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2022 | Book

# China Satellite Navigation Conference (CSNC 2022) Proceedings

## Volume II

Editors: Prof. Changfeng Yang, Prof. Jun Xie

Publisher: Springer Nature Singapore

Book Series: Lecture Notes in Electrical Engineering

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China Satellite Navigation Conference (CSNC 2022) Proceedings presents selected research papers from CSNC 2022 held during 22nd-25th 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.

#### GNSS and Their Augmentations

##### Satellite-Ground Link Planning Method for LEO Satellite Navigation Augmentation Network in the Case of Multiple Ground Stations

Aiming at satellite-ground link planning problem for LEO satellite navigation augmentation network in the case of multiple ground stations, we proposes a planning method based on graph theory. First, according to the boundary assumption and essential analysis of satellite-ground link planning problem for LEO satellite navigation augmentation network in the case of multiple ground stations, we establishes a corresponding mathematical model. Then, based on the need to quickly solve the approximate optimal solution of the above model, a graph theory-based satellite-ground link planning method is proposed, and the performance of the solution result of this method is theoretically proved. Finally, the simulation results verify the effectiveness of the method actually applied to the LEO satellite navigation augmentation network in the case of multiple ground stations.

Yanghongyi Kuang, Xianqing Yi, Zhenwei Hou
##### An Ionospheric Disturbance Index for SBAS Based on Gradient Variation

A simply constructed index is generally wanted to give direct indication of ionospheric status for Space-based augmentation system (SBAS) users. To this end, we make extensive analysis of ionospheric grid model performance under typical ionospheric storms. It was found that ionospheric delay gradients, instead of delays itself, are the main contributors for larger model errors. This feature makes indexes, which are defined on delay temporal variations, not preferred candidates for ionospheric condition indicating. A new index based on mean ionospheric delay gradients is then proposed and its applicability is analyzed. Results shows its consistence with grid model error variations, and the readily found threshold. Further analysis points out indexes based on delay spatial gradients, instead of temporal variations, is the key to construct sensible indicator for ionosphere status for SBAS.

Dun Liu, Yan Wang, Na Xu, Li Chen, Huafeng Wang
##### Validation of Relationship Between ROTI and S4 with Array of GNSS Measurements

With phase structure function, a theory model could be constructed to describe the rate of total electron content index (ROTI) and its relationship with amplitude scintillation index $$S_{4}$$ S 4 . The model is validated with measurements from GNSS array on short baseline. It is also found the effective scan azimuth angle $$\alpha_{{{\text{eff}}}}$$ α eff with value of 25° could serve as threshold for effective $$S_{4}$$ S 4 prediction from ROTI. Further analysis point out the effective scan speed $$V_{{{\text{eff}}}}$$ V eff and its ways passing through ionosphere determine the temporal and spatial sampling rate on irregularity, and when the different time separation for ROTI and $$S_{4}$$ S 4 locates in the same range of phase structure function, the model could be extrapolated to predict S4 with ROTI measurements. The results suggest the possibility of using regular GNSS observations for scintillation monitoring.

Dun Liu, Xiao Yu, Yan Wang, Li Chen, Weimin Zhen
##### Protection Level for Precise Point Positioning Based on Gaussian Mixture Model

In the integrity assessment for Precise Point Positioning (PPP), the Protection Level (PL) is usually calculated based on the assumption of Gaussian white noise. However, the code and phase noise don’t follow the Gaussian distributions due to the multipath effect in some situations. For this reason, it makes the PL too conservative by simply assuming the noise follows a Gaussian distribution. To deal with this problem, a PL calculation algorithm for PPP based on Gaussian Mixture Extended Kalman Filter (GMEKF) is proposed in this paper. Firstly, Gaussian Mixture Model (GMM) is introduced to accurately describe the non-Gaussian characteristics of the noise. Secondly, the sub-filters and corresponding test statistics are constructed for each independent Gaussian component. Finally, the PL calculation principle is deduced based on the concept of integrity risk. The results show that the GMM can better de-scribe the non-Gaussian feature of the observation noise. In the suburban scenario, the HPLs and VPLs based on GMEKF are reduced by 33.6% and 33.1% compared with Kalman filter respectively, so as to improve the availability of the PPP integrity monitoring algorithm.

Jitao Wang, Chengdong Xu, Moran Shi, Zhiwei Lu
##### Multi-parameter Characterization of Ionospheric Disturbances Based on GNSS Ground-Based CORS Data

As an important component of the near-Earth space environment, traveling ionospheric disturbances (TID) can affect the signal quality of radio communication and the positioning accuracy of navigation and positioning. In recent years, the further establishment of the Global Navigation Satellite System (GNSS) has provided good data support for the study of GNSS spatial environmental science. The ionospheric features can be studied by calculating the pseudorange and phase observations that allow estimating the Slant Total Electron Content (STEC) in the receiver-satellite paths. In this paper, we firstly achieve high accuracy extraction of STEC based on Undifferenced and Uncombined Precise Point Positioning (UC-PPP). Then, a 3D electron density sparse reconstruction based on Compressed Sensing-Principal Component Analysis (CS-PCA) is applied to Medium-Scale Traveling Ionospheric disturbances (MSTIDs) using the U.S. CORS navigation ground station. The MSTID occurring at 4:30 UT–4:45 UT was verified by data from the U.S. CORS stations on July 20, 2006, and the tomography results showed a clear perturbation trend in the electron density at altitudes of 100 to 220 km. It is demonstrated that the CS-PCA method can effectively invert the perturbation characteristics of ionospheric electron density during MSTID, and can obtain the 3D electron density characteristics that cannot be obtained from two-dimensional dSTEC maps.

Hongyi Qian, Yan Chen, Haiyang Fu, Junru Ye, Yun Sui, Jiayu Ma
##### Current Progress and Future Developments of PTABC LEO Navigation

The availability and security of GNSS services under increasingly complex jamming, spoofing and occlusion application environments are of great concern. The monitoring and protection of the electromagnetic environment in the navigation band is being strengthened by the international community. Global navigation jamming monitoring and locating based on LEOs (LEO satellites) has become a research hotspot, and efforts to seek complement backup measures. The integration of LEO narrowband Internet of Things, mobile communications, broadband Internet constellation to achieve complement backup of GNSS positioning and timing has become a hotspot of research as well as construction at home and abroad. At the same time, the demand for global fast centimeter-level positioning services has been proposed due to the development of autonomous driving and smart cities. Based on the LEO constellation, the new system of “space-based monitoring + signal augmentation” to reach the global fast centimeter-level positioning service has become a hotspot of research and verification at home and abroad. In this paper, from the perspective of Protection, Toughen, Augment, Backup, and Complement (PTABC) of GNSS based on LEO constellation, the related domestic and foreign technology research status and system construction status are classified and summarized. The PTABC-LNMS (PTABC LEO Navigation Meta-system) architecture, main performances and technology system are proposed. From the perspective of system implementation such as LEO navigation jamming source monitoring and locating, dedicated LNA (LEO Navigation Augmentation), LNA based on C&N (Communication and Navigation) fusion, and C&N backup, the main performance and development space are researched with representative system, and the challenges and opportunities of the system are presented. Finally, from a technical perspective, a short term and medium to long term development prospects are given for the PTABC-LNMS.

Yansong Meng, Xing Li, Lang Bian, Kun Jiang, Tao Yan, Ying Wang, Ye Tian, Qibing Xu
##### Design and Validation of CPQC-NAV, A New LEO Navigation Augmentation Signal Compatible with GNSS

Tian Li, Tao Yan, Lang Bian, Bo Qu, Ying Wang, Yansong Meng
##### Research on the Impact of the Decrease in Observation Stations on SBAS

The Satellite-Based Augmentation System (SBAS) realizes the correction and error envelope of the signal in space by broadcasting the ephemeris and satellite clock corrections and integrity parameters. During the research process, it was discovered that due to the interruption of the pseudo range observation data, the number of GPS satellites’ visible stations decreased instantaneously. This problem not only increased the correction error, but also caused glitches in the User Differential Range Error (UDRE), which affected the continuity of system. In order to solve this problem, an algorithm is proposed: at the epoch where the number of visible stations decreases, the Kalman Filter amplifies the observation noise covariance matrix to reduce the weight of observations, and gradually restore the observation noise covariance matrix over time before the effect of the decrease in the number of visible stations is eliminated. The results show that the algorithm can suppress the correction error amplitude caused by the instantaneous decrease in the number of observation stations by up to 90%, and can effectively suppress part of the UDRE glitches at the same time.

Qizhou Wang, Rui Li, Mingzhe Li
##### Research on BDSBAS Dual-Frequency Message Scheduler Optimization

By analyzing the broadcasting status of the BDSBAS-B2a message, it is found that there are some problems in its current strategy, such as low proportion of effective messages, poor flexibility, poor standard compliance and poor scalability. Based on this, this paper puts forward a dynamic scheduling strategy of dual-frequency message with fixed time sequence, which makes full use of dual-frequency ranging error change identifier (DFRECI) to represent the change of dual-frequency ranging error identifier (DFREI). At the same time, this paper simulated the broadcast of the strategy. The result shows that when the strategy enhances three basic constellations under the normal operation of BDSBAS, the proportion of effective messages can reach 100%. Compared with current arrangement, the time for users to receive all types of messages for the first time is shortened by 41.67%. By making effective use of MT34, the strategy can increase the number of enhanced satellites from the current 54 to 85, which greatly improves the problem of poor scalability of enhanced satellites caused by overseas stations and the increase of constellations in the future.

Jing Li, Rui Li, Jingcan Zhang, Tiantian Yang
##### Single Satellite Positioning Error Analysis and Performance Simulation Based on LEO Constellation

Low-earth orbit satellite positioning has been a research hotspot in the field of satellite navigation since it can be used as a backup positioning approach in the scene of GNSS signal occlusion and interference. However, the signal coverage of LEO satellites is small due to the low orbit altitude. In the case of limited constellation scale, it is difficult to achieve more than four-fold coverage, thus the traditional multi-satellite ranging and positioning method is not applicable. In this paper, based on the characteristics of low earth orbit satellite with fast moving speed and large Doppler frequency shift, the single satellite Doppler positioning has been proposed. And the single satellite positioning accuracy has been analyzed from the perspective of GDOP. What’s more, simulation has been made to analyze positioning accuracy versus on the satellite orbit accuracy, speed accuracy, observation period, and observation duration. The simulation results show that the single satellite positioning accuracy can converge to about 50 m in 8 min with the Doppler frequency shift observation accuracy of 1 Hz.

Menghuan Yang, Yachuan Bao, Cailun Wu
##### Pseudorange Bias Correction for BDSBAS Single Frequency Service

BDSBAS broadcasts SBAS corrections and integrity information via BDSBAS-B1C signals of BeiDou-3 GEO satellites to improve the accuracy and integrity for GPS L1CA single-frequency users in BDSBAS service area. However, if the GPS receiver type and technical status of BDSBAS reference station is quite different from the receiver of GPS ground operational control system and the BDSBAS receivers do not fully refer to the receivers of GPS ground operational control system to adjust the correlator spacing and front-end bandwidth, there will be inevitable relative pseudorange bias between the BDSBAS receivers and GPS ground operational control system receivers. Pseudorange bias is an important factor restricting the performance of BDSBAS single-frequency service. This contribution analyzes the impact of GPS satellite pseudorange bias on the accuracy of BDSBAS single-frequency service, and then proposes a pseudorange bias correction method based on the Timing Group Delay (TGD) parameters, which can eliminate the impact of pseudorange bias on the GPS L1CA SBAS positioning accuracy and improve the single-frequency service performance of BDSBAS. Six stations in the BDSBAS service area are used to carry out GPS L1CA SBAS positioning experiment, the experiment results reveal that the average 95% positioning accuracy has a significant improvement after using the mentioned method to correct the pseudorange bias. The positioning errors are reduced from 1.70 m to 1.38 m and from 2.83 m to 2.29 m in the horizontal and vertical directions, respectively.

Liqian Zhao, Biao Jin, Qijia Dong, Zixiao Li, Ningning Liu
##### LEO Spaceborne Receiver Autonomous Integrity Monitoring Algorithm Based on Dynamic Model Assistance

Spaceborne terminal receiver autonomous integrity monitoring can trigger alarm information to users in time when the orbit determination error of a Low Earth Orbit (LEO) satellite exceeds the allowable limit. It is indispensable for the application of LEO satellites in navigation services that involve life safety. The traditional Receiver Autonomous Integrity Monitoring (RAIM) based on the least square residual snapshot is implemented in the measurement domain. It fails to make full use of good dynamic characteristics of LEO satellites, resulting in relatively low availability. This paper proposes an RAIM for LEO satellite receivers based on dynamic model assistance. This method is based on the extended kalman filter and integrates the observation model and dynamic model of LEO satellites, then respectively construct test statistic and protection level. In this paper, RAIM based on least square residuals is used as a contrast, and simulation is designed to verify the performance of the proposed algorithm. Simulation results show that the fault detection ability is improved by introducing the dynamic model of the LEO satellite. At the same time, the availability of the proposed method is tested at 10, 20 and 50 m, and the results show that the availability of the proposed method is improved by 98.84%, 93.28% and 37.84%.

Chuanpeng Guo, Ruijie Li, Liuqi Wang, Yi Liu, Qiwei Ye
##### Global Ionospheric Total Electron Content Prediction Based on Spatiotemporal Network Model

Ionospheric delay is an important source of error in the Global Navigation Satellite System, and the ionosphere total electron content (TEC), as an important parameter describing the ionospheric properties, directly affects the magnitude of the ionospheric delay. Accurate modeling and forecasting of ionospheric TEC can serve to correct ionospheric delay and improve the accuracy of satellite navigation positioning. However, most of the current ionospheric TEC forecasting studies are only related to the temporal or spatial dimensions, without combining the temporal and spatial information of the global ionospheric TEC, ignoring the spatial and temporal autocorrelation, which seriously limits the forecast accuracy of the global ionospheric TEC. Therefore, we construct a spatiotemporal network forecast model with convolutional long short-term memory with spatiotemporal memory to achieve spatiotemporal forecasting of global ionospheric TEC by learning the temporal variation characteristics and spatial features of global ionospheric TEC and further suppresses the gross error and noise in ionospheric TEC data by using Huber loss function to improve the forecast accuracy of global ionospheric TEC. Compared with the one-day forecasts of global ionospheric TEC from the convLSTM model and the CODE’s spherical harmonic model, the average RMSE of the forecast results of our method is improved by 13.65% and 13.96%, respectively, which can be effectively applied to ionospheric delay error correction and improve the accuracy of satellite navigation and positioning.

Hongyue Wang, Xu Lin, Qingqing Zhang, Changxin Chen, Lin Cheng, Zhen Wang
##### Research on Integrity Monitoring of GNSS/AHRS Integrated Navigation

With the development of autonomous driving and UAV technology, users put forward higher demands for the integrity of GNSS positioning services in complex urban environments. Receiver Autonomous Integrity Monitoring (RAIM) is an essential means to ensure the integrity of location service. The conventional RAIM algorithm uses redundant observations for fault detection, availability judgment, and fault identification. However, in complex urban scenarios, users are faced with problems such as the reduction of visible satellites and the deterioration of satellite geometry distribution, which restrict the availability of user integrity monitoring services. In order to improve the availability of integrity services in complex urban environments, this paper proposes an integrity monitoring method based on GNSS/ Attitude and Heading Reference System (AHRS) information fusion. The attitude information provided by AHRS can improve the model strength, effectively reduce the requirement of RAIM algorithm on the number of visible satellites, and improve the availability of RAIM algorithm in complex urban environments. Compared with the traditional RAIM algorithm, the proposed method enhances the algorithm availability by about 29.8%.

Qiwei Ye, Xin Zhang, Chuanpeng Guo, Ruijie Li, Zewen Jiang
##### Analysis of Interference Effect of GPS Satellite Power Enhancement Signal

Satellite power enhancement technology is a key technology to improve the capability of satellite anti-interference and has very important application value. Aiming at the multi-access interference of GPS satellite power enhancement signal to the same frequency signal, this paper analyzes the mechanism of self-interference and mutual interference between signals. The interference of GPS P-code power enhancement signal to P-code and C/A-code expected signal under single-satellite enhancement and multi-satellites enhancement was quantitatively evaluated from multiple dimensions by using the equivalent carrier-to-noise ratio reduction calculation method based on spectral separation coefficient The results show that under the same conditions, the interference of P codes to C/A codes is larger than the self-interference between P codes; At the same time, the interference degree of multi-satellites enhancement is more significant than that of single-satellite enhancement; Power enhancement can effectively improve the carrier-to-noise ratio, but when the amplitude of enhancement exceeds a certain value, the interference effect will be greater than the power enhancement effect, and the carrier-to-noise ratio will no longer increase.

Xuyu Wang, Hai Sha, Li Wang, Yingying Zhao, Dongfang Jiang, Heng Wei
##### Evaluation and Analysis of Anti-jamming Performance of Navigation Signal in Satellite Retransmission Channel

Beidou RDSS (Radio Determination Satellite System) short message and inter-station measurement and data transmission system all belong to satellite retransmission channel. In order to solve the problems of difficult interference evaluation and inconsistent indicators in the retransmission channel, the anti-interference quality factors in the retransmission channel are proposed. In this paper, the problem is studied by establishing the forwarding channel model, calculating the channel parameters and analyzing the simulation results. Through the analysis of the uplink interference and the equivalent SNR (Signal-to-Noise Ratio) of the channel receiver, the calculation formula of the anti-interference quality factor in the forwarding channel is obtained, and the channel performance changes under different interference types and intensities are analyzed. It is found that when the repeater is saturated, the channel anti-interference capability will decrease sharply and the signal quality will be greatly lost. The research results of this paper can be applied to the interference evaluation of Beidou RDSS short messages, inter-station measurement and data transmission systems in China, and provide guidance and reference for anti-interference means.

Linyuan Hou, Xinming Huang, Jingyuan Li, Zengjun Liu, Zhengrong Li
##### Credibility Research of BeiDou Navigation Satellites Based on LEO Constellation Enhancement

The rapid development of Low Earth Orbit (LEO) constellation, with the advantages of strong landing signal, rapid change of satellite geometry and strong anti-interference capability of satellite signal, has become an important development trend of satellite navigation enhancement. In view of the problems such as weak landing signals of BeiDou-3 Navigation Satellite System (BDS-3) and vulnerability to external spoofing, combined with the potential advantages of LEO constellation, this paper explores the improvement of the credibility of BeiDou navigation satellites with the enhancement of LEO constellation, namely integrity and anti-spoofing. Through the receiver autonomous integrity monitoring algorithm (RAIM), based on the integrity fault detection rate index, the improvement of the integrity performance of the LEO constellation enhanced BDS-3 was analyzed. On this basis, an improved RAIM identification algorithm is proposed for both integrity and hostile faults. Based on the fault detection rate and recognition rate index, the anti-spoofing performance of LEO constellation enhanced BDS-3 is studied and analyzed. The simulation results show that, under the pseudorange deviation of 15 m to 30 m, the integrity fault detection rate of two different LEO constellations with 72 and 144 satellites is 8% and 10% higher than that of single BDS-3 respectively. The two different LEO constellations with 72 and 144 satellites have improved the detection rate of hostile faults by 8% and 10%, and the recognition rate by 40% and 50% respectively, compared with the single BDS-3 under the pseudorange deviation of 15 m to 50 m. Therefore, the enhancement of BDS by LEO constellation can effectively improve the credibility performance of BDS.

Kai Yin, Rui Li, Chongyv Wang, Jitao Teng
##### Study of PNT Signal and Its Performance on LEO Communication Constellation

This paper studies the requirements of positioning and navigation time service for low orbit communication constellation. Based on the analysis of the LEO communication constellation characteristics, a signal design framework with position and navigation timing (PNT) function for broadcasting on LEO communication satellites is proposed. At the same time, the critical performance of common-frequency multiplexing is evaluated. The results show that, after reasonable design, the reduction of equivalent CNR caused by navigation signals is better than 0.28 dB, the reduction of equivalent CNR and tracking accuracy caused by navigation signals is acceptable, and the tracking error after deterioration is better than 0.43 m. The research results can reference the design and construction of a new generation space-based PNT system.

Xing Li, Tao Yan, Lang Bian, Xia Guo, Yansong Meng
##### Research on the Method of Autonomous Integrity Monitoring of Satellite Ephemeris

At present, the autonomous integrity of satellites does not include the monitoring of the correctness of the message, that is, the message does not have an error, but the physical quantity of its own error occurs, the on-board integrity monitoring unit cannot monitor and alarm. Aiming at this type of anomaly in the telegram, this paper studies the method of monitoring the integrity of the ephemeris, and proposes a method for monitoring the integrity of the telegram on the satellite. The statistical analysis and error modeling of the actual ephemeris are carried out using a joint criterion. Alert. This paper proposes a multi-Gaussian variable joint probability calculation method to calculate the integrity risk corresponding to different monitoring thresholds. The monitoring method and integrity risk calculation method proposed in this paper are based on the current design status of the Beidou-3 satellite system. The project implementation cost is relatively small, and a good compromise can be made between service continuity and integrity.

Lei Chen, Xin Nie, Weiguang Gao, Shuo Zhang
##### Potential Performance of Satellite-Based Augmentation System Based on CMONOC in China

To satisfy the requirement of aviation navigation, many countries are committed to the development of Global Navigation Satellite System (GNSS) augmentation systems, especially Satellite-Based Augmentation System (SBAS), to improve the accuracy, integrity, continuity and availability of GNSS. SBAS has been an important solution to improve the comprehensive performance of GNSS for many years. Typically, SBAS in North America and Europe can provide Localizer Performance with Vertical guidance 200 (LPV200) services for their civil aircraft. The services provided by SDCM, MSAS, KASS and GAGAN have been gradually covering the surroundings of China. As both the SF service and the DFMC service provided by BeiDou Satellite-Based Augmentation System (BDSBAS) are being tested, it is urgent to perform the research of SBAS to provide technical support for the construction and subsequent performance improvement of BDSBAS. To improve the processing efficiency of BDSBAS, an architecture of system segment is designed for BDSBAS. Also, considering the problem that it is difficult to guarantee the satellite integrity in the edge area of the monitoring network, a pseudorange residual and satellite-station geometry-based method is proposed to perform satellite integrity monitoring. Results reveal that compared with the direct statistic method, the integrity bounding rate in the pseudorange domain and the availability in the position domain are improved by 45.39% and 2.32% respectively. The designed system can provide Approach Procedure with Vertical Guidance-I (APV-I) services for most parts of China and even LPV200 services for some parts of China.

Shuaiyong Zheng, Mengzhi Gao, Kun Li, Xiaoqin Jin, Juan Qin, Dan Xia
##### Study on the Relationship Between the Equivalent GDOP and the Convergence Time of LEO-Augmented BDS PPP

Compared with BeiDou satellites, low earth orbit (LEO) satellites travel faster and show greater changes in spatial geometry within the same duration. When they are served as navigation satellites and assist BDS precise point positioning (PPP), fast initialization can be realized. Usually, the geometry of a constellation is represented by the geometric dilution of precision (GDOP). However, traditional GDOP metric can only reflect the instantaneous positioning accuracy of standard navigation and positioning service rather than the convergence performance of PPP, and cannot be calculated when the number of instantaneous visible satellites is less than 4. Considering that the coverage fold of future LEO navigation-augmentation constellation may be below 4 and meanwhile it is meaningful to comprehensively describe the continuous impacts of satellite numbers, moving velocity, moving direction and geometric change level on the convergence process of PPP, the concept of equivalent GDOP (EGDOP) based on accumulated time is proposed. Then, thousands of LEO constellations and their observation data are simulated and used for the analysis of the relationship between the EGDOP of LEO constellation and the convergence time of LEO-augmented BDS PPP. The results show that for 1-min sessions the smaller the EGDOP, the shorter the convergence time and the higher the probability that PPP converge within 1 min. Under ideal ephemeris conditions, the probabilities of realizing fast PPP with the horizontal positioning accuracy better than 10 cm and convergence time below 1 min are 100%, 95% and 65% when the corresponding EGDOP are below 0.29, 0.30 and 0.51, respectively. The relevant results can be used as an important basis for the optimization design of future LEO navigation-augmentation constellations.

Fujian Ma, Jinjun Zheng, Chengbin Kang, Qiuli Chen, Ping Li, Xin Nie, Xiaohong Zhang
##### On the Design and Performance Analysis of BDS3 Ground Based Augmentation System Service

With the fast development of BDS3, the global service of BDS3 now is opened. During the past few years, more than ten thousand of BDS reference stations are established over the whole country. In this paper, firstly a BDS3-GBAS (Ground Based Augmentation System) is completed and tested with self-built nationwide CORS (Continuous Operation Reference Station) tracking network. More than 10 thousands of users can be served simultaneously with this this BDS3-GBAS service software. Besides, performance and positioning accuracy of the BDS3-GBAS service are analyzed with six different strategies, namely, BDS2-only, BDS3-only, BDS3_n-Only, BDS2+BDS3_n, GPS and GNSS-All. As demonstrated by the filed test results, all the strategies except BDS2 almost show a similar accuracy in horizontal direction, while the accuracy in vertical direction varies a lot. The vertical positioning accuracy of the above six strategies is 0.0405 m/0.0259 m/0.0213 m/0.0210 m/0.0215 m/0.0183 m in southern China, respectively. While, the vertical positioning accuracy is much more improved in northern China, and the accuracy is 0.0405 m/0.0259 m/0.0213 m/0.0210 m/0.0215 m/0.0183 m in southern China, respectively. Furthermore, the results also show that BDS3-only can achieve equivalent results to GPS-only in China. Moreover, different methods of ionospheric correction interpolation are also addressed in this paper. As the results shown, the LIM (Linear interpolate model) with residual correction performs the best while the LSM (Liner Surface Model) performs the poorest. And the performance is improved by 13.9% and 14.8% when compared with LSC (Least Squares Collocation) interpolation model and LIM (Linear Interpolation Model) interpolation model, respectively.

Lihua Wan, Huijun Guo, Ziyuan Huang, Peng Zhang, Yue Xu

#### Autonomous Navigation and Intelligent Operation

##### Design and Implementation of Intelligent Operation and Maintenance of BDS-3 RNSS Service

The RNSS service is one of the most basic services provided by BDS-3. It provides global users with RNSS function similar to GPS. As the core of satellite navigation system, the intelligent operation and maintenance of ground operation management system affects the service support ability to a certain extent. Combined with the satellite ground system composition and operation process status of BDS-3, this paper designs an intelligent operation and maintenance system scheme for RNSS service of BDS-3, which carries out system operation and maintenance monitoring, evaluation and processing from the aspects of satellite ground operation status monitoring and evaluation, system service performance monitoring and evaluation, fault diagnosis and prediction; Integrate satellite ground working condition status, data quality status and service application performance status, and use horizontal correlation, vertical mining and other technologies to conduct big data analysis according to different multi dimensions such as time, space, satellite, ground station, signal and application; The software integrating the functions of data reception, data governance, data storage, satellite ground operation status monitoring and evaluation, system service performance monitoring and evaluation, fault diagnosis and prediction, visualization and so on is developed, which realizes the monitoring, evaluation and analysis of the operation status and application performance of RNSS service of BDS-3, The operation and maintenance capability of RNSS service of BDS-3 is improved.

Liang Yuan, Longping Zhang, Guoping Jin, Nan Liang, Xiancai Tian, Hongliang Liu, Kai Zhao
##### Aircraft Trajectory Tracking Method Based on Terminal Angle Constraint and Inverse Proportional Guidance Obstacle Avoidance

Aiming at the issue of autonomous path tracking and obstacle avoidance of aircraft, in order to suppress the significant change of the speed direction during the path tracking process, the terminal angle constraint item is introduced into the guidance law to realize the smooth tracking of each path point. In addition, based on the relative positional relationship and movement direction between the aircraft and the obstacle, the obstacle avoidance guidance law is established in the target line of sight coordinate system in this paper. At the same time, the speed control item in the process of avoiding obstacles has been added. Through simulation, the aircraft which manipulated by the guidance law can achieve smooth tracking of the preset path and effectively avoid unexpected obstacles in the path as well.

Linxu Wu, Fengjuan Guo, Jiayu Liu, Jiale Han
##### Cooperative Localization of UUVs with Decentralized Method Based on Underwater Weak Communication

With the increasing difficulty and complexity of underwater tasks, it becomes an inevitable trend for cooperative localization of Underwater Unmanned Vehicles (UUVs) in the form of clusters, which can extend the spatial datum of Global Navigation Satellite System (GNSS) to seafloor and further expand the perception range of single UUV. Due to the weak underwater communication conditions and the complexity of meteorological environment, it has some problems for UUV sensors, e.g., observation limitation and time delay. In the former work, the huge communication of traditional decentralized method brings extremely difficult to operate in actual underwater scene, and the centralized method has the vulnerability and low fault tolerance. Therefore, a decentralized cooperative localization method of UUVs under the condition of underwater weak communication is proposed. Based on the rigorous mathematical theory, the decentralized framework based on extend information filter is constructed. The single UUV establishes its own state chain according to local sensor, and the UUVs cooperate to complete the recursive correction of the information matrix. Observation data in Nankai trough (Japan) are selected as the underwater sound velocity field, and the UUVs on the surface and underwater are simulated. Experimental results show that the proposed method can realize the decentralization of UUVs cooperative localization on the basis of ensuring the accuracy and consistency with the centralized method. Furthermore, data traffic is significantly reduced and the application field of UUV is further expanded.

Zhenqiang Du, Hongzhou Chai, Minzhi Xiang, Fan Zhang, Jun Hui, Zhaoying Wang
##### Covert Wireless Communication on Beidou Short Message Communication

As a significant feature and advantage of BeiDou navigation satellite system (BDS), short message communication (SMC) with the character of wide coverage and low communication cost, which is widely used in transportation, fishery, agriculture and forestry industries. However, due to the broadcast nature of wireless transmission, the security issue of SMC cannot be ignored. The existing security systems and research are mostly about encryption algorithms, without considering the protection of communication behavior and the transmitter’s location. Against this background, we explore the covert wireless communication to guarantee the security of BeiDou SMC. Firstly, the warden’s detection strategy is analyzed through hypothesis testing theory. Then, the covertness of SMC is discussed in two scenarios: whether the user’s location information is exposed or not. The simulation results indicate that the user’s SMC behavior can be effectively protected by using the jammer with random transmit power.

Maochun Wang, Weiwei Yang, Lu Xu, Xin Lv, Ye Chen, Qingchen Wu, Bing Liu
##### Integrity Monitoring of PPP-RTK Based on Multiple Hypothesis Solution Separation

Recent progress for high-precision positioning mainly focused on PPP-RTK, which is a precise point positioning (PPP) technique based on a real-time kinematic (RTK) network. PPP-RTK is expected to become the mainstream positioning solution for various intelligent transportation systems (ITS) such as autonomous driving, unmanned aerial vehicles, and urban air mobility. Prior studies on PPP-RTK mainly focused on improving navigation accuracy. However, for safety-critical applications, integrity is also an important performance index. Since PPP-RTK is usually implemented using a Kalman filter (KF), the well-known integrity monitoring schemes developed for least-squares-based systems cannot be directly applied to PPP-RTK. After considering the time-sequential nature of KF, we propose a user-end integrity monitoring scheme of PPP-RTK based on multiple hypothesis solution separation (MHSS) to offer high-reliability and high-precision position solutions with real-time integrity information. The proposed scheme includes two key functions: real-time fault detection and rigorous protection level (PL) evaluation. This scheme captures both the faults from PPP-RTK service products and those faults introduced at the user end. Experiments are carried out with real data and simulated fault scenarios. The results suggest the effectiveness of the proposed scheme and indicate that multi-constellation PPP-RTK can offer position solutions with decimeter-level PLs (integrity risk: 10–7/h) in open-sky areas.

Shizhuang Wang, Xingqun Zhan, Yingchao Xiao, Yawei Zhai
##### Applications and Prospects for Autonomous Navigation Technology in a Satellite Navigation System

Autonomous constellation navigation is an important means for improving the continuous delivery of services by satellite navigation systems when experiencing conditions such as major disasters and failure of ground operation control facilities. It is also a useful supplement to the normal operation and control mode, which can reduce dependence on the ground facilities while lowering operating costs. This article introduces a method for evaluating experiments on the autonomous constellation navigation of satellite navigation systems. These experiments were based on 12 days of BDS-3 satellite observation data. The evaluation results show that for the 12 days of autonomous constellation navigation, the user range error of the satellite orbit was 2.5 m, the accuracy of clock error was 3 ns, and the timekeeping accuracy was approximately 1373 ns. The pseudorange observation data of 7 domestic stations and 10 global stations of the International GNSS Monitoring and Assessment System (iGMAS) was used to evaluate the positioning accuracy. The results show a single-frequency horizontal positioning accuracy of 7.4 m, an altitude positioning accuracy of 9.6 m, a dual-frequency horizontal positioning accuracy of 7.1 m, and an elevation positioning accuracy of 8.9 m. Based on the results of the experiment, this paper analyses the time-space reference drift problem that affects the accuracy of autonomous navigation space signals and proposes an optimized solution.

Wei Zhou, Hongliang Cai, Haihong Wang, Qiuli Chen, Xia Lin, Jinglei Guo, Xiaojiie Li, Chengpan Tang, Ruiqiang Shao, Junyang Pan, Weisong Jia, Ziqiang Li
##### Performance Analysis of INS/ODO Integrated Navigation with Different Measurement Models in GNSS Denied Environment

GNSS/INS integrated system is widely used in vehicle navigation and positioning. However, in GNSS signal occlusion scenes such as underground garage, tunnel and viaduct, the low-cost inertial navigation error increases rapidly with time, which is difficult to ensure the continuity and reliability of vehicle trajectory. Wheel odometer can limit the drift of INS. Using observation information to construct appropriate constraints is the key to improve navigation accuracy. Aiming at GNSS/INS/ODO integration based on EKF, this paper deduces three measurement models of velocity, displacement and position. The models take into account the tire scale coefficient error, IMU placement deviation angle and lever arm value, and then design and implement the corresponding filters respectively. The positioning accuracy of the three combined models in typical urban scenes is compared and analyzed through vehicle carrying experiments. The results show that ODO can limit the trajectory drift, but the pose accuracy of the three measurement models is different. When GNSS signal loses lock for 3 min, the positioning accuracy of the position model is equivalent to that of the displacement model, the RMS is less than 3.5 m; The horizontal accuracy and stability of the velocity model are the best, and the RMS value is less than 3 m; The position model performs well in the path closed-loop scenario. The research results can provide reference for the model selection of INS/ODO integrated navigation.

Peidong Yu, Mengkui Liu, Yuanjun Chen
##### Application of LSTM Neural Network in RISS/GNSS Integrated Vehicle Navigation System

Zhejun Liu, Yanbin Gao, Yunlong Sun, Ye Wang
##### Research and Application of PNT Information Service System Based on “End + Network + Cloud”

Driven by modern information and intelligent technology, the application of PNT system is gradually developing from benchmark positioning and time service application to comprehensive spatio-temporal information service. This paper studies the technology ecosystem mainly composed of “end, network and cloud”, puts forward the overall architecture of PNT information service system based on “end + network + cloud”, studies the implementation of the system in practical application development, and gives the overall solution of PNT information service system based on “end + network + cloud”, It also expounds the core technical characteristics of the system and the service content provided. Lastly, through the integration joint test verification in the application of a network information system demonstration project, it shows the rationality and feasibility of the overall architecture of PNT information service system proposed in this paper.

Jiang Li, Weiyi Chen, Jintao Yao, Yuqi Wang
##### Multipath Error Correction for Smartphones and Its Impact on Single Point Positioning

With the release of multi-constellation and multi-frequency GNSS chips, the positioning capabilities of smartphones have been improved. However, smartphones are commonly equipped with low-gain microstrip antennas, which make GNSS observations suffer from severe multipath effects. The results of short baseline single difference (SD) show that the multipath error of smartphones is almost 5–10 times higher than that of geodetic receivers, which greatly limits the positioning accuracy of smartphones. The multipath effect is affected by various factors such as equipment, environment, and signal, and it is usually difficult to establish an effective mathematical model for correction in complex urban scenarios. Considering that multipath errors have low-frequency characteristics, this paper proposes a method based on wavelet transform, which can effectively detect and extract multipath errors. First, the short baseline SD residual between the smartphone and the reference station is decomposed into low-frequency error and high-frequency noise. Then, the low-frequency error is compensated to GNSS pseudorange observations after doing wavelet inverse transform reconstruction, thus weakening the influence of multipath errors on the positioning. The experimental results show that different wavelet bases and decomposition layers can effectively improve the positioning accuracy, and the improvement is more obvious when the number of decomposition layers is smaller. When dB1 wavelet base and one layer of decomposition coefficients are selected, the single point positioning (SPP) accuracy of Huawei P40 and Xiaomi 8 in U, N, and E directions reaches 1.07 m, 1.31 m, 0.59 m, and 1.32 m, 0.87 m, 0.47 m respectively after multipath error compensation. Compared with the uncompensated multipath, the positioning accuracy of the two phones is improved by 53.5%, 48.6%, 60.7%, and 25.4%, 32%, 55.2%, respectively.

Qingcheng Li, Jiale Wang, Wenyue Chao, Fu Zheng, Chuang Shi
##### An Auxiliary Heterogeneous Visual Localization Algorithm Based on Improved Hough Transform Line Matching

With the increasing demand for all-weather, uninterrupted aviation missions, heterogeneous visual navigation and positioning technology based on visible images and infrared images has been developed, and the key technology of heterogeneous image matching has become a research hotspot. Due to the different imaging mechanisms of heterogeneous images, it is difficult to directly apply the homogeneous image matching algorithm to heterogeneous images, and the feature extraction accuracy of algorithms based on line segment structure such as Hough transform needs to be improved. Therefore, an improved Hough transform line matching algorithm to assist heterogeneous visual positioning is proposed in this paper. Based on the heterogeneous image obtained by different optical sensors, the adaptive Canny operator of the improved maximum inter-class variance method is used for edge detection. The detected edge binary image is processed by Hough transform, and the line features in the heterogeneous images are extracted for matching. The experimental results show that the Hough transform line matching algorithm using the improved Canny operator has a line feature detection accuracy of 66%, which is 74.23% higher than the traditional Hough transform line matching algorithm. The number of correctly matched line features of the proposed algorithm is better than that of the traditional algorithm, which can provide ideas for the pose calculation based on heterogeneous images. The running time of the proposed algorithm is better than that of the traditional Hough transform line matching algorithm, and the total time is reduced by 46.62%.

Yixue Luo, Qinghua Zeng, Wenqi Qiu, Yineng Li, Kecheng Sun
##### Performance Analysis of Robust Tightly Coupled GNSS/INS Integration Positioning Based on M Estimation in Challenging Environments

The phenomena of limited satellite visibility and multipath is serious in challenging environments, which causes to decrease of the positioning accuracy dramatically. An effective solution is tightly coupled integration of Global Navigation Satellite Systems (GNSS) and Inertial Navigation System (INS) based on robust M estimation. However, the robust performance is directly influenced by both the selection of equivalent weight functions and the INS accuracy difference. In this paper, theoretical analysis and experiment validation of positioning accuracy and reliability for the robust integration system are implemented under the condition of various equivalent weight functions and different INS systems. Firstly, for constructing equivalent least square form of EKF, we combine classical EKF observation equation with redundant observation equation established by predicted state and corresponding covariance in propagation step. Then, robust extended Kalman filter (REKF) algorithm which is based on M estimation is introduced for purpose of weakening the influence of faults on location. Moreover, the features of three typical equivalent weight functions (Huber, Tukey, IGG-III) are analyzed respectively. Finally, a simulation experiment platform is built to analyze the influence of the choice of equivalent weight functions and the IMU grades on positioning accuracy and reliability, which is realized by integrating GNSS and various grades IMU to locate with three REKF solutions against traditional EKF. Simulation experimental results show significant enhancements for REKF based on M estimation in terms of precision and reliability of tightly coupled system. Furthermore, in the setting failure scenario, the solution scheme based on IGG-III equivalent weight function can obtain the optimal robust effect in comparison with REKF(Huber) and REKF(Tukey), whose horizontal positioning accuracy is kept within −0.5 m–0.5 m and vertical positioning accuracy is no more than 1 m. Meanwhile, compared with consumer grade IMU, using tactical grade IMU can further improve positioning accuracy and reliability.

Yingying Jiang, Shuguo Pan, Qian Meng, Min Zhang, Wang Gao, Chun Ma
##### Fast Semantic Segmentation of 3D Lidar Point Cloud Based on Random Forest Method

Fast semantic segmentation of the 3D lidar point cloud is useful for 3D reconstruction, mapping, and unmanned automobile. The challenges of semantic segmentation for the existing deep learning method require large amount data and high computational cost and hardware. This paper adopts a machine learning method based on random forest with few samples, which can process high-dimensional features in parallel for 3D lidar point cloud to achieve fast semantic segmentation. First of all, the proposed framework will analyze position, intensity and color to extract twenty features such as eigenentropy, verticality, average intensity and height statistics. Secondly, the feature representation of multi-scale neighborhood is constructed by grid downsampling and K-nearest neighbor (KNN) algorithm. Thirdly, the optimized feature set is re-input to the random forest classifier to achieve semantic segmentation based on the random forest feature selection (RFFS) process.The proposed method has been tested on the high-precision 3D lidar point cloud dataset of Fudan University Jiangwan Campus and the public dataset Toronto-3D. The results show that semantic segmentation can be achieved well. For roads, lane marking, vegetation, buildings, pedestrians, vehicles, and poles in the high-precision 3D lidar point cloud dataset of Fudan University Jiangwan Campus, the mean intersection over union (MIoU) and the overall accuracy (OA) are greater than 90%, the test results in the public dataset set Toronto-3D are better than pointnet++. The method described in this paper has a fast computation speed than the deep learning method, which may be applied to handle millions of lidar 3D point clouds more quickly in the future.

Songdi Jiang, Wei Guo, Yuzhi Fan, Haiyang Fu
##### Research on Visual-Inertial SLAM Technology with GNSS Assistance

In the new era of robustness and perception, the Visual-Inertial Odometry (VIO), which is tightly coupled by the camera and the Inertial Measurement Unit (IMU), can obtain high-precision local pose results in unknown environment. Its low cost and miniaturization have received widespread attention. However, due to the limitation of the measurement principle, in the long-term runs, error will still accumulate. In addition, the outdoor large-scale environment is also a major challenge facing VIO. The Global Navigation Satellite System (GNSS) can provide accurate global estimates for VIO in an open outdoor environment and correct drift caused by long-term operation. Similarly, VIO can still perform in environments where GNSS is denied, which makes it possible for seamless indoor and outdoor navigation. Therefore, this paper proposes a visual-inertial SLAM algorithm assisted by GNSS. Taking the optimized tightly coupled VIO as the main body, and the pose information obtained by GNSS is combined with the VIO solution result to enhance the global positioning while ensuring the accuracy of the local pose accuracy. To this end, a simulation experiment based on the KITTI data set was carried out. The results show that the VIO system with the aid of GNSS can achieve the accuracy of 1.687 m error average, 1.176 m standard deviation, and 2.056 m root mean square error, which is nearly 80% higher than that without assistance. And it can also play a role in the environment where GNSS is denied, and the robustness of the system is also enhanced.

Lin Zhao, Xiaohan Wang, Xiaoze Zheng, Chun Jia
##### Research on JPS Algorithm Route Planning Based on RNP

Navigation and positioning system, as the important part of battlefield environment perception, is the premise and basic guarantee to ensure the safety and accurate completion of route planning tasks of unmanned air vehicle (UAV). In the application of UAV route planning, due to navigation system error and flight technology error, the real-time position of UAV deviates from the scheduled flight path, which may cause the collision between the UAV and obstacles, into the dangerous area and other dangerous situations. In order to ensure the flight safety of UAV, this paper evaluates and monitors the navigation performance of UAV according to the UAV Navigation Monitoring Requirement specification. On this basis, the route of UAV is optimized, and the route planning model of jump point search based on Required Navigation Performance is established. The experimental results show that this method can reduce the protected area of UAV, reduce route planning path length, improve the efficiency of route planning, and provide support for the flight safety of UAV in complex environments.

Fengjuan Guo, Jiale Han, Linxu Wu, Jiayu Liu
##### Research on SINS/GNSS/CNS/Pressure Altimeter Federated Filtering Adaptive Fault Tolerance Method

A federated filtering integrated navigation system with dynamic step gradient descent algorithm was designed to reduce the performance of UAV attitude solution tracking under strong maneuvering and high speed motion. SINS/GNSS/CNS/PA federal filter was used to estimate the motion acceleration, and then the step size of gradient descent method was dynamically adjusted to suppress the influence of motion acceleration on the aircraft attitude solution. At the same time, the fault detection mechanism based on residual estimation can prevent information pollution caused by satellite signal jump or starlight occlusion in high speed maneuvering environment. The simulation results show that the proposed method improves the attitude calculation accuracy and enhances the filtering accuracy of the UAV integrated navigation system in complex motion state compared with the commonly used integrated navigation filter.

Xin-xian Liu, Xiu-bin Zhao, Chun-lei Pang
##### Research on Integrity Evaluation Method for PPP-RTK Service End

The integrity requirement should be satisfied especially when PPP-RTK is used in safe of life applications. From the procedure of PPP-RTK, the accuracy and integrity of the service end products play an extremely important role in positioning. So, it is of great significance to analyze the accuracy and integrity of these products. This paper presents an integrity evaluation method for PPP-RTK service end products, meanwhile the definitions and calculation methods of integrity parameters are given as well. Without loss of generality, taking the precise orbit and clock as an example, the integrity parameters for the orbit and clock are obtained through the analysis of the Signal in Space Range Error (SISRE). The integrity evaluation method for PPP-RTK service end products proposed in this paper can be regarded as a general method, which can be used to evaluate different kinds of correction products.

Yingchao Xiao, Shizhuang Wang, Xingqun Zhan, Yawei Zhai

#### GNSS Signal Processing

##### Space-Frequency Adaptive Processing Algorithm Based on STFT for LFM Interference Suppression

LFM interference is a typical non-stationary interference, which is common in the application of satellite navigation receiver. The normal SFAP does not distinguish the characteristics of received signals, and uniformly carries out covariance matrix estimation, weight calculation and adaptive filtering in each frequency bin, which may attenuate the performance of LFM interference suppression. To solve this problem, a SFAP algorithm based on short-time Fourier transform (STFT) was proposed. Firstly, the time-frequency characteristics of the received data were analyzed by short-time Fourier transform. Then the sampled data were grouped in two-dimensional time and frequency domain according to their time-frequency characteristics, and the sampled data with consistent time-frequency characteristics were divided into the same group. Finally, the covariance matrix estimation, weight calculation and adaptive filtering were carried out by using the grouped data to improve the interference to noise ratio, the null depth and the anti-interference ability. Both theoretical analysis and simulation results verify the effectiveness of the algorithm.

Peng Liu, Dun Wang, Qi Ren, Dingcheng Tang, Bo Peng
##### Trap Spoofing Algorithm for Target Using GNSS/INS-Integrated Navigation System Based on Prior Error Compensation

Black flights of unauthorized unmanned aerial vehicle (UAV) have occurred frequently in recent years, threatening public safety. UAV mainly uses GNSS (Global Navigation Satellite System)/INS (Inertial Navigation System) integrated navigation for positioning. Due to the weakness of GNSS signal, spoofing UAV is possible. Some scholars have conducted researches on the spoofing of targets with integrated navigation, but these studies all use radar to obtain the target’s position, speed and acceleration in real time. This method has high technical complexity and expensive cost. To solve this problem, this research proposes a trap spoofing algorithm for target using GNSS/INS-integrated navigation system based on prior error compensation. By setting a spoofing trap in a certain area of the target path, when the target moves within the trap range, it will be trapped in designated areas by spoofing signals. Finally, this paper verifies the feasibility of the trap spoofing algorithm through simulation experiments.

Jianyu Pan, Lei Chen, Xin Chen, Wenxian Yu
##### Design and Implementation of a Multi-mode P Code Direct Acquisition Module

Compared with civilian code, P code has higher anti-interference and anti-deception, especially in the military field. However, due to the non-periodicity, high rate and large amount of data processing of P code, the improvement of acquisition speed and acquisition sensitivity is restricted. Based on the parallel frequency algorithm of matched filtering combined with fast Fourier transform (PMF-FFT), this paper designs an FFT module, which is configurable to a certain extent in FFT length and phase search parallelism. Combined with the design of time division multiplexing acquisition mode, it can achieve the flexible switching of multiple acquisition speeds and acquisition sensitivity. The test shows that the acquisition module has a variety of working modes in acquisition speed and sensitivity, is compatible with signal processing of a variety of symbol modulation modes, and is suitable for a variety of application scenarios.

Yanjiao Yang, Fei Liu, Jing Chen, Kun Liu
##### Cross-Correlation Based Spreading Code Authentication Scheme for Civil GNSS Signals

Navigation signal authentication schemes are effective methods to protect civilian receivers against spoofing attacks by providing unforgeable information to verify the authenticity of signals. In this paper Cross-Correlation based Spreading Code Authentication, or CC-SCA, is proposed to authenticate GNSS civilian signals at high time resolution with small storage requirement. CC-SCA employs a cryptographically generated authentication spreading code punctured into public spreading code in civilian signals. Since initial code phases of authentication spreading code are different and derived from security code, a correlation peak can be detected and authenticated in the cross-correlation between baseband signals of different satellites. According to this principle, signal structure and authenticable receiver architecture are proposed while performance metrics and the selection of parameters are analysed. Finally, this scheme is demonstrated with a specific implementation and parameter selection for Beidou B1C civilian signals.

Muzi Yuan, Xiaomei Tang, Shengqiang Lou, Chunjiang Ma, Gang Ou
##### A Slowly Varying Spoofing Algorithm for Tightly-Coupled GNSS/IMU with Multiple Anti-spoofing Techniques

Satellite navigation user terminals will be seriously affected if they are not specially protected against signal interference and even spoofing. GNSS spoofing technology has gradually become the focus of jamming technology research because of its great threat and high concealment. In the face of navigation users increasingly adopt coupling GNSS and IMU to varying degrees and configuring a variety of anti-spoofing technologies to detect spoofing, even if the spoofing is carried out slowly, if the spoofing strategy is unreasonable, it will lead to the estimated parameters of the coupled filter output, or the spoofing measurement does not meet the reasonable range, which will lead to the detection of spoofing and greatly increase the difficulty of spoofing. In view of the above problems, in order to effectively counteract the unidentified object equipped with tightly-coupled navigation system by using spoofing technology, this paper establishes the GNSS spoofing model, based on the analysis of the influence mechanism of spoofing on tightly-coupled GNSS/IMU positioning, a slowly varying spoofing algorithm is proposed to spoof tightly-coupled GNSS/IMU system for configuring the least squares residual RAIM and verification and inspection of reasonable range of parameters, the algorithm gives a measurement deviation determination method to avoid a variety of anti-spoofing technologies. The algorithm can gradually pull the positioning results of the tightly-coupled system, and successfully avoid the detection of a variety of anti-spoofing technologies to achieve the purpose of spoofing. The experimental results show that the algorithm can gradually change positioning of tightly-coupled GNSS/IMU within 72 s, and the north displacement completely achieves purpose of spoofing, the east and down displacement basically achieve purpose of spoofing, the errors with the expected offset are 2.3 m and 13 m respectively. At the same time, it avoids the detection of the above anti-spoofing techniques. The mean value of test statistics for tightly-coupled is reduced by 83.1% and does not exceed alarm threshold, so as to achieve the purpose of spoofing, so that the spoofing algorithm has high concealment and application value.

Yangjun Gao, Guangyun Li, Li Wang, Ruoxin Zhu, Pengjin Zhou, Zhongpan Li
##### A Pulse Phase Estimation Method Based on Improved Particle Swarm Optimization

X-ray pulsar-based navigation (XPNAV) is a celestial autonomous navigation method based on X-ray pulsar observation. The pulse phase estimation has been the key point of XPNAV because the balance of accuracy and efficiency in pulse phase estimation is difficult to obtain. In response to this problem, a pulse phase estimation method based on improved particle swarm optimization is proposed. Experiments were conducted based on simulation data and real data. The results demonstrate that the proposed method significantly reduces the CPU time cost of pulse estimation on the premise of guaranteeing high reliability and accuracy.

Yike Qiao, Yusong Wang, Wei Zheng
##### Hybrid Channel Modeling and Multi-frequency Propagation Characterization for GNSS in Urban Canyons

In order to evaluate the multi-frequency transmission performance of satellite navigation in urban canyon environment, the channel model needs to take into account the difference of multi-frequency transmission channels. Besides, the deterministic channel model lacks the precise details of electromagnetic environment. To assess the multi-frequency propagation characteristics of the Beidou navigation system, this study proposes a hybrid channel model that combines the propagation graph model with ray-tracing technology. Based on the virtual simulation of urban canyon environment, the characteristics of pseudo-range error of multi-frequency satellite navigation system are initially revealed. The simulation results show that the model can consistently represent the dense multipath component and its impact on the power delay profile and channel transfer function. Furthermore, as compared to the traditional satellite navigation channel model, the modelling method of ray-tracing embedded propagation graph described in this study improves the simulation details of multi-frequency propagation characteristics.

Shun Zhou, Gang Ou, Xiaomei Tang, Wei Xiao, Pengpeng Li
##### Research on Optimizing the Carrier-to-Noise Ratio of RDSS Inbound Signal Based on Improved Moving Weighted Average Method

The measurement and control center has the problem that the estimation of the inbound signal Carrier-to-Noise Ratio (CNR) of RDSS users is relatively rough. A method for optimizing the CNR of the user’s inbound signal based on an improved moving weighted average method is proposed to solve the problem. Firstly, analyze and preprocess the characteristics of the inbound CNR of RDSS users. Then build an improved weighted moving average method model according to user characteristics. Finally, the actual engineering data is used to compare the improved moving weighted average method and the average method. The sliding parameters in the improved moving weighted average method are optimized to verify the feasibility and accuracy of the method. Experimental results show that the enhanced moving weighted average method is better than the average, and when the sliding parameter is 5, the effect of this method is better.

Li Wang, Hai Sha, Tianqiao Zhang, Xuyu Wang, Yingying Zhao, Dongfang Jiang, Heng Wei
##### Research on the Influence of Satellite Signal Transmission Channel’s Non-ideal Characteristics on the Quality of Different Envelope Signals

At present, most satellite navigation systems use constant envelope multiplexed signals, in order to reduce the non-linear influence of the power amplifier as much as possible. However, the actual signal transmission channel cannot be purely ideal. Various amplitude-frequency or phase-frequency distortions that may occur will affect the signal envelope characteristics and ranging performance, resulting in a certain difference between the actual signal received by the user and its theoretical design. Research has shown that the performance of the constant envelope signal after passing through the non-ideal channel may not be better than the corresponding non-constant envelope signal. In order to fully understand the specific effects of various non-ideal characteristics of the channel on the non-constant envelope signal and to judge under which non-ideal characteristics the non-constant envelope signal can show better performance, so as to provide new ideas for the design of navigation signals. This article first studies the non-ideal characteristics of the satellite signal transmission channel and establishes five channel distortion models. The BDS-3 B1 constant envelope and non-constant envelope simulation ideal signals are used as the research signals of this article, use the software receiver to evaluate the signal quality of the ideal signal after the distortion model, and use the evaluation index S-curve zero-crossing deviation to express the signal's ranging performance. Finally, the quantitative analysis and comparison of the ranging performance of different envelope signals under the influence of various distortions are realized. The results show that: Inaddition to amplitude ripple distortion, non-constant envelope signals show better ranging performance overall under the same distortion conditions. The research results of this paper have certain reference value for signal design and signal quality evaluation.

Qianqian Yang, Chengyan He, Zhigang Hu, Zibin Han
##### Research on Multi-parameter-based Spoofing Detection Method for Satellite-Based Train Positioning

Train positioning technology based on Global Navigation Satellite System (GNSS) is an important content of the next-generation railway train control systems. Under the complex train operation environment, spoofing to the navigation satellite signals can affect the accuracy and credibility of the train positioning result and may even lead to accidents. Based on the principle of spoofing, this paper designs multiple sets of experiments and analyzes the degradation mechanism of characteristic indices of navigation satellite signals under spoofing conditions. Base on that, the characteristic consistency detection and identification scheme to GNSS spoofing is proposed by multi-dimensional parameters within both the observation domain and position domain. Using a navigation satellite signal simulator and the filed data, a typical GNSS spoofing test scenario dedicated to the train operation process is generated, and the spoofing detection method proposed in this paper is validated. The results illustrate that this method can integrate multiple parameters to realize effective spoofing detection and identification, which enables the effective spoofing protection capability for GNSS-based train positioning.

Jun-xi Liu, Jiang Liu, Bai-gen Cai, Jian Wang
##### Dispersion Analysis of Ranging-Code Markers Applied to Beidou B1C Signal Based on Chimera

At present, in order to improve the security capabilities of the civil navigation signal system, both Galileo and GPS have proposed a navigation signal authentication scheme. However, there is no civil official navigation signal authentication scheme for Beidou Navigation System, so it is necessary to propose a navigation signal authentication scheme suitable for Beidou signal system. This paper is mainly to prepare for the subsequent research on the navigation signal authentication scheme adapted to Beidou B1C signal. Chimera is applied to Beidou B1C signal to study the impact of the dispersion of markers. In this paper, by setting other parameters constant, define the markers’ dispersion. Under circumstances of different dispersion, research the collision probability of the segment and the correlation performance of the encrypted ranging code. Draw the following conclusion that the dispersion of markers rarely affects the correlation performance. While the dispersion is higher, the collision probability of the segment will be greater. In the design of spreading code authentication scheme, it is sufficient to determine the dispersion of markers from the perspective of the collision probability of the segment.

Huanyu Wang, Xiaomei Tang, Muzi Yuan, Gang Ou
##### Band-Limited Multicarrier Multiplexing Technique for Navigation Signals

In order to reduce the complexity of the payload on the satellite, the navigation signals located at several adjacent frequency points usually need to be multiplexed and transmitted through a common transmission link. Existing multicarrier multiplexing techniques usually require that the composite signal have a constant envelope to reduce nonlinear distortion caused by the high-power amplifier (HPA). However, due to the bandwidth limitation of the filter, the constant envelope characteristic of the composite signal is damaged to a certain extent, so HPA linearization is still needed. In this paper, we assume that the HPA is well linearized, and propose a band-limited multicarrier multiplexing technique for navigation signals. Firstly, the mathematical model of band-unlimited multicarrier multiplexing problem is established. In this band-unlimited model, we clarify that the composite signal is composed of navigation signals and auxiliary signals introduced to reduce the peak-to-average power ratio (PAPR) of the composite signal. Then, the band-unlimited navigation signals and the auxiliary signals are simultaneously filtered. Next, we establish an optimization problem which takes the linear combination coefficients of the filtered auxiliary signals as the optimization variables and minimizes of the infinite norm of the composite signal, so as to optimize the amplification efficiency of the useful navigation signals. This optimization problem is convex, therefore the global optimum can be obtained easily. At the same time, the proposed method ensures that the introduced auxiliary signals do not adversely affect the reception of useful signals. Simulation results show that the proposed method can achieve lower PAPR and higher amplification efficiency compared with existing methods. In addition, the proposed method has high flexibility, which deals with single carrier multiplexing and multicarrier multiplexing in a uniform framework, and can support diversified modulation schemes.

Junjie Ma, Zheng Yao, Mingquan Lu, Yinqiao Li, Yaxing Cai
##### A GNSS Spoofing Detection and Discrimination Method for Smart Terminals

With the widely use of global navigation satellite system (GNSS) and smart terminals such as mobile phones and vehicle navigation devices, the security issue has gradually attracted our attention. It is necessary and urgent to study the applicable GNSS anti-spoofing method for smart terminal users. As a commercial receiver, the smart terminal has many limitations in defending spoofing, but the provided massive GNSS measurements make it possible to develop spoofing detection and discrimination method via multiple smart terminals. In this paper, we utilize Doppler and clock drift information produced by motion smart terminals, and use them to calculate Doppler with clock drift correction, which is different in the authentic scene and spoofing scene due to the Doppler effect of user motion. Based on this, in this paper we design a spoofing detection and discrimination algorithm, analyze the performance, and make field experiments. Experimental results show that the proposed method can detect and discriminate spoofing signals effectively when the smart terminal is at a low speed and provides measurements with a low data rate.

Zhongxiao Wang, Xiaolin Zhao, Hong Li, Mingquan Lu
##### Design of LEO Navigation Signal System Based on Variable Period Spread Spectrum Code

Sixin Wang, Xiaohui Liu, Xiaomei Tang, Feixue Wang, Zhaowen Zhuang
##### Acquisition Algorithm Optimization Based on Amount of Computation and Performance Joint

Signal acquisition is the prerequisite for the receiver’s work. The current optimization of the signal acquisition algorithm is mainly focused on the improvement of the acquisition performance, and the optimization of the signal acquisition calculation amount is relatively ignored. Aiming at the computational optimization problem of the navigation signal acquisition algorithm, this paper establishes the equivalent detection capability factor under the unit computational complexity, determines the optimal search interval, and establishes the computational model of the acquisition process. The three common signal acquisition search algorithms are analyzed in detail, and the joint optimization of signal acquisition performance and computational complexity is established. In this paper, a joint optimization function of signal acquisition performance and computational complexity is established, the optimal pre-detection integration time is determined, and the acquisition algorithm is optimized. For the parallel acquisition algorithm in the frequency domain, the acquisition performance can be optimized by only about 1.87 dB, and nearly 60% of the acquisition calculation amount can be optimized, sacrificing part of the acquisition performance in exchange for a smaller computational complexity. The acquisition algorithm optimization method in this paper can alleviate the shortage of computing resources caused by the rapid increase in the number of signals during the development of low-orbit systems, and can also be applied to low-power receivers to reduce the resources consumed by acquisition.

Pengcheng Zhang, Xinming Huang, Jingyuan Li, Zengjun Liu, Gang Ou
##### Backmatter
Title
China Satellite Navigation Conference (CSNC 2022) Proceedings
Editors
Prof. Changfeng Yang
Prof. Jun Xie