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About this book

China Satellite Navigation Conference (CSNC 2021) Proceedings presents selected research papers from CSNC 2021 held during 22nd-25th May, 2021 in Nanchang, 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 CSNC2021 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

Time Frequencies and Precision Timing

Frontmatter

Research on the Method of Autonomous Establishing and Maintaining the Synthetic Atomic Time of Satellite Navigation Constellation

The autonomous establishment and maintenance of synthetic atomic time in satellite navigation constellations is increasingly becoming the development requirements of satellite navigation systems, this article systematically discusses the composition framework of synthetic atomic time in satellite navigation constellations. Inter-satellite/satellite-to-ground time-frequency comparison measurement technology, satellite navigation constellation synthetic atomic time distribution technology, and constellation dynamic clock group management technology have been modeled, using Beidou precision clock error data provided by IGS’s multi-GNSS experiment project (MGEX). The performance simulation of the synthetic atomic time of the satellite navigation constellation was carried out. Based on the synthetic atomic time established by six MEO satellites equipped with on-board hydrogen clocks in orbit, the astronomical stability has been increased from 5E−15/d for a single satellite (hydrogen clock) to 3.28E−15/d, with a 24-h forecast error increased from 14 cm for a single satellite (hydrogen clock) to 9 cm, which preliminarily proved the feasibility and effectiveness of the autonomous establishment and maintenance method for the synthetic atomic time.

Jun Lu, Richang Dong, Chengpan Tang, Yinan Meng, Gong Zhang, Jianhua Shen

A New Method to Suppress the AC-Stark Shift of Compact Cesium Beam Atomic Clocks

Cesium beam atomic clocks are widely used as frequency standards in time-keeping, communication, navigation and positioning as primary frequency standards. Compared to cesium beam clocks with magnetic state selection, optical pumping clocks have several advantages like high utilization rate of cesium atoms, no Majorana transition, etc. However, they have an obvious drawback, the AC Stark effect, or the so-called light shift. In order to solve this problem, this paper presents a new method to suppress the light shift in cesium beam clocks. The clock used in experiment uses the optically detected magnetic-state-selection scheme. We demonstrate theoretically that the α and β coefficients can be strongly suppressed by introducing the detuned light into the detection light. In addition, we experiment this scheme and the α-coefficient is successfully reduced from 1.23E−12/mW to 8E−14/mW. We also test the long term frequency stability with additional laser intensity noise. It’s shown that the Allan deviation at 20000s is reduced from 2.0E−13 to 5.9E−14, which reveals the suppression of the light shift with our method. Although the scheme proposed in this paper is based on optically detected magnetic-state-selection scheme, this method can be easily applied to compact optical pumping Cs clocks. These results are relevant for improving the long-term frequency stability of compact cesium beam atomic clocks.

Shaohang Xu, Sifei Chen, Chang Liu, Yining Li, Jiale Wang, Yanhui Wang

A Compensation Method of Satellite Clock Day-Boundary Jumps Based on Epoch-Differenced

The satellite clock products are essential for precise point positioning (PPP). They can be obtained from International GNSS Service (IGS) analysis centers for most users. However, the final clock products provided by IGS analysis centers have day-boundary jumps between two adjacent days. The traditional compensation method based on single-epoch may introduce satellite clock errors, and then leads to a poor accuracy of PPP at the day-boundary. In this paper, a compensation method based on epoch-differenced is proposed. The method makes full use of all the satellite clock data before and after the day-boundary. After averaging clock data based on epoch-differenced, the day-boundary compensation items are estimated accurately. The final satellite clock products provided by Center of Orbit Determination in Europe are used to verify the compensation effect of the method proposed in this paper. The results show that, compared with the traditional compensation method based on single-epoch, the RMS and STD of clock model fitting residuals are improved by 1.80% and 9.83%, respectively. In addition, the RMS and STD accuracy of PPP are improved by 47.73% and 55.64% within two hours after the day-boundary, respectively.

Weiquan Huang, Menghao Li, Hui Li, Renlong Wang, Nan Li, Liang Li

Research on Integrity Monitoring Techniques for Atomic Clocks Based on DualKalman Filter

As the core component of time-frequency reference generation of satellite navigation system, atomic clock is the guarantee for high-precision navigation signal generation and reception. The integrity monitoring of atomic clocks is the basis for time reference generation and spatial high-precision measurement. This paper adopts the idea of Kalman filter prediction residuals for integrity monitoring, establishes an accurate Kalman filter model of the atomic clock, constructs the Kalman prediction residual vector, and performs two-level Kalman filtering to form a DualKalman filter to improve detection sensitivity. Using IGS data to analyze the calculation examples, the results show that the DualKalman filter integrity detection technology proposed in this paper has the characteristics of high-sensitivity detection and can be used as a GNSS ground/satellite clock integrity monitoring method.

Xinming Huang, Zhiling Ren, Jing Peng, Hang Gong

The Beam Optics Analysis Based on Monte Carlo Simulation of the Magnetic State Selection and Optical Detection Cesium Beam Clock

Compact cesium beam clocks are of great importance in navigation, time-keeping and precision measurements. In traditional cesium clocks, cesium atoms are deflected by strong inhomogeneous magnetic fields, whose velocity distribution and populations of different quantum states are altered. Normally, the distributions are hard to describe with analytical functions. An alternative solution is to apply the Monte Carlo simulation to sample the atoms and calculate the trajectories. We apply the method to cesium beam clocks based on the magnetic state selection and fluorescence detection scheme. The state distributions of the detectable atoms are obtained with Monte Carlo simulation inside the collimator and finite element simulation of the magnetic field. The performance of the cesium beam tube is also estimated via the sampled atoms, such as the signal amplitude and the signal-to-noise ratio (SNR) of atomic shot noise and laser frequency noise. The estimated SNR of the designed cesium beam tube is over 7000 in a 1 Hz detection bandwidth. The influence of the deflection angle of the collimator on the performance of the beam tube is analyzed. The method can be used to guide the design of the cesium beam tube and is easily applied to different cesium beam clocks.

Sifei Chen, Shaohang Xu, Chang Liu, Yuanhao Li, Yanhui Wang

High Precision Time Synchronization of LEO Constellation Based on PPP

Low earth orbit (LEO) constellation has significant advantages in enhancing the accuracy and integrity of GNSS. Navigation enhancement using LEO satellites has become a hot topic in the field of satellite navigation. The success of self-height accuracy time synchronization is the key to realizing LEO navigation enhancement. The non-difference precise point positioning is applied to LEO navigation enhanced satellite system to achieve high-precision time synchronization of LEO constellation. In this paper, the “scale factor” method is used to model the ionosphere above the orbit altitude of LEO satellite, and other errors such as receiver clock offsets are modeled. The accuracy and convergence rate of time synchronization of LEO satellite with different orbit altitude are analyzed when the ionosphere is not modified or the dual frequency correction is adopted. The results show that the PPP convergence rate of LEO satellite can reach less than 10 min; the influence of ionosphere on the time synchronization accuracy of LEO satellite can be ignored when the orbit altitude is above 850 km; when the orbit altitude is below 850 km, the ionosphere needs to be modified by dual frequency, and the time synchronization accuracy of LEO satellite after correction can reach less than 1 ns.

Wei Wang, MeiTing Yu, Hang Gong, Ming Ma, GuangFu Sun

A Rubidium Atomic Frequency Standard with Stability at Level Operated Under Atmospheric Condition

Among several kinds of traditional atomic clocks, rubidium atomic clock shows more extensive applications for its small size, low power and simple structure. In last 20 years, driven by the demands of satellite navigation and relevant fields, the Rb atomic clock has been greatly improved on its frequency stability. Now the long-term stability of satellite-borne Rb atomic clock is better than $$5 \times 10^{ - 15}$$ 5 × 10 - 15 at one day. However, when Rb clock runs under atmospheric condition, its long-term stability performance deteriorate seriously. There is a 10 to 100 times deterioration at $$10^{4}$$ 10 4 s and one day, which makes Rb clock impossible to reach $$10^{ - 15}$$ 10 - 15 level. For solving these problems, to develop a high-stability, low-drift and compact-structure type of high performance Rb clock which could fit the atmospheric environment, we conducted a sufficient research on high-performance Rb clock’s environment adaptation. Finally, we developed a prototype whose stability reached $$6.5 \times 10^{ - 13} /\sqrt \tau$$ 6.5 × 10 - 13 / τ , $$7.0 \times 10^{ - 15}$$ 7.0 × 10 - 15 at $$10^{4}$$ 10 4 s and $$5.0 \times 10^{ - 15}$$ 5.0 × 10 - 15 at one day.

Junyao Li, Gang Ming, Feng Zhao, Fang Wang, Pengfei Wang, Ganghua Mei

A Closed-Loop Calibration Method of the BeiDou Time Receiver

The receiver calibration error is the major error source for the common-view time transferring. Presently, the Bureau International des Poids et Measures (BIPM) only provides the official calibration on the GPS signals. The receiver calibration on the BeiDou signals is still under test. A closed-loop calibration method of the BeiDou time receiver was proposed based on the closed-loop of the BeiDou time (BDT) from the ground segment to the space segment, the user segment. Further, the effect of the differential code bias (DCB) on the calibration method has been analyzed. The experiments show that the calibration uncertainty on the BeiDou signals of the golden receiver is better than 1.3 ns. The uncertainty of a new receiver which is calibrated with the golden receiver is better than 1.8 ns.

Guojun Li, Di Zhang, Yongxin Lin, Jiawei Wang

Feasibility Analysis for Evaluating On-Board Atomic Clocks by Inter-satellite Clock Offset

Inter-satellite link (ISL) plays an important role in GNSS. First inter-satellite clock offset is analyzed, which is used for evaluating the on-board clocks. Then, the feasibility of evaluating on-board atomic clock is discussed which is produced by ISL data. After building the model of evaluating inter-satellite clock offsets and simulating on-board clock offsets, the on-board clock performances are evaluated by polygon hat method. The result is compared with precise clock offset. The conclusion shows inter-satellite clock offset can be used for evaluating performance for BDS-3 on-board atomic clocks which the frequency stability is reaching E-15.

Bin Yang, Yiwei Wu, Shichao Wang, Maolei Wang, Shenghong Xiao, Yufei Yang

Relativistic Effect in the Two-Way Time Comparison Between Navigation Satellites

Influenced by the high-speed of satellites and the gravitational field of the earth, the satellite-borne clock is affected by the effect of special and general relativity. The classic Newtonian theory in the earth space only achieves time-transfer accuracy within 1 × 10–8, which is far from matching the performance of the current satellite-borne clock and satisfying inter-satellite time comparison accuracy. This paper has studied the inter-satellite two-way time comparison under the framework of relativity, and the real data of inter-satellite links is used to analyze the relativistic effect of the Beidou-3 inter-satellite two-way time comparison. The results have demonstrated that the gravitational delay of the inter-satellite measurement signal caused by the central gravity of the earth reaches the order of sub-nanosecond, but the asymmetry of gravitational delays in the two-way time comparison is only 0.01 ps which can be ignored with the sub-nanosecond time comparison accuracy; the amplitude of the periodic relativistic effect introduced by the central gravitational field of the earth is about ±1~ ±2 ns, which must be corrected as a systematic error; the periodic relativistic effect introduced by the gravitational J2 perturbation of the earth reaches ±0.1 ns, which needs to be compensated with the time comparison accuracy of the sub-nanosecond order. In the currently released satellite precision clock products and broadcast ephemeris, only the relativistic effect correction caused by the central gravitational field of the earth is considered. With the continuous improvement of the performance and time transfer accuracy of the spaceborne atomic clock, further consideration of the relativistic effect modification from gravitational J2 perturbation of the earth is required.

Leyuan Sun, Shuaihe Gao, Jun Yang, Feng Xiao, Yuankun Fang, Sen Feng

Performance Evaluation and Analysis of BeiDou In-Orbit Satellite Atomic Clocks Based on Multiple Source Data

As a key payload, the performance of the satellite-based atomic clock will have an important impact on the whole navigation system. At present, the on-orbit performance evaluation of satellite-based atomic clocks is mainly based on the precise clock bias products released by IGS MGEX, iGMAS, and other organizations. Due to the influence of space environment changes, equipment aging, and other factors, there are gross errors in the clock bias data. In this paper, we propose a method of using SAIM clock monitoring telemetry data to assist in the detection and rejection of gross errors in the precision clock products, and then select the typical satellites C19, C20, C36, C37, C41, and C42 of Beidou-3 with different life spans to evaluate and analyze the in-orbit performance of rubidium atomic clocks. The multi-source data of Beidou-3 satellites are from 2019-01-01 to 2020-11-21. On this basis, the in-orbit performance of the rubidium atomic clock is analyzed and evaluated in terms of satellite clock stability, frequency accuracy, frequency drift rate, and other indicators. The evaluation results show that the Beidou C19, C20, C36, C37, C41, C42 satellites 10,000 s frequency stability reached the order of 10−14, frequency drift rate (days) overall in the order of 10−13, frequency accuracy overall in the order of 10−11.

Songtao Huangfu, Weisong Jia, Hui Yang, Jin Chang, Lifang Yuan, Junwu Zhai

Research Progress of Inter-satellite Precision Measurement and Time-Frequency Synchronization Technology Based on USO

Ultra-stable oscillator (USO) is a kind of OCXO with excellent short-term frequency stability performance. It has been gradually applied in the aerospace field such as high-precision measurement and time-frequency synchronization with very good results and exhibited huge application potential in China in recent years. Firstly, the paper outlines the characteristics of USO and the development status at home and abroad. The background of the first use of USO in China and the progress of localization is introduced. Secondly, for high-precision inter-satellite time synchronization requirements, we have achieved inter-satellite time synchronization performance with accuracy better than 0.1 ns using USO and low-orbit GPS receiver. Relevant performance evaluation method and actual measurement results are introduced. Finally, an inter-satellite ranging system combining USO and GPS precision orbit determination with actual measurement performance better than 5 um accuracy is achieved. The overall plan, evaluation mechanism, progress and results are given as well. The article gives the potential application direction of USO in the future, which has certain reference and reference significance for future gravity field detection, gravitational wave detection and load research in other scientific fields in China.

Xuan Liu, Xingwang Zhong, Dalei Xue, Pan Zhang, Yifeng He

Design and Fabrication of Thermostat for the Hydrogen Maser

In this paper, a temperature thermostat used for the hydrogen maser is designed and fabricated based on the analysis of heat dissipation of the hydrogen maser. The high power and precise temperature control is realized by using the PID temperature control and semiconductor refrigeration techniques in the design and fabrication of thermostat. Under the condition of 300 W heat dissipation, the temperature fluctuation is within ±0.05 ℃, better than the existing similar products in the worldwide. The thermostat could provide excellent temperature environment for a high performance hydrogen maser.

Shuo Liu, He Yang, Weili Wang, Kai Huang, Yushan Lu, Yaxuan Liu, Liang Wang

Design of Low Additional Stability Multi-channel Digital Phase Comparator

In this paper, the multi-channel low additional stability phase comparator is designed and fabricated based on the technique of digital double mixing cascaded analog double mixing while noise suppression is used in the frequency doubling link. Compared to the single analog double mixing technique, the method presented in this paper is more advanced in the low additional stability. When the input frequency is 10 MHz, the additional stability reaches 1.7E−14@1s 2.7E−15@10s, 4.6E−16@100s, 1.37E−16@1000s, 4.4E−17@10000s. The multi-channel comparator designed in this paper will satisfy the requirement of high performance atomic clocks in the time keeping lab and novel frequency clocks and microwave sources.

Kai Huang, Yanjun Chen, He Yang, Shuo Liu, Yushan Lu, Yaxuan Liu, Liang Wang

Monitoring Assessment and Impact Analysis of BeiDou and GNSS Time Offset

Global Navigation Satellite System (GNSS) time offset is one of the most important foundations for GNSS interoperability. BeiDou satellites broadcast BeiDou time and other GNSS time offset parameters (BGTO parameters) through navigation messages, ensuring that receivers can use multiple GNSS systems for integrated positioning. In this paper, the definition of the time offset error (BGTOE) are studied; the quantitative relationships between BGTOE and joint positioning result and accuracy are derived. Then the BGTOE is accessed based on the data of UTC(k) and BIPM Circular T. Evaluation results show that the fluctuation range of BGTOE is about 27 ns, and the standard deviation is about 10 ns. It will produce a position offset of 12.6 m and a time offset of 14.7 ns for joint positioning results. In a longer time scale, it will bring about a loss of position accuracy of about 10 m and a loss of time accuracy of about 20 ns, which can basically meet the needs of joint positioning, but there is still room for optimization from the prospect of improving the joint positioning performance.

Shichao Wang, Ying Liu, Maolei Wang, Bin Yang, Lin Zhang, Haibo Yuan

A Satellite-Ground Precise Time Synchronization Method and Analysis on Time Delay Error Caused by Motion

Currently for the accuracy of long-range time transfer can only reach up to 100 ps, limiting the wide application of high-precision time-frequency reference in space science. The study of the satellite-ground precise time synchronization method can provide an effective solution for developing long-range time transmission technology. In this paper, a satellite-ground time synchronization method based on two-way time difference measurement is studied. Simultaneously, we propose a method for correcting the time delay error caused by satellite and ground station motion, and the related analysis is carried out. The simulation results show that when we control the attitude error within 72 as (0.02°), the phase center calibration error is less than 1 mm, the precise orbit determination error is less than 10 cm (three axes), the satellite-ground time synchronization performance is better than 0.02 ps after correcting the time delay error caused by target motion based on the two-way time difference measurement without considering other error factors. With the other error impacts (ignore calibration error of atmospheric parameters), the satellite-ground synchronization performance can reach 0.45 ps. The research of satellite-ground precise time synchronization and error correction can provide an inevitable technical accumulation and reference for high-precision time-frequency transmission technology in space.

Yanming Guo, Yan Bai, Shuaihe Gao, Zhibing Pan, Zibin Han, Yuping Gao, Xiaochun Lu

Ground Environment Test and In-Orbit Performance Verification of Spaceborne Cesium Atomic Clock

Spaceborne cesium atomic clock with magnetic selectors (SCAC) has been used in the global navigation satellite system (GNSS), which can not only improve the positioning accuracy, but also enhance the ability of autonomous operation. So a SCAC product is very favored, but it is very difficult to manufacture. Until November 2019, among the world’s four largest GNSS, only GPS in the U.S. and GLONASS in Russia are equipped with the SCACs. But this situation has been changed now, the first SCAC product in China has been developed by improving its cesium beam tube, frequency standard circuit etc. based on the prototype [1]. The product has been carried on the Beidou navigation satellite and its working state is stable in orbit at present. The analysis results of on-ground and in-orbit data show that the key performance indexes such as frequency accuracy, long-term stability and frequency drift rate could meet the application requirements, and that the product has good space environment adaptability. This paper discusses on the ground environmental test items, methods, conclusions and in-orbit verification related to the product, and summarizes some achievements and experiences in tackling the key technology of the SCAC environmental adaptability, which is very helpful for improving the design ability in space environmental adaptability of atomic clocks.

Jun Yang, Ning Zheng, Jingzhong Cui, Shiwei Wang, Wei Yang, Pei Ma, Zhidong Liu, Jiang Chen, Yinguang Ma, Yulong Zhao, Liangyu Huang, Pengling Dong

Analysis of In-Orbit Data of Domestic Space-Borne Cesium Atomic Clock

Space-borne cesium clock is the load of space time keeping system of navigation system, which provides frequency information with high accuracy and high stability for positioning and timing. Satellite-borne cesium clock has the characteristics of low drift, high frequency accuracy and high environmental adaptability. The Beidou Navigation Satellite carried a cesium clock, which is the first time that China has sent a domestic cesium clock into space. The performance of the cesium clock can be characterized by frequency stability, accuracy and drift. Taking the passive hydrogen clock as a reference, the output frequency signal of the cesium clock was measured and transmitted down to the ground. Based on the phase comparison data of 29.17 million valid data points, Allan Deviation was used to calculate the frequency stability of the space-borne cesium clock, which was 1.91E−12 per second, 4.95E−14 per 100,000 s. And the frequency accuracy was 1.73E−12. The frequency drift rate was 1.12E−16/day.

Pei Ma, Jun Xie, Jingzhong Cui, Zhidong Liu, Pengling Dong, Shiwei Wang, Jiang Chen, Wei Yang, Lu Wang, Ji Wang, Yinguang Ma, Jianxiang Wang, Jiqing Lian, Liangyu Huang, Jun Yang, Yulong Zhao, Ning Zheng, Dongjun Wang

GNSS Signal Processing

Frontmatter

Low Complexity Acquisition and Tracking Methods for CSK Modulated Signals

In order to meet the demand of high-precision positioning, GNSS PPP service needs to broadcast the precise correction message frequently. The required data rate is usually above 500 bps, which is significantly higher than the 50 bps rate of the traditional GNSS signal. Therefore, QZSS L6 signal adopts CSK modulated signal. CSK modulated signal has become an important candidate for GNSS signal with high data rate. Compared with the BPSK signal, CSK modulated signal uses code phase to carry data bits, and can flexibly increase the data rate while keeping the code period unchanged. However, the existing CSK modulated signal is mainly used for data transmission, which is not suitable for signal acquisition and tracking. Other signal components are required to assist the demodulation of CSK modulated signal. To solve this problem, this paper extends the definition of CSK modulated signal, and on this basis, proposes a low complexity acquisition and tracking method for the CSK modulated signal. This method can acquire and track the CSK modulated signal directly without relying on the extra signal components. Theoretical analysis and simulation results verify the effectiveness of the proposed method. Compared with BPSK signal in terms of the acquisition and tracking performance, the direct acquisition and tracking performance of CSK modulated signal is degraded. However, the performance of CSK modulated signal can be compensated by coherent accumulation. In addition, CSK modulated signal does not rely on other signal components for acquisition and tracking, which enhances significantly the independence of receiving CSK modulated signal.

Tao Yan, Ying Wang, Tian Li, Ye Tian, Lang Bian, Yansong Meng

Reflection Objects Sensing and Localization with GNSS Multipath Signals

In urban canyon environments, the reception of GNSS multipath signals will cause the degradation of positioning precision of a GNSS receiver, and sometimes will lead to hundreds of meters positioning error. However, multipath signals, which are generated by reflections of the satellite line-of-sight signal, contain information about positions and velocities of the reflection objects. Therefore, they give means for a receiver to sense surrounding objects and environments. In this paper, an algorithm for he reflection object sensing and localization with GNSS multipath signals is proposed. The results of experiments show that this algorithm is able to estimate the distance, azimuth, and elevation of the reflection object with respect to the receiver with a root mean squared error of 10 m, 10°, and 5°, respectively. This method enables a GNSS receiver with the capability of environment sensing, avoidance of obstacles, and even positioning augmentation apart from its original positioning and navigation ability.

Xin Chen, Yilun Shao, Di He, Wenxian Yu

A High-Precision Doppler Frequency Estimation Algorithm for CDMA-TDMA Navigation Signal Structure

In the pseudolite-based area navigation system, the code division multiple access (CDMA) and time division multiple access (TDMA) signals are usually jointly applied to solve the near-far effect. However, the effective integration time during acquisition is shortened due to the characteristic of TDMA signal, and the accuracy of Doppler frequency estimation is then reduced, which does not meet the requirement of carrier tracking loop. To solve this problem, this paper proposes a high-precision Doppler frequency estimation algorithm. In this algorithm, the low-precision estimation of Doppler frequency is obtained during acquisition. Thereafter, the medium-precision estimation is realized by non-coherent integration and quadratic interpolation. Finally, Prolonging the effective coherent integration time via data code searching, high-precision Doppler frequency estimation is obtained. Experiments are carried out with the measured data, and the results show that the accuracy of Doppler frequency estimation is greatly improved, and meets the requirement of carrier tracking loop.

Jiancheng Zhang, Lina Xu, Mengting Zhang

Research and GPU Parallel Implementation of the Compatibility Analysis Methodology Between FDMA and CDMA Navigation Signals

Many major countries are actively developing their own Global Navigation Satellite Systems (GNSSs) and the compatibility between GNSS signals has become a focus of research. The methodology provided by Recommendation ITU-R M.1831 only applies to interference analysis between CDMA navigation signals and currently there are no compatibility analysis methods applied to FDMA navigation signals. Based on the ITU Recommendation, we propose a new concept named Frequency Division Spectral Separation Coefficient (FD-SSC) for FDMA signals. Furthermore, a compatibility analysis methodology between FDMA signals and between FDMA and CDMA signals is presented based on FD-SSC. Besides, we propose a GPU parallel computing implementation scheme for large scale compute-intensive link calculations in order to improve the computation efficiency. Experimental results show that GPU parallel computing implementation shortens the computation time by more than 20% compared with traditional serial computing implementation. Finally, an application example of the proposed methodology for compatibility analysis between BDS and GLONASS in the B2/L3 band is demonstrated.

Weinan Zhang, Xia Ge, Zheng Yao, Jiemin Shen

A GNSS Loop Tracking Structure Based on Unscented Kalman Filter

In GNSS Vector Tracking (VT) receiver, the tracking loop information is used to update the navigation solution. Different from the traditional GNSS receiver, changes of phase and frequency in the tracking loop can affect navigation results directly. In order to improve the fluctuation of the carrier frequency, a GNSS loop tracking structure based on Unscented Kalman filter (UKF) is proposed in this paper. A frequency-locked loop system model is constructed, which includes the state and the measurement equations. The noise variance of each part is used to assist UKF to complete the carrier loop tracking. The experimental results show that the UKF-based tracking carrier algorithm can output stable pseudorange rate changes in weak signal environment. The carrier-to-noise ratio of UKF is higher than the traditional tracking method when the tracking loop lock successfully.

Mingxing Gu, Yuan Hu, Minghui Mou, Shengzheng Wang, Wei Liu

A Vector Tracking Structure of FLL-Assisted PLL for GNSS Receiver

Satellite-based navigation applications have become one of the most common navigation methods in the world. The tracking of satellite navigation receiver in weak signal environments is challenging. To improve receiver tracking performance, a frequency locked loop (FLL) assisted phase locked loop (PLL) vector tracking structure for GNSS receiver is proposed in this paper. In the carrier loop, a carrier tracking algorithm of Kalman filter (KF)-based FLL-assisted PLL is used. In the code tracking loop, the pseudo-range information is fed back to the code numerically controlled oscillator (NCO) through vector tracking, and the code frequency of each tracking channel is adjusted to realize the information sharing of all channels. Experimental results show that, the FLL-assisted PLL vector tracking algorithm can quickly re-lock the satellite signal with good robustness after severe signal fading.

Minghui Mou, Yuan Hu, Mingxing Gu, Shengzheng Wang, Wei Liu

Evaluation of Signal in Space Accuracy of New System Signal of BDS-3 Satellite

Broadcast ephemeris is the basis for satellite navigation system to provide basic positioning and timing service. The precision of signal in space accuracy reflects the distance error caused by the accuracy of broadcast orbit and clock. BDS-3 new system signal has stronger performance and better compatibility. Based on the precise orbit clock error of Wuhan University and DCB products of Chinese Academy of Sciences, the signal in space accuracy of BDS-3 new signal is assessed and analyzed. The results show that the broadcast orbit accuracy of BDS satellite is better than 0.7 m, in which radial direction is about 0.1 m, tangential direction and normal direction are about 0.40 m and 0.45 m respectively. MEO satellite orbit is better than IGSO satellite, which is 0.55 m and 1.12 m, respectively. MEO satellite broadcast clock error accuracy is better than IGSO, 1.7 ns and 3.4 ns, respectively. In terms of signal in space ranging error, BDS satellite is better than 0.6 m, MEO satellite and IGSO are 0.53 m and 1.16 m respectively, which meet the open service performance standard.

Haichun Wang, Xiancai Tian, Longping Zhang, Wei Hu, Junwei Zhang, Shiming Gu, Dezhi Zhang

Interference Mitigation Based on Polarized Pattern Constrained Minimum Variance (PCMV) Using Dual-Polarized Array

The signals of Global navigation satellite system (GNSS) are susceptible to wideband RF interference. Polarized Pattern Constrained Minimum Variance algorithm (PCMV) is proposed to mitigate the interference and retain signal when interference and signal incident in the same direction. Due to polarization sensitive characteristics of dual-polarized array, the DOA and polarization of interference are estimated by TLS-ESPRIT algorithm. PCMV is to constrain the polarized pattern ratio between signal and interference so that the beam towards signal and the null towards interference are achieved in the respective polarized pattern simultaneously. Simulation with a 7-elememt array shows that array using PCMV can form nulls towards interference while form main beam towards signal even when the signal and interference are in the same direction.

Ke Zhang, Lei Chen, Zengjun Liu, Jingyuan Li, Daping Hu, Guangfu Sun

Double Estimation Tracking Method Based on Chirp Delay Locked Loops for BOCC Modulations

Due to the higher power and faster geometric changes, the enhanced GNSS based on LEO satellites has received more and more attention while it has brought the new interference problem. Binary offset chirp carrier (BOCC) modulation has been proposed for better reception performance and anti-jamming ability. The paper has focused on the BOCC modulation and time-frequency characteristics, and presented a double estimation method based on chirp delay locked loops (CDLL) for reception. By analysis of the tracking method, there is no another zero-crossing point in the CDLL, and the phase of the coherent integral is not affected by the delay, which is the key of unambiguous tracking. The simulation shows that the double estimation method can stably track BOCC signal, and the tracking performance is similar with BOC signal. It is worth noting that the tracking performance of BOCC signal with narrowband and correlation interference is better than the corresponding BOC signal. Assuming that the sampling rate is 10 MHz, the power ratio of jamming to signal is 20 dB, the code and carrier tracking performances of BOCC signal are increased by 20% and 29% comparing with BOC signal, respectively. Therefore, the tracking advantages under the jamming can be proved for BOCC modulations, and BOCC modulations provide a new choice for future navigation-augmented signal design and application.

Xin Zhao, Xinming Huang, Xiaomei Tang, Guangfu Sun

An Improved GNSS Vertical Time Series Prediction Model Using EWT

GNSS vertical time series are non-stationary, non-linear, noisy, etc. Based on the in-depth study of the Prophet prediction model and Empirical wavelet transform (EWT), Aiming at the poor effect of the decomposed trend item and the single cycle item in the Prophet prediction process, an improved Prophet prediction method using EWT is proposed. First, the original time series is decomposed by EWT. Then, prophet prediction is performed on every component and the predicted time series signal is reconstructed. Finally, the accuracy and reliability of the prediction result are verified. This paper uses the measured GNSS vertical time series data from BJFS, WUHN and URUM stations provided by China Earthquake Administration to conduct four short-term prediction experiments with different time spans. The results show that the improved model can better represent the change trend of the original time series. Compared with the single model, its prediction effect is increased by 31.5%, 35.03%, 19.32%, 10.76% in the root mean square error, respectively. The average percentage error increased by 32.76%, 43.61%, 29.28%, 14%, respectively. It shows that the improved model has better short-term prediction effect and better applicability.

Rui Tao, Tieding Lu, Yuanming Cheng, Xiaoxing He, Xin Wang

A Carrier Tracking Algorithm Based on Adaptive Unscented Kalman Filter Under Ionosphere Scintillation Conditions

The rapid change in the phase and amplitude of GNSS signals can cause the strong nonlinearity of carrier tracking under scintillation conditions. Moreover, the noise caused by ionospheric scintillation is non-Gaussian, resulting in difficult determination of the covariance of measurement noise. These would degrade the accuracy and robustness of conventional phase lock loop and extended Kalman filter (EKF)-based carrier tracking algorithms. This work proposes an adaptive unscented Kalman filter (UKF)-based carrier tracking algorithm to mitigate the adverse impacts of ionospheric scintillation. For one thing, the unscented transformation can effectively mitigate the linearization error of strong nonlinear cause by ionospheric scintillation, For another, we employ the phase lock indicator (PLI) to estimate the covariance of the measurement noise adaptively according to different scintillation scenarios. Through the adaptive UKF-based algorithm, the performance of carrier tracking under ionospheric scintillation can be improved, and the probability of divergence can be decreased. Simulation results demonstrate the validity of the analysis and the proposed method.

Pengyue Sun, Shengqiang Lou, Xiaomei Tang, Yangbo Huang

GNSS Spoofing Detection Based on Combined Monitoring of Acquisition Function and Automatic Gain Control

Due to long-distance transmission from satellite to Earth, the received power of GNSS signals is extremely weak, causing that receivers are vulnerable to spoofing attack. Monitoring multiple correlation peaks in the acquisition function and abnormal deviation in the AGC values are two common methods to detect the presence of spoofing. However, it is found that the combination mode of these two methods and the corresponding combined performance have not been fully analyzed and verified. In this paper, the detection performances of these two methods are first analyzed. Next, a combined monitoring based on these two methods is proposed, and its combined performance is analyzed. Finally, a set of experiments are conducted to verify the correctness of theoretical analysis and test the combined detection performance.

Tao Zhang, Xin Chen, Weihua Xie, Wenxian Yu, Weimin Zhen

LFM Interference Mitigation Method Based on Robust Statistics

Global Navigation Satellite System (GNSS) signal interruptions can degrade the quality of service of GNSS-based applications. In order to solve the problem of the Linear Frequency Modulation (LFM) jamming on GNSS signal, this study applies a robust analysis method based on Joint Time-Frequency Analysis (JTFA) to improve the performance of GNSS receiver. The design of robust estimator in the Time-Frequency (TF) domain is realized through the Zero-Memory Non-Linearity (ZMNL) transformation, which is derived from considering the signal as conforming to two-dimensional Laplace distribution. In addition, Monte Carlo experiments are designed for verification of the effectiveness of the robust method. Although this method has a 0.325 dB Loss of Efficiency (LoE) in output Carrier to Noise Ratio (CNR) of the tracking loop compared with the traditional receiver under the jamming-free condition, its performance is better than that of the traditional JTFA method under the condition of LFM interference: under the condition of high jamming to noise ratio, the carrier to noise ratio of the tracking loop is increased by 7 dB. In high sweep rate and multiple LFM interference occasion, the jamming to noise signal ratio is increased by 20 dB under the condition of the receiver loop losing lock limit unchanged.

Yiming Wang, Qiongqiong Jia, Renbiao Wu

A Code Phase Pull-In Method Based on the Zero-Crossing Point of the S-Curve Under the Strong Multipath Environment

The pull-in or traction module in the Global Navigation Satellite System (GNSS) receiver is an important bridge between the acquisition and tracking process, which can compress the code phase and carrier frequency estimation error introduced by the coarse acquisition stage. The method commonly used in the pull-in process of code phase fine-estimation is the interpolation based on multi-correlators, which has a better ability when the power of the multipath signal is lower than that of the direct signal. However, when there are strong multipath signals with higher power than direct signals or spoofing with small delay about one chip, both of them will cause large distortion of correlation peak. As a result, the code phase interpolation method directly leads to a large code phase estimation deviation. In this paper, a traction method based on the first zero crossing of the phase discrimination function is proposed. The S-curve is fitted by the code phase discrimination function based on the code correlation reference waveform (CCRW). Then the code phase value of the first zero crossing of the fitted S-curve is taken as the estimation result. The simulation results show that the code phase traction method proposed in this paper can work well in different multipath scenarios, and can mitigate the code phase estimation deviation introduced by the traditional interpolation method under strong multipath environments.

Pengcheng Ma, Xiaomei Tang, Zhe Liu, Chunjiang Ma, Gang Ou

Anti-jamming Performance Evaluation Method of GNSS Receiver Based on Path Selection

At present, the electromagnetic environment of navigation signals is complex, the anti-jamming performance of GNSS receiver needs to meet higher requirements. At present, there is no systematic method to measure the anti-jamming performance of the receiver, and the dynamic performance is not taken into account. This paper mainly studies the measurement method of anti-jamming performance of GNSS receiver, and analyzes that the anti-jamming performance of GNSS receiver fluctuates with the change of the arrival angle of jamming signal. In view of this, a method of moving vehicle is proposed, that is, the receiver is placed on the vehicle and moves on the closed path with interference source, so that the azimuth angle and elevation angle of the interference signal entering the receiver are wide. In order to quantitatively measure the DOA range of the receiver on different closed paths, the directional coverage index is proposed in this paper. Finally, the three paths of the example are simulated and verified.

Binbin Ren, Shaojie Ni, Feiqiang Chen, Zukun Lu, Jian Wu

Modeling and Evaluation of Pseudorange Deviation of Satellite Navigation Digital Receiver

In GNSS, the pseudo-range deviation of the receiver reduces the positioning and timing accuracy of the user, which significantly affects the service performance of the system. In this paper, the pseudo-range deviation introduced by baseband digital signal processing has been studied. This error is related to the satellite and the receiver, and it is difficult to eliminate it even with differential technology. A digital code phase pseudo-range deviation signal model is established, and it is proposed that the deviation can be decomposed into resolution error and zero-bias error. Combining the characteristics of the error, the applicability error evaluation method is proposed, and the theoretical evaluation result is given. The simulation results show that the error model and evaluation method proposed in the article have the applicability of bandwidth limited effect and Doppler effect, which is helpful to guide the parameter design of satellite navigation receiver.

Chunjiang Ma, Xiaomei Tang, Pengcheng Ma, Song Li, Guangfu Sun

Research on GNSS Time Series Noise Reduction Combining Principal Component Decomposition and Compound Evaluation Index

As a tool of adaptive signal decomposition, SSA can decompose GNSS time series into several SSA components, and select meaningful components to reconstruct, so as to reduce noise. In view of the fact that there is no general method to objectively determine the number of reconstruction layers, an adaptive SSA noise reduction method combining principal component decomposition and composite evaluation indicators is proposed: by combining the root mean square error and smoothness of the denoising signal Negatively correlated indicators are normalized, and then the coefficient of variation is used to determine the weight, and the two indicators are linearly combined to obtain the composite evaluation indicator T; then based on the principle component decomposition idea, the indicator T is combined to determine the number of reconstruction layers, T The smaller the value, the better the denoising effect and the better the number of corresponding reconstruction layers, so that the SSA method has adaptive denoising ability. This method no longer uses qualitative analysis, but uses quantitative analysis to accurately determine the optimal number of reconstruction layers. Through the analysis of simulation data and measured GNSS time series data, it is concluded that adaptive SSA can achieve the best ratio of the two negatively correlated indicators of noise reduction results in detail information and approximation information, and can be applied to GNSS time series under complex noise background.

Xinrui Li, Shuangcheng Zhang, Zhiqiang Dong, Xinyu Dou, Yiming Xue, Lixia Wang, Chuhan Zhong, Yunqing Hao, Qintao Bai, Pingli Li

A Spoofing Detection Algorithm Based on Coprime Array for GNSS Receiver

Spoofing is a deliberate attack that can coerce global navigation satellite system (GNSS) receivers into generating false position/time solutions. The characteristics of spoofing are very similar to authentic GNSS signals, therefore, it is difficult to discriminate their presence. In this paper, we propose a spoofing detection technique based on coprime array before the de-spreading of GNSS receivers. The direction of arrival (DOA) estimation and cross-correlation peaks monitoring are combined to provide a reliable spoofing separation and detection method, in which the coprime array instead of the conventional uniform linear array (ULA) is adopted to DOA estimation so that the proposed technique is effective when the number of signals (include spoofing and satellite signals) is higher than array elements. It is worth noting that all the processes are performed on the raw digital base-band signal samples without de-spreading GNSS signals. The simulation results demonstrate the effectiveness of the proposed spoofing detection technique. Furthermore, the estimated DOA is helpful for spoofing mitigation and location in some applications.

Yuqing Zhao, Feng Shen, Dong Zhou

Unambiguous Tracking Technique for Multicarrier Modulation Signals in the Framework of Cognitive Receivers

With the continuous construction and improvement of global navigation satellite systems (GNSSs), the number of navigation signals broadcast by GNSSs has increased significantly, and the spectrum resources are becoming increasingly scarce. In order to solve the contradiction between limited spectrum resources and the growing demand for positioning, navigation and timing services, some scholars have proposed a multicarrier modulation scheme which multiplexes narrow-band signals in several adjacent spectrum slots into a composite wide-band signal. On the one hand, multicarrier modulation signals can make full use of the spectrum resources, and on the other hand such signals can provide diversified processing strategies. Based on the idea of cognitive receivers and the inherent characteristics of multicarrier signals, we propose two different unambiguous tracking techniques named energy aggregation method and multi-dimensional loop tracking method respectively. In the first method, the energy of different signal components is aggregated, which can improve the positioning performance while maintaining the unimodal characteristic of the correlation function. In the second method, the potential high-precision ranging performance of high-frequency subcarriers in the multicarrier signal is further exploited. By introducing additional subcarrier loop, the one-dimensional correlation function is extended to two-dimensional. In the dimension of subcarrier, the correlation function is sharper and still has the characteristic of multiple correlation peaks, but in the dimension of pseudo-random noise (PRN) code, the correlation function presents the unimodal characteristic, so it can assist the subcarrier loop to eliminate ambiguity. The proposed tracking methods can be embedded in the architecture of cognitive receivers, where GNSS receivers can flexibly configure the receiving parameters according to the internal and external environment, and select proper receiving strategy. For example, in scenarios where the requirement in positioning precision is moderate, the system could select single-component receiving and processing strategy. In scenarios with high requirement for positioning performance, the system will choose multicomponent receiving mode. Simulation results show that in the above two methods, multicomponent wideband reception can improve the ranging accuracy successfully. Besides, the ranging accuracy of the second method is much better than that of the first method.

Junjie Ma, Zheng Yao, Mingquan Lu

GNSS User Terminals

Frontmatter

Optimal Design of Multi-channel Correlator for the Same Code Signal and Its Application in Anti-jamming for GNSS

With the increasing complexity of electromagnetic environment, the appearance of multipath interference in urban canyon and man-made intentional sliding code correlation jamming makes the performance of the traditional satellite navigation receiver, which has the same code acquisition and tracking loop with three channels: early, present, late complex correlators, greatly reduced or even failed. In order to solve this problem, it is pointed that the multiplication and integration of PN code and signals can be realized by using a simple logic operation and a digital adder in the receiver. Based on this idea, a multi-channel correlation operation for the same code is proposed to get the correlation curve for a duration window in real time, so as to discriminate the artificial sliding code correlation jamming. The detection, identification and discrimination on the process about multi correlation peaks meeting, merging and separation caused by the jamming signal ensure the receiver to track the real signal correlation peak continuously and stably. It effectively avoids the situation that the delay locking loop in the traditional navigation receiver is wrong or out of locking. The simulation results verify the effectiveness and correctness of this method. It provides an important reference for the architecture design and anti-jamming application for the next generation satellite digital navigation receiver.

Rong Shi, Junhao Chen, Jinchen Bao

Impact Analysis of Meaconing Attack on Timing Receiver

GNSS timing receivers are widely used in power distribution systems and cellular towers to provide precise timing service, the vulnerability of GNSS makes users face the threat of spoofing. Meaconing brings challenges to time security since it can attack receivers that use military signal. This paper analyzes the impact of two kinds of common meaconing attack on the timing receiver. Aiming at the abnormal step of the receiver clock bias after being attacked, a spoofing detection method based on RFFLS clock bias prediction is proposed. The main factors affecting the detection probability of the method are analyzed, and the conditions that need to be met for the detection probability to reach 99% or more under different clock types are given. The results show that the higher the frequency stability of the clock, the farther the distance between the meaconer and the receiver, and the sooner the detection time from the last time correction, the higher the probability of spoofing detection. High quality TCXO or a clock with higher frequency stability can make the timing receiver have effective spoofing detection capability in short term.

Dong Fu, Jing Peng, Hang Gong, Ming Ma, Gang Ou

An Unambiguous Acquisition Algorithm for TC-OFDM Signals Based on BOC Modulation

The utilization of binary offset carrier (BOC)-modulated signal in communication and navigation fusion system is promising, which can share the communication and navigation frequency band as well as improve the positioning accuracy. In this paper, BOC modulation is introduced into the time and code division orthogonal frequency division multiplexing (TC-OFDM) system, leading to multiple peaks of autocorrelation function (ACF), which will absolutely result in acquisition ambiguity in the traditional BPSK signal receiver. An unambiguous acquisition method based on reconstruction of side peak suppression (RSPS) is proposed. By constraining the non-linear combination of local waveform and received signal without side peak, the local waveform unambiguous waveform set is obtained, and the autocorrelation function is reconstructed. Theoretical analysis and simulation results show that under a good condition of SNR, the unambiguous acquisition algorithm RSPS proposed in this paper can compress the correlation peak width of the BOC (14, 2) modulated communication and navigation fusion signal by more than 80% under the same detection probability as the traditional acquisition method.

Jingrong Liu, Zhongliang Deng, Kai Luo, Shihao Tang, Xiwen Deng

Research on Carrier Tracking Algorithm of INS-Assisted TC-OFDM Receiver with Fuzzy Control

The Time and Code Division-Orthogonal Frequency Division Multiplexing (TC-OFDM) system multiplexes the resources of mobile communication network and has an indoor distributed system, which can achieve indoor and outdoor wide-area coverage of positioning signal. Considering the indoor complex environment, dynamic stress or occlusion will cause a large fluctuation of positioning signal. In order to prevent the sudden change of carrier to noise ratio (CNR) and the loss-of-lock, this paper proposes an INS-assisted receiver carrier tracking algorithm. Through the introduction of fuzzy control, the observation output by the TC-OFDM receiver loop and INS are judged, the fusion switching of INS aided TC-OFDM receiver carrier tracking loop state is controlled, so as to improve the indoor environmental adaptability of the receiver and ensure the robustness of the deeply integrated system in a complex environment. The simulation results show that the algorithm can effectively prevent the loss-of-lock and the divergence of deeply integrated navigation system caused by the sudden change of CNR, and improve the dynamic performance of the receiver.

Guoshun Tang, Fuxing Yang, Zhongliang Deng, Xiwen Deng, Shiwen Jiang

DPCCRW: An Unambiguous Acquisition Technique for High-Order Binary Offset Carrier Modulated Signal

Binary offset carrier (BOC) modulation has been widely adopted in modern global navigation satellite system (GNSS) not only for its characteristic of spectrum-split, but also for its high measuring precision and good multipath mitigation ability. BOC modulation brings the ambiguity problem due to its multiple peak auto-correlation function (ACF). Especially for high-order BOC modulated signal, the ambiguity problem is more serious as its ACF is more complicated. In the paper, an unambiguous acquisition technique with side-peak cancelation method is proposed for high-order BOC modulated signals. By constructing a new local auxiliary signal, and with the help of the traditional Bump-Jump technique, the risk of false lock has been completely removed. Performance analysis results show that the proposed technique has a significant performance improvement compared with the existing methods.

Xinming Huang, Zhang Ke, Jingyuan Li, Zengjun Liu, Gang Ou

Robust GNSS Position Estimation Using Graph Optimization Based Vector Tracking

Vector tracking (VT) is proposed and demonstrated as a superior method to obtain more robust navigation solutions. In VT, instead of individually tracking the signals, VT accomplishes signal tracking and navigation solutions estimation through a central navigation filter, mutual aiding between the channels is realized in this manner. Commonly, a Kalman Filter (KF) is employed as the center navigation filter to estimate the navigation solutions, the estimated navigation solutions are then fed back to calculate the signal tracking parameters. However, KF works in a recursive manner, relationships between the current state and all the past states are ignored, which might degrade the estimation of the navigation solutions. In this paper, we proposed a Graph Optimization (GO) based on VT. GO optimized the state estimation utilizing all the past information instead of KF, the state transformation, and measurement model were all added to the GO as the constraints to optimize the state estimation. An experiment was carried out for assessing the proposed GO-VT, statistical analysis of the navigation solutions and the corresponding comparisons demonstrated the superiority of the proposed GO-VT method.

Changhui Jiang, Yu Chen, Bohao Wang, Yuwei Chen, Shuai Chen, Juha Hyyppä

An Attitude Estimation Algorithm for Satellite Navigation Array Against Gross Error

Based on the assumption that the signal waveform of satellites is known, the DOA of each satellite signal can be estimated by using the maximum likelihood estimation method, and then the antenna array attitude can be estimated by using the DOA of two satellites. Under the jamming condition, the accuracy of DOA estimation of different satellites is different, even wrong estimation may happen, which leads to the failure of attitude estimation. In this paper, according to the accuracy analysis of the maximum likelihood estimation method and the attitude determination error analysis conclusion, the RANSAC based attitude estimation method against gross error is proposed in the process of the antenna array attitude determination, so as to improve the estimation accuracy and fault tolerance. Finally, the simulation results show the effectiveness of the proposed method.

Jie Wang, Wenxiang Liu, Haibin Wang, Lu Zukun, Ou Gang

Self-supervised Calibration Method of Array Antenna for High-Precision GNSS Application

GNSS array antenna have been widely used for single-tone, narrow-band, wide-band interference mitigation in satellite navigation application, however, this induces biases to code phase and carrier phase measurement, which will restrict its usage in high-precision application. Biases could be compensated based on calibration of array pattern in Microwave Anechoic Chamber, which is complicated and could not handle platform influence. Towards this issue, this paper proposed a self-supervised calibration method of array antenna phase center for high-precision GNSS application cooperated with inertial technology. Firstly, high-precision GNSS receiver is designed for amplitude and carrier phase measurement of multi-antennas simultaneously. Secondly, we use a single axis servo turntable to speed up the calibration process by rotation scheme optimization, satellite direction vectors are projected to array coordinate system based on platform attitude measured by an inertial north finder. Finally, data smoothing and local interpolation are utilized for measurement pattern fitting. Open-sky test is carried out, thus validating the effectiveness of this method.

Gang Liu, Kefan Wei, Xiaowei Cui, Mingquan Lu

An Evaluation Method for Anti-sEU Effects Design of SRAM-Based FPGA on Navigation Satellites

In the space application of electronic equipment on navigation satellites, static random access memory (SRAM)-based field programmable gate array (FPGA) circuits will encounter single event effects (SEEs) in space radiation environment, which may lead to functional abnormalities. The mainstream measures often apply hardening technologies such as triple modular redundancy and refreshing error correction to the anti-SEU effects protection designs of FPGA circuits on navigation satellite. Since not all single event upsets (SEUs) will lead to system function failure, in order to comprehensively evaluate the validity of the protection design methods, based on FPGA resource characteristics, this paper firstly proposes an index called classified configuration data abnormal rate. On this basis, according to the effects of single event upsets in different configuration areas on the circuit function, the failure rate and curves of reliability change of different configuration structures are obtained. And through bit-by-bit upset fault injection tests based on the internal configuration access port (ICAP) circuits to verify these evaluation indicators, the experimental results prove the validity of the evaluation method.

Xuhui Liu, Shaojie Ni, Shengqiang Lou, Pengyue Sun, Yangbo Huang

BeiDou Satellite Navigation Terminal Effectiveness Evaluation Based on Cloud Theory

With the continuous development of the Beidou satellite navigation system, the Beidou satellite navigation terminal has been transformed from “bus slot + board card” to modularized and chip-based. Its functions, performance and practicability have been continuously improved, and it has been more and more widely used in military and civil fields. The effectiveness evaluation of the Beidou navigation terminal can accurately grasp the capabilities of the equipment in the process of use, and can provide an important basis for the design demonstration, appraisal and finalization of Beidou navigation terminal equipment. Effectiveness evaluation indicator system for BeiDou equipment is constructed based on the function of the equipment, and index weights are calculated through AHP method. Considering the randomness and uncertainty of the BeiDou equipment effectiveness evaluation, an integrated evaluation method which feasibility is studied by an example, is given using backward cloud and integrated cloud. The evaluation example and result analysis show that this method combining qualitative and quantitative analysis, is not only reduces the subjective factors in the evaluation, but also gets overall and visualized evaluation results, which provides a new way for effectiveness evaluation of BeiDou user equipment.

Juan Wu, Xiaolin Jia, Ting Zang

An Algorithm for Satellite Power Anomaly Detection Based on Time Series Prediction

With the popularity of mobile terminals and various location-based service applications, people’s demands for location information are increasing day by day. As an infrastructure, GNSS plays a pivotal role in both military and civilian usage. Real-time monitoring of GNSS services and early warning of abnormalities are essential. In this paper, by processing the GNSS satellite observation data monitored by the IGS tracking stations, a method for judging satellite power anomalies based on time series prediction is proposed. This method can effectively solve the problems of high false and false negative alarming rate in the traditional alarming mechanisms based on the ratio comparing and the sliding window methods, and it is difficult to deal with unknown abnormalities due to excessive reliance on manual experience to set the thresholds. Experiments show that this method can effectively find GPS satellite power abnormalities, and it can be applied to other scenarios.

Yibo Si, Yuan Gao, Huaang Chen

Null Control Method Based on GNSS Array Anti-jamming Antenna

The traditional adaptive nulling anti-jamming array antenna does not consider the effect of nulling on the antenna phase center when performing anti-jamming calculations, so that the antenna phase is not constant and causes positioning errors. This article starting with analyzing the anti-jamming of the adaptive nulling antenna array, the influence of the null depth on the phase change is deduced, and a method to control the null depth is proposed to reduce the phase error caused by the array antenna by controlling the null depth. The simulation results verify the rationality and effectiveness of the algorithm, and can be used to improve the positioning accuracy of GNSS receivers using anti-interference array antennas.

Zhengwang Luo, Kejin Cao, Yinbing Zhu, Bao Li

W-Test Aided Quality Control Algorithm for GNSS/IMU Integrated Navigation in Urban Environments

Global Navigation Satellite Systems (GNSS) is often integrated with Inertial Measurement Unit (IMU) in order to improve the overall accuracy and reliability of the navigation system. The performance of the integrated system relies greatly on the quality of the GNSS measurement, however. In particular, contamination of GNSS measurements due to multipath interference and non-line-of-sight reception in urban environments affects the final performance of such integrated navigation. This paper therefore proposes two W-test aided quality control algorithms to achieve effective quality control for integrated GNSS/IMU navigation systems in urban areas. Each algorithm applies a different class of approach: i.e. the scoring strategy and the minimum error strategy. Experimental results showed that the solution with our proposed algorithms achieves the improvements of average 84% in horizontal positioning accuracy and 88% in vertical positioning accuracy compared with the pure IMU/GNSS solutions.

Ming Qiu, Rui Sun

Carrier Phase Multipath Error Elimination Method for GNSS Signals Based on an APCRW Correlator

Carrier phase multipath effects are sources of error for high-precision applications of Global Navigation Satellite Systems (GNSS). In this work, we propose a correlator based on the Auxiliary Punctual Code Reference Waveform (APCRW), which is composed of an Auxiliary Code Reference Waveform (ACRW) correlator and a Punctual Reference Waveform (PCRW) correlator. In the carrier tracking loop, both lossless carrier tracking and carrier multipath error estimation can be achieved by combining the ACRW and the PCRW correlators. Simulation results show that when the gate width of the code reference waveform is 1/8 chip, the carrier tracking loop based on the APCRW correlator improves the carrier phase multipath suppression capability by approximately 73.8% without any loss to the received power of the signal. In addition, the effectiveness of the algorithm is verified by experimental results using both simulator-generated and real-world satellite signals.

Chunjiang Ma, Xiaomei Tang, Zengjun Liu, Honglei Lin, Guangfu Sun

Fault Identification Method of GNSS/INS Integrated Navigation System Based on the Fusion of Chi-Square Test and Multiple Solution Separation Algorithm

In view of the problem that the fault identification algorithm of Global Navigation Satellite System (GNSS)/Inertial Navigation System (INS) integrated navigation is difficult to balance the complexity and performance, this paper proposes an efficient fault identification method. Firstly, the propagation process of GNSS faults in Kalman filtering is analyzed, and the chi-square and multiple solution separation test statistics considering fault propagation are designed. Secondly, a fusion algorithm of chi-square and multiple solution separation using multiple solution separation algorithm on demand is proposed, only when the chi-square test statistic is greater than the threshold, the multiple solution separation algorithm is activated for fault identification, and use the chi-square test to replace the corresponding steps in the multiple solution separation algorithm to complete the exclusion test to reduce the number of subsets. Finally, aiming at the threshold design for the above fault identification method, the total continuity risk and integrity risk are allocated according to the integrated navigation mechanism, and the calculation and selection of the algorithm threshold are completed by using the allocation results. The simulation results show that the fusion of the two algorithms can complement each other’s advantages, identify faulty satellites accurately and efficiently, record the capture time of the fault, and complete fault exclusion. At the same time, the comparison with the (m − 1) method, multiple solution separation algorithm, and discarding all observations of the faulty sensor, etc., proves that this method achieves a good balance between algorithm performance and complexity.

Xin Li, Kun Fang, Xiao Li, Jichao Dong, Zhipeng Wang

Policies, Standards and Intellectual Property Rights

Frontmatter

Evaluation of Beidou Satellite Navigation Service Anti-jamming Capability Under International Standard Framework

Anti-jamming capability is an important index of satellite navigation service. The anti-jamming capability is standardized in relevant standard documents such as International Civil Aviation Organization (ICAO), Radio Technical Commission for Aeronautics (RTCA), Aeronautical Radio, Incorporated (ARINC) and American Federal Aviation Administration (FAA). According to the basic framework of the international standard mentioned above, this paper carries out test and test on the anti-jamming ability of Beidou B1C signal, and carries out the baseline test on the pseudo-range tracking accuracy of the receiver of Beidou B1C signal in the aviation electromagnetic environment, and obtains relevant test data. On standardized test framework, Beidou B1C signal in limited bandwidth white noise interference tolerance, continuous wave interference tolerance and tolerance of the pulse interference and so on various types of interference tolerance under receiver capture signal carrier to noise ratio remained above 31 dB-Hz, the tracking error is lower than 0.5 m (1 sigma) of support the Beidou draft standards and recommended measures to develop and validate, which laid a foundation for the Beidou satellite navigation system to join the international standard system.

Ying Chen, Yuan Liu, Jianhua Shen, Cheng Liu, Wei Wang, Chengqian Lou

Research on the Trademark Strategy of Beidou Industry

The Beidou-3 global satellite navigation system has been opened, the innovation entities of China attach great importance to the patent layout of Beidou-related technologies and the cultivation of high-value patents. At the same time, the trademark protection of the Beidou industry and key innovation entities is slightly weak. To this end, this article starts from the aspect of theory and practice, analyzes the current status of Beidou trademark applications and trademark litigation cases, studies the trademark strategy of Beidou industry. In order to improve the intellectual property protection performance of China’s satellite navigation industry, this paper puts forward the mechanism and path from the perspective of improving the awareness of trademark protection, increasing the operation model of collective trademarks and certification trademarks, strengthening research on the trademark system of the targeted Belt and Road countries, exploring the protection of well-known trademarks and strengthening the training of intellectual property rights.

Yuxuan Wang

Research on Business Model Innovation of Beidou Satellite Navigation System

With the completion of the global constellation deployment of beidou-3, Beidou satellite navigation system has entered the stage of industrial application. In this paper, the business model structure of GPS, GLONASS, Galileo and Beidou system is analyzed from the perspective of resource capacity complementarity and transaction value. Through comparative analysis, this paper studies the interaction, main practices, characteristics and effectiveness of Beidou business model, and discusses the optimization direction of Beidou system business model in the future. It assist Beidou Systems and related companies to optimize their business models and strengthen their competitive advantages in the global GNSS market.

Qingyi Gao, Jiachen Fan, Jinping Yu, Wuxiang Zhu

Insights and U.S. GPS International Cooperation Under Legal Regulation

The U.S. National Space Policy, enacted on December 9, 2020, states that the United States shall lead, encourage, and expand international cooperation in mutually beneficial space activities to ensure compatibility and interoperability. Based on this principle, the U.S. has been actively engaged in international cooperative activities with foreign governments and international organizations related to GPS. Now, it has developed a comprehensive legal system for international cooperation: all international cooperation actions of GPS comply with the laws and regulations of the United States, international treaties or agreements signed by the United States and other applicable international laws, and are strategically consistent with the national and homeland security requirements, foreign policy and national interests of the United States. Thanks to the maturity of its legal system, the United States has basically achieved its high-level goal of promoting GPS technology innovation and maintaining U.S. leadership and technological leadership in the field of satellite navigation, as well as the basic goal of meeting the growing national security, homeland security, economic security, civil needs science and commercial needs. In this paper, we will study the U.S. Code, SPD-7, National Space Policy, the U.S. Radio Navigation Plan, then analyze the legal system of the U.S. GPS international cooperation in terms of subject, legal content, and legal mode to provide legal advice for the international cooperation activities of China’s BDS.

Linlin Niu

Study on the Legal Model of International Cooperation in the Field of Satellite Navigation

The current rules and order of international cooperation among States in the field of satellites depend mainly on three legal models: multilateral cooperation under international conventions, bilateral cooperation under intergovernmental agreements and guidelines for global regional conferences. These three legal models show different characteristics in terms of legal effect, normative content and timeliness and flexibility of normative matters. Combined with these characteristics, the path selection of countries in the process of international cooperation in the field of satellite navigation shows a certain trend. These will provide development ideas for China to develop international competition and cooperation in the field of satellite navigation.

Xiaomeng Fan

Study on the Security Protection System of Foreign Satellite Navigation System Infrastructure

In 2020, the Beidou-3 global satellite navigation system announced the official opening, officially providing services to the world, and the Beidou system has also entered a new era of scale, industrialization, internationalization and popularization. New era gave birth to the new requirements, how to provide safer, more stable, more reliable, higher-quality fixed navigation users worldwide location service has become a new target. In order to provide better navigation and positioning services, we must not only pay attention to technological innovation, but also maintain the safety of the satellite navigation system. Security issues have long been the focus of attention of all countries, and are also the main points of centralized regulation of laws and regulations. Infrastructure security is the most basic and most important point in system security. This article starts with the security protection system of satellite navigation systems and infrastructure, focusing on combing and analyzing the security protection systems of the three global satellite navigation systems in the United States, Russia, and the European Union. From the aspect, we will elaborate on the specific measures taken by foreign satellite navigation systems to protect their infrastructure.

Wenqing Zhang, Chen Yu

The Standardization Status and Standard Sets Construction of Beidou Satellite Navigation System

In this Paper, we summarize the current status of relevant standard setting and revision of Beidou satellite navigation system, and systematically state the demonstration and construction progress of the Beidou satellite navigation system standard system. Besides, we show that the standards at all levels play an important role in the construction and operation of the Beidou satellite navigation system. In addition, with the demonstration progress of the national comprehensive PNT system, we tend to state the development priorities and main tasks of the standardization work in the future, and try to put forward the research and demonstration ideas for the national comprehensive PNT standard system.

Kai Wang, Weijia Wang, Ying Liu, Ji Guo, Xiangyi Zhang, Dongliang Liu

Intellectual Property Risk and Prevention of BeiDou’s “Going-Out” Strategy

With the acceleration of BeiDou’s industrialization process, the application of BeiDou’s relevant technology has penetrated into all industries. It is an inevitable trend for BeiDou to enter into and compete in the global market. However, due to the discrepancy in competitors’ intellectual property strategies, legal systems and enforcement mechanisms among different countries as well as high international concern over the intellectual property issues in China, the intellectual property situation confronting BeiDou’s “going-out” strategy has become ever more complex and severe. Based on the analysis of the types and causes of intellectual property risks faced by BeiDou’s “going-out” strategy, this paper puts forward measures to prevent and counter risks from the levels of the government, the industry and BeiDou enterprises, so as to promote BeiDou’s “going-out” strategy in a better way and eventually enhance the cooperation and development of global satellite navigation.

Lin Su, Jixuan Xiao, Yuexuan Wang

The Consideration of BDS International Standardization in Civil Aviation Industry

The BeiDou satellite navigation system (BDS) is the core of China’s future civil aviation CNS/ATM system. In order to accelerate the application and innovative development of BDS in the international civil aviation, it is necessary to establish an international standard system for the BDS civil aviation industry. A framework recommendation of the BDS civil aviation international industrial standards is proposed according to the existing and planned international civil aviation standards of GNSS. At this stage, it is urgent to push forward the BDS core system industrial standard, including the core system airborne equipment industrial standard, focusing on the development procedures and technical content of RTCA DO-368 GLONASS/GPS airborne equipment industrial standard, which will provide a reference to develop a minimum operational performance standards (MOPS) for airborne equipment compatible with BDS. This paper will also give some consideration on the promotion of industrial standards for dual-frequency multi-constellation (DFMC) airborne equipment.

Xin Jiang, Zhan Zhang, Zhe Fan, Tieshuai Li, Boyuan Gong

Preliminary Study on BDS Participation in ISO Standardization

On the requirement of devlopment and revision of standards for global navigation satellite systems (GNSS) in the International Standardization Organization (ISO), the GNSS-related standards, which either have been standardized or are being developed in ISO, are firstly investigated in detail in this paper. Secondly, for promotion of the global application of the BeiDou Navigation Satellite System (BDS), the major areas and the key directions in the ISO technical committees are comprehensively analyzed for the future standardization by our nation. Furthermore, the specific measures and the cultivation projects that can be carried out in ISO are also presented.

Yuxia Zhou, Qian Tan, Haofang Quan, Dengbang Kang, Kanglian Zhao

Research on Protocol Architecture and Standard System of Next Generation Navigation Integrated Space and Onboard Network

This paper focuses on the requirements of integrated space and onboard high-speed networking, standardization of satellite ground interface, reliable transmission, dynamic routing and dynamic access of the next generation navigation satellite constellation, conducts a comprehensive investigation on the protocols of Consultative Committee for Space Data Systems (CCSDS), ECSS, Internet Engineering Task Force (IETF) and other international standards organizations, establishes integrated space and onboard network protocol architecture for next generation navigation satellites. The standards involved in the protocol architecture are systematically constructed, and suggestions on standard formulation and application are given, so as to provide technical support for the establishment of next generation navigation network protocol architecture.

Xiongwen He, Mingwei Xu, Dong Yan, Zheng Qi, Hongcheng Yan, Lijun Yang, Weisong Jia

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