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2022 | Book

China Satellite Navigation Conference (CSNC 2022) Proceedings

Volume I

Editors: Prof. Changfeng Yang, Prof. Jun Xie

Publisher: Springer Nature Singapore

Book Series: Lecture Notes in Electrical Engineering

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About this book

China Satellite Navigation Conference (CSNC 2022) Proceedings presents selected research papers from CSNC 2022 held during 25th-27th May, 2022 in Beijing, China. These papers discuss the technologies and applications of the Global Navigation Satellite System (GNSS), and the latest progress made in the China BeiDou System (BDS) especially. They are divided into 10 topics to match the corresponding sessions in CSNC2022 which broadly covered key topics in GNSS. Readers can learn about the BDS and keep abreast of the latest advances in GNSS techniques and applications.

Table of Contents

Frontmatter

Professional GNSS Applications

Frontmatter
Platform Attitude Measurement Technology by Single Antenna Navigation Receiver Fused with Electronic Reconnaissance DF

Accurate attitude measurement on the electronic reconnaissance aircraft, ship and other platform is the necessary prerequisite for electronic reconnaissance tasks. The traditional method depends on the inertial navigation or GNSS attitude instrument with multi antennas. In addition, for platforms with the electronic reconnaissance and DF (Direction Finding) equipment, their DF capability can be fully utilized. Through the phase difference measurement among signals in interferometer channels based on codeless phase discrimination in frequency domain, combined with the positioning and velocity measurement results from the single antenna satellite navigation receiver, and using the Doppler frequency shift difference of each navigation signal to realize signal separation and direction matching, three attitude parameters of the platform, such as heading, pitch and roll angle can be measured. Finally, the correctness and effectiveness of this method are verified by the analysis and processing on the actual signal from the electronic reconnaissance receiver. This method makes full use of the functionality of the existing hardware platform. It does not add new hardware modules, and only needs to be upgraded in the software. So it explores a new way for the attitude measurement on the electronic reconnaissance platform.

Rong Shi, Junhao Chen, Jiang Liu
Interpretation of Soil Moisture Using CYGNSS and SMAP Satellite Data in Henan Province

In order to improve the temporal and spatial resolution of soil moisture in the monitoring area, the comprehensive use of tropical cyclone global navigation satellite system (CYGNSS) and soil moisture active-passive detection (SMAP) satellite data was analyzed and researched. The results show that: Compared with interpreting soil moisture using only SMAP satellite data, the method used in this paper improves the time resolution of soil moisture interpretation while ensuring the same spatial resolution, and can obtain more complete soil moisture information in the study area. Compared with the measured data from the ground stations in the International Soil Moisture Database (ISMN), the root mean square error of the interpretation results in this paper varies from 0.0258 to 0.042, and the correlation coefficient varies from 0.5502 to 0.5886. It validates the validity and reliability of the proposed interpretation method comprehensive utilization of CYGNSS and SMAP satellite data for soil moisture.

SHengwei Hu, Shuangcheng Zhang, Huilin Wu, Hongli Ma, Yuxuan Feng, Qinyu Guo
Agricultural Cold Chain Logistics Monitoring Platform Based on Beidou-3 Satellite Internet of Things

Since Beidou-3 satellite navigation system has improved the communication capacity and coverage compared with beidou-2 greatly, navigation and short message of Beidou-3 satellite navigation system have broad application prospects in scenarios that cannot be covered by conventional communication methods such as monitor, alarm, emergency rescue etc. The method of 4G mobile communication plus GPS positioning is widely used in the cold chain logistics environment monitoring. In order to effectively solve the problems of data transmission, navigation and positioning in extreme environments, this paper uses the positioning and short message functions of beidou-3 satellite navigation system to design the application support platform architecture based on Satellite Internet of Things, and propose a solution to implement the application of cold chain logistics monitoring. The above method can provide full-time, all-region and high-reliability environment monitor for the transportation of agricultural products and drugs, especially in the region, such as sea, air and mountain where there is no mobile internet, and in the areas where conventional communication means cannot cover or weakly cover.

Wei Chen, Lei Lei, Xiao-fei Fan, Rui-Ming Zhao, Rong-lin Hao, Si-zhe Cai
Landslide Displacement Prediction Based on VMD-LSTM-GM Model Considering Rainfall

Thetime series analysis and prediction of landslide GNSS monitoring displacement is of great significance to the early warning research of landslide disasters. To improve the accuracy of landslide cumulative displacement prediction, this study proposes a combination of variational mode decomposition (VMD) algorithm, long short term memory (LSTM) network model and grey model (GM) to integrated landslide cumulative displacement prediction model. Based on the variational modal decomposition algorithm, the cumulative displacement of the GNSS landslide is decomposed to obtain the trend displacement and the fluctuation displacement. The LSTM model considering the rainfall influence factor is constructed to predict the fluctuation displacement, and the dynamic GM(1,1) prediction model is established to predict the trend displacement. Decomposition predictions are then superimposed to obtain predicted values. Taking the Bazimen landslide as an example, compared with VMD-BPNN-GM and LSTM models, the experimental results show that the established combined model has the highest prediction accuracy, and the prediction results conform to the change of landslide displacement, which has certain engineering application value in the monitoring of landslide disasters.

Xi Chen, Yaping Gao, Guo Chen, Jiali Yang, Wenguang Yang
Rapid Satellite Selection Algorithm Based on Clifford Algebra

GNSS Multi-system provide more visible satellites, however, the amount of computation will increase exponentially and the realtime requirement of navigation solution will be affected when all visible satellites are used for computing the three-dimensional position. Reasonable satellite selection algorithm can meet the accuracy of navigation, as well as the efficiency of navigation. Based on this, according to the characteristics and shortcomings of the elevation angle satellite selection algorithm, combined with the representation advantages of Clifford algebra, a rapid satellite selection algorithm based on Clifford algebra is proposed here. The specific implementation of the algorithm is as follows: taking the station center as the vertex, combining with the regional division of high, medium, and low angle of the elevation angle satellite selection algorithm, an umbrella matching benchmark model for low angle area to select satellites is constructed based on Clifford algebra; the coordinates of the visible satellites about local Cartesian coordinates coordinate system are calculated, and the multi vector set of visible satellites is constructed based on Clifford algebra theory; the matching threshold angle is calculated according to the designed total number of selected satellites and the number of zenith satellites first. Based on Clifford algebra theory, multiple vector sets of visible satellites are constructed. According to the preset total number of selected satellites and the number of top satellites, the matching threshold angle is calculated. Based on the vector angle operation of Clifford algebra, the multiple vector sets visible satellites and the umbrella model are matched and selected satellites. When the total number of the low elevation angle area and the high elevation area visible satellites is smaller than the designed total number, the visible satellites of the medium elevation angle area will be added, until the number of visible satellites meets the total number of selected satellites for the design. The experiment results about BDS/GPS/GLONASS show that when the number of selected satellites reaches 8, the result of this algorithm is close to that of the minimum GDOP method. When selecting the quantity of satellite is not less than 13, the algorithm selected satellite GDOP value is less than 2, show that the algorithm can meet the accuracy requirement of high precision navigation. Moreover, the calculation efficiency of this algorithm is much better than using the minimum GDOP method.

Shuaikang Lv, Kezhao Li, Ning Wang, Yingxiang Jiao
The Preliminary Realization and Evaluation of CTRF2020 Based on New BDS3 Technology

The current research of the international and regional coordinate reference framework is mainly realized by GPS technology. The launch of the last BDS3 satellite on June 23 of 2020 marked the completion of the global deployment of BDS. Therefore, it is urgent to study and establish the corresponding coordinate reference framework. We aim to preliminarily realize and evaluate the BDS3/COMPASS terrestrial reference framework (CTRF2020). CTRF2020 reference epoch is 2020.0, and it can be expressed with the coordinates and velocities of a series of reference sites at the epoch of 2020.0. Firstly, the evaluation of the actual service performance of BDS in the global region reflects the high visibility and change trend of BDS satellite in recent three years, which provides basic input data for CTRF2020. Then, the BDS observations of about 100 global stations in the recent three years are calculated by PPP and NET solution, to obtain the global high-precision BDS coordinate time series. Then, the BDS time series of the two solutions are fitted and compared with the IGS14 velocity field. The results show that the series accuracy of PPP-BDS and NET-BDS solutions is equivalent, and there is an mm-level systematic deviation with IGS14 solutions. The horizontal series fitting accuracy of PPP-BDS and NET-BDS solutions is better than that of the vertical direction, the accuracy of NET-BDS solution is slightly better than PPP-BDS, and the difference of fitting accuracy is 0.12, 0.13, and 0.50 mm in the NEU direction. The velocity field accuracy of PPP-BDS and NET-BDS solution is the same, and the overall three-dimensional velocity difference is less than 0.2 mm/a. The velocity fields of PPP-BDS and NET-BDS solution have little difference from IGS14, and the overall difference is less than 0.5 mm/a. Finally, we give the limitations and improvement direction of CTRF2020. The preliminary realization and evaluation of CTRF2020 may be expected to provide a reference for the future realization of a comprehensive terrestrial reference framework dominated by BDS3 technology and supplemented by multi-source space geodetic technology.

Yingying Ren, Hu Wang, Yangfei Hou, Jiexian Wang, Yingyan Cheng, Pengyuan Li
Application of BDS-3 PPP-B2b Signal Service in the Measurement of Vertical Deviation

In order to further improve the measurement accuracy of vertical deviation and expand the application of astrogeodesy. Based on the theory of astrogeodesy, combined with the real-time PPP provided by BDS-3 and Digital Zenith photographing positioning model, this paper analyzes the principle and related work flow of the vertical deviation in detail, gives the relevant error correction model of the real-time PPP, and deduces the error calculation model in the measurement of Helmert vertical deviation. Through theoretical analysis and actual measurement verification, The real-time PPP provided by BDS-3 PPP-B2b signal is better than 0.1 m in the horizontal direction and 0.2 m in the elevation direction under static measurement mode. combined with the current high-precision zenith photograph positioning system, the vertical deviation measurement accuracy can be better than 0.06″ in the meridian component and 0.08″ in the unitary component. The research results can provide theoretical and data reference for the establishment of high-precision gravity field model and geoid refinement in China.

Lei Ren, Tian-He Xu, Yu-Guo Yang, Dong-Dong An
GNSS High Precision Quasi Real-Time Landslide Monitoring Algorithm for the Universal Receivers

GNSS high-precision quasi real-time positioning results are important reference information for the early warning of landslide disaster. The high-precision quasi real-time three-dimensional position information of the universal receivers installed on the land-slide is usually obtained by the continuous static filtering or the total estimation of the monitoring period, but the continuous static filtering cannot respond to the landslide sliding in time, and the ambiguity parameters of the total estimation cannot be fixed or fixed incorrectly when the quality of the observation data is poor. To solve the above problems, the quasi real-time landslide monitoring algorithm is proposed, which estimates the ambiguity parameters and position parameters separately in the monitoring period. Firstly, the continuous static filtering is used to solve the observation data in the monitoring period epoch by epoch, obtain the double difference float ambiguity parameters of each observation epoch, and optimize the ambiguity subset in the way of partial ambiguity resolution to improve the ambiguity fixed rate. Then, the position parameters in the monitoring period are estimated by the robust sequential least square, and the high-precision quasi real-time position parameter solution results are obtained. The test results of the observation data of Guizhou landslide monitoring net-work show that the success rate of the monitoring period solution of the algorithm scheme in this paper is 100%, which not only reflects the sliding trend of the landslide in quasi real time, but also the external coincidence accuracy of the positioning results in the plane direction and elevation direction can reach the millimeter level. The above experiments verify the feasibility and effective-ness of the proposed algorithm in quasi real-time landslide monitoring.

Yanhui Li, Hongyu Shan, Guofu Pan, Qinggen Yi, Zhongrong Yang
Research on Monitoring Strategy of Loess Landslide with GNSS Meteorology

Landslide is a common geological disaster with wide distribution and great harmfulness, which poses a serious threat to the safety of human life and property. Rainfall is the biggest influencing factor of loess landslide. Since rainfall is closely related to the PWV content, the Global Navigation Satellite System (GNSS) can not only obtain the three-dimensional deformation information of the location of the observation station, It can also be used to invert the moisture content. In order to make GNSS play a better role in landslide monitoring, based on the landslide event in Linxia city, In this paper, GAMIT software is used to calculate the data of three IGS stations combined with the monitoring station in Linxia city, and the PWV is inverted and compared with the rainfall, The PWV value accumulates continuously from low to high, and when it reaches a certain peak value and lasts for a period of time, rainfall events will occur. The results show that PWV has an obvious correspondence with actual rainfall, which proves the feasibility of ground-based GNSS inversion of moisture content. The three-dimensional surface deformation information obtained by the universal receiver is analyzed synthetically. The experimental results show that there is a correlation between the shape variables, PWV and rainfall, which proves the feasibility of GNSS meteorology for loess landslide monitoring. By analyzing the historical meteorological data of Linxia city, the rainy season is concentrated in May to September, during which the real-time calculation scheme can be adopted. When there is less rainfall from October to April of the next year, sky solution or weekly solution can be adopted. In addition, when the PWV is greater than 20 mm, real-time calculation can be performed to monitor landslide conditions. The cumulative PROCESS of PWV before rainfall is of great significance for monitoring loess landslide. Therefore, GNSS inversion of PWV provides a new monitoring strategy for loess landslide.

Jianwen Jiang, Shuangcheng Zhang, Cunpeng Jia, Xuqiao Wang, Xinrui Li
Analysis of the Vertical Coordinate Time Series in China Taking into Account the HYDL Under the ITRF2014 Framework

The GNSS coordinate time series is affected by the hydrological loading (HYDL) in the surface elastic deformation information. This paper uses the CMONOC coordinate time series under the ITRF2014 framework and the MERRA2 hydrological loading model provided by IMLS to analyze the influence of China's regional HYDL on the GNSS coordinate time series. The results show that in the vertical component, the HYDL has a particularly significant impact on the GNSS coordinate time series. The maximum velocity can reach 3.52 mm/year, of which 37.1% of the stations are corrected by the HYDL, the velocity decreases, and 63.3% of the stations are corrected by the HYDL, the velocity value increases. The influence on the periodic term is mainly reflected in the annual amplitude and the annual phase. Among them, 82.4% of the stations are corrected by the HYDL and the annual amplitude is reduced, and the nonlinear amplitude is weakened. As for the annual phase, 22.5% of the stations is significantly reduced after the HYDL correction, and the remaining 77.5% of the stations is increased after the HYDL correction. This shows that the influence of HYDL on the annual phase of the GNSS coordinate time series cannot be ignored.

Yuefan He, Guigen Nie, Shuguang Wu
Performance Analysis of GPS at Three Ephemerides on Medium and Long Baselines

With the continuous improvement and updating of GPS technologies, medium and long baselines are widely used in GPS data processing. Currently, the International GPS Geodynamic Service Center (IGS) provides the final precise ephemeris (IGSF), rapid precise ephemeris (IGR) and ultrarapid precise ephemeris (IGU). These three different precise ephemerides are different in terms of accuracy and update frequency, and have different effects on the accuracy of the baseline solution in practical applications. Therefore, in order to analyze the influence of the published accuracy of these three ephemerides on the results of the baseline solution. Based on 7-day observation files and their corresponding ephemeris files, this study uses Trimble Business Center (TBC) 5.2 software to perform the baseline solution with three different ephemeris files. We take the baseline result of the IGSF solution as the true value, and compare the baseline results of the other two ephemeris solutions. There are specific discussions about baseline length within 200 km, 500 km–1300 km and 1300 km–2600 km. Results show that when the baseline length is 1300 km–2600 km, the 7-day average of the difference of ΔX, ΔY and ΔZ of IGR-IGSF are all less than 1.19 mm, while IGU-IGSF are all less than 8.64 mm. In terms of root mean square, the 7-day average accuracy in the X, Y, and Z directions of the TBC equipped with IGSF is less than 11.76 mm, while the equipped IGU is less than 12.94 mm. Therefore, in the solution of medium and long baselines, the final precise ephemeris and the rapid precise ephemeris have higher accuracy, and the ultrarapid precise ephemeris is less accurate. When the final precise ephemeris is not acquired in time, the fast precise ephemeris can be used for the baseline solution.

Xiongwei Peng, Xiaoxing He, Xiaping Ma, Dejun Wang, Hui Jin
Research on GNSS-IR Height Measurement Performance of Smartphone Platform

The technology of Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) is widely used, which has a relatively broad development space in sea level monitoring, snow depth detection, soil moisture inversion and determination of sea ice thickness. As it matures, GNSS-IR technology is also becoming more popular and low-cost. This study uses the Signal-to-Noise Ratio (SNR) data received by the smartphone Redmi Note 9 Pro 5G and the GNSS receiver Trimble R10 to perform a GNSS-IR test for the inversion effect of the reflection height. The common SNR types are GPS-S1C, GLONASS-S1C and BDS-S2I. Three evaluation indicators evaluate the accuracy of the inversion result of each SNR type: mean (MEAN), median (MEDIAN) and root mean square error (RMSE). It is known from the ground height retrieved by the experiment that both the Redmi Note 9 Pro 5G and Trimble R10 receiver maintain a good monitoring result. After the result of the three satellite navigation system are fused, the ground height retrieved by the Redmi Note 9 Pro 5G is compared with the measured height. And the RMSE is 10.4 cm. The MEAN is 1.646 m, which is only 2.4 cm away from the true value. The MEDIAN is 1.668 m, which is only 0.2 cm away from the true value. This study verifies the applicability and reliability of smartphone SNR data in GNSS-IR ground height inversion, laying a foundation for the low-cost development of GNSS-IR technology in the future.

Naiquan Zheng, Lingqiu Chen, Hongzhou Chai, Tengfei Bai, Xueying Yang
A Method for Evaluating the Performance of Unmanned Aerial Navigation Systems Based on Fuzzy Decision Trees

In the process of application, unmanned aerial vehicles (UAVs) are faced with the threat of a complex electromagnetic environment, causing the airborne navigation system to fail to achieve ideal working conditions, and seriously restricting the overall effectiveness of the UAV system. Therefore, accurate assessment of UAV navigation system performance is an important prerequisite for scientific decision-making on the use of UAVs in complex environments in the future. In system design and experimentation, the more realistic electromagnetic interference environments that UAVs may be exposed to are difficult to build, resulting in insufficient data being collected to verify UAV navigation system performance. However, as real data from UAVs is continuously accumulated in various application scenarios at a later stage, it is necessary to explore a data mining-based method for UAV navigation system performance evaluation. In this study, a decision tree algorithm was used to construct a UAV navigation performance level classification assessment model. UAV performance was analysed through UAV navigation capability and survivability indicators. Finally, simulation experiments were conducted to further develop the construction and testing of the decision tree model. The experimental results showed that the model accuracy is above 90%, validating the feasibility of the method.

Changyuan Chen, Chunlin Shi, Teng Liu, Haojie Li, Qiyang Li, Li Ma
Spatiotemporal Filtering of GNSS Coordinate Time Series Based on Variational Bayesian Independent Component Analysis

Denoising and refining GNSS coordinate time series can significantly increase the application level since they contain rich constructive and non-constructive information and are combined with noise due to observation conditions and other factors. To reduce the influence of common mode errors, we used the variational Bayesian independent component analysis (vbICA) technique to filter the GNSS coordinate time series of 12 stations in the Sichuan and Yunnan areas from 2011 to 2015. The experimental findings reveal that root mean square of coordinate residual series in the N, E, and U directions of the selected 12 stations were decreased by 26.5%, 23.7%, and 39.1% respectively, after vbICA filtering. The station velocities were estimated from the coordinate time series before and after filtering, and velocity uncertainties in the N, E, and U directions were reduced by 40.71%, 41.2%, and 52.34%, respectively. The results show that the vbICA method is effective for filtering coordinate time series. Meanwhile, the vbICA and PCA filtering algorithms are compared, and the former outperforms the latter on average.

Han Gao, Cuilin Kuang
Study on Real-Time Monitoring of Landslide Deformation with RTKLIB

With the continuous advancement of the national comprehensive risk survey of natural disasters, universal GNSS equipment has been widely used in real-time three-dimensional deformation monitoring of geological disasters. In view of the open source RTKLIB software with GNSS data communication, data stream decoding, precision positioning and other functions, this paper takes RTKLIB for landslide real-time precision positioning as the research object, and builds a universal GNSS system architecture for landslide real-time monitoring. The main functions of the system are Conducted a comprehensive study. Combined with Guangxi Chongzuo expansive soil highway slope to conduct comprehensive experimental tests, analysis from GNSS data quality, precision positioning accuracy, system stability and other aspects. The experimental results show that the availability of RTKLIB real-time data stream is 70% under good observation conditions for universal GNSS equipment; the multi-path MP1 value is about 0.3 m; when only GPS satellite systems are used, the fixed solution of real-time positioning is successful The rate can reach 83%, the real-time monitoring accuracy of RTKLIB software in the horizontal direction is better than 10 mm, and the real-time monitoring accuracy in the elevation direction is better than 20 mm. After joining the BDS satellite system, the fixed solution success rate of real-time positioning can be increased to 96%, the accuracy of the horizontal direction is increased to 5 mm, and the accuracy of the elevation direction is increased to within 10 mm. Based on universal GNSS equipment and relying on open source RTKLIB software for upgrade research and development, it can be efficiently used for geological disaster deformation monitoring and early warning.

Xuqiao Wang, Yupei Wang, Shuangcheng Zhang, Yong He, Xinrui Li
Review of the LEO Orbit Determination Using GNSS and Application Prospect in TT&C

For a LEO satellite with an onboard GNSS receiver, the TT&C equipment on the ground can receive dual-frequency GNSS observation data with an arc length of about 12 h of the satellite within about 10 min of the visible arc. At the same time, the international GNSS Monitoring and Assessment System (iGMAS) of China can provide Ultra-rapid orbit and clock offset products of the BDS, GPS, GLONASS and Galileo satellites, and high-precision Earth Orientation Parameters (EOP) in this data arc. Therefore, using these Ultra-rapid products and the dual-frequency GNSS data, we can achieve the precise orbit determination and complete the orbit prediction. Based on this technology, it is possible to reduce the number of laps of satellite tracking by ground equipment, and to achieve precision orbit determination; at the same time, the orbit determination software can realize automatic and autonomous operation.

Chong Wang, Jun Zhu, Yanan Fang, Jie Li
Monitoring of Terrestrial Water Storage Variations and Floods in Sichuan Province Using GNSS and GRACE

Continuous and dense GNSS stations can accurately measure the monsoonal precipitable water (PWV) and vertical crustal displacement caused by the hydrological load on a small scale. The Gravity Recovery and Climate Experiment (GRACE) time-varying gravity field data can accurately and effectively retrieve the changes of medium and long-scale terrestrial water storage variations. Sichuan Province is an important industrial and agricultural production base in China, where meteorological disasters such as drought and flood often occur. Monitoring terrestrial water storage variations can play a significant role in human production activities in the region. To analyze terrestrial water storage variations in Sichuan, GNSS data (PWV and vertical displacement) from 2016 to 2018 are used with the changes of vertical displacement and terrestrial water storage variations of GRACE, the TWS changes of GLDAS and the surface precipitation data. Due to data gaps in the GRACE satellite, GNSS data are combined with GRACE to monitor flood disasters. The results show that the spatial distribution and seasonal characteristics of GNSS-derived mass change time series are consistent with the results of GRACE/GRACE Follow-On satellite observations, especially in the areas with dense GNSS stations. The FPI (Flood Potential Index) calculated by GRACE TWSA (Terrestrial Water Storage Anomaly) can accurately reflect the flood events in Sichuan. Furthermore, there is a strong correlation between GNSS vertical displacement and FPI index. It is verified that the combination can effectively monitor flood events.

Luzhen Wu, Ming ShangGuan, Xu Cheng
Convolutional Neural Network GNSS-R Sea Ice Detection Based on AlexNet Model

Sea ice detection studies is beneficial for surface climate change analysis, global environmental monitoring and ice hazard prevention. The Global Navigation System-Reflectometer (GNSS-R) technology uses Delay Doppler Map (DDM) in relation to surface type to detect sea ice, and existing studies have made good progress. Feature extraction of DDM data is an important basis to ensure the accuracy of sea ice remote sensing. In this paper, we introduce the convolutional neural network algorithm based on the AlexNet model, and use the northern hemisphere DDM data of TDS-1 satellite in February 2018 for sea ice detection to verify the feasibility of the convolutional neural network algorithm based on the AlexNet model. The experimental results show that the accuracy of sea-ice - seawater oriented detection is 97.71% with a correlation coefficient of 0.89 with the surface data of NOAA station. The AlexNet-based convolutional neural network is confirmed to be used for GNSS-R sea ice detection.

Jiang Zhihao, Hu Yuan, Yuan Xintai, Liu Wei
Evaluation of FY-3D Radio Occultation Wet Profiles with Radiosonde Measurements

The meteorological satellite named Fengyun-3D (FY-3D) was launched on November 15th, 2017 (UTC+8). The Global Navigation Satellite System (GNSS) Occultation Sounder (GNOS) is loaded on the FY-3D, which can use the received the GNSS signals including Global Positioning System (GPS) and Chinese Beidou (BDS) to detect the global atmosphere. The combination of FY-3D and FY-3C plays an important role in improving the accuracy of atmospheric detection and enhancing the detection of space environment and meteorological remote sensing capabilities. Radiosonde data from 201 stations around the world are used to evaluate the FY-3D radio occultation (RO) wet profile products (temperature and specific humidity) in 2020. The results show that the bias between the temperature profile of FY-3D and radiosonde is about −0.0073 K, and the mean standard deviation (STD) is 1.84 K at 15 pressure layers. In the range from 925 hPa to 250 hPa, the bias between specific humidity profile of FY-3D and radiosonde is 0.2 g/kg–1.7 g/kg at 7 pressure layers, and the mean STD is about 25%. The results show that the RO wet profile products of FY-3D in 2020 have reached a high precision, the temperature profile is 8% higher than that of FY-3C, and the quality of specific humidity profile is comparable to FY-3C.

Jiaqi Shi, Kefei Zhang, Wenliang Gao, Laga Tong, Minghao Zhang
A Long Short-Term Memory-Based INS Error Modeling Algorithm for GNSS/INS Integrated Navigation in Urban Environments

Without the assistance of GNSS, errors in low-cost INS will spread rapidly resulting in a steady decline in accuracy. Yet, GNSS signals are easily blocked by various obstacles in urban environments. To solve the problem above, this paper proposes an INS error modeling algorithm for GNSS/INS integrated navigation in urban environments based on Long Short-Term Memory (LSTM). The dynamic nonlinear mapping and long-term memory ability of LSTM allows us to make full use of the relationship between past and current navigation information to realize accurate prediction. When sufficient GNSS satellites are observable, the LSTM model is trained with the specific force, angular velocity, position, velocity from the last epoch of INS, combined with the position and velocity from the current epoch of integrated system, so that it can fully learn the rules to compensate for the INS navigation error. Then, when insufficient satellites are observable, the trained LSTM model outputs the corresponding position and velocity to correct the error of INS. The proposed algorithm is verified using the RTK/INS loosely-coupled model, observing GPS and BDS satellites at the same time. When the GNSS are unobservable for 30 s, compared with the pure INS solution, the accuracy of RTK/INS based on LSTM is improved by 69.83%, 78.90% and 80.74% in three different experimental scenarios. This demonstrates a significantly better navigational ability during periods of GNSS outages.

Lei Jiang, Rui Sun
Research on GNSS Deformation Monitoring Based on Multi-baseline Solution

The existing GNSS deformation monitoring systems often adopt the single-baseline solution (SBS) model due to its simplicity and ease of implementation. When monitoring long-span linear objects such as bridges and railways, or large-area land subsidence, multiple reference stations are often used. However, the SBS model neglects the mathematical correlation between baselines, and sometimes the accuracy and reliability can be limited due to long baseline length and satellite occlusion. This paper proposes to use the multi-baseline solution (MBS) model to solve the deformation monitoring network. Based on real monitoring datasets, the accuracy of MBS model and SBS model were compared. The experimental results show that, compared with SBS, MBS can improve the ambiguity fixing rate and the coordinate accuracy by up to 22.7% and 27.8% respectively.

Haonan Wang, Wujiao Dai, Wenkun Yu
Analysis of Precipitable Water Vapor Change Based on GNSS Observations During Typhoon Mangkhut Event

Typhoon is a kind of natural disaster that often happens in coastal cities in summer, which endangers people's life and property safety. Typhoons often carry a large amount of precipitable water vapor, precipitable water vapor distribution and dynamic change during the typhoon transit process is of great significance for the monitoring and forecast of typhoon. Compared with the traditional use of sounding balloon observation water vapor, PWV (Precipitable Water Vapor) retrieval using ground-based Global Navigation Satellite System (GNSS) has the advantages of high temporal and spatial resolution and near real time. Therefore, this paper inversed the PWV based on GNSS observation data in Guangxi, verified the reliability of GNSS inversion PWV by using the PWV observed by high-precision sounding station, and finally analyzed the dynamic changes of water vapor in Guangxi during the passing of Typhoon Mangkhut in combination with ERA5 reanalysis data. The results showed that: (1) GNSS-PWV has good consistency with the measured data of sounding station, which can be used to monitor the change of precipitable water vapor in extreme weather. (2) GNSS-PWV and ERA5 PWV can directly and clearly reflect the dynamic transport process of precipitable water vapor in time and space during typhoons, providing reference for predicting the movement, intensity and precipitation of typhoons.

Zhedong Liu, Tengxu Zhang, Junyu Li, Jiao Xu, Liangke Huang, Lv Zhou, Lilong Liu
A Novel Method Corrected Multipath Error Oriented the Oceanic Buoy

The signals always form the reflection over the sea. The characteristics and correct method of the multipath over the sea are worthy of research. Based on the assumption that the high-precision posterior residual only contains multipath error and noise, this paper adopts forward and backward filtering estimation and PPP-AR strategy to obtain the high-precision observational post-residual and then calculates the multipath error effect based on the mean denoising method. The azimuth and elevation angle mapping relationship of the azimuth angle and elevation angle are constructed, the station center multipath hemispherical map (MHM) is constructed, and the different grid resolutions of MHM are experimentally studied. The experimental results show that the MHM model can effectively improve the positioning effect of the marine buoy rather than no multipath correction. Not only the positioning accuracy can be improved, but the ambiguity fixed-rate and convergence time of positioning can also be improved, especially the 2° × 2° resolution of the MHM model has good results in both static and dynamic scenarios.

Xiangyu Tian, Hongzhou Chai, Min Wang, Qiankun Zhang, Tengfei Bai
Processing and Analysis of Multi-antenna GNSS/INS Fully Combined Model

Attitude measurement provides important decision information for navigation and positioning of moving vehicles. At present, the single-antenna GNSS/INS system has a limitation in performance and cost. This paper proposes to obtain the high-precision absolute attitude information of the moving carrier in real-time through the fusion of multi-antenna GNSS and INS. Since GNSS navigation is greatly affected by the external observation environment, it reduces the navigation and positioning results in the full combination mode. In this paper, the method of constructing the adaptive measurement noise model is presented by using the PDOP value of GNSS observation information and whether the ambiguity is fixed. The position, velocity and attitude of the moving carrier were obtained by the multi-antenna GNSS/INS adaptive Kalman filtering algorithm model. The results show that the position accuracy of GNSS/INS is 0.067 m, 0.044 m and 0.058 m, respectively. The speed-accuracy is 0.007 m/s, 0.006 m/s and 0.006 m/s respectively. The attitude accuracy is 0.011°, 0.015° and 0.085°. Experimental results show that multi-antenna GNSS/INS can realize high-precision and highly reliable positioning, velocity measurement and attitude measurement services of the carrier.

Liangliang Hu, Jin Wang, Shengli Wang, Haonan Cui
A Centimeter-Level Continuous Measurement Method After the Differential Data of RTK Interruption

Aiming at the problem that the positioning accuracy of the rover station will decrease rapidly with the increase of the differential period when the differential data is interrupted in RTK measurement technology, and the centimeter-level position service cannot be provided. A continuation method of breakpoint based on single station is proposed. When the differential data of the rover is interrupted, the data of the rover will be processed through the double-difference model between epochs and satellites based on the broadcast ephemeris. In order to calculate the high-precision time baseline and then get the centimeter-level position of the rover station, the ionospheric error, tropospheric error, satellite clock error and orbit error are all corrected or estimated. In this paper, the method is verified by the static data and dynamic data. The experimental result shows that the positioning accuracy at plane can maintain at centimeter level within 10 min, which can effectively improve the reliability and continuity of RTK results in the scenarios of unstable differential data.

Qi Yu, Hongyu Shan, Guofu Pan, Yanhui Li, Zhongrong Yang
GNSS for Train Localization Trajectory Generation Featuring Depth-First-Search Method

Global Navigation Satellite Systems (GNSS) for train localization does not rely on trackside equipment, which realizes “trainborne centric” positioning using onboard localization sensors. It is one of the important methods for the future train operation & control system as an advancement for train localization. European Next Generation of Train Control (NGTC) and Chinese Dynamic Spacing Train operation & control system (DTCS) all apply GNSS and Digital Track Map (DTM) together for train localization. Before field test of the train localization, it is necessary to establish a GNSS test environment, generate train trajectories, carry out important research contents of laboratory simulation testing of train operation & control system functions and performance in-lab-test. Based on the DTM, this paper generates a topology model includes point of interests (POIs) and track pieces relationships. Considering train operation safety constrains and track constrains, using the depth-first-search (DFS) and dual-stack data structure, all possible paths from origin and destination (OD) are generated as a path candidate set, the consistency of safe route in the path candidate set is performed, and the safe and available path is validated. Then the path geographical information is generated using DTM. The Haergai-Muli Railway in Qinghai is used in this paper to investigate the method, 6 planned trajectories are generated. The generated trajectory is verified by GNSS simulator, and the 95th quantile error between the received data and the original data is 0.62 m, which meets the DTCS accuracy requirement.

Jiahao Lu, Jie Lu, Debiao Lu, Baigen Cai, Wenbiao Zhang
Increasing Trend of Precipitable Water Vapor in Antarctica and Greenland

Polar precipitable water vapor (PWV) is expected to increase under a warming climate. However, the conventional approach cannot provide sufficient long-term PWV records due to the high maintenance costs. Fortunately, the exponential explosion in the number of geodetic-quality Global Navigation Satellite System (GNSS) stations has broken this deadlock. Utilizing radiosonde and GNSS data over two decades (1994–2020), we analyzed and evaluated the spatial and temporal variability characteristics of PWV in Antarctica and Greenland. The multi-year mean PWV values for Antarctica and Greenland were 5.63 ± 1.67 mms and 7.63 ± 1.35 mms, respectively, with annual standard deviations (STD) of PWV of 1.60 ± 0.77 mms and 3.44 ± 0.92 mms, respectively. In both Antarctica and Greenland, the PWV annual STD shows a gradual increase from the land center to the edge; while the PWV mean decreases with increasing latitude in Greenland, there is no significant latitudinal correlation in Antarctica. There is no significant regional difference in PWV trends, and from the statistical results, both Antarctica and Greenland show an increasing trend from year to year. The PWV trends in Antarctica and Greenland were 0.29 ± 0.77 mm/decade and 0.27 ± 0.64 mm/decade, respectively, with relative PWV trends of 5.98 ± 12.93%/decade and 3.87 ± 8.45%/decade, respectively.

Junsheng Ding, Junping Chen, Wenjie Tang
An Adaptive Networking Solution Strategy Based on Real-Time Relative Positioning of Linkage Targets

Aiming at the problem of unstable formation status due to communication delays or other factors during the operation of multiple moving target formations. This paper proposes an adaptive network solution strategy based on real-time relative positioning of linked targets. The target role is dynamically generated through the formation autonomous space state confirmation technology, and the corresponding tasks are performed. The formation’s anti-destroy ability is improved. At the same time, the time baseline processing scheme is adopted. To ensure that the system can not only work normally when the data is delayed and temporarily interrupted, but also can ensure the accuracy of the benchmark. Finally, dynamic experiments show that the adaptive network solution strategy based on real-time relative positioning of linked targets is reliable and effective in practical applications, and can reach centimeter-level positioning accuracy.

Cunting Chen, Dangwei Wang, Dongdong An, Qi Zhang

GNSS Applications for the Mass Market

Frontmatter
Research on Development and Analysis of Miniaturized Antenna for GNSS High-Precision Applications

As an essential base component, the high-precision antenna has an important impact on the quality of the signal. The performance of high-precision antenna is a key factor in determining the performance indicators of satellite navigation terminals. This article proposed small-scalarized antennas for high-precision applications. Toward the flat antenna and cylindrical antenna, the study on the miniaturization of multi-band active circuits is introduced. It solved contradictions between multi-band combination and antenna size miniaturization. Through simulation and analysis, we found a composite radiator is formed by adding the coupling ring around the double layer 3D microstrip antenna. And the stereo radiator is formed, with the coupling ring around the top microstrip antenna linked with the patch surface of the underlying 3D microstrip antenna. Those can effectively broaden the antenna gain of 3 dB beam width (GBW), and axial ratio of 3 dB beam width (ARBW), with increasing the low elevation gain. Accordingly, those antennas can provide good gain properties under smaller dimensions.

Ji Guo, Tian Wang, Weiguang Gao, Xia Chen, Shanbin Shi, Kai Wang
Design and Realization of a Fusion Application Based on Beidou and National Encryption Algorithm

In this paper, a data security application based on the fusion of Beidou and National encryption algorithm in the Beidou intelligent terminal is proposed. It can well solve the information security problem of the Beidou industry terminal in the public wireless network. In order to realize the safe local storage and network transmission of Beidou data, the method of hardware and software realization are proposed, that is, through hardware encryption, plaintext data such as the Beidou location data and terminal video data are encrypted into ciphertext, which is transmitted to the background from the public wireless network, and the plaintext is obtained after decryption. The purpose of this design is to ensure the transmission security of related sensitive data based on the Beidou in public wireless networks, and to provide a solution of Beidou-based the data encryption storage and transmission for industrial applications with special requirements. On the data source, the terminal calls the national encryption algorithm in the encryption chip to encrypt the data. On the background, the instruction control of the Beidou intelligent terminal is carried out by sending encrypted signaling. The research conclusion shows that the multi-channel data encryption storage and transmission based on the hardware national encryption algorithm of the Beidou application can well solve the information security problem of the Beidou industry terminal in the field of data transmission.

Lei Xing, Linna Zhao, Xiaowang Sun, Yi Zhang, Xuefeng Zhang
Algorithm and Application of the Iterative Running Mean Filter on the Pseudo-Range Differential Positioning Based on the Smartphone GNSS Observations

The significant improvement of the performance of the modules of GNSS inside the smartphones, giving a great promotion of precise applications at the mass market. Considering the instability of GNSS carrier phase from the smart phones in urban environment, the pseudo-range is still the main source of the GNSS positioning when the carrier phase is greatly disturbed. Therefore, it is of great practical significance to improve the accuracy and reliability of pseudo range positioning, particularly the pseudo-range differential positioning. Aiming at solving the problem that the pseudo-range differential positioning accuracy of smart phone is not enough for the precise navigation and positioning, we give a method of the iterative running mean filter algorithm. The precision and effectiveness of the proposed method were assessed through a practical test, and the test result show that the precision of the iterative running mean filter pseudo-range differential is equivalent to that of the carrier differential, which is at the sub-meter level. The algorithm has a simple structure that can be implemented easily, and the obvious precision improvement can be witnessed at the application of the double differential pseudo-range positioning. Hence, this method has great potential at the precise navigation and positioning application in the urban canyon in the case of great disturbance of the GNSS carrier observations.

Wenlin Yan, Fangfang Chen, Xingchi Pan
Realization and Performance Assessment of Uncombined Multi-GNSS PPP-RTK for Expressway Scenarios

Network Real-time Kinematic (NRTK) technology performs the error corrections in the Observation Space Representation (OSR) format, thereby being regardless of the temporal characteristics of various errors, and increasing transmission rate of corrections, while PPP usually requires a long initial convergence time, which restricts real-time mass-market applications. As a result, a new method, namely PPP-RTK, that combines the advantages of the two technologies began to develop. The current PPP-RTK technology mostly uses the “wide-lane/narrow-lane” method to achieve undifferenced ambiguity resolution, however, it is easy to amplify observation noise and is not easy to extend to multi-frequency observation. To this end, this paper derives the theoretical feasibility of PPP-RTK ambiguity resolution based on the original frequency observation, and conducts GPS/Galileo/BDS PPP-RTK tests in the scene of the intercity expressway from Hangzhou to Shanghai. Taking Multi-GNSS NRTK fixed solutions as the true coordinates, the results show that the correct fixing rate of Multi-GNSS PPP-RTK is better than 90%, the positioning accuracy in horizontal and vertical direction are better than 3cm and 5cm, respectively, and the probability of reconvergence time less than 10s is over than 95%, which can basically meet the requirements of mass-market applications such as automotive driving and drones.

Xiao Yin, Hongzhou Chai, Liang Zhao, Yize Zhang
Magnetic Matching/PDR Combined Positioning Method Under the Constraint of Error Ellipse

This paper studies the fusion positioning method of the combination of magnetic matching/pedestrian dead reckoning (PDR) based on the smartphone. The magnetic matching is referred to the Weighted K-Nearest Neighbor (WKNN) to estimate the position. The PDR estimated position is used to constrain the magnetic fingerprint database in the circular domain, which does not fully utilize the candidate points’ position information in the WKNN algorithm. This paper takes advantages of the candidate points on the basis of the circular domain constraint to construct an error ellipse for additional constraint, obtaining a magnetic fingerprint sub-library for reducing the dimensions of fingerprint library and improving the positioning accuracy. The fingerprint database was established through Redmi K30, while Redmi K30, Xiaomi 8 and Huawei mate40 were used for experiments in positioning stage. The experimental results show that the proposed fusion method has higher positioning accuracy. The average positioning errors are reduced from 0.64 m, 0.64 m, and 0.75 m to 0.51 m, 0.53 m, and 0.48 m, respectively, and the accuracy is improved by 20.3%, 17.2%, and 36.0%.

Kefan Shao, Zengke Li, Zhaoyuan Wang, Zhenbin Liu, Qiang Guo
Analysis on the PPP Performance of Android Smart-Phone: A Case Study of Huawei P40 Pro

With the development of mass market, the demand for high-precision and high-stability navigation and positioning functions of Android smart phones is increasing. However, compared with the traditional receiver, the positioning accuracy of the mobile phone is seriously degraded caused by low gain and weak mulitpath suppression ability. Many scholars have analyzed the signal quality of mobile phones and improved the stochastic model algorithm, which are mainly based on certain types of mobile phones such as xiaomi 8 and huawei mate 20. In view of the fast iterative development of mobile phones, as well as different GNSS chips have different positioning performance, here we analyze Huawei’s new mobile phone P40 pro to test its position accuracy. We conduct two sets of static and dynamic experiments to verify the positioning performance for the mobile phone. The results show that it takes about 5 min for the static PPP (Precise Point Position) error to converge to 2 m, and 15 min to converge to 1 m. The RMS (Root Mean Square) of position bias in the E, N and U directions are 0.25, 0.10 and 0.57 m, respectively. Compared with the results of SPP (Single Point Position), the accuracy of PPP results is improved in three directions.

Shili Yang, Yan Xu, Tianhe Xu, Nan Jiang
Research on PPP/INS Algorithm Based on Sequential Sage-Husa Adaptive Filtering

In the complex urban environment, the satellite navigation signal is polluted by gross errors due to external factors such as signal reflection, signal occlusion, signal electromagnetic. These factions cause the error of the satellite prior measurement noise random model based on satellite elevation angle in PPP/INS tight integrated navigation. In the traditional gross error detection method, the improper setting of the empirical threshold causes the traditional gross error detection algorithm to be insensitive to the small gross error of the measured value, which reduces the accuracy of the tight integrated navigation solution. In this paper, the sequential Sage-Husa adaptive filtering algorithm, combined with the upper and lower bounds of the measurement noise variance technology, effectively improves the non-positive definite problem of the measurement noise matrix, and guarantees the stability of the adaptive filtering algorithm. The algorithm estimates the filter adaptive factor in real time based on the measurement residual, and combining with the random model of satellite elevation angle, and the satellite elevation angle random model deviation caused by small pseudo range gross error is corrected in real time through the adaptive factor. Finally, the experiments show that when there are small gross errors in pseudo range observations, this algorithm is 2.7% higher than that of the traditional satellite elevation angle random model, the position accuracy is increased by 2.8%, 32.2%, 41.2%. Effectively improve the accuracy of the PPP/INS tight integrated navigation system in the complex urban environment.

Haoran Song, Sixiang Cheng, Zhaoxin Xu, Nan Zang
Instantaneous Centimeter-Level PPP-RTK Positioning Technology Based on Low-Cost Mass Market GNSS Devices

PPP-RTK technology is gradually mature and widely used in intelligent driving, intelligent agriculture, mobile inspection, and other fields in recent years. Usually, to acquire accurate position, users must spend tens of thousands of Yuan to buy professional receiver and antenna. In contrast, the low-cost equipment is cheap but the acquired GNSS measurements from it often suffer from low signal-to-noise, high level multipath et al. When users use it to for positioning, it usually takes much time to converge to centimeter level. In this paper, we use two low-grade mass-market devices and one cheap double frequency antenna to conduct PPP-RTK experiments. During the tests, the Qianxun SI self-developed multi-GNSS SSR correction service is also used to accelerate the convergence. The result shows that it only takes several seconds to fixed for first time. Once fixed, the PPP-RTK can achieve and maintain centimeter level. It is proved that it is possible for users to acquire instantaneous centimeter-level positioning based on mass-market devices.

Jinpei Chen, Jun Wang, Denghui Wang, Wen Zhao, Hua Chang, Shaojun Feng
Research on Adaptive SSA for GNSS Landslide Multipath Effect Elimination

With Global Navigation Satellite System (GNSS), landslide monitoring often uses the short baseline relative positioning mode and its monitoring sequence is mainly affected by measurement noise and multipath effects. In the real-time landslide monitoring, its results are subject to problems such as ambient environment and high cost. And multipath effect in the time series of the monitoring results will be more noticeable. In order to effectively eliminate the multipath errors in landslide monitoring results and improve the accuracy of monitoring results, this paper proposes a new idea of adaptive SSA extracting multipath errors with weighted fusion algorithm. In this regard, firstly, gross errors caused by the multipath effect will be estimated and retained considering the position. Then, extracting the multipath errors of the first three days with adaptive SSA, and analyzing its time series of the first three days to obtain the multipath error correction model, which is used for real-time correction of the time series. Through comparative analysis with traditional sidereal filtering algorithm, the results show that adaptive SSA and weighted fusion algorithm can effectively identify gross errors caused by multipath effect and obtain more accurate multipath error correction models, and improve the accuracy of real-time GNSS landslide monitoring.

Xinrui Li, Chuhan Zhong, Shuangcheng Zhang, Wanlin Liu, Xin Zhou, Xuqiao Wang
Neural Network-Based GNSS Localization Error Estimation Method

With the development of the Global Navigation Satellite Systems (GNSS), GNSS-based localization techniques have become the vital source of location for many fundamental applications. However, GNSS localization performance can be affected by the environment on the propagation trajectory, which leads to varying degrees of accuracy degradation. The GNSS localization errors can vary from centimeters to meters level in different environments, an accurate position error estimation model is of great significance, which provides basic information for error correction. GNSS receivers work obeying the same principle, with differences in location algorithms. In this paper, parameters such as SNR (signal noise ratio), elevation angle, azimuth, and HDOP are extracted as the observed quantities, and the relationship between the total localization error and the observed quantities is studied using neural networks and localization data in different environmental scenarios. The localization error model is then validated using field collected data, and the mean square error of the loss function and the goodness-of-fit values illustrate that the training effect of the Long short-term memory (LSTM) network is better than that of deep neural network (DNN), and the generalizability of DNN model parameters is better than that of LSTM, both of which can be used to improve the accuracy of static localization and the smoothness of dynamic localization paths.

Xinyi Li, Baigen Cai, Debiao Lu, Jiang Liu
Smartphone Heading Correction Method Based on LSTM Neural Network

The error of heading estimation is the main factor that affects the accuracy of the navigation and positioning of the smartphone based on the pedestrian dead reckoning. In this paper, aiming at the heading error caused by gyroscope drift in smartphone pedestrian heading estimation, a smartphone heading error compensation model based on Long Short-Term Memory network (LSTM) is proposed. Due to the low precision of inertial devices in smartphones, the direct integration will lead to cumulative errors that the neural network can correct. Considering that the calculation method of inertial navigation is dead reckoning, the data of the preceding and following moments is related. And LSTM performs better in the long sequence than the ordinary neural network, so this paper uses a motion capture system to get high-precision attitude information. The information is used as true value to establish the heading error correction model of smartphones. By comparing the proposed algorithm with traditional quaternion heading estimation method, the error correction model presented in this paper can effectively suppress the influence of gyroscope drift. The result is better, which can meet the basic needs of pedestrian navigation and positioning.

Yan Huang, Qinghua Zeng, Qiyao Lei, Zhijun Chen, Kecheng Sun
A GNSS Quality Control Based GNSS/IMU Integrated Navigation Algorithm in Urban Environments

Global Navigation Satellite Systems (GNSS) and Inertial Measurement Units (IMU) are often integrated to provide an essential Positioning, Navigation and Timing (PNT) solution for vehicles. Nevertheless, the accuracy and reliability of this PNT solution are degraded greatly in complex urban environments due to the deterioration of GNSS measurement quality. To deal with this issue, we here propose a two-stage GNSS quality control algorithm for integrated GNSS/IMU systems. In stage one, a novel Fault Detection and Exclusion (FDE) scheme is applied at each epoch to calculate fault detection statistics based on two datasets: 1) the universal set of the pseudorange and 2) the subsets of the observed pseudorange based on the single-fault hypothesis. In stage two, an adaptive Kalman filter is applied to the GNSS/IMU integration with the parameters in the measurement noise covariance matrix optimized according to the changes in the satellite elevation angle. In addition, the Non-Holonomic Constraint (NHC) is applied to suppress the accumulation of positioning errors. Field test results show that the proposed algorithm can improve the horizontal and 3D positioning accuracy by 32.39% and 31.68%, respectively. It can also improve the accuracy of the velocity and heading angle by more than 25% compared to the traditional GNSS/IMU integrated algorithm.

Hanzhi Chen, Rui Sun
A Smartphone RTK Algorithm Based on Velocity Constraint

Aiming at the problem of low accuracy and stability of smartphone RTK positioning results, this paper proposes a smartphone RTK algorithm based on velocity constraint. The double difference of time-difference carrier phase (DD-TDCP) is used to constrain the vehicle velocity to improve the accuracy of state prediction. Moreover, we also use Huber-based Kalman filter to improve the accuracy and stability of the positioning. Experiments show that, compared with the original solution without velocity constraints, the solution accuracy of the proposed algorithm is centimeter-level in ambiguity-fix state in the static test, and the fix rate is 28.7% higher than the original solution, with a faster convergence speed. In the driving test, the accuracy of our solution is 23.9% better than the original solution and is more robust. On an open-sky road, the absolute normal error CEP95 is within 1.2 m, and in better conditions, the CEP90 is within 0.5 m.

Qiang Zhang, Zhengdong Bai, Haohao Xin, Yilong Yuan

GNSS User Terminals

Frontmatter
Multipurpose Satellite Navigation Receiver with Three Antennas Amplitude Comparison DF Based on Baseband Information Fusion

The traditional satellite navigation receiver with multi antennas forming long baselines is based on carrier phase difference measurement for DF (Direction Finding). It has many problems, such as cumbersome baseline calibration, complex phase ambiguity removing algorithm and high application cost. A new satellite navigation receiver with three antennas amplitude comparison DF based on baseband information fusion is designed in this paper. Its working principle, parameter optimization, and solution to DF are described in detail. Through associated baseband information, the parameters guidance for each channel to receive the navigation signal is realized for rapid acquisition and tracking. DF is completed by measuring the carrier to noise power ratio of signals from different antennas for the same navigation satellite. Finally, a prototype system is developed by using the commercial satellite navigation receiving antennas, and experiments are carried out for the actual navigation signals to verify the effectiveness of the design. This kind of receiver not only has many uses, such as attitude measurement, DF for navigation signals, and anti-deception based on DF information, but also shows many advantages, such as high antenna integration, small installation spaces, convenient use and high performance. So it will have wide application in the future.

Rong Shi, Junhao Chen, Da Ma
Characteristic Analysis on Anti-jamming Degrees of Freedom of GNSS Array Receiver

Facing the increasingly complex electromagnetic environment, the anti-jamming ability of navigation receiver can be improved by space-time-frequency domain filtering. The ability of space-time adaptive filter (STAF) and space-frequency adaptive filter (SFAF) anti-jamming receiver to suppress how much number of interferences is related not only to the number of array elements, but also to the characteristics of interference signals. In this paper, the anti-jamming degree of freedom characteristics of STAF/SFAF are obtained through theoretical derivation and numerical analysis. The relationship between spatial anti-jamming degree of freedom of array receiver and the characteristics of jamming signal bandwidth and central frequency point is fully elucidated and the quantitative expressions under different scenes are given.

Jie Wang, Gang Ou, Wenxiang Liu, Feiqiang Chen
Reconfigurable Quad-Channel GNSS RF Receiver for High-Precision Positioning and Orientation

To offer services in the safety-critical application, such as the advanced driving assistance system and unmanned aerial vehicle (UAV) navigation, the navigation systems require more precise and reliable receivers, which are large-size and high-cost in the traditional solution due to multi-chip RF receivers. A highly integrated quad-channel global navigation satellite system (GNSS) RF receiver is proposed in this paper, which can be configured to receive all-band GNSS signals and L-band satellite-based augmentation system (SBAS) for high-precision positioning. The single-chip quad-channel receiver can also be configured to receive L5 + L1/L2 signals for high precision double antenna orientation, which will dramatically reduce the size and cost. Measurement results show that the proposed RF receiver achieves a noise figure (NF) of 2.7–3.2 dB, an output-referred 3rd order intercept point (OIP3) of +34.7 dBm and a programmable filter bandwidth of 0.8–80 MHz, with RF frequency covering from 1.15 GHz to 1.65 GHz for all-band GNSS signals. Due to IQ mismatch compensation and layout improvement, an image rejection ration (IRR) of 58.1 dB and a channel isolation of 57 dB is achieved.

Riyan Wang, Bin Li, Fangfang Zhang, Heng Peng, Zhijian Chen, Hongyin He, Kunming Yang, Shiguang Zhong, Jiawen Liu
Performance Analysis of Real-Time Precise Point Positioning Based on PPP-B2b Signal

China’s Beidou global navigation satellite system (BDS-3) can provide real-time precise point positioning (PPP) service for users in China and surrounding areas with PPP-B2b signal. In order to evaluate the service performance, most of the existing studies store real-time PPP-B2b messages and then recover them to precise satellite orbits and clock offsets, but do not consider the receiving delay in a real-time scene. Therefore, this paper restores the precise product of the corresponding observation epoch in real time. The delay characteristics of PPP-B2b corrections and its impact on PPP positioning are analyzed in detail, and a random model compensation scheme based on delay is proposed. Results show that the orbit recovered accuracy is better than 7.5, 34.2 and 37.2 cm in directions of radial(R), along(A) and cross(C) for MEO (Medium Earth Orbit) satellites, and the standard deviation value of the clock offset errors is better than 7.3 cm. The clock offset whose delay exceeds the official validity period accounts for more than 17%, which can easily lead to point hopping in the positioning results. The random model optimization scheme in this paper can effectively solve the point hopping problem. In terms of static positioning performance, the horizontal accuracy of BDS and BDS/GPS combination is better than 2 cm, the vertical accuracy is better than 4 cm, and the convergence time of dual systems is less than 11 min. In terms of dynamic positioning performance, the horizontal and vertical accuracy of BDS are better than 23 and 26 cm respectively, and the convergence time is about 60 min; The above indexes of dual-systems are 17 cm, 20 cm and 17 min respectively.

Zhihao Yu, Guofu Pan, Xiang Zuo, Yihao Tang
Lightweight Miniaturized Terminal Based on High Precision GNSS Module

To overcome the disadvantages of complex structure design, high power consumption, huge volume and prominent cost of traditional high-precision GNSS terminals, a dual band multi-system GNSS terminal based on high precision GNSS module is proposed in this study. The terminal adopts low profile, broadband quadrifilar helix antenna (QHA) and centimeter level RTK navigation and positioning module, combined with dual channel low-noise amplifier circuit and laminated shielding structure. Peak gain of the QHA in the whole working frequency band is greater than 0 dBi with the axis ratio less than 1.1 dB, and the maximum gain is greater than 2.5 dBi, which shows excellent circularly polarized radiation and broadband working characteristics. In the open test scenario, the effectiveness of capturing satellite and RTK performance are analyzed. The carrier-to-noise density ratio (C/N0) of multiple Galileo and Beidou satellites is close to or even greater than 50 dB-Hz. The static RTK positioning results show that the horizontal and elevation accuracy of internal coincidence is 0.84 cm and 1.24 cm, respectively. Finally, the sensitivity, single point positioning and velocity accuracy are quantified in the wireless simulation test system. Research results indicate that the terminal not only has the excellent characteristics of small volume, light weight, low power consumption and high portability, but also can achieve centimeter positioning accuracy. It’s especially suitable for the requirements of small bearing platforms, such as Unmanned Aerial Vehicle (UAV), hand-held and piggyback operation and other application scenarios.

Guanjun Wang, Liang Zhu, Chao Lu, Yayun Xie
Weak Signal Processing Technology Based on Long-Term Correlation and Autonomous Navigation Application of BDS

The service area of BDS navigation system is designed generally in the near-Earth space, which is below the orbit of 1500 km. However, with the development of deep space exploration and other tasks, the positioning requirements of GEO and above orbit satellites or space crafts are increasingly strong. Therefore, it is necessary to analyze and evaluate the position service ability of BDS in high orbit. In this paper, the broadcast signal strength of BDS-3 navigation system satellites is evaluated by using satellite resources already in orbit. In view of the continuous positioning demand of GEO satellite, the simulation verification is carried out, and the sensitivity demand of high-orbit receiver is decomposed. In order to solve the problem of high-sensitivity navigation and positioning reception, long-term correlation (integration time greater than 1 s) technology is used, and orbit-based information assistance technology is used. The sensitivity can reach over −152 dBm under limited embedded computing resources. Compared with traditional processing methods, the sensitivity is improved by more than 9 dB. The GEO orbit operation environment simulation is built through the signal simulator. The high-sensitivity acquisition and tracking technology can improve the coverage rate of BDS positioning in GEO orbit by 30%. Through the orbit dynamics orbit determination method, the positioning accuracy is better than 50 m, which meets the needs of satellite measurement and control.

Qijia Dong, Qi Ren, Kun Liu, Zhiqin Xue
Jamming Test Scenario Design for Satellite-Based Train Positioning in Railway Signaling Systems

The implementation of satellite positioning technology in determining the train speed and location has been an important choice to promote the autonomous and intelligent development of new generation railway signaling systems. The vulnerability of satellite positioning makes its positioning performance susceptible to GNSS (Global Satellite Navigation System) jamming signals, which may fail in satisfying the safety requirement of the railway signaling system. Scenario-based GNSS jamming test is an effective approach to evaluate and verify the availability and safety of GNSS-based train positioning. Considering test costs and test coverage requirements of the test scenarios, this paper presents a scenario generation method for jamming test dedicated to the GNSS-based train positioning. The key factors of the test scenarios are analyzed and the AHP (Analytic Hierarchy Process) algorithm is involved to realize the hierarchy division and determine the factor importance. A test case generation algorithm is designed based on the combinatorial testing tool. A continuous test scenario generation framework is established, with which discrete test case clustering is carried out according to the importance of key factors. A specific jamming test platform for GNSS-based train positioning is built, and typical jamming scenarios are adopted for test and verification. The results demonstrate that the proposed solution improves the coverage of the scenarios with a reduced cost level for test operations. It enables the “zero-on-site test” for novel GNSS-based railway signaling systems.

Kang-zhi Xu, Jiang Liu, Bai-gen Cai, Jian Wang, De-biao Lu
Fault Detection Method of Tightly Coupled GNSS/INS Integration Assisted by LSTM

Aiming at the problem that the traditional fault detection method of tightly coupled GNSS/INS integration is not efficient for small-amplitude faults and gradual faults, a dual-threshold fault detection method based on long-short term memory neural network is proposed. This method establishes GNSS pseudo-range and pseudo-range rate prediction models through a long-short term memory neural network, sets the lower detection threshold based on the accuracy of the prediction model and the residual distribution characteristics, and assists the residual chi-square detection method for fault detection and isolation. The actual measurement data is used for simulation verification from the perspectives of fault detection performance and positioning accuracy. The results show that the proposed method retains the excellent detection performance of the residual detection method for large-amplitude faults, and has better detection sensitivity for small-amplitude faults and gradual faults, which can improve the positioning accuracy and fault detection performance of the system effectively.

Zihan Shen, Xiubin Zhao, Chunlei Pang, Liang Zhang, Lijian Ren, Haowei Chang
A Navigation Interference Detection and Orientation Technology Based on GNSS Handheld Terminal

The electromagnetic interference faced by modern GNSS terminals is becoming more and more severe. In most cases, there is a lack of professional interference detection equipment to accompany interference, which brings inconvenience to users. Adding navigation interference detection and orientation capabilities to GNSS handheld terminals is of great significance for enhancing the user's ability to perceive interference and improving the efficiency of interference investigation. Based on the comparison and analysis of commonly used interference signal detection and orientation technologies, this paper proposes an interference energy detection technology and a comprehensive orientation technology suitable for GNSS handheld terminals. The software and hardware implementation principles of the verification prototype are given. Performance tests were carried out in the anechoic chamber and outdoor environment. The test results show that the prototype can detect continuous wave, FM wideband/narrowband and AM narrowband interference signals with an power of −110 dBm~−60 dBm. The detection success rate achieves 100%, and the interference power measurement accuracy can reach 3 dB. The interference orientation error is lower than 15°. The results of this paper can be used to guide GNSS handheld terminals to improve their ability to perceive interference.

Linfeng Zhang, Bin Tang, Chong Zheng, Xianning Chen, Linfeng Xu
Research on Robust Location Method of Opportunistic Signal Network Under Information Entropy Constraint

In the GNSS denial environment, the radio frequency wireless opportunistic signal network positioning system becomes a backup method for GNSS. However, in urban canyons and other complex environments, NLOS errors such as building occlusion and multipath seriously affect the positioning accuracy. This paper aims at solving the problems of high complexity and strict prior knowledge requirements for robust positioning in a mixed environment of NLOS and LOS. This paper combines information entropy and the least squares algorithm to reduce the requirements for prior information and transforms the least square problem into a generalized trust region optimization problem to reduce the complexity, and realizes the robust positioning capability of the RF opportunistic signal network in the mixed environment of NLOS and LOS. The proposed algorithm transforms the least squares problem into a generalized trust region sub-problem, and obtains the global optimal value of the non-convex function. The complexity of this algorithm is lower than that of the convex optimization. Meanwhile, the information entropy constraint is introduced to change the weight of the traditional iteration. This algorithm realizes the accurate weight distribution without prior statistical information. In an area of 5000 × 5000 square meters (the number of anchor points is 10), when the probability of NLOS is accurately estimated (the probability of NLOS is 40%), the simulation results show that the positioning error is less than 400 m, and when the probability of NLOS is estimated very conservatively (50%), the positioning error is still significantly better than other algorithms, indicating that the proposed algorithm has strong fault tolerance to prior knowledge. The experimental results prove that the algorithm in this paper has better robust positioning accuracy for NLOS and LOS mixed environments, improves the feasibility of engineering implementation of robust positioning technology, and has good real-world application scenarios.

Zhiang Bian, Hu Lu
Backmatter
Metadata
Title
China Satellite Navigation Conference (CSNC 2022) Proceedings
Editors
Prof. Changfeng Yang
Prof. Jun Xie
Copyright Year
2022
Publisher
Springer Nature Singapore
Electronic ISBN
978-981-19-2588-7
Print ISBN
978-981-19-2587-0
DOI
https://doi.org/10.1007/978-981-19-2588-7