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Objectives: Non-ideality of navigation satellite signals can cause ranging bias between different receivers, which is an important factor that may degrade the accuracy and integrity performance of global navigation satellite system. In civil aviation and other high integrity services, it is necessary to consider the non-ideality characteristics of the signal and define the design constraints of the user receiver, so as to reduce the impact of non-ideality and ensure service safety. Methods: The B1C and B2a signals of BeiDou satellite navigation system (BDS) are planned to join the international civil aviation standard, so it is necessary to study their non-ideality characteristics and define the receiver design constraints. This paper analyzed the non-ideality characteristic of BDS B1C and B2a signals. In order to avoid the influence of noise and multipath, a large aperture antenna was used to collected all the in-orbit satellite broadcasting B1C and B2a signals (including 27 satellites) to obtain pure signal samples. Then, the software receiver was used to process the signal samples under various receiving parameters to obtain the ranging biases under different receiver front-end bandwidth and code discriminator space, and the ranging bias range and variation with the receiving parameters are evaluated. Furthermore, taking the application in dual frequency multi-constellation satellite based augmentation service as an example, the receiver design constraints of the two signals were analyzed. Results and Conclusions: The experimental results show that the range biases introduced by the non-ideality of B1C and B2a signals are less than 0.68 m and 0.44 m, respectively, under the parameters range commonly used by receivers. Under the requirement of range bias less than 0.1 m, the applicable parameter range of receiver design constraints for B1C and B2a signals is better than the relevant requirements of the international civil aviation organization draft standard. There is sufficient margin to further consider other constraints. [ABSTRACT FROM AUTHOR]

Objectives: As BeiDou satellite navigation system‑3 （BDS‑3） starts to provide service for global users, it is possible to get global‑coverage and all‑time positioning service for space application using BDS alone. The performance of space‑borne BDS positioning is thoroughly analyzed with the broadcast ephemeris and the in‑orbit data of global navigation satellite system occultation sounder (GNOS) aboard FengYun‑3D (FY‑3D) satellite. Methods: Firstly, the visibility and position dilution of precision of BDS satellites in different low‑erath‑orbit （LEO） are calculated based on broadcast ephemeris. Moreover, the orbit, clock error of broadcast ephemeris and signal‑in‑space range error (SISRE) are studied. Secondly, the real visible satellite number, signal strength, precision of pseudo range and position accuracy are verified with the measurement data of GNOS. The code biases of BDS‑2 satellites are focused on. Finally, the total electron content above 836 km LEO orbit is measured using BDS dual‑frequency measurements. Results: The results show that the global coverage usability from ground to 2 000 km height orbit has already been 100%. The mean visible BDS satellite number across the world is 50% larger than that of global positioning system （GPS） . For BDS broadcast ephemeris, the 3D orbit error is 1.5 m and clock error is 2.4 ns. SISRE is about 0.79 m and the clock accuracy of BDS‑3 has reached the same level of GPS. The in‑orbit data results show that GNOS in FY‑3D could get 100% positioning with BDS‑2 signals in service areas, and 3D position accuracy is 5.53 m. All BDS‑2 satellites including geosynchronous earth orbit （GEO）, inclined geosynchronous orbit and medium earth orbit satellites have code biases. As GEO satellite is static relative to ground users, the code biases of GEO is firstly measured directly, in which the maxium code bias can reach about 0.6 m. The total electron content above 836 km can cause relative pseudo range delay of about 0.6 m. Conclusions: The research in this paper verifies the usability and performance of BDS for space‑based users . [ABSTRACT FROM AUTHOR]

Observation quality is one of the key issues to assess the performances of satellite navigation system. As the main error of positioning and navigation, the multipath delay mitigation has be‐ come the focus of the research in global navigation satellite system. Because the traditional multipath model‐ ling strategy cannot obtain the global optimal solutions, this paper proposes a real-time multipath correction model for BeiDou navigation satellite system (BDS) observation with information constraints. Methods: Firstly, the regularization algorithm combined with total variation term is used to denoise and solve the mul‐ tipath delay series based on the estimated BDS multipath delays. Secondly, the trend and random parts of multipath delays are separately processed and together modelled, in which the strategy of least square plus autoregression is used to estimate model coefficients of multipath delay model by one-step solution. Finally, the multipath mitigation model is further optimized by introducing the estimated model coefficients as the prior information constraints in the BDS real-time applications.Results: The results of real-time experiments of BDS precise point positioning show that, compared with the traditional strategy, the position ac‐ curacy of BDS-2 PPP in east (E), north (N) and up (U) directions can be improved with 10.6%−64.9%, 0.0%−59.1% and 12.6%−67.2% (B1I+B3I), respectively. Moreover, the position accuracy of BDS-3 PPP can be optimized with at least 13.9%, 60.0%, 45.9% (B1I+B3I) and 19.1%, 46.5%, 23.9% (B1C+B2a) in E, N and U directions, respectively. Conclusions: Therefore, the proposed mitigation multipath delays method can significantly improve the BDS observation quality in the BDS real-time positioning services. [ABSTRACT FROM AUTHOR]

Objectives: In precise point positioning (PPP) technology, the correct fixing of ambiguity is al⁃ ways an essential part of achieving high-precision positioning. However, the wrong fixing of ambiguity will lead to serious positioning errors. Therefore, it is necessary to optimize the selection of the ambiguity sub⁃ set to ensure a more reliable fixing of PPP ambiguity. Methods: This paper proposes a PPP partial ambiguity resolution (PAR) method that combines quality control and Gram-Schmidt orthogonalization. By utilizing the multi-GNSS(global navigation satellite system) experiment (MGEX) observations in the un-differenced and un-combined PPP model, the PAR method based on Gram-Schmidt orthogonalization was com⁃ pared and analyzed with the selected reference satellite method with maximum elevation, and the performance of ambiguity resolution and positioning was assessed under the multi-GNSS conditions. Results: Experimental results show that the average epoch fixing rate of each day and each station based on the Gram Schmidt method is improved by 7.74% and 11.46% in the static mode, and 7.90% and 7.78% in the pseudo-kinematic mode, respectively, compared with that of the selected reference satellite method considering the maximum elevation. Meanwhile, time-to-first-fix (TTFF) of each day and each station based on the Gram-Schmidt orthogonalization can be significantly reduced by 22.30% and 25.42% in the static mode, corresponding to an improvement of 20.44% and 19.65% in the pseudo-kinematic mode, respectively, compared with that of the selected reference satellite method considering the maximum elevation. As far as multi-GNSS PPP AR is concerned, multi-GNSS PPP AR has a significant improvement on the convergence time of BDS (BeiDou navigation satellite system) only. The convergence time of horizontal components is shortened by 20.00 min on average at 95% confidence level, and the vertical components are shortened by 19.00 min on average. For the positioning accuracy aspects, the positioning accuracy of horizontal components is improved by 1.50 cm on average, while that of vertical components is improved by 1.12 cm on average. Conclusions: The PPP PAR algorithm based on the Gram-Schmidt method can significantly improve the performance of ambiguity resolution and positioning accuracy. [ABSTRACT FROM AUTHOR]

The basic construction of BeiDou global satellite navigation system (BDS) has played a key role in promoting the development of global navigation satellite system, which provides an important guarantee for multi⁃constellation fusion positioning, navigation and timing. Multi⁃system fusion positioning provides users with more navigation information, and also provides a better guarantee for the realization of navigation performance indicators. At present, in order to ensure integrity, it is necessary to warn users when navigation service is unavailable. Due to satellite failure, the protection level exceeds its alert limit. However, under the condition of multi⁃frequency and multi⁃constellation, the number of satellites is sufficient. After a few satellite faults are eliminated quickly, the influence on the overall navigation accuracy is very small and no alarm is needed. A protection level reconstruction method based on robust estimation is proposed. The protection level is reconstructed by using robust information and posterior variance. In order to verify the feasibility of the algorithm, the accuracy and protection limits required by localizer performance with vertical guidance 200ft (LPV⁃200) approach phase are selected as the standard of this paper, and the global positioning system (GPS)/BDS combination of dynamic and static data are used for calculation and analysis. The GPS adopts L1 pseudo range observation, and the BDS adopts B1 pseudo range observation. Each group of experiments is divided into two parts, fault detection and elimination and the method of adding abnormal error is calculated respectively, the vertical protection level is calculated by the protection level calculation method based on a posteriori variance and the protection level reconstruction method based on robust estimation. The results show that our proposed method can reduce the alarm frequency on the premise of ensuring the positioning accuracy. [ABSTRACT FROM AUTHOR]