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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]

Train positioning method based on the global navigation satellite system (GNSS) is a key development direction for the next generation train operation control systems. To enhance the safety and autonomy of train positioning, while fully considering the cost of integrated positioning systems and the complementary performance of heterogeneous sensors, this study employed the BeiDou navigation satellite system (BDS) and inertial measurement unit (IMU) to build an onboard integrated positioning scheme. Addressing the issue of cumulative error divergence in IMU standalone navigation with BDS under conditions where satellite signals were limited, resulting in positioning failure, such as in tunnels, a method aided by grey combination prediction model was proposed to maintain positioning accuracy. An algorithm model was established based on location information from integrated BDS/ IMU system prior to BDS signal failure. When the train entered an environment with limited satellite signals, the grey combination model continuously corrected the IMU's cumulative errors using the predicted train positioning data sequence, ensuring the availability of positioning output throughout the entire train operation. The proposed method was validated on a simulation platform in a laboratory environment. The results showed that the BDS/ IMU combination maintained high positioning accuracy under normal working conditions, with the eastward/ northward position errors less than 2 m and the eastward/ northward velocity errors under 0. 2 m/ s. In scenarios where BDS positioning failed, the grey combination model corrected the IMU's cumulative errors using the predicted data, reducing eastward/ northward position errors by more than 85% and eastward/ northward velocity errors by over 80% compared to IMU standalone navigation. The positioning accuracy meets the train operation control system's requirements for train positioning. [ABSTRACT FROM AUTHOR]

Abstract With the rapid development of technologies such as autonomous driving and robotic navigation, the demand for accurate and reliable positioning results with BDS has increased. The current status and future development of BDS high precision services are reviewed. The operational PPP-B2b of BDS-3 achieves positioning accuracy at decimeter-level within 14 min and has the drawbacks in regional coverage and long convergence time compared with the international counterparts, such as CLAS of QZSS and HAS of Galileo. A development frame for multi-layer BDS high-precision services is proposed by considering its construction cost, compatibility of user terminal, operating maintenance burden, and service level. The global high-precision service with the improved orbit and clock accuracy enhanced with the inter-satellite link is taken as the most fundamental layer. By incorporating inter-satellite link observations, the orbit errors URE and clock errors are significantly reduced to approximately 0.05 m and 0.16 ns, respectively, which will expand PPP service to global. Based on this, the regional PPP-AR and PPP-RTK services with improved convergence performance are taken as the second layer. With PPP-AR, the convergence time drops to 10 min. With PPP-RTK, the convergence time would be further shortened to less than 3 min. The LEO enhanced PPP service is taken as the third layer which overcomes both drawbacks of the long convergence time of the inter-satellite link enhanced service (the first layer) and the regional coverage of the PPP-AR/PPP-RTK services (the second layer). The simulation results show that by introducing a LEO constellation of 288 satellites, the LEO enhanced PPP can achieve positioning accuracy better than 5 cm within approximately 1 min. In addition, the integration of LEO constellation and PPP-RTK is further proposed to enable instantaneous convergence. The implementation challenges are also presented.

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]

With the rapid development of technologies such as autonomous driving and robotic navigation, the demand for accurate and reliable positioning results with BDS has increased. The current status and future development of BDS high precision services are reviewed. The operational PPP-B2b of BDS-3 achieves positioning accuracy at decimeter-level within 14 min and has the drawbacks in regional coverage and long convergence time compared with the international counterparts, such as CLAS of QZSS and HAS of Galileo. A development frame for multi-layer BDS high-precision services is proposed by considering its construction cost, compatibility of user terminal, operating maintenance burden, and service level. The global high-precision service with the improved orbit and clock accuracy enhanced with the inter-satellite link is taken as the most fundamental layer. By incorporating inter-satellite link observations, the orbit errors URE and clock errors are significantly reduced to approximately 0.05 m and 0.16 ns, respectively, which will expand PPP service to global. Based on this, the regional PPP-AR and PPP-RTK services with improved convergence performance are taken as the second layer. With PPP-AR, the convergence time drops to 10 min. With PPP-RTK, the convergence time would be further shortened to less than 3 min. The LEO enhanced PPP service is taken as the third layer which overcomes both drawbacks of the long convergence time of the inter-satellite link enhanced service (the first layer) and the regional coverage of the PPP-AR/PPP-RTK services (the second layer). The simulation results show that by introducing a LEO constellation of 288 satellites, the LEO enhanced PPP can achieve positioning accuracy better than 5 cm within approximately 1 min. In addition, the integration of LEO constellation and PPP-RTK is further proposed to enable instantaneous convergence. The implementation challenges are also presented. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In dynamic environments, the traditional relative positioning methods based on the Kalman filter model suffer from low accuracy and stability due to the influence of noise and outliers. This paper proposes a variational Bayesian filtering algorithm based on the combination of four-frequency observations from BDS (BeiDou Navigation Satellite System) and models the observation noise using the T-distribution to enhance the stability of filtering. Firstly, a geometrically correlated ambiguity resolution model is constructed based on the characteristics of the combined observations, effectively improving the precision of float ambiguity resolution and fixing rate. Moreover, considering the characteristics of outliers that are likely to occur in dynamic conditions, a T-distribution-based variational Bayesian filtering approach is employed to estimate the time-varying observation noise and system states. Experimental results demonstrate that the proposed method exhibits robustness and stability in dynamic short baseline scenarios, leading to further improvements in positioning accuracy, float ambiguity resolution precision, and fixing rate.

The present work analyzes the long‐term in situ comparison of Si and GaAs solar array based on two BeiDou Navigation Satellite System satellites in medium Earth orbit (MEO). From the 6 year long‐term perspective, both Si and GaAs solar arrays exhibit significant yearly periodic variations in remote sensing current and temperature due to periodic variations in the Sun–satellite distance. The practical in situ photogenerated current degradation of Si and GaAs solar arrays in MEO orbits is analyzed by the light intensity and working temperature after calibrating. The annual degradation coefficients of Si and GaAs solar arrays are calculated to be 0.986 and 0.990, respectively, which means 13.2% and 9.6% current degradation for Si and GaAs solar arrays at the end of the 10 year life MEO satellite. Also, this article examines the temperature of the MEO orbit, with the working temperature ranging from −144.7 to 56.3 °C for Si solar array and −136.9 to 60.9 °C for GaAs solar array. The present work provides a critical accurate degradation parameter for the MEO satellite's precise design and the space application of the low‐cost silicon solar cell. [ABSTRACT FROM AUTHOR]

Regarding the system composition of the heavy haul railway train control system based on Beidou, the key equipment of the system is taken as the tested equipment. A semi-physical simulation testing system architecture is designed, and key technologies and solutions such as the simulation of the Beidou Navigation Satellite System, block system simulation, and heavy haul train simulation are analyzed. Through system implementation, it has been verified that the design scheme of this simulation testing system is feasible, capable of executing typical operating scenarios of the heavy haul railway train control system based on Beidou, supporting feasibility verification of system technical solutions, facilitating equipment debugging and testing, providing environmental support for equipment research & development and engineering implementation, and offering strong technical support for laboratory system integration testing. [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]

At present, metro engineering vehicles rely on visual driving by the driver, and there are safety problems such as rushing cross signals, overspeed and impacting switch in complex operation scenarios. This paper proposes a piece of shunting protection software based on the BeiDou satellite positioning system, and expounds its function design, software interface, mode conversion and protection method in detail. The shunting protection software uses safety computer platform tools, adopts modular design, and makes comprehensive use of the BeiDou satellite positioning system, beacon positioning system, computer-based interlocking system and binary tree theory to realize precise protection of metro engineering vehicles in shunting operation, effectively solve the safety risks in the operation process, and improve the safety of the metro engineering vehicles in shunting operation. At the end of 2020, the shunting protection software was tested in Guangzhou Metro Line 5 and Yuzhu Rolling Stock Depot.The results show that it can timely protect against rushing cross signals, overspeed and impacting switch, and meet the safety protection requirements of users for shunting operation.

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]

Contrasting the dilemma that the traditional time-domain least mean square (LMS) algorithm in the existing satellite navigation receiver anti-interference system cannot satisfy the convergence time is short and maintain a low level of steady-state error at the same time, an inverse cosine variable step size LMS algorithm (ICVS-LMS) is proposed. To begin with, the LMS algorithm, with a fixed step size focuses on its effectiveness in attenuating and suppressing interference signals, is analyzed, and then the proposed ICVS-LMS algorithm is analyzed. In conclusion, both the ICVS-LMS algorithm and the traditional algorithm are simulated and compared in terms of their effectiveness in suppressing interference in satellite navigation signals. The experimental results demonstrate that the improved algorithm significantly reduces convergence time while maintaining a small steady-state error. The improved algorithm demonstrates high robustness and an obvious suppression effect on interference signals. The anti-interference performance is 8.41–12.22% higher than that of the proposed algorithm. [ABSTRACT FROM AUTHOR]

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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]

Atmospheric water vapor plays a prominent role in weather forecasting and climate change, which can be measured accurately with conventional water vapor observing techniques and the global navigation satellite system (GNSS). However, there are limited studies that assess the retrieval of PWV exclusively using Beidou over oceans, as well as for GLONASS and Galileo. In this contribution, we investigate retrieving the real-time precipitable water vapor (PWV) based on shipborne GNSS kinematic precise point positioning (PPP) solutions through an 8-days experiment over the South China Sea. Observations from multi-constellation and single-constellation, including GPS, GLONASS, Galileo, and Beidou are processed. Real-time shipborne GNSS PWV is validated using ERA5 PWV products. The results obtained from the single-constellation analysis indicate that Beidou performs comparably to Galileo in PWV retrieval, surpasses GLONASS, but slightly falls behind GPS. It exhibits an accuracy of 3.19 mm when compared to the ERA5 PWV products after an average initialization time of 43.9 min. Furthermore, it is demonstrated that real-time multi-GNSS PWV achieves an accuracy improvement of more than 15% compared to single-constellation resolutions, reaching an accuracy of 2.34 mm. Real-time shipborne GNSS can accurately sense atmospheric water vapor over oceans and contribute to time-critical meteorological applications. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

After the BeiDou navigation satellite system (BDS) global services were formally commissioned, the large-scale applications of BDS have entered a new stage of marketization, industrialization, and internationalization. Strengthening research on risk analysis and response of BDS global services is not only an inherent requirement for supporting national strategies and promoting international development of BDS, but also an inevitable choice to cope with international competition and achieve stable and long-term development of BDS. This study summarizes and analyzes the current risks and development trend of BDS global services from the perspectives of international development trends of satellite navigation and development characteristics of BDS global services. Moreover, it summarizes the risks faced by BDS global services: national, strategic, market, security, and legal risks, and analyzes corresponding causes of the risks. In view of these risks, the following countermeasures are proposed: strengthening the top-level planning of risk response, establishing a response system considering all factors, improving risk response capabilities of BDS global service related entities, and consolidating a solid foundation for risk response.

The international application of the BeiDou navigation satellite system (BDS) is a new requirement for BDS development in the new development stage; it is also significant for promoting the high-quality development of the Belt and Road, establishing a new development pattern that features domestic and international dual circulations, and promoting global sharing of BDS development achievements. This study explores the internationalization demand for BDS application, examines the development status and trend of global navigation satellite systems, and analyzes the advantages, disadvantages, opportunities, and challenges of BDS internationalization. Moreover, the implications of BDS internationalization are proposed, comprising BDS image, service, application product, and business operation internationalization. The development objectives and specific indicators of BDS internationalization is also clarified. Furthermore, to promote the international application of the BDS, we propose the following suggestions: establishing an overall coordination management mechanism, strengthening product service and supply capabilities, building a multi-level enterprise system, improving the level of international cooperation, increasing the fiscal, taxation, and financial support, coordinating domestic rule of law and that concerning foreign affairs, and encouraging international application and promotion.

To promote the international application of the BeiDou navigation satellite system (BDS) can facilitate the BDS to serve as a global public service infrastructure and better serve the world. This study examines the international application strategies of GPS of the United States, GLONASS of Russia, and GALILEO of the European Union, and proposes several basic strategies considering the current status and trend of the international application of the BDS. Specifically, the international application of the BDS should follow a leap-forward application path and adopt five application modes: building confidence, diversified development, integration and collaboration, government-enterprise linkage, and shaping the international environment. To promote the BDS to the global market, we suggest to take the Asia-Pacific market as the primary development region, the countries and regions along the Belt and Road as the key application region, while taking into account the European and American markets as well as the potential markets in Africa and the Middle East. Moreover, the international application of the BDS can be realized gradually through three steps: reform and adaptation, market expansion, and global application.

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]

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When traditional weighted fusion realizes firefighter positioning, the problem of inaccurate positioning in the intersection area is due to poor sensor positioning accuracy and the inaccurate measurement of random error. To this end, an ultra-wideband (UWB) and Beidou satellite navigation system (BDS) intersection area fusion positioning algorithm based on the circular probability error (CEP) method is proposed, Inertial Navigation System initial positioning accuracy used to detect and improve UWB positioning errors. The accuracy and real-time of CEP are used to analyze the random positioning error, which enables more accurate weighting to improve positioning accuracy. The initial position coordinates obtained by INS detect and mitigate the non-line-of-sight error of UWB, eliminate abnormal deviation data when processing data, improve the probability of the CEP method to 95% and optimize the average method for more accurate real-time analysis of UWB and BDS positioning error, then calculate the optimal weight value through the error value to achieve fusion positioning. The algorithm is compared with the traditional UWB/BDS weighted fusion algorithm, and the experimental results show that the average positioning accuracy of the proposed fusion positioning algorithm in the intersection area is improved by 47.4%. [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]

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During the evolution of global navigation satellite systems (GNSS), many new GNSS signals have been proposed to meet the demand of various applications for high-precision positioning. The single-sideband complex subcarrier (SCBOC) modulated signals, which are contained in China's third-generation BeiDou Navigation Satellite System (BDS-3) B1 wideband composite signals, have extremely high-precision ranging potential. Although high-precision ranging performance of SCBOC signals has been demonstrated by implementing a cross-assisted tracking (CAT) technique in previous studies, ambiguity threats are not effectively relieved, resulting in ambiguous ranging. Therefore, we propose a robust unambiguous ranging technique, which utilizes an ambiguity model established by observations derived from CAT to resolve ambiguous ranging results. Simulation experiments are implemented to quantitatively evaluate the proposed method's performance and explore its effective ranges. Real data experiments are also implemented in static and dynamic cases to furtherly verify the effectiveness of the proposed method, exhibiting that the proposed method can take full advantage of the high-precision ranging potential contained in BDS-3 B1 wideband composite signals with less ambiguity threats. [ABSTRACT FROM AUTHOR]

Transmit/Receive (T/R) time-sharing is a critical technology to ensure accurate space–time reference information of navigation signals, which solves the problem of co-channel interference between receiver and transmitter. The rapid development of the electronic information industry has led to severe frequency band conflicts between different electronic systems. Satellite navigation receivers must take measures to suppress interference to eliminate the effects of narrowband interference, mainly unintentional interference. Time-domain anti-jamming is widely used in navigation receivers for its simple and easy advantages in ensuring the validity and stability of navigation data. However, because the satellite-ground link receivers adopt transmit/receive time-sharing technology to realize the bidirectional measurement and communication function of the link, the stability of the data solution is greatly affected by anti-interference in the time domain. The anti-jamming filter of the traditional navigation receiver usually re-converges from the initial state in each signal-receiving time slot, which leads to the receiver losing high volume data due to repeated convergence. This paper proposes a robust time-domain anti-jamming technology based on transmit/receive time-sharing technology. The continuity and stability of the interference signal are used to obtain the preliminary information of the periodic transceiver. The results show that robust anti-jamming technology based on a T/R time-sharing navigation signal can effectively improve the carrier-to-noise ratio loss and data loss caused by traditional time-domain anti-jamming technology, reduce the convergence time to nanosecond level, and has bright prospects in the future application of other navigation systems. [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]

BeiDou high-precision power line inspection can improve the efficiency and automation level of inspection operations, reduce labor intensity, and save inspection costs. However, although the satellite-based augmentation technology can solve the problem of large-scale positioning, it will introduce too many parameters into the positioning system through the method of parameter estimation. As a result, the behavior of the equation deteriorates, which makes it difficult to separate some parameters, and the convergence time of ambiguity parameters is too long. Under normal circumstances, the satellite-based augmentation standard positioning service needs at least about 30 min to converge to the centimeter level, and the ground-based augmentation system can provide an accurate model. This paper proposes a fast positioning method for satellite-based augmentation assisted by the BeiDou ground-based augmentation station. The receiver adopts the least square method, combined with the extended Kalman filter positioning, to achieve the improvement of the regional positioning effect of the satellite-based augmentation system. Positioning accuracy error does not exceed 1.6 meters. The error in the three directions of X, Y, and Z can be converged to the centimeter level in about 8 min. It can significantly improve the convergence time of satellite-based augmentation, and maintain continuous, stable and high-precision positioning of unmanned aerial vehicle in power line inspection.

Abstract The BeiDou Navigation Satellite System (BDS) provides global Positioning, Velocity, And Timing (PVT) services that are widely used in various areas. The BDS satellites frequently need the orbit maneuvers due to various perturbations to keep satellites in their designed positions. During these maneuvers, PVT services may be abnormal if the data from a maneuvering satellite is used. In this paper we developed an approach to recover the abnormal PVT services. By using BDS observations from multiple tracking stations, the orbital errors of a maneuvering satellite can be in real time obtained and corrected, thereby avoiding any influence on the performance of PVT services. The tests show that the average precision of position, velocity and timing services are improved by 0.8 m, 0.1 mm/s and 0.16 ns, respectively, using the developed orbital maneuver recovery approach. In addition, the approach can also be used for the orbital maneuver detection and monitoring.

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