Satellite Navigation System and Augmentation Session was held

On May 27, 2021, the 12th China Satellite Navigation Conference Satellite Navigation System and Augmentation Session was held in International Hall C of Primus Hotel Nanchang International Expo City. The Session was chaired by Researcher Jiao Wenhai, Member of Scientific Committee of CSNC and Chairmen of the Session Li Rui, Meng Yansong, Liu Wenxiang, Li Xingxing and Yang Long. Experts and scholars from relevant fields at home and abroad gathered to share and exchange the frontiers and latest developments of satellite navigation augmentation technologies in the system segment, satellite segment and ground segment.


The conference hall was full of people


Researcher Jiao Wenhai, Member of Scientific Committee of CSNC, is chairing the Session


Chairman Li Rui chairing the Session

Beijing Institute of Tracking and Telecommunications Technology (BITCT) presented its thoughts on the future operation and management of the giant LEO, MEO and HEO satellite constellations. With the rapid development of large satellite constellations, the increasingly complex constellation operation and management needs and the increasingly difficult operation and management of BDS in the future, there are difficulties in the joint operation and management of giant satellite constellations, such as the complex relationships among multiple satellite constellations, higher service support requirements, higher multi-tasking and parallel processing capability requirements, more evolutionary transition requirements, and higher user experience requirements. The operation and management technologies in the future will be developed with fouses on service-oriented open architecture, service-oriented architecture, networked service management technology, integrated crosslink technology, high-precision spatio-temporal information generation technology, multi-source data fusion and processing technology, space node automation, intelligent technology, systematic system security prevention and control technology and intelligent system operation and maintenance technology and methods.


Invited expert Wang Bo giving the presentation

Aerospace Tianhui Technology Co., Ltd. (Xi’an) introduced the  analysis of impact of the polar region on positioning performance of the complete BDS-3 system. The polar region is rich in natural resources and is of both important scientific value and important strategic value, and is a hot spot for scientific expeditions and research by countries around the world. By using data from 29 stations of International GNSS Monitoring & Assessment System (iGMAS) observation network, it conducted coverage performance analysis, data quality analysis, user equivalent range error analysis and positioning performance analysis to understand the coverage area and basic navigation and positioning performance of the complete BDS-3 system after official operation. The results show that the complete BDS-3 system has good geometric coverage in the polar region, with over 10 visible satellites, the PDOP value of less than 1.6 and the PDOP availability being 100%. The addition of BDS-3 satellites enables BDS to enjoy better spatial and geometric configuration conditions, and have better accuracy than that of BDS-2 system.


Chairman of the Session Meng Yansong presentsing a certificate to the academic presenter

Satellite Navigation System Engineering Center of the 9th Academy of  China Aerospace Science and Technology Corporation presented the preliminary results of the evaluation of BDS-3 PPP service performance. Firstly, it introduced the basic information of BDS-3 PPP service, including information type, information structure and current service status and characteristics, and selected eight iGMAS tracking stations in the service area to carry out the evaluation of precise positioning service performance, including PPP and convergence time. The results show that the accuracy of BDS-3 satellite orbit in radial /tangential/normal direction is 0.06/0.25/0.25m, the clock error accuracy is 0.22ns, and the SISRE is about 0.10 m. Under the statistical conditions of HDOP≤2&&VDOP≤4 and above, the availability of BDS-3 single system and BDS-3&GPS dual system PPP services can reach more than 90% in most regions in and around China, with the availability of dual-system PPP services being relatively larger.

Beijing Satellite Navigation Center introduced the research on the design of civil signal authentication services for satellite navigation, and proposed a preliminary design of BDS civil signal authentication (BDSSA) according to the design requirements of bit commitment, one-way key chain and time correlation, in response to the current problems of lower threshold for GNSS spoofing and increasing number of related criminal spoofing activities. The BDSSA protocol uses spread spectrum code authentication, and introduces the design concept of the TESLA protocol, which is mainly used for message authentication, into the design of spread spectrum code authentication. BDSSA key is broadcasted in messages to support independent receivers and all satellites use the key on the same key chain. For integrated receivers supporting external channels such as 5G, the A-BDSSA method can be added to distribute BDSSA keys through external assistance, which can significantly reduce the authentication cycle TBA and improve the replay attack capability.

The 54th Research Institute of China Electronics Technology Group Corporation introduced the automatic calibration technology and ground verification for satellite navigation system time delay. Considering the current manual calibration of satellite navigation system link time delay, it proposed an automatic calibration technology for navigation link transceiver time delay, and carried out the implementation and technical verification of the design in the ground test and verification system. At present, the satellite navigation system has been equipped with the  automatic high-precision time delay calibration capability for satellite-ground and inter-satellite transceiver link time delays and the calibration results can effectively support the satellite-ground and inter-satellite orbit determination tests. The technology’s time delay test calibration stability is better than 0.2ns, effectively reducing the errors introduced by manual operation, while enabing an increase of 60%  in the test calibration efficiency, which greatly reduces the costs of manual labor. The ground test and verification system will further carry out test and verification work for the upgrading of satellite-based augmentation services and precise positioning services, while continuing to upgrade capacity of LEO-based augmentation, communication-navigation integration, multi-source fusion and other technologies to support the construction of comprehensive PNT system and self-innovation platform.


Participants asking questions onsite

BD NavTech introduced a high-precision time-synchronized pseudolite implementation method, which could address the problems related to tunnel scenario (no satellite signal), park scenic area scenario (canyon area with fewer visible satellites), vehicle and aircraft maintenance scenario (enclosed space that receives a small number of satellite signals), and proposed a pseudolite system implementation method, which could achieve joint positioning without changing the existing receivers and could effectively improve the system positioning accuracy. The actual test results show that the designed pseudolite system can achieve a positioning accuracy of 5m with joint pseudolite and GNSS positioning, and a positioning accuracy of 1m with independent pseudolite system positioning.

Piesat Information Technology Co., Ltd introduced the evaluation of satellite-based augmentation service performance of BDS-3 SBAS-B1C, and offered the BDSBAS-B1C orbit, clock error and ionospheric correction models, as well as the methods for positioning and integrity protection level calculation. In terms of ionospheric correction effect, BDS-3 SBAS-B1C can achieve better than 0.5m or even better accuracy in most areas of China. In terms of service performance, the average accuracy of all evaluated stations for 7 days is 0.94m, 0.92 and 2.32m in directions of E, N and U respectively, and the level of integrity protection also meets the ICAO indicator requirements for Category I vertically guided approach (APV-I).

Beijing Satellite Navigation Center analyzed GPS power augmentation effects based on data from multiple ground stations. By downloading the GPS observation data released by IGS, it has found that the GPS P(Y) code signal shows signs of power augmentation. In order to analyze the GPS signal power variation, it proposed a method of analyzing the sudden moment of change in GPS signal power based on data from multiple ground stations. Based on this method, it drew up the schedule for GPS satellite power change for the day on February 16, 2020, and then mapped the distribution of availability of satellites with GPS signal power augmentation for the day, which could be applied in the analysis and research of GPS power augmentation effects.


Chairman of the Session Liu Wenxiang presenting a certificate to the academic presenter

Northwestern Polytechnical University introduced an energy efficiency optimization algorithm for single-station multi-satellite MIMO  uplink systems. With the rapid growth of satellite communication business, the traditional single-station single-satellite uplink system can no longer meet the existing satellite transmission demand. The single-station multi-satellite uplink system has become the main trend in the future. An  energy-efficiency optimization algorithm for fast convergence was therefore proposed for the single-station multi-satellite MIMO uplink method. It accurately modeled the single-station multi-satellite MIMO uplink method, solved the explicit expression of the optimal power allocation matrix, and proposed an energy efficiency optimization algorithm for fast convergence. In the future,  the optimization objectives can be expanded to achieve the joint optimization of energy efficiency, spectral efficiency and BER etc bssed on the algorithm.

Wuhan University introduced the opportunities and challenges of PPP-RTK technology, the current globalization, refinement and intelligence of social production activities, the more urgent demand for wide-area real-time high-precision positioning, the opportunities brought by multi-system  multi-frequency GNSS, the new signal which was conducive to the capturing of weak satellite signals in complex urban environments, multi-system observations that could improve the availability of satellite navigation in complex urban environments, multi-system that could accelerate PPP convergence, multi-frequency that could shorten PPP AR initialization time, and also the augmentation of PPP with LEO satellite constellations. PPP-RTK enables the provision of wide-area, seamless, and uniform real-time high-precision positioning services by enabling real-time precise orbit determination and clock error estimation, accurate estimation of real-time UPD, and real-time estimation and fine modeling of ionospheric delay. However, PPP-RTK also faces problems such as how to further improve the accuracy of ionospheric model, how to determine the variance of a priori ionospheric constraint information adaptively, the PPP-RTK response method in complex ionospheric disturbance environment (ionospheric scintillation), PPP-RTK continuity and reliability in complex urban environment.


Invited expert Zhang Xiaohong giving the presentation

Beihang University introduced the research on the improvment of BDSBAS single-frequency message arrangement strategy. The BDSBAS message arrangement simulation was performed by the fixed-time sequence and dynamic message arrangement method according to the maximum amount of messages to be broadcast after the BDSBAS service was officially provided, and compared with the BDSBAS B1C messages, the results show that the BDSBAS message arrangement strategy can ensure that: no empty messages are broadcasted, and the percentage of valid messages reaches 100%; the first time for reception of all types of messages by users is shortened from 240s to 212s, which is about a reduction of 11.7%; the update cycle of MT 2/3/4 integrity messages is shortened from 6s to 4s, which is about a reduction of 33.3%; the update cycle of the remaining types of messages is improved to different degrees, which provides more time slot margin support for message alarms and uplink failure cases. This method is more suitable for BDSBAS GEO satellite Re-generate message broadcast, which can improve the flexibility of BDSBAS message broadcast, shorten the update cycle of all types of BDSBAS single-frequency augmented messages, and better guarantee the integrity and continuity of BDSBAS service.

School of Electronic Information and Communication of Huazhong University of Science and Technology referred to the method of onboard co-channel interference cancellation based on deep neural network, analyzed the co-channel interference generation mechanism of augemnted LEO satellite signals and established the interference signal model, and proposed a deep neural network-based interference cancellation method, which does not need the a priori information of onboard non-ideal characteristics, and can fit the channel characteristics end-to-end with high fitting accuracy and reach 40dB co-channel interference suppression ratio. It can be done in purely digital domain with high flexibility and limited suppression capability, and can be combined with other methods to solve the problem of co-channel interference in augmented LEO satellite signals, which can provide a technical reference for the  broadcast of augmented LEO satellite signals.

Wuhan University introduced a multi-source GNSS/IMU/Vision/LiDAR fusion navigation and positioning based on graph optimization, and implemented a complete set of combinted GNSS/Vision/IMU/LiDAR algorithm based on graph optimization for complex observation environment, which was tightly coupled based on the original observation level and made full use of each sensor information to provide ontinuous and high-precision navigation and positioning results in a weak GNSS environmentand. It fully exploited the complementary characteristics of vision and LiDAR, and introduced LiDAR raw observations in the graph-optimized tightly coupled visual inertial odometry, which achieved higher accuracy local pose estimation, thus the system errors accumulated more slowly under the GNSS loss-of-lock condition. It implemented the vision-enhanced LiDAR closed-loop optimization algorithm, which provided accurate closed-loop constraint information for the optimization of the back-end pose graph through effective detection of the closed-loop information, thus significantly improving the optimization of the pose graph and obtaining globally consistent and higher precision positioning and pose determination results.


Invited expert Li Xingxing giving the presentation


Invited expert Prof. Li Xingxing and Prof. Wang Ershen having a lively discussion

Beijing Research Institute of Telemetry introduced real-time PPP algorithm based on BDS-3 PPP-B2b augmentation information, which is the first in China to carry out research on BDS-3 PPP-B2b signal and information, restore it to a precise ephemeris and evaluate its accuracy. The radial accuracy and clock error accuracy of PPP-B2b ephemeris orbit is 5-150px, which meets the demand of real-time PPP. Research on real-time PPP algorithm based on the new BDS signal has been conducted, in which the success rate of the cycle slip restoration algorithm is above 99%, which can avoid the problem of reinitialization after signal interruption. Based on the PPP-B2b signal and real-time PPP algorithm, it designed a PPP-B2b-BRIT type receiver for real-time high-precision positioning, time service and atmospheric monitoring without relying on communication networks. Static positioning and dynamic positioning tests were also carried out. The precise positioning accuracy is 2-100px, the dynamic positioning accuracy is about 250px, and the convergence time is 4-6 minutes. In summary, real-time PPP based on PPP-B2b signals meets the needs of scientific research and engineering applications at static centimeter level as well as dynamic decimeter level accuracy.

Beihang University introduced the method of analyzing monitoring station data quality. High precision positioning services are applied in precision agriculture,traditional mapping, meteorological observation and automatic driving technology.In order to evaluate whether the BDS GBAS  can provide services to highly dynamic users, a similar Chinese land state network monitoring station was selected for comparison with WAAS stations and US CORS. The data continuity indicators were used to differentiate among the date provided by WAAS, U.S. CORS, and Chinese land state network monitoring stations. The satellite constellation, the minimum elevation angle of the satellite, the carrier-to-noise ratio, and the difference with the observed data availability have an impact on the data continuity, so these factors should be taken into consideration when assessing the data continuity. The existing standards of multipath errors, cycle slip ratios, and observation data availability are not comprehensive enough to describe the reliability. If the BDS GBAS is to provide services for highly dynamic users, it is suggested that data continuity indicators be added to the BDS GBAS standards.


Chairman of the Session Li Xingxing presenting a certificate to the academic presenter

Beijing Satellite Navigation Center introduced the pseudorange deviation weakening test based on the parameter constraints of BDS monitoring receiver. The unsatisfactory signal is the main factor causing the deviation of receiver pseudorange measurement, and the receiver filter bandwidth, loop parameters and other factors will affect the amount of pseudorange deviation. The pseudorange deviation of low code rate navigation signal is relatively large, which will affect the service processing or PNT resolution accuracy, which needs to be focused and solved; the pseudorange deviation of high code rate navigation signal is relatively small and negligible. For the navigation satellites in the space segment, there’s a need to optimize satellite payload design, strengthen satellite quality control, improve signal quality, and ensure the consistency of all satellite navigation signals. As for the monitoring of receiver signal obervations, there’s a need to unify and standardize key receiver design parameters such as filter bandwidth and relevant spacing. At the system information processing level, there’s a need to build a navigation service processing method that takes into account pseudorange deviation, and eliminate the impact of pseudorange deviation on navigation service processing.

Beijing Satellite Navigation Center introduced the threat model and threat space research related to BDS B1C and B2a signal distortion. The signals broadcasted by navigation satellites have different degrees of distortions, which may lead to catastrophic consequences for life-critical differential services such as SBAS. The SBAS uses “real-time signal quality monitoring” to avoid the threat of distortions. Therefore,it conducted a study on the signal distortion model and receiver constraints of BDS B1C and B2a, and introduced the needs and internal relationships in civil aviation standards, and specified the signal distortion threat model of BDS B1C and B2a, which can provide information reference for B1C and B2a to join  ICAO standards.

The Department of Electronic Engineering of Tsinghua University introduced the BDS dual-frequency signal quality monitoring algorithm in DFMC SBAS.  For signal quality monitoring (SQM) techniques, it extracted the source of observations and made progressive improvments, so as to be free from the limitations introduced by the processing of the original signal information subsequently; the more forward the source of observations and the more original and rich the information, the higher the implementation complexity required for a single receiver. Each SQM technique, depending on its processing characteristics and implementation complexity, has its own applicable signal types in practical applications. The hybrid SQM approach for BDS dual-frequency signals, based on existing results and the threat models and threat space already adopted by ICAO, can achieve better detection performance without significantly increasing the implementation complexity, where the SCSQM8r algorithm has high sensitivity for better steady-state and low SQM method’s performance smoothing needs can produce better transient SQM performance. The SRPQM3 algorithm has sufficient performance and saves hardware overhead.


Chairman of the Session Yang Long actively participating in academic exchanges

On May 28, 2021, the 12th China Satellite Navigation Conference Satellite Navigation System and Augmentation Session continued to be held in International Hall C of Primus Hotel Nanchang International Expo City. The Session was chaired by Chairmen Li Rui, Meng Yangsong, Liu Wenxiang, Li Xingxing and Yang Long. Experts and scholars from relevant fields at home and abroad gathered to share and exchange the frontiers and latest developments of satellite navigation augmentation technologies in propagation segment, user segment and LEO-based augmentation segment.


Chairman of the Session Li Rui is chairing the Session

National Astronomical Observatories of Chinese Academy of Sciences presented the regional equatorial ionization anomaly in China (mechanism, characteristics and its impact on GNSS positioning). The ionosphere not only varies with time but also shows spatial variation due to solar variation and Earth’s rotation and revolution, i.e., it has regional characteristics. The equatorial ionization anomaly (EIA) and the irregular structure of the ionosphere in the EIA region are two very important phenomena. They have high variability and can have a significant impact on the radio system's wave propagation. The EIA is formed by the action of the eastward electric field, the geomagnetic field and the gravitational force on the plasma, often referred to as the fountain effect. The EIA has a “valley” at the magnetic equator and two “peaks” at the lower latitudes north and south of the magnetic equator, and is therefore often called the hump region. The EIA in China is the North Hump. Its measured TEC is characterized by significant daily and seasonal variations, with sharp spatial variations and large latitudinal gradients.  It also has large deviations from the IRI model TEC. The developed EIA in the Chinese region can seriously affect the local GNSS positioning and its differential positioning performance. In addition, a higher accuracy EIA model and EIA effect mitigation still needs to be the focus of the research.


Invited expert Researcher Ma Guangyi giving the presentation

Qianxun SI Network Co., Ltd introduced the development of a high-precision ionospheric monitoring system for regions in China by taking ROTI maps as an example and described the process of changes in ionospheric ROTI maps and TEC maps in and around China during the main phase of a major magnetic storm. During this process, different regions in China were affected differently: (a) in Guangdong, Guangxi, and Hainan, the impact was more obvious, and the depletion and augmentation of electron density coexisted; (b) in Gansu and Shaanxi, the depletion of electron density was dominant; (c) in Xinjiang and Qinghai, the augmentation of electron density was dominant; and (d) the whole Northeast and North China were basically unaffected. At present, this real-time ionospheric monitoring system is still under continuous development and needs to connect the link of the whole architecture before it can be finally implemented. In the future, it’s expected that the monitoring system  will be used by the general public in their daily lives like the daily live weather broadcast, and fulfill a greater application value.

Shanghai Jiao Tong University presented the research on double-difference ionospheric interpolation based on Gaussian process regression. The ionospheric variation has a tendency to move from east to west with time, and the traditional algorithm interpolates each ephemeris individually, which cannot make good use of the correlation between the ephemerides. The Gaussian process regression for interpolation analysis was used instead. In this case, the interpolation input was improved by introducing multiple ephemeris data. More specifically, the interpolation input was improved to three dimensions compared with the traditional algorithm, and the input was improved by considering the effect of direct solar radiation. Then the kernel function of double-difference ionospheric delay was derived. Based on the assumption of the zenith ionospheric delay kernel function, the kernel function of double-difference ionospheric delay was further derived to make the kernel function more suitable for the actual observations.


Chairman of the Session Li Rui precensting a certificate to the academic presenter

Fudan University presented ionospheric disturbance observations based on CORS stations in the North American region. Traveling Ionospheric Disturbances (TIDs) are quasi-periodic fluctuating structures (e.g., density, velocity, temperature) caused by the coupling of lower atmospheric gravity waves with the ionosphere, and their propagation direction and velocity have traveling wave characteristics. In order to detect the TID fluctuation structure and detrend the STEC sequence, the Singular Spectrum Analysis (SSA) method was used. The PPP/SSA method can be used for MSTID detection and propagation velocity parameter estimation that is applied in the U.S. CORS data, and can be further used for China's BDS GBAS to observe travelling ionospheric disturbances. The method can be used to study the structure of TID in vertical direction by using the chromatographic technology in the future.

Fudan University presented BDGBAS-based ionospheric sparse reconstruction of the EIA region during the solar eclipse. The ionosphere is an important part of the solar-terrestrial space environment, affecting space radar shortwave communication, navigation, positioning and other technologies. As the electromagnetic wave signals that pass through the ionosphere will cause group delay, dispersion, Faraday rotation and other effects, the construction of real-time high-precision ionosphere chromatography model is therefore very important for modern communication and satellite navigation systems. It used UCPPP (fixed solution)  to extract the ionospheric delay amount, project matrix construction and compressed perception algorithm, and  the performance was verified in the end based on high accuracy positioning results. Its conclusions are as follows: the  data-driven sparse reconstruction algorithm can achieve high precision chromatography with accuracy lower than 0.2TECU, which improves the positioning accuracy of UCPPP algorithm by 12.2% and convergence time by 40.9%. The active ionospheric region and large-scale EIA region chromatography model have been constructed. Also ,the reliance on the number of base stations is reduced based on the sparse reconstruction algorithm.

GNSS Research Center of Wuhan University presented an overview of high-precision positioning integrity. In the RAIM/CRAIM test, the protection level was 2.50 meters in the horizontal direction and 0.91 meters in the vertical direction when the availability was 99%; when the availability was 95%, the protection level was 1.88 meters in the horizontal direction and 0.73 meters in the vertical direction. In the actual test scenarios, the indicator availabilities were 23.08% and 8.57% for the high-speed open/obscured scenarios; and 23.26% and 2.70% for the low-speed open/obscured scenarios respectively. Under the conditions of RTK operation supported by measurement receivers, the availability in complex urban environments was quite low and devices such as inertial navigation devices must be used. The positioning accuracy was only about 1m  when relying solely on high-precision positioning technologies such as RTK for high-precision vehicle navigation (non-automated driving),  and the availability was only 90% under ideal conditions; even when multi-mode dual-frequency RTK devices were used, the availability was not be fundamentally improved. GNSS-based high-precision positioning means such as RTK and PPP can be used in precise vehicle navigation in the field of transportation under non-life safety scenarios, but the problems of continuity and availability still need to be solved.


Invited expert Liu Hui giving the presentation


Chairman of the Session Li Rui actively participating in academic exchanges

Beijing Satellite Navigation Center introduced analysis of the applicability of the DFMC SBAS receiver design constraints to B1C and B2a signals. It conducted research on BDS B1C, B2a signal distortion model and receiver constraints. It first tudied receiver constraint applicability to normal signals, coupled non-idealistic errors with other errors, and encountered stripping difficulties, as in-orbit satellites were different from each other with obvious differentiated characteristics. It used large-aperture antenna to collect signals and obtain pure signal samples with high carrier-to-noise ratio, no multipath and no interferenc.These signals covered all B1C and B2a signals broadcasted by BDS3 in-orbit satellites (including 24 MEOs and 3 IGSOs). It then used software receivers to evaluate the worst-case scenario by processing and evaluating the collected signals afterwards. It also introduced needs and intrinsic relationships included in civil aviation standards, specified the applicability of receiver constraints to  B1C and B2a signals, and confirmed available minimum values of B1C and B2a receiver constraint filter roll-off parameters. The method used can provide information reference for B1C and B2a signals to join ICAO standards.

The 772th Research Institute of China Academy of Aerospace Electronics Technology/Beijing Institute of Microelectronics Technology introduced a multi-fault satellite anti-error positioning and integrity fault monitoring and troubleshooting method based on non-Gaussian distribution of errors, using the EM algorithm for estimating the maximum likelihood parameters, which can simultaneously acquire the posterior probability of the observation values containing faults, which is equivalent to adaptively adjusting the weights of each satellite according to the fault size and fault probability of each satellite to perform anti-error positioning. The observation information of all satellites can be used as much as possible to obtain good positioning accuracy for anti-error positioning. Simulation tests show that with a random deviation of 5-30 meters added to the uniform distribution, the positioning error of GM3 method is slightly higher than that of MM method when the number of faults is less than or equal to 4, but the difference is less than 0.4 meters and still lower than that of M method and LS method.For the protective level and false alarm and missed alarm analysis, the actual error VPE is smaller than the protective level VPL in most cases (confidence level 5%), which indicates that the VPL calculation is effective and can reflect the size of real-time errors, and can be used for real-time integrity monitoring. The number of iterations of the EM algorithm and the time required to calculate the initial value increase when the number of faults increases.


Participants asking questions onsite

The effect of different ISB processing strategies on the FCB estimation accuracy and PPP-AR was presented by the School of Geospatial Information of PLA Information Engineering University. The accuracy of all estimated wide alley FCB products is the same when the ISB is processed as a constant, white noise, and random walk process. However, for the narrow-alley FCB products, the WN-FCB and RW-FCB accuracy is the same and is better than that of the CV-FCB products, with approximately 7.5%, 10.6%, and 12.2% improvement in the ranges of (-0.25, +0.25), (-0.15, +0.15), and (-0.05, +0.05) respectively. In terms of first fuzzy convergence time and fixation success rate, PPPAR-WN and PPPAR-RW are basically comparable but better than the PPPAR-CV model, with improvements of about 19.5% and 15.5% respectively. Based on different FCB products for PPP-AR, in terms of positioning accuracy, the 3D positioning accuracy of PPPAR-CV model is 276.75px, 183.75px, and 152.25px at 30min, 60min, and 120min respectively, while PPPAR-RW and PPPAR-WN are basically comparable, but better than PPPAR-CV, with improvements of about 157.5px, 97.5px, and 90px respectively.

School of Electronic Information Engineering of Shenyang Aerospace University introduced theimproved RAIM algorithm based on M estimation, and proposed the improved BDS receiver autonomous integrity monitoring algorithm based on M estimation. The following conclusions are drawn by collecting navigation data for experiments: the improved M algorithm as well as the M algorithm and LS algorithm can detect satellite faults; the improved M estimation algorithm is better than the M estimation in terms of gross error suppression effectd; by comparing the M estimation and the improved M estimation algorithm, the improved M estimation algorithm can improve the fault detection and identification rate. It used the weighted least absolute value (WLAV) algorithm as the initial value of the M estimation algorithm to improve the fault detection rate and the fault identification rate. However, this method has many shortcomings, and it still needs to continue to be improved in the future. In the future, the integrity monitoring algorithm under LPV-200 can be studied, and for the multi-satellite fault problem, the robust estimation algorithm can be combined to suppress the gross errors and improve the fault detection and identification capability, and then improve the global availability of this algorithm under LPV-200.

National Time Service Center of Chinese Academy of Sciences introduced the application of GNSS differential technology in LEO dual-satellite passive positioning. In recent years, the statistics of European Telecommunications Satellite Organization (EUTELSAT) show that there are hundreds of incidents of interference with satellite communication every year, and the dual-satellite passive positioning system is to locate non-cooperative targets with the help of two satellites for observation, but the multi-epoch time difference positioning method will create blind zones. In response to the positioning problems related to blind zone caused by time and frequency difference, the multi-epoch time difference positioning method was proposed to effectively solve the blind zone positioning problems. It also applied the differential technology of satellite navigation system in the system, and proposed the position differential and pseudo-range differential of the dual-satellite passive positioning system, which could achieve the positioning accuracy of better than 5km. By using the navigation satellite as the reference station, it further proposed the single-satellite differential observation method for the dual-satellite passive positioning system, with the positioning accuracy of better than 4km.


Invited guest Xue Yanrong giving the presentation

Beihang University presented the WAAS satellite broadcast message consistency analysis. When the SBAS satellites are all healthy and available, there are small differences in the messages broadcasted by different GEO satellites. Most of the differences in the number of corrections in the pseudo-range domain are within 1x quantization interval, and very few of them reach double or triple quantization interval, and the augmentation effect of SBAS messages broadcasted by two GEO satellites is the same. For WAAS satellites, the redundancy provided by its multi-coverage broadcast architecture allows the user to choose to use another SBAS satellite for positioning in case of an anomaly in the augmented message broadcast by the current SBAS satellite, which improves the reliability of the system. It also put forward several considerations and discussions on the constraints of SBAS signal selection for users caused by WAAS satellites and specified that the ephemeris and clock corrections and integrity information of all satellites observed by the aircraft during the approach phase can only be obtained from the same GEO satellite; in the non-approach phase, the SBAS augmentation information of different GNSS satellites can be obtained from different GEO satellites, including GEO satellites of different SBAS systems; when the user observes multiple GEO satellites at the same time, the GEO satellite with the highest elevation angle is selected as the SBAS signal source; when multiple GEO satellites are observed, the SBAS receiver equipment needs to have the ability to switch SBAS signals.


Invited guest Li Rui giving the presentation

National University of Defense Technology introduced the spectral compatibility analysis of augmented LEO navigation satellite signals and GNSS signals. The large Doppler shift of LEO navigation satellite signals will have a large impact on the spectral compatibility assessment, therefore it analyzed the impact of large Doppler shift on the spectral compatibility analysis, and used the simulation to analyze the interference of augmented LEO navigation satellite signals with GNSS signals in the L1/E1/B1 bands, where Doppler frequency difference between LEO navigation satellites and GNSS MEO and HEO satellites arriving at the same receiver at different moments is taken into account. The analysis results show that the equivalent carrier-to-noise ratio attenuation caused by the LEO navigation satellite signals to the GNSS signals is small and in an acceptable range due to the large Doppler frequency difference between the signals. The analysis of the spectral compatibility between the augmented LEO navigation satellite signals and GNSS signals using different number of satellites and different signal systems can be confucted later. Moreover, the spectral compatibility analysis of GNSS signals in all frequency bands can be used to find the frequency band with the least interference caused by augmented LEO navigation satellite signals.

The General Department of Communication and Navigation of China Academy of Space Technology presented the LEO satellite constellation design and PPP performance study based on dual-objective optimization. Based on the constellation design, the PPP performance based on LEO satellite constellation under different boundary conditions was analyzed by simulation. It also shared with audience the PPP performance under different constellation configurations, multi-system combinations and typical usage scenarios. The results show that the convergence time of single GPS (G) and combined GPS/BDS (GC) is 20.6, 16.2min respectively, and the convergence time of GREC positioning is about 9min. After LEO satellites participate in positioning, the convergence time is greatly reduced. 96 LEO satellites can reduce the convergence time to less than 5min, which is 75.3% reduction compared with GC convergence time. When the number of satellites is increased to about 120, the GRECL positioning time is reduced to 1 min. Meanwhile, for high observation cutoff angles, multiple systems will help to improve the continuity and availability of positioning services. The proposed method can be widely applied in LEO satellite navigation augmentation system design, and the research results can provide reference and support for the corresponding system demonstration and analysis.


Chairman of the Session Yang Long presenting a certificates to the academic presneter

China Satellite Navigation Engineering Center introduced the research and performance analysis of key technology system of BDS navigation augmentation based on LEO satellite constellations, studied a BDS navigation augmentation system architecture based on LEO satellite constellations, analyzed the key links affecting the system performance realization, and conducted design and performance analysis in terms of spatio-temporal datum establishment and maintenance, constellation design, signal design and user positioning solution etc. Adding to BDS the LEO backbone satellite constellation (L150) can reduce the convergence time by more than 96%, and the convergence time can be reduced by more than 17% and 21% further by continuing to add LEO integrated satellite constellations (L72 and L144), and the method can provide a reference for the design and construction of the new generation PNT system.


Li Xing of China Satellite Navigation Engineering Center giving the  presentation

The School of Electronic Science of National University of Defense Technology introduced a genetic algorithm-based design of LEO satellite  constellation for communication-navgation integration, and propsoed a  hybrid LEO satellite constellation for communication-navigation integration in response to the problem that it is difficult to achieve uniform global coverage using a single-configuration LEO satellite constellation and to focus matching of the number of visible satellites in user-dense areas. Under the constraint of the same number of satellites, the hybrid constellation is more conducive to the matching in the key areas. The Walker Delta sub-constellation design in the hybrid constellation matches the ground user distribution model, and the sub-constellation inclination is between 40°-60° for the best visibility to the global target users. The increase in the number of satellites in the hybrid constellation, especially the increase in the number of satellites in the Walker Delta sub-constellation, can help greatly increase the number of visible satellites in the target area and reduce GDOP.


Lively discussion during the Session