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Special Column on “BeiDou Satellite-Based Augmentation and Aeronautical Application Technology”

Development status and trend of international satellite based augmentation systems

SHAO Bo, DING Qun, ZHANG Jian, LI Pingli, WU Xianbing

, Available online , doi: 10.12265/j.gnss.2024104

[Abstract](16) [FullText HTML] (9) [PDF 2244KB](0)

Abstract:
In order to promote the application of GNSS in the field of high life-safety, augmentation means, represented by Satellite Based Augmentation Systems (SBAS), have emerged to comprehensively improve the accuracy, integrity, continuity and availability of GNSS service. The United States, Europe, Japan and other countries have started the SBAS performance improvement work, from single frequency SBAS to dual-frequency SBAS transition, to further improve SBAS performance. This paper summarizes the system composition, service performance, system progress and follow-up development planning of the international SBASs, and focuses on the system architecture, service capability, application verification and internationalization process of BeiDou Satellite-based Augmentation System (BDSBAS). With the implementation of the latest International Civil Aviation Organization(ICAO) Annex 10 to the Convention on International Civil Aviation, BDSBAS has become an internationally recognized provider of SBAS service. Subsequently, to promote the application of BDSBAS in the field of high life safety, it is necessary to complete the verification of civil aviation applications as soon as possible, so that BDSBAS can be included in the official services.

CAT II/III precision approach guidance flight verification at xianyang airport based on domestic GBAS

HAO Shuo, YU Baoguo, GE Mao, WANG Jiachen, WANG Yao, ZHAO Jingbo

, Available online , doi: 10.12265/j.gnss.2024091

[Abstract](29) [FullText HTML] (13) [PDF 6432KB](0)

Abstract:
Ground-Based Augmentation System (GBAS) can improve the accuracy, integrity , continuity and availability of satellite navigation, making it possible for aircraft to achieve safe and efficient approach and landing in complex weather and harsh environment, which can meet the high-precision navigation needs of civil aviation such as precision approach and landing guidance. At present, the GBAS Category I (CAT-I) service level has been verified and applied, but its service level, such as positioning accuracy, still can’t fully meet the needs of civil aviation. The technology and application of GBAS Category II/III (CAT II/III), which have better service level, are still under development and validation. In order to improve the efficiency and safety of civil aviation operations, there is an urgent need to carry out flight verification activities based on CAT II/III. Currently, GBAS is mainly based on single-frequency GPS, which is very limited in terms of system availability, safety and autonomy, so it is necessary to develop an autonomous and controllable GBAS system which is compatible with BDS. This article designs a flight verification scheme, which has completed the GBAS flight verification for CAT II/III blind approach and landing guidance at Xi'an Xianyang Airport by using the domestic GBAS system. The test results show that GBAS compatible with BDS has the ability to support CAT II/III precision approach and its performance is far superior to the traditional instrument landing system. This achievement provides a strong guarantee for the safety of air transporation in China.

Performance evaluation method and flight test analysis of BeiDou satellite-based augmentation dual-frequency service

WANG Ershen, CHEN Yitong, YU Tengli, ZHANG Jian, YANG Jian, XU Song, WANG Yongkang

, Available online , doi: 10.12265/j.gnss.2024087

[Abstract](29) [FullText HTML] (19) [PDF 15305KB](0)

Abstract:
The BeiDou satellite-based augmentation system (BDSBAS) realizes simultaneous augmentation of multiple satellite constellations by broadcasting dual-frequency augmentation messages through B2a signal to provide users with more accurate and reliable positioning and navigation services. In order to meet the demand of civil aviation for the positioning performance of BDSBAS in the approach phase, this paper researches the BeiDou satellite-based augmentation dual-frequency positioning algorithm, and evaluates the performance of the dual-frequency service of BDSBAS based on the data of the static station and the flight data in terms of the accuracy and integrity. The static experiment data were collected from the BDSBAS site in Beijing on January 17, 2024, for the whole day. The flight measurement data were collected from the aviation test conducted at Faku Caihu General Aviation Airport in Shenyang. The static evaluation results show that the positioning errors of Beijing, Xi’an and Jiayuguan stations were relatively stable during the evaluation period. The horizontal positioning accuracy(95%) was better than 2 m; the vertical positioning accuracy(95%) was better than 3 m. Horizontal availability was better than 99.998% and vertical availability was better than 99.984%. The results of the flight test show that the horizontal and vertical accuracy during the test were 1.8269 m and 2.6014 m, respectively, and no integrity event occurred. The static and dynamic evaluation results met the requirements of the International Civil Aviation Organization (ICAO) APV-I indexes for accuracy and integrity. The results of this study are meaningful for the performance evaluation of BDSBAS.

Research on code noise and multipath error processing methods of Satellite-based augmented system

ZHANG Jian, SHAO Bo, DING Qun, LI Pingli, WU Xianbing

, Available online , doi: 10.12265/j.gnss.2024103

[Abstract](25) [FullText HTML] (12) [PDF 2050KB](0)

Abstract:
The Satellite Based Augmentation System (SBAS) uses the pseudorange measurement corrections to enhance the integrity of navigation satellites, the code noise and multipath error processing accuracy are important factors affecting the service performance of the system and the accuracy of user positioning. In this paper, three different methods for dealing with raw pseudorange code noise and multipath error are introduced, including the single-frequency smoothing method, the code noise and multi-path correction (CNMC), and the code noise multipath method (CNMP) used by the Wide Area Augmentation System (WAAS). Through the data of the satellite-based augmentation system in operation, the influence of different code noise multipath error methods on the user’s positioning accuracy is verified. The results show that CNMP can effectively eliminate the influence of code noise and multipath error in the service performance evaluation of satellite-based augmentation system, and the horizontal accuracy of 95% is increased by 0.2 m, and the vertical positioning accuracy of 95% is increased by 0.47 m.

Review of SBAS authentication techniques

SONG Jiangyao, CHEN Xiao, LIU Ting, WU Zhongwang

, Available online , doi: 10.12265/j.gnss.2024123

[Abstract](17) [FullText HTML] (10) [PDF 2292KB](0)

Abstract:
In response to the threat of vulnerability of satellite navigation systems to spoofing, which will seriously affect the impact of navigation, positioning and timing services. How to enhance the security of navigation system services has become one of the issues that need to be addressed in satellite navigation services. Satellite navigation signal authentication is an emerging technical means to enhance civil signal anti-spoofing in satellite navigation systems, and it is also one of the important development directions and research hotspots of major satellite navigation systems at present. As the core augmentation system of the satellite navigation system, the satellite-based augmentation system (SBAS) system is currently promoting the SBAS message authentication standard under the framework of the International Civil Aviation Organization (ICAO) with a view to providing SBAS message authentication service in the future. Along with the completion of the construction of China’s BeiDou satellite-based augmentation system and the design and development of the next-generation BeiDou navigation system, the BeiDou satellite-based augmentation system needs to consider the provision of SBAS message authentication services under the framework of ICAO standards, in order to provide users with more secure and trustworthy PNT services. This paper firstly elaborates on the concept of SBAS message authentication, then combs through the development history of SBAS message authentication, and then analyzes the hot issues faced by SBAS message authentication technology, which will provide technical support for the subsequent message authentication service of BeiDou satellite-based augmentation system.

Improvement of ionospheric availability for Beidou satellite-based augmentation system based on SHAKING method

LIU Ang, LI Zishen, WANG Ningbo, ZHANG Zhouyu, WANG Liang, SHAO Bo

, Available online , doi: 10.12265/j.gnss.2024076

[Abstract](33) [FullText HTML] (20) [PDF 3174KB](1)

Abstract:
The BeiDou Satellite-Based Augmentation System (BDSBAS) provides ionospheric correction and integrity monitoring services for users in China and surrounding regions through domestic monitoring stations. Therefore, it demands high availability of ionospheric algorithms. This paper utilizes the adjusted Spherical Harmonics Adding Kriging (SHAKING) method to calculate ionospheric parameter information for BDSBAS. Performance analysis of existing SBAS ionospheric models reveals that some SBAS systems broadcast delay correction information marked as unmonitored points. Demand analysis of regional SBAS grid points in China shows that when the satellite elevation angle is set as 15°, SHAKING provides 189 usable points and 3 unusable points. Combined with clock and orbit correction information provided by BDSBAS, SHAKING improves the availability range of Approaches with Vertical Guidance by approximately 30% compared to the Inverse Distance Weighting (IDW) method.

Technical Report and Application

Research on tropospheric refractivity prediction method based on BP neural network

QIAN Zhigang, YANG Dongsheng, GUO Xiaotong, LI Xue

, Available online , doi: 10.12265/j.gnss.2024043

[Abstract](19) [FullText HTML] (9) [PDF 2374KB](0)

Abstract:
For satellite navigation systems, positioning errors are affected by the refractive index of the troposphere atmosphere. Improving the accuracy of predicting the refractive index of the troposphere atmosphere can reduce navigation positioning errors. The refractivity of tropospheric atmosphere is the main parameter for studying the influence of the troposphere on the propagation of electromagnetic waves, and the accuracy of its predictions is of great significance for radio systems. In this paper, a tropospheric refractivity prediction method based on BP neural network is proposed, which takes the year, month, day, time, surface refractivity, and altitude as the input of the BP neural network, and the corresponding refractivity at the input altitude as the output of the model. Similarly, by adjusting the input and output parameters, the BP neural network can also be used to predict the refractivity gradient of 1 km near the ground. Finally, the proposed algorithm is calculated and analyzed by using the historical aerial exploration data of Hongkong and Taiyuan, and compared with the methods in the existing papers. The results show that the proposed method has certain advantage in the calculation accuracy.

Precision orbit determination research of LEO satellite simulated downlink data

WANG Qining, WANG Le, LAI Wen, SHE Haonan

, Available online , doi: 10.12265/j.gnss.2024148

[Abstract](25) [FullText HTML] (4) [PDF 2984KB](0)

Abstract:
This study focuses on precision orbit determination utilizing simulated downlink data from low earth orbit (LEO) satellites. A comprehensive investigation is conducted on the orbit determination performance, considering a simulated Walker 90/10/1 LEO satellite constellation with an orbit altitude of 1 000 km and an inclination angle of 48°, along with 150 ground stations equipped with corresponding orbit clocks and observation data. The observational data from global station networks, featuring station numbers ranging from 60 to 150, are utilized for precise orbit determination of LEO satellites, followed by a detailed analysis of orbit accuracy and station position dilution of precision (SPDOP) values. Results indicate a significant enhancement in LEO satellite orbit accuracy from 117.5 mm to 39.8 mm upon increasing the number of stations from 60 to 150. Furthermore, sparse station distribution leads to a rapid degradation in LEO satellite orbit accuracy. The study underscores the effectiveness of augmenting the number of ground stations in improving both visible station SPDOP and LEO satellite orbit accuracy over terrestrial regions. However, due to the constrained tracking range of stations, enhancing the orbit accuracy of LEO satellites in marine regions remains challenging.

A clock synchronization/calibration system combining EKF and LSTM neural networks

XU Tao, GUO Chenyu, ZHAO Cheng

, Available online , doi: 10.12265/j.gnss.2024083

[Abstract](20) [FullText HTML] (8) [PDF 2827KB](0)

Abstract:
Research on methods to improve the timing accuracy and timekeeping capability of timing signals under satellite timing. By using a crystal oscillator counter, the crystal frequency information at the moment of each second pulse is recorded; the recorded historical information is input into an extended Kalman filter (EKF) for filtering, to eliminate the random error of the satellite second pulse signal, and extract the accumulated time of the first $N$ seconds of the BeiDou satellite pulse ${t_{CN}}$, and the crystal oscillator frequency $fre(k)$ at time $k$; and the crystal oscillator change rate $v(k)$ at time $k$; and the historical data output by the EKF is used as the training set, input into the long short-term memory (LSTM) network to establish a prediction model; the algorithm parameters are debugged using the control variable method to find the most suitable prediction model. The experimental results show that the maximum error of the timing signal output by the timing algorithm is 34 ns; the cumulative error of the timing algorithm in 8 hours is 1.001 μs, and the average error is less than 0.125 μs/h. This effectively improves the timing and timekeeping accuracy of the system.

Correction of ionospheric correction deviation in network RTK based on conditional adjustment

SHI Xin, ZHANG Xi, CHENG Bing, KE Yuanying, LEI Chuanjin

, Available online , doi: 10.12265/j.gnss.2024069

[Abstract](17) [FullText HTML] (6) [PDF 3035KB](0)

Abstract:
Aiming at the problem of low accuracy of ionospheric delay modelling in the afternoon in network RTK, a deviation correction method for ionospheric correction values based on conditional adjustment is proposed, using the condition that the theoretical closure difference of the three baselines in the triangle with double-difference ionospheric delays is 0, to adjust the ionospheric correction values obtained by modelling, and the scheme of determining the weighting array in the correction process is discussed. The experiments show that the correction algorithm can effectively improve the accuracy of ionospheric correction when the accuracy of the ionospheric correction model is not high, and at the same time, the determination of the weight array based on the ambiguity fixing of the known baselines can achieve a better correction effect, with the maximum value of the deviation of the ionospheric correction value reduced by 58.0 percent and the overall accuracy improved by 51.1 percent.

The design research of intelligent operation and maintenance monitoring platform for road, port and navigation based on BeiDou System

YAN Ying, ZHOU Yukai, WANG Jian

, Available online , doi: 10.12265/j.gnss.2024050

[Abstract](18) [FullText HTML] (13) [PDF 2092KB](0)

Abstract:
As the road and port shipping industry continue to develop and the scale of operations expands, efficient operation and maintenance monitoring is crucial to ensure the safety and operational efficiency of the entire logistics chain. This study proposes a design solution for a road and port shipping intelligent operation and maintenance monitoring platform based on the BeiDou Navigation Satellite System (BDS), aimed at enhancing the efficiency and safety of road and port shipping operations. Using the positioning and communication capabilities of BDS, integrating advanced sensors and internet of things technology to achieve real-time monitoring and management of ships, vehicles, and equipment and providing related data analysis and decision support functions. Effectively enhancing visualization and tracking capabilities during transport, ensuring stable information exchange under harsh conditions; At the same time, a large amount of operation and maintenance data is analyzed and processed in real time using integrated big data technology, improving the proactivity and accuracy of risk prevention and management. This effectively solves the core problems faced by the road and port shipping industry in operation and maintenance monitoring, contributing to the development of the transportation industry towards a more efficient, safer and more intelligent direction. This paper specifically studies and explores the construction principles of the intelligent operation and maintenance monitoring system, platform construction solutions, data service platforms, and geographic information platforms, achieving a comprehensive, multi-dimensional intelligent operation and maintenance solution based on BeiDou, enhancing the efficiency and safety of entire road and port shipping operations.

Research on precipitable water vapor prediction method based on lightGBM algorithm

LU Houxian, LI Kai, LI Li, HE Qimin, YU Hang, DONG Zhounan

, Available online , doi: 10.12265/j.gnss.2024079

[Abstract](23) [FullText HTML] (9) [PDF 4113KB](0)

Abstract:
The precipitable water vapor (PWV) represents the content of liquid water vapor in a unit cross-sectional area vertically from the Earth's surface to the top of the troposphere, reflecting the concentration of water vapor in the atmosphere. In this study, data from seven radiosondes in the Yangtze River Delta region from 2014 to 2019 were utilized to analyze the correlations between PWV and zenith tropospheric delay (ZTD), zenith hydrostatic delay (ZHD), zenith wet delay (ZWD), water vapor pressure (E_s), atmospheric pressure (P_s), surface temperature (T_s), and weighted mean temperature (T_m). A new Light Gradient Boosting Machine (LightGBM)-based PWV prediction model for the Yangtze River Delta region was established, and then the prediction accuracy of the LightGBM-PWV model was analyzed. The results show that the correlation coefficients (R) between PWV and T_m, T_s, P_s, E_s, ZHD, ZWD, and ZTD were 0.74, 0.76, –0.59, 0.76, –0.43, 1.00, and 0.94 respectively. The average biases of the yearly, seasonal, and monthly LightGBM-PWV model were 0.10 mm, 0.11 mm, and 0.12 mm respectively, and their RMSE are 0.25 mm, 0.26 mm, and 0.31 mm. The accuracy of the yearly, seasonal, and monthly LightGBM-PWV model decreased sequentially, different from the traditional linear fitting PWV models. The yearly LightGBM-PWV forecasting models demonstrate the highest accuracy. It can be applied for the GNSS-PWV forecasting, analysis, and research in the Yangtze River Delta region.

A random forest-based prediction model for ionospheric f_oF₂ in China and surrounding regions

LIN Ziyang, CHEN Longjiang, JIN Ruimin, OU Ming, YANG Huiyun, JI Guangwang, CUI Xiang, GU Mingyue

, Available online , doi: 10.12265/j.gnss.2024140

[Abstract](28) [FullText HTML] (11) [PDF 3378KB](2)

Abstract:
The square of the critical frequency of the ionospheric F2 layer (f_oF₂) is proportional to the peak electron density (N_mF₂) and serves as a crucial parameter affecting the performance of Global Navigation Satellite Systems (GNSS). Enhancing the prediction accuracy of f_oF₂ is essential for optimizing GNSS broadcast ionospheric models, thereby improving the positioning accuracy of GNSS. This study develops an ionospheric f_oF₂ prediction model for China and its surrounding regions using the random forest algorithm, based on data from 18 ionosonde stations of the China Research Institute of Radiowave Propagation and COSMIC occultation observations. The model incorporates multiple features, including Universal Time, day of the year, geographic location, solar, and geomagnetic activities. A comparative analysis with the International Reference Ionosphere (IRI-2020) model validates the prediction accuracy of our model. The results indicate that the random forest model reduces the mean absolute error by 14.81% and 17.11%, and the root mean square error by 11.21% and 13.14%, compared to the IRI CCIR and IRI URSI models, respectively. Additionally, the model exhibits superior prediction accuracy under various latitudes, local times, solar, and geomagnetic activity conditions when compared to IRI-2020. This research not only significantly enhances the f_oF₂ prediction accuracy for China and its surrounding regions but also lays a critical foundation for improving the accuracy and reliability of GNSS globally.

Analysis of extreme rainfall characteristics of Datong “817” based on BDS-3 and FY-4A

ZHAO Lijiang, ZHAO Jianyun

, Available online , doi: 10.12265/j.gnss.2024067

[Abstract](37) [FullText HTML] (12) [PDF 5341KB](0)

Abstract:
Adequate water vapor and cloud phase changes are two necessary conditions for rainfall to occur. Based on the BeiDou-3 satellite navigation system, water vapor can be retrieved, which has the advantages of high time resolution and accuracy; FY-4A can provide cloud phase parameters with a resolution of 15 minutes. This article uses the BDS-3 and FY-4A data to analyze the spatiotemporal changes in atmospheric precipitation and cloud phase before and after the occurrence of all precipitation in August 2022. Through comparison, three characteristics of extreme rainfall in Datong “817” were obtained: firstly, the atmospheric precipitation rapidly increased one hour before rainfall, reaching a rate of 3.17 mm/h, significantly exceeding the general rainfall level of the same period; before the second rainfall, there were multiple changes in cloud types between multi-layer clouds and opaque ice clouds, and eventually extreme rainfall occurred in the form of opaque ice clouds; the third reason is that the height of extreme rainfall cloud tops is usually greater than 10000 meters.

Research on roll angle estimation method based on deep learning

FENG Lu, WU Peng, ZHENG Yu, ZHANG Zhuxian

, Available online , doi: 10.12265/j.gnss.2024078

[Abstract](22) [FullText HTML] (17) [PDF 3330KB](0)

Abstract:
Attitude measurement technology serves as a fundamental component in monitoring vehicle motion states and ensuring safety. The spinning motion of vehicles leads to a coupling of attitude angles, which significantly impacts flight control. In this paper, a deep learning approach based on the Long Short-Term Memory (LSTM) neural network is proposed to determine the real-time roll angle of a vehicle. The energy characteristics exhibited by a single antenna receiving satellite signals during the vehicle's rolling state have been analyzed in detail. A correlation between the real-time roll angle and the energy amplitude of the received signal has been established. The influence of changing satellite positions on these measurements is also discussed. Subsequently, the LSTM neural network training method is employed to extract periodic variation features from the measured signals, thereby obtaining various network parameters. These parameters are then used to predict and denoise the received signal, with the roll angle being computed by model matching. To validate the efficacy of the proposed method, a rolling experiment was conducted. The experimental results demonstrate that the LSTM-based deep learning approach effectively restores the features of the received signals, enabling accurate real-time measurement of the vehicle's roll angle.

Analysis of the impact and effects of the solar storm on the ionosphere from May 8 to 16, 2024

WANG Shuai, QUAN Lin, LI Ling, WANG Kunpeng, HUANG Jian, YUAN Gang

, Available online , doi: 10.12265/j.gnss.2024107

[Abstract](118) [FullText HTML] (43) [PDF 5661KB](8)

Abstract:
Solar storms can cause severe disturbances to the state of Earth’s ionosphere and affect navigation and positioning performance. According to the ionospheric disturbance event occurring during the solar storm from May 8 to 16, 2024, the changes of ionospheric total electron content, ionospheric total electron content change rate, ionospheric F₂ layer critical frequency, satellite navigation single point positioning error and so on at different latitude stations in the eastern and western hemispheres are analyzed. The analysis result shows that the sun-lit hermisphere of the ionosphere will respond to X-ray flares, but the main source of the disturbance is the geomagnetic storm caused by the solar wind southward magnetic field energy injection. The responses at the top and bottom of the ionosphere during solar storms are not synchronized; The single point positioning error of satellite navigation will increase significantly during the solar storm, especially in the vertical direction it will increase to about ±10 m. It will continue to exist during the recovery phase of ionospheric storms, and gradually weaken with the calm of the ionospheric state.

Application research of RINGO software in multi-system GNSS data preprocessing

FAN Jiuguo, LI Jianyong

, Available online , doi: 10.12265/j.gnss.2023202

[Abstract](363) [FullText HTML] (137) [PDF 4282KB](50)

Abstract:
Data preprocessing is a prerequisite for achieving high-precision positioning with the Global Navigation Satellite System (GNSS) and is also a vital step in data processing. As the number of satellite systems, numbers, and versions of Receiver Independent EXchange format (RINEX) increase, the GNSS data types and formats become progressively complex. Thought there are various data preprocessing software options available, multiple programs are required to complete the preprocessing stage, resulting in inefficiency and complexity. Therefore, to achieve efficient data preprocessing, developers have created the “RINGO” data preprocessing software, which supports all RINEX versions of multi-system data preprocessing. To achieve effective data preprocessing, developers created the “RINGO” software which supports all RINEX versions of multi-system data preprocessing. The study demonstrates the main functions, usage and principles of RINGO, with a focus on investigating and explaining confusing functions such as receiver clock jump correction. The test results demonstrate that RINGO can effectively and independently preprocess vast amounts of multi-system GNSS data, which can significantly ease the complex task of GNSS data management and foster the adoption of the latest version of RINEX observation records.

Architecture design of radiation source positioning system based on TDOA

HU Anyi, WANG Dengliang, QIN Bingkun, ZHANG Faxiang

, Available online , doi: 10.12265/j.gnss.2023174

[Abstract](169) [FullText HTML] (120) [PDF 2726KB](17)

Abstract:
To ensure the normal application of the Global Navigation Satellite System (GNSS), monitoring and localization of GNSS interference radiation sources are required. This paper presents the design of a radiation source positioning system architecture. By designing the system functions, architecture, grid monitoring equipment and workflows, high-precision time synchronization and reliable time difference measurements are achieved using BeiDou/GPS timing + high-stability crystal oscillators and a generalized weighted time delay estimation algorithm, which ensures the accuracy of time difference of arrival (TDOA) localization. The effective location of radiation source is realized through system application test.