper summarizes the challenges of precise orbit determination and time synchronization faced and specific solutions sought from the regional BDS-2 system to BDS-3 global system at the control segment. It is interesting to compare BDS with other GNSS systems in terms of technical characteristics. Finally, aiming at higher accuracy and more reliable PNT services, a road map of precise orbit determination and time synchronization technique for next generation navigation systems is discussed, which will lead to better and better global navigation satellite systems. [ABSTRACT FROM AUTHOR]

Firstly, the influence of the improvement of the BeiDou navigation satellite system(BDS) and GPS satellites visibility using the three low earth orbit (LEO) satellites GRACE ‐ A/B and Fengyun3C (FY3C) is analyzed. Results show that the improvement to BDS medium earth orbit (MEO) satellites is the most significant, with the single coverage increased by 45.7% and quad ‐ coverage increased by 10.7%, which is equivalent to that of GPS satellites. Then, satellite positioning and dilution of precision (SPDOP) is used to analyze the contribution of LEO satellites to enhance the geometry structure in navigation satellite orbit determination. With the enhancement of three LEO satellites, the SPDOP of the BDS geostationary orbit (GEO) satellites, inclined geosynchronous orbit (IGSO)satellites, MEO satellites and GPS satellites are decreased by 49%, 39.8%, 34.9% and 41.2% respectively. The orbit determination experiment based on the observations from seven regional ground observation stations and three LEO satellites are carried out. The results show that one‐dimensional root mean square (1D RMS) of GPS satellites orbit is reduced from 14.4 cm to 10.2 cm, improved by 29.1%. The 1D RMS of BDS GEO,IGSO and MEO satellites in overlapping arcs decrease from 359.8 cm to 90.5 cm, 175.6 cm to 52.1 cm, and 90.5 cm to 30.4 cm, improved by 74.8%,70.3%,and 66% respectively. [ABSTRACT FROM AUTHOR]

Remote island construction environment is complicated, there are problems such as poor wireless communication conditions and difficulty in powering the positioning devices. In order to promote the application of Beidou navigation satellite system (BDS) in coastal island construction projects, the static positioning accuracy of BDS in coastal islands was assessed. Considering the power consumption and communication pressure, the BDS positioning accuracy of different distances, different observation periods and different sampling rales were analyzed. Statistics show, short-distance positioning accuracy of BDS B1 and B2 earner is equivalent to GPS; The 1 h positioning precision is comparable to 2 h at the sampling interval 10 s, the difference from the GPS positioning solution is less than 1 cm; With 1 h observation periods, the positioning accuracy of sampling interval 30 s is basically the same as the 10 s solution. Short—distance positioning technology of BDS B1 and B2 carrier can completely replace GPS in coastal island projects. [ABSTRACT FROM AUTHOR]

In the form of satellite ephemerides and clock parameters, the space datum and system time information of one global navigation satellite system (GNSS) is transferred to users. With the continuous updating in the satellite payload such as the high-precision atomic clock, the monitoring and tracking technique such as the inter-satellite link, and in the data processing technique, the accuracy and real-time performance of the satellite ephemeris and clock error products are steadily improved. Starting from December 27th, 2018, the BeiDou Navigation System 3, or BDS-3, has provided the accurate and reliable basic positioning, navigation, and timing (PNT) service for the users in the countries within the "one belt and one road". This paper has summarized the faced challenges of the precise orbit determination and time synchronization from the regional BDS-2 system to the BDS-3 global system, and the specific solutions at the control segment. In addition, this paper has compared the BDS with other GNSS systems in terms of technical characteristics. Finally, aiming at a higher accuracy and more reliable PNT service, the road map of precise orbit determination and time synchronization technique for the next generation navigation systems is discussed, which will provide a reference for developing the global navigation satellite systems with an even higher accuracy. [ABSTRACT FROM AUTHOR]

A method for calculating the rate of loss-of-lock(LOL)at carrier phase and pseudo-range measurements of GNSS L1 and L2 was introduced， and the impacts of different satellite elevation angles on the LOL rate were also investigated. Using global GNSS observations， the qualities of GNSS signals during two strong geomagnetic storms at the 23rd solar cycle were analyzed. The results showed that the LOL rates of L1， L2， p1 and p2 signals significantly increased during strong geomagnetic storms comparing with the quiet days. The LOL mainly occurred in the main phase and the early recovery phase of the storm. The LOL rate of L2was significantly higher than L1， and the LOL duration was longer. This means the L2 was more sensitive to geomagnetic storm than L1. The high correlation between the LOL rate and SYM-H index indicated that the abnormal increase of global LOL rate was driven by the strong geomagnetic storm. The results could provide methodological support for the assessment of signal quality of the Beidou navigation satellite system. [ABSTRACT FROM AUTHOR]

Remote island construction environment is complicated, there are problems such as poor wireless communication conditions and difficulty in powering the positioning devices. In order to promote the application of Beidou navigation satellite system (BDS) in coastal island construction projects, the static positioning accuracy of BDS in coastal islands was assessed. Considering the power consumption and communication pressure, the BDS positioning accuracy of different distances, different observation periods and different sampling rates were analyzed. Statistics show, short-distance positioning accuracy of BDS B1 and B2 carrier is equivalent to GPS; The 1 h positioning precision is comparable to 2 h at the sampling interval 10 s, the difference from the GPS positioning solution is less than 1 cm; With 1 h observation periods, the positioning accuracy of sampling interval 30 s is basically the same as the 10 s solution. Short-distance positioning technology of BDS B1 and B2 carrier can completely replace GPS in coastal island projects. [ABSTRACT FROM AUTHOR]

The BeiDou Navigation Satellite System (BDS) has equipped its new-generation satellites with inter-satellite link (ISL) payloads to improve navigation services and system operation. When the inter-satellite ranging and communication are satisfied, we analyze the exploitation of the spare ISL capability for serving atmospheric reentry users. These users can be monitored over the atmospheric reentry segment with ISL transmission, even in the absence of visibility to ground stations and escaping the blackout. We modeled the problem and proposed a link assignment method combining parallel assignment of ISLs and dynamic access of monitor links. First, ISLs were assigned for inter-satellite ranging and communication, which were quantified with the number of different links and timeslot delays respectively. Corresponding assignment algorithm operated in the stations and the computing resource was abundant. Therefore, the heuristic algorithm was used to search the shortest route and the fitness function was determined with a shortest path algorithm. Based on the ISL assignment, extended users were accessed to the ISL network dynamically without influencing performances of the constellation. Because of the uncertainty of users' states, the monitor link assignment was implemented onboard with short-term predicted states and therefore the computing resource was scarce. Short-term predicted states conquered the deviation of satellite-user visibility. And a simple smallest delay strategy was used to determine the access nodes for users. To evaluate performances of the algorithm, link assignments were implemented for the BeiDou global constellation with 3 users. Each satellite was linked with at least 10 satellites and communicated with stations within 3 timeslots on the basis of ISL assignments. The assignment of monitor links demonstrated the user access did not influence the ranging and communication index of the ISL network and 1-, 2-, and 3-timeslot route delays of users occupy the main parts and the total ratio is larger than 95%. [ABSTRACT FROM AUTHOR]

In this study, a model of precise time transfer is developed based on the triple-frequency un-combined observations of the BeiDou navigation satellite system, known as UC-PPP. In this model, except for the traditional position, troposphere delay and receiver clock parameters, ionosphere delays are estimated as unknown parameters by adding the prior, spatial and temporal constraints. In addition, receiver differential code biases (DCB) are also estimated as unknown parameters. The standard triple-frequency ionosphere-free model is also introduced, named as IF-PPP. To assess the performance of the model, datasets with short baseline and common external time frequency are used. The results show that the triple-frequency UC-PPP model can be used for precise time transfer, with accuracy and stability identical to those of the IF-PPP model. The model can also provide the receiver DCB and ionosphere total electron content products. [ABSTRACT FROM AUTHOR]

In this paper, we derived a high-efficiency formula for calculating the precision of carrier phase relative positioning, analyzed the various factors that affect the positioning accuracy using the carrier phase, and proposed the concept of using a frequency dilution of precision to describe the quantitative effect of different frequency combinations on the positioning precision. To this end, we computed and plotted the global spatial distribution map of the relative positioning dilution of precision for single-day solution, half-hour solution, and single-epoch solution of the global positioning system (GPS), regional Beidou navigation satellite system (BDS2), future global Beidou navigation satellite system (BDS3), and their fusion systems. Using processing software with autonomous intellectual property rights (GCN and VENUS/ARSNet), we solved the measurement data and examined the positioning precision of the single-day solution and single-epoch solution of GPS and BDS2. The analysis demonstrated that the B1/B2 frequency positioning precision of BDS2 was better than that of L1/L2 frequency positioning of GPS, but the positioning precision of the BDS2 is worse than that of GPS over most of the service region of the BDS2. Further, the positioning precision of BDS3 is better than that of GPS in the Asia-Pacific region, while it is the opposite in other regions. Based on these conclusions, we put forth some optimization recommendations regarding the signal frequency of the navigation system and GPS measurement standards to serve as references for optimizing the system performance and formulating standards. [ABSTRACT FROM AUTHOR]

Abstract There are code biases on the pseudo-range observations of the Beidou Navigation Satellite System (BDS) that range in size from several decimeters to larger than one meter. These biases can be divided into two categories, which are the code biases in the pseudo-range observations of Inclined Geo-Synchronous Orbit (IGSO) satellites and Medium Earth Orbit (MEO) satellites and the code biases in the pseudo-range observations of Geosynchronous Earth Orbit (GEO) satellites. In view of the code bias of the IGSO/MEO satellites, the code bias correction model is established using the weighted least square curve fitting method. After the correction, the code biases of the IGSO and MEO satellites are clearly mitigated. A methodology of correcting GEO code bias is proposed based on the empirical mode decomposition (EMD)-wavelet transform (WT) coupled model. The accuracies of the GEO multipath combination of the B1, B2 and B3 frequencies are improved by 39.9%, 17.9%, and 29.4%, respectively. Based on the corrections above, the ten days observations of three Multi-GNSS Experiment (MGEX) stations are processed. The results indicate that the convergence time of the precise point positioning (PPP) can be improved remarkably by applying a code bias. The mean convergence time can be improved by 14.67% after the IGSO/MEO code bias correction. By applying the GEO code bias, the mean convergence time can be further improved by 17.42%. [ABSTRACT FROM AUTHOR]

The BeiDou navigation satellite system (BDS) has been widely applied in many areas, including communications, transportation, emergency rescue, public security, surveying, precise positioning, and many other industrial applications. The integration of BDS and an inertial navigation system (INS) has the ability to achieve a more consistent and accurate positioning solution. However, during long BDS outages, the performance of such an integrated system degrades because of the characteristics of the inertial measurement unit—the sensor errors accumulate rapidly with time when operated in a standalone mode. In this paper, a BDS/INS/odometer/map-matching (MM) positioning methodology for train navigation applications is proposed to solve the problem of positioning during BDS outages when trains pass through signal obstructed areas such as under bridges, inside tunnels, and through deep valleys. The seamless transition of the train operation in various scenarios can be, therefore, maintained. When the train operates in an open-sky environment, the BDS signals are available to provide accurate positioning, and the integrated BDS/INS/odometer/MM system is used to correct the INS errors using BDS measurements and to calculate the velocity using the odometer in the navigation frame so as to improve the system reliability and accuracy. In addition, the integrated system also delivers accurate positioning measurements at a high update rate. When the BDS signals are blocked, the integrated system switches to the INS/odometer/MM mode, and the integrated system corrects the INS errors by using odometer measurements. In order to evaluate the proposed system, a real experiment was conducted on the Qinghai–Tibet railway in western China. The experimental results indicate that the proposed system can provide accurate and continuous positioning results in both open-sky and BDS signal-obstructed environments. [ABSTRACT FROM AUTHOR]

Autonomous orbit determination is the ability of navigation satellites to estimate the orbit parameters on-board using inter-satellite link (ISL) measurements. This study mainly focuses on data processing of the ISL measurements as a new measurement type and its application on the centralized autonomous orbit determination of the new-generation Beidou navigation satellite system satellites for the first time. The ISL measurements are dual one-way measurements that follow a time division multiple access (TDMA) structure. The ranging error of the ISL measurements is less than 0.25 ns. This paper proposes a derivation approach to the satellite clock offsets and the geometric distances from TDMA dual one-way measurements without a loss of accuracy. The derived clock offsets are used for time synchronization, and the derived geometry distances are used for autonomous orbit determination. The clock offsets from the ISL measurements are consistent with the L-band two-way satellite, and time-frequency transfer clock measurements and the detrended residuals vary within 0.5 ns. The centralized autonomous orbit determination is conducted in a batch mode on a ground-capable server for the feasibility study. Constant hardware delays are present in the geometric distances and become the largest source of error in the autonomous orbit determination. Therefore, the hardware delays are estimated simultaneously with the satellite orbits. To avoid uncertainties in the constellation orientation, a ground anchor station that “observes” the satellites with on-board ISL payloads is introduced into the orbit determination. The root-mean-square values of orbit determination residuals are within 10.0 cm, and the standard deviation of the estimated ISL hardware delays is within 0.2 ns. The accuracy of the autonomous orbits is evaluated by analysis of overlap comparison and the satellite laser ranging (SLR) residuals and is compared with the accuracy of the L-band orbits. The results indicate that the radial overlap differences between the autonomous orbits are less than 15.0 cm for the inclined geosynchronous orbit (IGSO) satellites and less than 10.0 cm for the MEO satellites. The SLR residuals are approximately 15.0 cm for the IGSO satellites and approximately 10.0 cm for the MEO satellites, representing an improvement over the L-band orbits. [ABSTRACT FROM AUTHOR]

In order to solve the security problems of the Internet of things, considering the high security requirements of the military Internet of things and the terminal load capacity of the nodes, this paper proposed an authentication scheme suitable for military things. It could realize the mutual authentication between nodes based on the optimization of one-time password authentication scheme,got timestamp and coordinates information as multi-factor authentication factors by Beidou navigation satellite system. Theoretical analysis and formal analysis of protocol based on SVO logic show that the scheme can achieve the expected authentication target with no security vulnerabilities. In all,it has good security and reliability. [ABSTRACT FROM AUTHOR]

The Bernese ECOM solar radiation pressure model is widely used in precise orbit determination (POD) for GNSS navigation satellites[1]. But when used for BeiDou POD, the accuracy may not be the best when all the nine parameters are solved. The MGEX precise ephemerides of one year were collected. A one-year time series of the nine parameters were analyzed by orbit fitting. The results show that there are strong correlations between Bc/Bs parameters and Yc/Ys parameters. At the same time, the Bc/Bs parameters have a one year cycle and are an order of magnitude larger than Yc/Ys parameters. Sgnificance testing of the ECOM regression model results show that the significance level of Bc/Bs parameters is higher than Yc/Ys parameters. Experinments on orbit determination using different schemes with data from MGEX monitoring stations were carried out. The results show that only the five parameters that D0/Y0/B0/Bc/Bs yielded the highest precision of orbit determination, thus the five parameter EOCM model is better for BeiDou POD. [ABSTRACT FROM AUTHOR]

Multipath delay is one of major error sources which limit global navigation satellite systems positioning accuracy. Due to the orbit characteristics, multipath effects are more evident on the code range observables of BeiDou Navigation Satellite System (BDS) geostationary earth orbit (GEO) satellites. We employed zero-phase filter to extract the low-frequency components of multipath series with the definite cutoff frequency and pass-band gain, and introduced a modified sidereal filtering for mitigating the multipath effects on code measurements of GEO satellites. The applications of this modified sidereal filtering show that the corrections for the standard deviation of code observables residuals on BDS B1, B2, and B3 frequency have reached more than 30, 22, and 14%, respectively. After resolving the GEO satellites code measurement multipath effects, the precisions of code-only single-point positioning were also improved. [ABSTRACT FROM PUBLISHER]

Along with the rapid development of the Global Navigation Satellite System (GNSS), satellite navigation signals have become more diversified, complex, and agile in adapting to increasing market demands. Various techniques have been developed for processing multiple navigation signals to achieve better performance in terms of accuracy, sensitivity, and robustness. This paper focuses on a technique for processing two signals with separate but adjacent center frequencies, such as B1I and B1C signals in the BeiDou global system. The two signals may differ in modulation scheme, power, and initial phase relation and can be processed independently by user receivers; however, the propagation delays of the two signals from a satellite are nearly identical as they are modulated on adjacent frequencies, share the same reference clock, and undergo nearly identical propagation paths to the receiver, resulting in strong coherence between the two signals. Joint processing of these signals can achieve optimal measurement performance due to the increased Gabor bandwidth and power. In this paper, we propose a universal scheme of asymmetric dual-band tracking (ASYM-DBT) to take advantage of the strong coherence, the increased Gabor bandwidth, and power of the two signals in achieving much-reduced thermal noise and more accurate ranging results when compared with the traditional single-band algorithm. [ABSTRACT FROM AUTHOR]

This paper assesses the navigation and positioning performance of BeiDou Navigation Satellite System at Zhongshan station, Antarctic, after it is officially announced in operation. The availability of satellites, position dilution of precision, pseudorange data quality, precision of ionosphere model and positioning accuracy are analyzed by real data. The results show that:1)BeiDou is currently capable of providing basic navigation and positioning services through all day at Zhongshan Antarctic station. The overall availability and quality of pseudorange measurements of BeiDou is as good as that of GPS. However, there are some problems, such as uneven distributed satellites over the sky, low elevation of GEO satellites, and the low accuracy of ionosphere model, which would reduce the positioning performance. 2)The precision of BeiDou-only positioning is much worse than that of GPS-only solutions; for single-frequency point positioning, we can only expect accuracies higher than 22 m, 9 m and 25 m in the north, east and up component, respectively; for single-frequency pseudorange differential positioning, the accuracies are 3.6 m, 2.3 m and 3.3 m in the north, east and up component, respectively. 3)The combined system of GPS and BeiDou provides increased reliability and improves the 3D precision of GPS by approximately 10 percent, 22 percent for single-frequency point positioning and single-frequency pseudorange differential positioning, respectively. [ABSTRACT FROM AUTHOR]

The new generation of GNSS satellites, including BDS, Galileo, modernized GPS, and GLONASS, transmit navigation sdata at more frequencies. Multi-frequency signals open new prospects for precise positioning, but satellite code and phase inter-frequency biases (IFB) induced by the third frequency need to be handled. Satellite code IFB can be corrected using products estimated by different strategies, the theoretical and numerical compatibility of these methods need to be proved. Furthermore, a new type of phase IFB, which changes with the relative sun-spacecraft-earth geometry, has been observed. It is necessary to investigate the cause and possible impacts of phase Time-variant IFB (TIFB). Therefore, we present systematic analysis to illustrate the relevancy between satellite clocks and phase TIFB, and compare the handling strategies of the code and phase IFB in triple-frequency positioning. First, the un-differenced L1/L2 satellite clock corrections considering the hardware delays are derived. And IFB induced by the dual-frequency satellite clocks to triple-frequency PPP model is detailed. The analysis shows that estimated satellite clocks actually contain the time-variant phase hardware delays, which can be compensated in L1/L2 ionosphere-free combinations. However, the time-variant hardware delays will lead to TIFB if the third frequency is used. Then, the methods used to correct the code and phase IFB are discussed. Standard point positioning (SPP) and precise point positioning (PPP) using BDS observations are carried out to validate the improvement of different IFB correction strategies. Experiments show that code IFB derived from DCB or geometry-free and ionosphere-free combination show an agreement of 0.3 ns for all satellites. Positioning results and error distribution with two different code IFB correcting strategies achieve similar tendency, which shows their substitutability. The original and wavelet filtered phase TIFB long-term series show significant periodical characteristic for most GEO and IGSO satellites, with the magnitude varies between - 5 cm and 5 cm. Finally, BDS L1/L3 kinematic PPP is conducted with code IFB corrected with DCB combinations, and TIFB corrected with filtered series. Results show that the IFB corrected L1/L3 PPP can achieve comparable convergence and positioning accuracy as L1/L2 combinations in static and kinematic mode. [ABSTRACT FROM AUTHOR]

Using the BeiDou Navigation Satellite System (BDS) for baseline settlement, the key problem is the correct solution of ambiguity. Using carrier phase observations of BDS to make up wide lane double difference observations, the best effect algorithm of LAMBDA is used to calculate wide lane double difference integer ambiguity. However, the algorithm has the disadvantage of large deviation of ambiguity float solution and large search range. So, the paper put forward to use Tikhonov to improve LAMBDA algorithm, singular value decomposition of the coefficient matrix of the unknown parameters in the wide lane double difference observation equation, replacing the covariance matrix of the LAMBDA algorithm with the decomposition of the covariance matrix and searching for the ambiguity of wide lane double difference, the precision of the float solution of the wide lane double difference integer ambiguity and the accuracy of ambiguity are improved. Deviation average values of ambiguity float solution of improved LAMBDA algorithm were reduced from 1.0829 cycles to 0.0059 cycles, variance values were reduced from 4.0534 cycles to 0.0479 cycles, the accuracy of the degree is raised from 93.52% to 100%. [ABSTRACT FROM AUTHOR]

The differential code bias (DCB) of BeiDou satellite is an important topic to make better use of BeiDou system (BDS) for many practical applications. This paper proposes a new method to estimate the BDS satellite DCBs based on triple-frequency uncombined precise point positioning (UPPP). A general model of both triple-frequency UPPP and Geometry-Free linear combination of Phase-Smoothed Range (GFPSR) is presented, in which, the ionospheric observable and the combination of triple-frequency satellite and receiver DCBs (TF-SRDCBs) are derived. Then the satellite and receiver DCBs (SRDCBs) are estimated together with the ionospheric delay that is modeled at each individual station in a weighted least-squares estimator, and the satellite DCBs are determined by introducing the zero-mean condition of all available BDS satellites. To validate the new method, 90 day’s real tracking GNSS data (from January to March in 2014) collected from 9 Multi-GNSS Experiment (MGEX) stations (equipped with Trimble NETR9 receiver) is used, and the BDS satellite DCB products from German Aerospace Center (DLR) are taken as reference values for comparison. Results show that the proposed method is able to precisely estimate BDS satellite DCBs: (1) the mean value of the day-to-day scattering for all available BDS satellites is about 0.24 ns, which is reduced in average by 23% when compared with the results derived by only GFPSR. Moreover, the mean value of the day-to-day scattering of IGSO satellites is lower than that of GEO and MEO satellites; (2) the mean value of RMS of the difference with respect to DLR DCB products is about 0.39 ns, which is improved by an average of 11% when compared with the results derived by only GFPSR. Besides, the RMS of IGSO and MEO satellites is at the same level which is better than that of GEO satellites. [ABSTRACT FROM AUTHOR]

As BeiDou Navigation Satellite System (BDS) has been operational in the whole Asia-Pacific region, it means a new GNSS system with a different satellite orbit structure will become available for deformation monitoring in the future. Conversely, GNSS deformation monitoring data are always processed with a regular interval to form displacement time series for deformation analysis, where the interval can neither be too long from the time perspective nor too short from the precision of determined displacements angle. In this paper, two experimental platforms were designed, with one being at mid-latitude and another at higher latitude in China. BDS data processing software was also developed for investigating the accuracy of continuous deformation monitoring using current in-orbit BDS satellites. Data over 20 days at both platforms were obtained and were processed every 2, 4 and 6 h to generate 3 displacement time series for comparison. The results show that with the current in-orbit BDS satellites, in the mid-latitude area it is easy to achieve accuracy of 1 mm in horizontal component and 2–3 mm in vertical component; the accuracy could be further improved to approximately 1 mm in both horizontal and vertical directions when combined BDS/GPS measurements are employed. At higher latitude, however, the results are not as good as expected due to poor satellite geometry, even the 6 h solutions could only achieve accuracy of 4–6 and 6–10 mm in horizontal and vertical components, respectively, which implies that it may not be applicable to very high-precision deformation monitoring at high latitude using the current BDS. With the integration of BDS and GPS observations, however, in 4-h session, the accuracy can achieve 2 mm in horizontal component and 4 mm in vertical component, which would be an optimal choice for high-accuracy structural deformation monitoring at high latitude. [ABSTRACT FROM AUTHOR]

In this paper, we got the optimal linear combinations which can effectively detect and repair all types of cycle slips considering the characteristics of BeiDou Navigation Satellite System(BDS). In the detection process, five geometry-free linear combinations were applied based on a three-step cycle slip detection process. For different sorts of cycle slips, specific frequency carrier phase linear combinations are used for repairs. Finally, based on Beidou triple-frequency data with different levels of ionospheric delay variation under different sampling intervals of 1s, 15 s, 30 s respectively -the ability of cycle slip detection and repairs were verified. The results were optimum. [ABSTRACT FROM AUTHOR]

This paper presents a high precision method to automatically calibrate the transmission delay of satellite transceivers in real time. The real-time self-calibrated capability is achieved by employing a bidirectional channel into the traditional satellite transceiver. The bidirectional channel can act as a transmitting or receiving path. Three signal loops in the transceiver can be created with a combination of the traditional transmitting channel (Tx), traditional receiving channel (Rx), and the proposed bidirectional channel. Then, the absolute delay of Tx and Rx can be calculated through the total delays in these three loops. The clock error and the distance measurement error between two satellites are calibrated based on the absolute delays, accordingly. A K-band satellite transceiver prototype integrated with a compact bidirectional channel has been developed to verify the proposed method. The measured delay of the cables between the transceiver and the simulator after calibration is temperature-insensitive and close to the true value. [ABSTRACT FROM AUTHOR]

BeiDou satellites transmit triple-frequency signals, which bring substantial benefits to carrier phase Ambiguity Resolution (AR). The traditional geometry-free model Three-Carrier Ambiguity Resolution (TCAR) method looks for a suitable combination of carrier phase and code-range observables by searching and comparing in the integer range, which limits the AR success probability. By analysing the error characteristics of the BeiDou triple-frequency observables, we introduce a new procedure to select the optimal combination of carrier phase and code observables to resolve the resolution of Extra-Wide-Lane (EWL) and Wide-Lane (WL) ambiguity. We also investigate a geometry-free and ionosphere-eliminated method for AR of the Medium-Lane (ML) and Narrow-Lane (NL) observables. In order to evaluate the performance of the improved TCAR method, real BeiDou triple-frequency observation data for different baseline cases were collected and processed epoch-by-epoch. The results show that the improved geometry-free TCAR method increases the single epoch AR success probability by up to 90% for short baseline and 80% for long baseline. The A perfect (100%) AR success probability can also be effortlessly achieved by averaging the float ambiguities over just tens of epochs. [ABSTRACT FROM AUTHOR]

The Beidou Navigation Satellite System (BDS) manages to estimate simultaneously the orbits and clock offsets of navigation satellites, using code and carrier phase measurements of a regional network within China. The satellite clock offsets are also directly measured with Two-way Satellite Time Frequency Transfer (TWSTFT). Satellite laser ranging (SLR) residuals and comparisons with the precise ephemeris indicate that the radial error of GEO satellites is much larger than that of IGSO and MEO satellites and that the BDS orbit accuracy is worse than GPS. In order to improve the orbit determination accuracy for BDS, a new orbit determination strategy is proposed, in which the satellite clock measurements from TWSTFT are fixed as known values, and only the orbits of the satellites are solved. However, a constant systematic error at the nanosecond level can be found in the clock measurements, which is obtained and then corrected by differencing the clock measurements and the clock estimates from orbit determination. The effectiveness of the new strategy is verified by a GPS regional network orbit determination experiment. With the IGS final clock products fixed, the orbit determination and prediction accuracy for GPS satellites improve by more than 50% and the 12-h prediction User Range Error (URE) is better than 0.12 m. By processing a 25-day of measurement from the BDS regional network, an optimal strategy for the satellite-clock-fixed orbit determination is identified. User Equivalent Ranging Error is reduced by 27.6% for GEO satellites, but no apparent reduction is found for IGSO/MEO satellites. The SLR residuals exhibit reductions by 59% and 32% for IGSO satellites but no reductions for GEO and MEO satellites. [ABSTRACT FROM AUTHOR]

A The current constellation of BeiDou Navigation Satellite System (BDS) is described and the relationship between the accuracy of BDS relative positioning and its regional constellation characteristic is discussed in relation to the RDOP (Relative Dilution of Precision) and positioning errors. Experiments were conducted, the results obtained when using BDS relative positioning on short baseline in our country show that: (1) the accuracy of BDS relative positioning is better in the east-west direction than in the south-north direction and the elevation direction; (2) positioning errors in the south-north direction and elevation direction are negatively correlated; (3)the improvement of positioning accuracy reduces as the latitude increases; (4)BDS positioning accuracy is slightly less than GPS in the south-north direction; (5)the impact of BeiDou regional constellation on carrier phase relative positioning accuracy is slightly larger than the single-frequency pseudo-range differential. [ABSTRACT FROM AUTHOR]