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Positioning by means of the Global Positioning System (GPS) is a traditional and widely used method. However, its performance is affected by the user environment, such as multi-path effects and poor anti-interference abilities. Therefore, an Inertial Navigation System (INS) has been integrated with GPS to overcome the disadvantages of GPS positioning. INSs do not rely on any external system information and has strong autonomy and independence from the external environment. However, the performance of GPS/INS is visibly degraded in low-observability GPS environments (tall buildings, viaducts, underground tunnels, woods, etc.). Fortunately, with the emergence of Low-Earth-Orbit (LEO) satellites in recent years, the constellation configuration can be extended with the advantages of lower orbits, greater speeds, and richer geometric structures. LEO improves the geometric structure between users and satellites and provides many more observations. Meanwhile, a robust theory approach is applied that can restrain or remove the impact of low-accuracy observations. In this study, we applied LEO data and a robust theory approach to enhance the GPS/INS tight integration. To verify the effectiveness of this method, a set of vehicles and simulated LEO data were analyzed. The results show that robust Kalman filtering (RKF) provides a visible enhancement in the positioning accuracy of GPS/INS integration. This effectively restrains the mutation error and has a smoothing effect on the positioning results. In addition, the addition of LEO data significantly improves the positioning accuracy of a sole GPS and GPS/INS integration. The GPS/LEO/INS integration has the highest positioning accuracy, with Root-Mean-Square Errors (RMSEs) of the north, east, and vertical positions of 2.38 m, 1.94 m, and 2.49 m, respectively, which corresponds to an improvement of 30.21%, 47.43%, and 34.13% compared to sole GPS-based positioning and 8.60%, 17.24%, and 12.14% when compared to the GPS/INS mode. Simultaneously, the simulation results show that LEO and INSs can improve the positioning performance of GPS under GPS-blocked conditions. [ABSTRACT FROM AUTHOR]

The nonlinear navigation payload transmission channel introduces errors at a system level, resulting in a distortion of the received signal and affecting differential positioning users. This work models the transmission channel of the navigation payload and uses the joint estimation algorithm to calculate the digital distortion and analog channel response of the transmission channel from the received signal. On the above basis, the algorithm and model are verified by GPS-L5 measured data, and the channel characteristics of GPS II and GPS III are deeply analyzed. The results show that the existing GPS IIF satellites have a digital distortion, which is negligible in GPS III satellites. Regarding the analog channel response, GPS III has better amplitude and group delay consistency than GPS II. Lastly, the ranging bias caused by the transmission channel of the navigation payload is provided to the user for reference, and GPS III is improved by approximately 0.02 m compared with GPS II. This study provides support for adjusting the satellite signal pre-distortion and enriches subsequent GNSS signal quality assessment work; it can also be used as a reference for differential positioning users. [ABSTRACT FROM AUTHOR]

In 2018, China established the primary constellation of the BeiDou-3 global navigation satellite system (BDS-3), and the construction of this satellite system is due to be completed in 2020. The signal emitted by BDS-3 will provide global positioning, navigation and timing services. This study assessed the performance of network real-time kinematic (NRTK) in reference to the new BDS-3 signals. The ambiguity resolution, retrieval, and interpolation of the double-differenced (DD) observation corrections and positioning precision are assessed based on datasets collected using four SR480 receivers that track the open signals of BDS-3. Subsequently, the NRTK, using the combined BDS-2 and BDS-3 measurements, is compared with the NRTK using only BDS-2 measurements. In addition, the positioning results of NRTK are compared with those of RTK. The results show that the DD atmospheric delay corrections with centimeter-level accuracy can be derived from the network of regional reference stations, and the positioning accuracy of NRTK is improved by incorporating the BDS-3 measurements. [ABSTRACT FROM AUTHOR]

The signal-in-space (SIS) anomalies caused by satellites and control segments can greatly affect the reliability and safety of navigation and positioning users. The prior information associated with the failure of the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) algorithm were obtained by the evaluation of SIS failure rates broadcasted with navigation ephemeris to investigate the integrity of navigation and positioning. For the existing ARAIM algorithm, the failure rate of satellites in the BeiDou Navigation Satellite System (BDS) is a conservative estimate, which is inconsistent with the actual SIS performance of BDS. Only the accurate detection of the SIS anomalies of BDS satellites can provide an effective reference to associate with failure. Therefore, to improve the accuracy of SIS anomaly detection for BDS satellites, and to provide higher integrity services for users, this study presents an improved method of SIS anomaly detection with precise ephemeris. The median method was used to detect a gross error in clock data before the calculation of clock datum, and the combination of an experience threshold and trimmed mean was used to determine the anomaly detection threshold. The feasibility and efficiency of the proposed method were also analyzed using data collected between 2015 and 2016. The detection results show that the constellation fault caused by erroneous clock data can be avoided, and the SIS anomalies can also be detected using the proposed method. Additionally, through the comprehensive tests performed in this study, it was found that from 2015 to 2016, the average accumulated duration of anomalies for BDS satellites was 10 h for geostationary orbit (GEO) and incline geosynchronous orbit (IGSO) and 55 h for medium earth orbit (MEO), respectively. These anomalies were primarily caused by the satellite clock. [ABSTRACT FROM AUTHOR]

China is promoting the construction of an integrated positioning, navigation, and timing (PNT) systems with the BeiDou Navigation Satellite System (BDS) as its core. To expand the positioning coverage area and improve the positioning performance by taking advantage of device-to-device (D2D) and self-organizing network (SON) technology, a BDS/SON integrated positioning system is proposed for the fifth-generation (5G) networking environment. This system relies on a combination of time-of-arrival (TOA) and BeiDou pseudo-range measurements to effectively supplement BeiDou signal blind spots, expand the positioning coverage area, and realize higher precision in continuous navigation and positioning. By establishing the system state model, and addressing the single-system positioning divergence and insufficient accuracy, a robust adaptive fading filtering (RAF) algorithm based on the prediction residual is proposed to suppress gross errors and filtering divergence in order to improve the stability and accuracy of the positioning results. Subsequently, a federated Kalman filtering (FKF) algorithm operating in fusion-feedback mode is developed to centrally process the positioning information of the combined system. Considering that the prediction error can reflect the magnitude of the model error, an adaptive information distribution coefficient is introduced to further improve the filtering performance. Actual measurement and significance test results show that by integrating BDS and SON positioning data, the proposed algorithm realizes robust, reliable, and continuous high precision location services with anti-interference capabilities and good universality. It is applicable in scenarios involving unmanned aerial vehicles (UAVs), autonomous driving, military, public safety and other contexts and can even realize indoor positioning and other regional positioning tasks. [ABSTRACT FROM AUTHOR]

• The SEID model is used to efficiently correct the ionospheric delay of single frequency stations. • The SEID model to BDS-2 and BDS-3 new signals single frequency PPP are evaluated. • The performance between single- and dual-frequency PPP is compared for GPS and BDS. The Satellite-specific Epoch-differenced Ionospheric delay (SEID) model can effectively correct ionospheric errors, which is of great significance in the application of entailing low-cost global positioning system (GPS) single-frequency (SF) receivers for retrieving tropospheric delays and deformation monitoring. This study aims to explore the impact of the SEID model on SF and dual-frequency (DF) precise point positioning (PPP) based on the GPS–, BeiDou Navigation Satellite System (BDS) –only and the GPS–BDS dual-system. Two sets of data were collected, corresponding to three test networks with DF stations separated by 34, 139, and 172 km, respectively. The GPS, BDS, and GPS–BDS dual-system observations in the networks were utilized to test positioning results, tropospheric delay and the impact of satellite-induced code bias variations existing in BDS on the positioning of DF PPP with ionosphere-free combinations, ionosphere-constrained SF PPP, and SF PPP based on SEID model transformation (STSF). The results show that the positioning results of STSF PPP became slightly inaccurate with increasing reference station separation distances. However, the SF PPP based on the SEID model exhibited substantially improved positioning accuracy and coordinate repeatability of SF PPP especially with regard to BDS, and obtain similar positioning results of DF PPP. The difference in the Standard Deviation (STD) and Root Mean Square (RMS) of the positioning bias of the GPS-only and GPS-BDS dual systems between DF PPP and STSF PPP was similar within 1 cm, but the difference in the case of BDS was as large as 2 cm in the E and U directions in the networks with separations of 139 and 172 km. Furthermore, the improvement of the STD and RMS of the STSF PPP positioning result was the greatest more than 67% for GPS–, BDS–only, and GPS–BDS dual- system in the networks separated by 34 km compared to SF PPP. [ABSTRACT FROM AUTHOR]