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2022 Vol. 47, No. 3

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2022, 47(3): 1-2.

[Abstract](239) [FullText HTML] (156) [PDF 1543KB](48)

Abstract:

Analysis of common mode error of GNSS coordinate time series in Xinjiang with independent component analysis

LEI Chuanjin, WEI Guanjun, GAO Maoning, ZHANG Pei

2022, 47(3): 1-8. doi: 10.12265/j.gnss.2021111201

[Abstract](342) [FullText HTML] (97) [PDF 7442KB](55)

Abstract:
The common mode error (CME) is one of the major error sources in the regional Global Navigation Satellite System (GNSS) network. Aiming at the problem that GNSS time series is subject to no-Gaussian distribution, and the principal component analysis (PCA) with second-order is inaccurately employed to separate the CME. In this paper, the independent component analysis (ICA) introduces high-order statistics to extract the CME. The effectiveness of the method is validated by processing the data of GNSS stations from 2011 to 2018 in Xinjiang, China, and then compared and verified the filtering effect of PCA. We analysis the influence of the CME for GNSS coordinate time series and the yearly signal of the CME. The results show that the CME mainly consists of the 6th independent components and can be attributed to satellite orbit, surface mass loading, and clock errors. After the ICA filtering, the reduction of mean RMS is 31.83%, 32.29%, 35.49% for the north (N), east (E), and up (U) components, respectively. The reduction of velocity uncertainty can achieve 44.14%, 38.49% and 35.49% in three components. In addition, the yearly amplitude of each GNSS station is more consistent that before spatiotemporal filtering, indicating that the ICA can effectively extract the CME and further improve the accuracy of coordinate time series.

Method for eliminating pseudolite near-far effect based on orthogonal subspace projection

SHI Shang, WANG Qing, ZHANG Bo, YANG Yuan, XU Jiujing

2022, 47(3): 9-15. doi: 10.12265/j.gnss.2021111701

[Abstract](344) [FullText HTML] (90) [PDF 3850KB](34)

Abstract:
Receivers in ground-based pseudolite systems are often affected by the near-far effect, causing failure acquisition of far-field pseudolite signals. An optimization method based on orthogonal subspace projection is introduced in this paper, which is applied to code division multiple access (CDMA) pseudolite signals. Firstly, strong-signal code phases and Doppler frequencies are obtained through conventional sliding correlation to calculate the orthogonal projection operator. Then the weak-signal space is obtained by the received signal subtracting its projection in the strong-signal space. Finally, the re-acquisition is done in the weak-signal space to eliminate of the interference of strong signals. The experimental result indicates that the orthogonal subspace projection can effectively improve weak-signal acquisition performance in the power ratio range of lower than 30 dB, which is of great importance to widen the effective working range of ground-based pseudolite systems and the limitation of pseudolite receivers’ signal power ratio tolerance.

Application of Helmert variance component estimation in GPS/GLONASS/BDS/Galileo combined precise point positioning weight determination

LI Qin, YAO Wanqiang, TU Rui

2022, 47(3): 16-24. doi: 10.12265/j.gnss.2022047

[Abstract](583) [FullText HTML] (128) [PDF 3403KB](74)

Abstract:
Multi-constellation combined positioning can improve the performance of navigation and positioning, but a suitable stochastic model needs to be considered when combining observations from different constellations. The traditional method is to directly set the equivalent weight of each system based on experience, which will lead to inaccurate determination of the stochastic model, and thus affect the performance improvement of the combined system. In this paper, Helmert variance component estimation method is applied to GPS/GLONASS/BDS/Galileo combined precise point positioning to adaptively determine the weight ratio between systems. The static and pseudo-dynamic tests were carried out using the daily observation dataset collected at 10 stations in the global International GNSS Service (IGS) Multi-GNSS experiment (MGEX) observation network over one week of February 8 to February 14, 2021. The results show that the Helmert variance component estimation weighting method can significantly improve the convergence speed of GPS/GLONASS/BDS/Galileo combined precise point positioning (PPP), with an average increase of 52% in static mode and 64% in pseudo-dynamic mode. Because the positioning accuracy is mainly determined by the carrier phase observation accuracy and error correction level, the Helmert variance component estimation method has no obvious improvement on positioning accuracy in static and pseudo-dynamic tests.

ARAIM protection level calculation method for BeiDou decimeter level single epoch point positioning

WEI Yiran, GUO Jiang, FANG Shushan

2022, 47(3): 25-33. doi: 10.12265/j.gnss.2022021

[Abstract](572) [FullText HTML] (104) [PDF 4507KB](54)

Abstract:
Precision positioning quality control and integrity assessment is an integral part of real-time Global Navigation Satellite System (GNSS) navigation applications, especially in GNSS vulnerable urban canyon scenarios. Wide-area precise point positioning (PPP) instantaneous decimeter level positioning can be realized by using the observation values of two wide lanes formed by GNSS three-frequency signal. However, in the complex urban environment, the impact of reflected signals, serious multipath and other signal interference on positioning cannot be accurately evaluated and identified, which limits the application of PPP instantaneous decimeter-level point positioning. advanced receiver autonomous integrity monitoring (ARAIM) in the concept of integrity can calculate the upper limit protection level (PL) of the minimum confidence interval of user positioning error to evaluate the positioning effectiveness, which can be used for quality control of PPP instantaneous positioning after some improvement. Aiming at the problem that the error model used to calculate the PL in ARAIM is difficult to meet the requirements of high-precision positioning, an improved ARAIM PL algorithm which is called B-ARAIM is proposed in this paper. The residual of PPP three-frequency combination observation value is used to modify the ARAIM weight and error model to calculate the PL. This paper verifies the algorithm based on on-board data collected in environments with different complexity levels, and evaluates the improvement of PL and the improvement of navigation availability. The results show that the PL obtained by the improved B-ARAIM algorithm is more in line with the needs of city positioning than that obtained by the traditional method, and the PL is reduced by 30% to 70% in different environments. This method is helpful to the application of ARAIM algorithm in GNSS positioning.

Design and verification of semi-physical simulation platform for LEO satellite navigation enhancement system

LIU Tianli, YANG Xuan, LIU Xiaoxu

2022, 47(3): 34-39. doi: 10.12265/j.gnss.2021112601

[Abstract](456) [FullText HTML] (98) [PDF 2417KB](50)

Abstract:
Low Earth Orbit Satellite (LEO) has the advantages of rapid change of geometric configuration relative to the ground and low loss of broadcast signal link. With the gradual reduction of low orbit satellite load development and launch cost, low orbit satellite navigation enhancement technology has become a research hotspot in the field of satellite navigation. At present, the research on LEO navigation enhancement technology at home and abroad is in its infancy. There is no mature LEO navigation satellite constellation, and there is no effective means to verify the service performance of LEO navigation enhancement system. In this paper, the orbit extrapolation method of LEO navigation satellite and the signal acquisition and tracking technology of LEO satellite are studied, and the semi-physical simulation platform of LEO navigation enhancement system is designed and constructed. On the basis of the simulation platform, the high-precision fast precision positioning method of the combined application of BeiDou / LEO enhancement system is verified, which realizes the rapid convergence of precision single point positioning (PPP) and has high internal coincidence accuracy. It has certain scientific and engineering value for the construction and application of LEO satellite navigation enhancement system.

Research on data processing method of BDS assisted unmanned aerial vehicle image-free control triangulation

FAN Yanwei, MA Cheng

2022, 47(3): 40-45. doi: 10.12265/j.gnss.2021122101

[Abstract](217) [FullText HTML] (74) [PDF 2700KB](27)

Abstract:
Aiming at the problem of large number of field control points and heavy workload in the spatial triangular processing of unmanned aerial vehicle , the BeiDou Navigation Satellite System (BDS) assisted unmanned aerial vehicle large-scale image control free accuracy verification method is proposed in this paper. The unmanned aerial vehicle photogrammetry platform equipped with dual frequency Global Navigation Satellite System (GNSS) receiver is used to receive BDS data. The key technologies of high-precision BDS camera station coordinate solution and joint adjustment of BDS data and unmanned aerial vehicle image data are discussed and analyzed. Finally, an engineering example is given to verify the effectiveness of the method. The experimental results show that the method can meet the accuracy requirements of 1∶500 large scale mapping without the participation of image control points.

Research and application of encryption conversion parameters in urban CORS system

ZHANG Wei, WANG Lin

2022, 47(3): 46-50. doi: 10.12265/j.gnss.2021123101

[Abstract](258) [FullText HTML] (212) [PDF 2130KB](24)

Abstract:
Aiming at the strict confidentiality of coordinate transformation parameters and quasi geoid model results in urban satellite navigation and positioning continuous operation reference station (CORS) system, a general real-time encryption transformation method of urban CORS system is proposed based on bursa seven parameters and bilinear interpolation method, which realizes the real-time acquisition of plane and normal height results of urban local coordinate system This method has been verified in the application of CORS in Hefei city (HFCORS), and can provide reference for the application service of urban CORS surveying and mapping benchmark.

A GNSS control network configuration selection method considering geometric precision factor

GU Jiachen, TIAN Kunjun, SONG Chuanfeng

2022, 47(3): 51-55, 72. doi: 10.12265/j.gnss.2021051401

[Abstract](209) [FullText HTML] (129) [PDF 11883KB](24)

Abstract:
In the relative positioning baseline calculation process, selection of the coordinate position of the control network constraint point has a certain impact on the data calculation accuracy. This paper discusses the site selection method of the control network configuration considering the minimumgeometric factor of precision (GDOP), the selection of 6 constraint point reference stations for the global MGEX (Multi-GNSS Experiment) stations, and the use of BeiDou-2/BeiDou-3 (BDS-2/BDS-3) actual measurement data to compare the results of 18 Interactive Generator of Multimedia Application System (iGMAS) stations around the world. The station coordinates are calculated and compared with the accuracy of the results of the global grid-based random station selection method. The experimental results show that compared with the grid-based random station selection method, when the GDOP value selection method is used to calculate the relative positioning baseline, the standard deviation of the baseline length above 6 000 km can be increased by about 7 mm. For the long baseline, the standard deviation accuracy in east (E), north (N), up (U) can be increased by about 5 mm; the position accuracy of the pending point can be increased by about 40%. It can be seen that GDOP method can improve the relative positioning accuracy of BDS-2/BDS-3.

Optimization algorithm of earthquake early warning based on multi-station high frequency GPS

ZHANG Wenhao, YIN Ling, HU Wenbo

2022, 47(3): 56-64. doi: 10.12265/j.gnss.2021120205

[Abstract](310) [FullText HTML] (99) [PDF 4190KB](22)

Abstract:
With the development of precision positioning technology, high-frequency GPS has been able to accurately record surface displacement data. Research on high frequency GPS can make a certain supplement to earthquake early warning. In view of the high false alarm rate of single station in earthquake early warning, we introduce deep learning technology and use the long short-term memory (LSTM) neural network to combine with surrounding stations to give early warning to single station. First, the seismic-free time series of multiple stations are obtained by solving the 1 Hz high-frequency GPS data in the southern region of New Zealand Then the data is used to train the network to obtain a high-precision model that integrates regional features. The model can predict the seismic-free time series and dynamically formulate a threshold interval. When the actual observation value exceeds the confidence interval, an abnormality is determined. By comparing with the traditional short-time window averaging/long-time window averaging algorithm (STA/LTA) and the single station model without regional features, the results show that the single station model fusing regional features can effectively reduce false alarms. It performs better than traditional methods on seismic-free long sequences of multiple stations and has certain application values.

Cycle-slip detection and reparation algorithm for satellite-ground two-way time difference measurements

HAN Zibin, BAI Yan, ZHANG Feng, GUO Yanming, LU Xiaochun

2022, 47(3): 65-72. doi: 10.12265/j.gnss.2021120202

[Abstract](270) [FullText HTML] (131) [PDF 2914KB](34)

Abstract:
High precision time-frequency reference requires high precision time-frequency transfer technology. The satellite-ground two-way time difference of carrier phase measurement can achieve higher time-frequency transfer accuracy. However, in the complex satellite-ground environments, due to the high flight dynamics of the spacecraft and the high transmission frequency of the time-frequency link, and the carrier doppler effect is large, gross errors and cycle slips are more likely to occur. This paper focuses on a carrier phase cycle slip detection and reparation algorithm for satellite-ground two-way time difference measurement system in high dynamic environment, and proposes a two-way cycle slip detection and reparation method for three-frequency mode. This method combined with Melbaurne wubbena (MW) combination method can realize the detection and repair of different types of cycle slips. For the three links, the existence of cycle slips can be detected and the mm-level cycle slip repair accuracy can be realized. The satellite-ground time synchronization performance of the satellite-ground two-way time difference measurement system based on carrier phase measurement is further analyzed. After cycle slip detection and repair, and link delay data processing, the time synchronization accuracy is better than 0.3×10^–12 s.

An efficient demodulation algorithm for CSK modulated signals based on partial output FFT

LI Ye, ZHOU Guodong, XIAO Linwei, CHEN Huaming

2022, 47(3): 73-78. doi: 10.12265/j.gnss.2022019

[Abstract](432) [FullText HTML] (205) [PDF 2421KB](44)

Abstract:
In order to broadcast precise ephemeris data with high speed, code shift keying (CSK) modulation is likely to be adopted in next generation satellite navigation system. The correlation values of various code phase offsets are needed during demodulation, so the frequency domain demodulation algorithm based on fast Fourier transform (FFT) is usually used. According to the characteristic that only partial output are needed in CSK frequency domain demodulation, an efficient demodulation algorithm for CSK signal based on partial output FFT is proposed in this paper. The algorithm optimizes the butterfly-shaped structure of traditional FFT, and reduces the computational complexity of demodulation by defining computing nodes to eliminate invalid computations irrelevant to the output results. Taking the CSK(4,1023) modulated signal with a code rate of 1.023 Mcps as an example, the algorithm proposed in this paper can reduce about 45.6% of the calculation, which is of great significance to the design of the next generation satellite navigation receiver.

Research on automatic test and evaluation method of GNSS/INS Integrated Navigation Attitude performance based on high-precision three-axis turntable

WANG Jianping, PAN Shuguo, GAO Wang, YU Guorong, HE Liujie, WANG Hao

2022, 47(3): 79-84. doi: 10.12265/j.gnss.2021120901

[Abstract](312) [FullText HTML] (90) [PDF 4368KB](29)

Abstract:
At present, for the Global Navigation Satellite System /Inertial Navigation System (GNSS/INS) performance test and evaluation the evaluation method is single and automatic data processing is still at a low level. Aiming at the attitude performance evaluation of the system, this paper studies a new dynamic test and evaluation method of GNSS/INS performance, and develops corresponding automatic control test and evaluation software. Based on the high-precision three-axis dynamic benchmark simulation turntable, this method first tests through the task of multi rotation and multi attitude motion scene, collects the three-axis motion attitude data of turntable and the output data of integrated navigation system, then processes the measured data by Thompson singular value elimination method, and finally analyzes the uncertainty combined with the measured data of turntable so as to complete the test and evaluation work. In this paper two groups of tests are carried out on a Micro Electro Mechanical System (MEMS) integrated navigation product. Results show that this method can better suppress the singular value points in the integrated navigation system, and the uncertainty values of the turntable are within 0.2", which verifies the high feasibility and reliability of the test and evaluation method.

Design and implementation of navigation synthetical baseband equipment

ZHANG Jintao, HAN Shuanglin, YANG Liyun, HU Zhengqun

2022, 47(3): 85-90. doi: 10.12265/j.gnss.2021092603

[Abstract](463) [FullText HTML] (161) [PDF 3344KB](91)

Abstract:
Chinese area positioning system (CAPS) is a new satellite navigation system with independent intellectual property rights in China. Based on the working mode of the satellite forwarding the navigation signal generated on the ground, the satellite navigation function is realized. Navigation integrated baseband is an important terminal equipment of the main control station of CAPS. The architecture of navigation integrated baseband is designed by software radio design. Standard PCI extensions for instrumentation (PXI) chassis structure and bus-based design with strong scalability is selected. The key technologies of baseband are described including frequency compensation technology of transmitting signals, high precision receiving technology, high stability delay keeping technology of equipment. The actual test results show the good performance of the integrated baseband equipment. The measurement accuracy of pseudorange is better than 0.20 ns. The stability of channel delay is better than 0.25 ns, and the accuracy of frequency compensation is better than 0.8 Hz, which can meet the needs of CAPS.

UAV track planning algorithm in concave polygonal area based on remote sensing mission

LIU Xulin, LI Ronghao, CAI Xiangyuan, CHEN Xiaotong, WEI Jiangnan, LI Qin, ZHAO Hongying

2022, 47(3): 91-98. doi: 10.12265/j.gnss.2022050

[Abstract](492) [FullText HTML] (371) [PDF 2746KB](50)

Abstract:
For the needs and characteristics of remote sensing observing. We proposes an unmanned aerial vehicle (UAV) track planning algorithm based on remote sensing tasks in concave polygonal areas. The algorithm aims to ensure UAV’s non-collision and full area coverage with shorter total time consumption. According to remote sensing image acquisition characteristics, the UAV track planning is carried out by unified main flight direction and fixed-point shooting. The UAV track optimization under the selected main flight direction is obtained through five steps: route segmentation point calculation, polygon division, UAVs assignment, fragment polygon merging and UAVs reassignment, and waypoint information calculation. The global optimal solution is obtained by selecting the main direction of the edges of the concave polygon and its convex hull, respectively. The experimental results show that the algorithm can reasonably assign UAVs and carry out track planning, which is more efficient and more applicable than traditional methods.

Comparative analysis of three GNSS data download methods

WU Tangting, LIANG Qiao, CHEN Benfu, LU Liguo

2022, 47(3): 99-103. doi: 10.12265/j.gnss.2021120602

[Abstract](369) [FullText HTML] (175) [PDF 3954KB](55)

Abstract:
In order to comprehensively evaluate the performance of single-thread, multi-thread, and multi-coroutine in Global Navigation Satellite System (GNSS) data download, this paper uses the International GNSS Service (IGS) data center of Wuhan University as the download source and analyzes the download effects of three methods in terms of the time span and magnitude of the download file. The results show that in the process of small and medium-sized files download, multi-thread has more advantages than single-thread and multi-coroutine,while for large file downloads, the download effect of multi-coroutine is slightly better than multi-thread, and both have better performance than that of single-thread. Since GNSS data file is generally small and medium-sized file, multi-thread is more suitable for GNSS data download.

Research on normal height service method of grid CORS

ZENG Xiangqiang, CHEN Chunhua, ZHOU Fengsong

2022, 47(3): 104-108, 113. doi: 10.12265/j.gnss.2021121401

[Abstract](3086) [FullText HTML] (146) [PDF 3008KB](146)

Abstract:
In this paper, a method of continuously operating reference station (CORS) normal height service based on grid is proposed. By modifying the data generation and broadcast mode of the traditional virtual reference station technology, the grid virtual observation data is generated through the way of grid division, and the elevation anomaly correction is added to the grid virtual observation data, so as to realize real-time normal height measurement. The method provides users with real-time normal height measurement results without reducing their accuracy, which can enhance the service capability of the CORS system and can provide reference for the construction of CORS systems in other provinces and municipalities.

Positioning principle and engineering application practice of Inertial Navigation System RTK technology

ZHANG Xiangping, YANG Mingguang

2022, 47(3): 109-113. doi: 10.12265/j.gnss.2021121601

[Abstract](770) [FullText HTML] (185) [PDF 2002KB](55)

Abstract:
When using the traditional real-time dynamic positioning (RTK) technology, one must keep the antenna phase center of the Global Navigation Satellite System (GNSS) receiver relatively perpendicular to the measurement point during the measurement to ensure the accuracy of the measurement results. Generally a tripod should be erected. When using the centering rod for measurement, the surveyor must ensure that the leveling bubble of the centering rod call is relatively centered in order to ensure the accuracy of the measurement results. The measurement process is time-consuming and laborious. The emergence of Inertial Navigation System (INS) technology has changed the traditional habit of RTK Surveying and mapping technology. In the measurement process, there is generally no need to erect a tripod, and the measuring centering rod maintain an arbitrary tilt state within a certain range. The measurement process is relatively easy and free, which greatly reduces the labor intensity of measurement and improves the efficiency of surveying and mapping. This paper mainly analyzes the positioning principle and technical advantages of INS technology, and emphasizes that only by mastering the precautions of INS RTK technology in practical application, can it give full play to its maximum benefit and efficiency.

Positioning precision analysis on 5G mmWave and sub-6G signals

QUAN Yiming, CHEN Shian, LIU Guangyin, TANG Xu

2022, 47(3): 114-118, 126. doi: 10.12265/j.gnss.2021120604

[Abstract](350) [FullText HTML] (100) [PDF 2397KB](53)

Abstract:
With the persistent research and rapid commercialization of 5th generation mobile communication technology (5G), China has built one of the largest commercial 5G network. Suppliers of 5G equipment start to provide new positioning features based on 5G new radio (NR). It is highly probable that the high-precision positioning technology will be gradually commercialized in the next few years. Compared with 4G long term evolution (LTE), denser network deployments and wider transmission bandwidth of 5G can bring about a significant improvement in positioning accuracy. Hopefully, 5G positioning can mitigate coverage and accuracy problems of Global Navigation Satellite Systems (GNSS) in difficult environments such as indoor and urban canyons. This article describes the differences between 5G and 4G in the measurement domain. Then the precision of Sub-6G (FR1) and high frequency mm wave (FR2) ranging measurements with Cramér-Rao bound is assessed. Followed by the description of positioning algorithms, eleven scenarios are listed with typical simulation parameters based on 3GPP specifications and commercial network configurations. The simulation results show that the precision of network synchronization is the main factor affecting the positioning quality. If the time synchronization error is 50 ns, 5G positioning precision is over 10 m. A larger bandwidth can significantly improve the ranging precision of 5G signals if the time synchronization problem can be solved by ideal synchronization or double-differencing with positioning nodes near a user end. Under ideal conditions, 5G FR1 can achieve an accuracy of about 1 m, and FR2 can achieve an accuracy of 0.16 m.

Study on FY-4A PWV correction model in Beijing-Tianjin-Hebei region

WANG Yong, JIANG Nuohan, LIU Yanping, LIU Xiao, ZHAN Wei

2022, 47(3): 119-126. doi: 10.12265/j.gnss.2021092604

[Abstract](287) [FullText HTML] (74) [PDF 2467KB](33)

Abstract:
Integrating Global Navigation Satellite System (GNSS) and Fengyun meteorological satellite FY-4A can obtain high-precision and high-spatial resolution water vapor distribution information. This paper used the GNSS observation data from crustal movement observation network of China (CMONOC) to carry out the FY-4A water vapor correction study in the Beijing-Tianjin-Hebei region. Firstly, the Beijing-Tianjin-Hebei region was divided into four regions, and the correlation analysis between GNSS precipitable water vapor (PWV) and FY-4A PWV was carried out by regions and seasons. Secondly, different function models were selected by region and season and combined with GNSS PWV data to construct the FY-4A PWV correction models. Then, the GNSS PWV was compared with the results of the regional model and the single-site model respectively to carry out the reliability test of the model. Finally, the corrected FY-4A PWV distribution in the Beijing-Tianjin-Hebei region was obtained through regional FY-4A PWV correction and mosaiced. Research shows that the FY-4A PWV has a good correlation with GNSS PWV, and the accuracy of the regional FY-4A PWV correction model is equivalent to that of the single-site model, which can replace the single-site model for the FY-4A PWV correction. The regional model based on CMONOC GNSS PWV can improve the accuracy of FY-4A PWV to a certain extent, and provide references for the short-term weather forecast and InSAR atmospheric correction.