全球定位系统

2021 Vol. 46, No. 5

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2021, (5): 1-2.

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Abstract:

Oven controlled crystal oscillator disciplined based on GPS/BDS receiver

WANG Qi, PENG Liangfu

2021, 46(5): 1-4. doi: 10.12265/j.gnss.2021040801

[Abstract](670) [FullText HTML] (167) [PDF 2454KB](89)

Abstract:
A method to improve the long-term stability of crystal oscillator is studied in this paper. The 1 pulse per second signal (1 pps) from GPS/BDS receiver is used as the reference signal to correct and compensate the frequency offset of crystal oscillator, to obtain better long-term stability without destroying the short-term stability of crystal oscillator. Median average filter and Kalman filter are mainly used to eliminate the jump and random jitter of phase. Based on this value, the incremental PID algorithm with dead zone is used to control the crystal oscillator frequency to synchronize with GPS/BDS signal. The test results show that the peak-to-peak value between the crystal oscillator and cesium clock is less than 47 ns, the Allan variance of 100 second sampling is 6.22×10⁻¹¹, and the Allan variance of 10 000 second sampling is about 1.02×10⁻¹². It is proved that this method can help the crystal oscillator obtain better long-term stability, it is a reliable method.

Observation prediction strategy of GNSS RTK reference station based on first-order model compensation

XU Zhuo, TAO Jun, LONG Yuhao

2021, 46(5): 5-9. doi: 10.12265/j.gnss.2021062102

[Abstract](442) [FullText HTML] (153) [PDF 2408KB](29)

Abstract:
In this paper, high-precision method to predict observations from reference station of real-time kinematic (RTK) is proposed, which may be caused by the interruption of reference station communication. The satellite ephemeris, ionosphere, troposphere and other error sources that affect the prediction of the Global Narigation Satellicte System (GNSS) observations are analyzed, and the sensitivity of various error sources to the length of delay is compared. Results show that the forecast error accumulates linearly as the delay increases, and is negatively correlated with the satellite elevation. When the elevation angle is lower than 10°, the error caused by the precise ephemeris forecast for 5 minutes can reach 174.6 cm. At the same time, the linear trend can be calculated when the reference station data is not missing which can be used to compensate predicted observations. Under the same conditions, cumulative error of compensated observation is reduced to 64.4 cm. The RTK positioning results show that when delay is 1 min, the RMS of the three directions of E, N, and U are 0.37 cm, 0.41 cm, and 0.86 cm respectively, which is 71.1%, 77.2% and 90.0% better than that without compensation. By comparison with 5 minutes’ delay, the centimeter-level accuracy can still be maintained.

Evaluation of the positioning performance of the multi-frequency multi-system RTK for smart phones

WANG Chuji, LONG Chiyu, WANG Feng, LI Guangcai

2021, 46(5): 10-16. doi: 10.12265/j.gnss.2021060301

[Abstract](659) [FullText HTML] (231) [PDF 4560KB](64)

Abstract:
With the development of location-based service, people’s demand for the accuracy of smartphone positioning is increasing rapidly. At present, the smartphones positioning mainly relies on the chip solution provided by the Global Navigation Satellite System (GNSS) modules, whose accuracy is only at metre level. In 2016, Google announced to open the right to access to GNSS observation data, which supports the study of smartphone positioning algorithms. In order to explore the positioning accuracy and reliability of multi-frequency RTK with GNSS module for smartphones, the paper conducts experiments under static and dynamic conditions using Huawei P40 cellphone respectively. The results show that the real-time kinematic (RTK) positioning accuracy of the smartphone multiple-frequency multi-system is better than the chip solution in the static environment, with the root mean square (RMS) of positioning error in the east (E), north (N) and high (U) directions being 0.20 m, 0.39 m and 0.31 m, respectively, which is 57%, 71% and 75% better than the chip solution. The localization accuracy in dynamic environment can still reach the decimeter level, which is 37.84%, 47.22%, and 53.68% better than the chip solution in the three directions of east, north, and high respettlvely.

Analysis of spatio-temporal change of land use around Erhai Lake from 1991 to 2020 based on GEE platform

LI Xiaoxiang, HUANG Liang, LI Kai

2021, 46(5): 17-25. doi: 10.12265/j.gnss.2021041802

[Abstract](433) [FullText HTML] (361) [PDF 3612KB](74)

Abstract:
Erhai Lake is one of the key protected lakes in China. In the past 30 years, the contradiction between economic development and human and land has become increasingly prominent. It is of great significance to study the law of land use change around Erhai Lake in a long time series and analyze the influence degree of human activities. Based on the google earth engine (GEE) cloud platform, and based on the Landsat TM/OLI image data of 7 periods from 1991 to 2020, the random forest method was adopted to classify the land use within 10 km around Erhai Lake by combining the characteristics of spectrum, normalized difference index and enhanced vegetation index. The land use change map and human activity index model were combined to quantitatively analyze the evolution trend of land use types and human activity intensity around Erhai Lake under the background of urbanization. The results show that from 1991 to 2020, the area of forest land and grassland showed a decreasing trend, and the main direction was farmland. The area of construction land continued to increase, and the main source was farmland. The change of water area was small, and the wetland showed a trend of increasing first and then decreasing. The intensity of human activities increased year by year, mainly in the low-impact areas and remained relatively stable. The high-impact areas and medium-high impact areas were mainly concentrated in the south and west of the surrounding lake. The medium-low impact areas presented a sporadic and block-like distribution and a decreasing trend.

Real time and high precision time synchronization method of LEO satellite based on RT-PPP

WANG Wei, ZANG Wenchi, PENG Jing, GONG Hang, SUN Guangfu

2021, 46(5): 26-32. doi: 10.12265/j.gnss.2021050301

[Abstract](556) [FullText HTML] (398) [PDF 2585KB](75)

Abstract:
The key premise of the low orbit navigation enhancement is to realize the whole network time synchronization of the low earth orbit (LEO) constellation. In order to solve the problem of real-time and high-precision time synchronization of LEO constellation, a high-precision time synchronization method based on real-time precise point positioning (RT-PPP) is proposed for LEO navigation augmentation system. This paper analyzes all kinds of errors in the process of processing, introduces the processing flow of real-time and high-precision time synchronization method of LEO satellite using state space representation (SSR) correction information and precise point positioning, and applies this method to the processing of measured data of constellation observing system for meteorology, ionosphere and climate (COSMIC) satellites. The results show that the standard deviation of orbit error is in decimeter level, and the standard deviation of clock error is about 2.4 ns and 2.3 ns respectively, which can reach nanosecond level. By comparing the results of different methods, it can be seen that the PPP method using SSR correction information is obviously better than the pseudorange method using broadcast ephemeris, and the accuracy is equivalent to the PPP method using post precise ephemeris.

Indoor location algorithm based on improved AP selection and random forest fusion

MU Ping, LING Ming, HU Rui

2021, 46(5): 33-38. doi: 10.12265/j.gnss.2021042101

[Abstract](425) [FullText HTML] (192) [PDF 2377KB](23)

Abstract:
Aiming at the problem of the received signal strength (RSS) value and dimension change in complex indoor environment, an improved access point (AP) selection method and a random forest (RF) classification algorithm for real-time indoor location are proposed. The improved AP selection method in the off-line phase uses the RSS data variance of the AP and the AP appearance frequency to measure the AP stability and selects the first m stable APs. When the variance is processed, the Laplacian smoothing is performed to avoid the variance of 0, and construct a preliminary fingerprint database. The online phase uses the RF in the integrated learning to vote on the classification result to arrive at the final position. The improved algorithm is compared with the traditional random forest, the improved AP selection fusion weighted K-nearest neighbor algorithm (WKNN) and the information gain (IG)-based AP selection algorithm plus random forest. The experimental results show that the proposed method Compared with the other three algorithms, the positioning error decreased by 29.3%, 23.2%, and 17.2%, respectively, and the positioning time is also improved.

QZSS broadcast ephemeris accuracy evaluation and fitting accuracy analysis

KOU Ruixiong, YANG Shuwen

2021, 46(5): 39-47. doi: 10.12265/j.gnss.2021030906

[Abstract](368) [FullText HTML] (256) [PDF 2140KB](26)

Abstract:
Broadcast ephemeris is needed to calculate the satellite position in real-time navigation and positioning. The continuous iteration is used to improve the calculation accuracy in the quasi-zenitic satellite system (QZSS) built by Japan during calculating the satellite position, which can result in the real-time calculation efficiency reduction. In order to ensure the calculation accuracy and improve the calculation efficiency of QZSS broadcast ephemeris coordinates, a chebyshev polynomial is proposed to fit the satellite orbit. Firstly, the traditional methods are used to calculate satellite position, the precision ephemeris is regarded as a reference to verify that the satellite coordinate accuracy of QZSS broadcast ephemeris is meter-level. And then, a chebyshev polynomial is used to fit satellite three-dimension coordinates, and the factors affecting the fitting accuracy are discussed. When the fitting time-interval is fixed, the optimal fitting order increases with the number of nodes; Under different time-intervals, the optimal fitting order is not equal in different orbit types, and the optimal fitting order of the same orbit is equal, but the fitting error gradually increases with the increase of time-interval. The result shows that QZSS broadcast ephemeris can be fitted by using a chebyshev polynomial and choosing appropriate fitting time-interval and fitting order for different orbit types. The fitting accuracy and computational efficiency can meet the needs.

An indoor location method based on smart phone's RSS fingerprint in four directions

YU Jiahao, YU Min

2021, 46(5): 48-54. doi: 10.12265/j.gnss.2021031501

[Abstract](382) [FullText HTML] (122) [PDF 2375KB](28)

Abstract:
To address the problem that traditional location fingerprint matching algorithm can only represent the characteristics of single dimensional fingerprint points, an indoor locating method based on smartphone's received signal strength (RSS) fingerprint was proposed. In this methods richer fingerprint point information was extracted by data collection, feature extraction and access point (AP) weight assignment in the offline phase, and the improved K nearest neighbor (KNN) algorithm was used to match the test Point with the fingerprint Point in the online phase. In addition, a Bluetooth sensor was used for experimental verification on a smartphone with Android 10 as the operating system version, and 30 test points were randomly selected. Two conclusions can be drawn from the experiment. First, the four-way RSS fingerprint is better than the traditional one-way RSS fingerprint. Under the same experimental conditions, the four-way RSS fingerprint can reduce the positioning error by up to 13.4%. The second is the algorithm proposed by combining the four-way RSS fingerprint, with an average positioning error of about 1.61 meters and a response time of milliseconds.

GPS elevation fitting of BP neural network optimized by genetic simulated annealing algorithm

SHI Chenyang, YUAN Xiaoyan, JIANG Zhicheng

2021, 46(5): 55-59. doi: 10.12265/j.gnss.2021040901

[Abstract](431) [FullText HTML] (159) [PDF 2214KB](32)

Abstract:
In order to solve the problems of slow convergence speed of traditional BP neural network, easy to fall into local optimum and premature convergence of genetic algorithm optimized BP neural network (GA-BP) algorithm, a genetic simulated annealing algorithm optimized BP neural network (GSA-BP) algorithm was proposed. The simulated annealing algorithm (SA) was added to the genetic algorithm (GA) to keep the diversity of the population. GSA-BP algorithm is used to fit the elevation anomaly in a certain area, and the results are compared with BP algorithm and GA-BP algorithm. The results show that the GSA-BP algorithm can improve the accuracy by 51% and 25%, and the speed by 77% and 39% respectively, and can basically meet the requirements of the fourth grade leveling accuracy. This method proves to be feasible in GPS elevation fitting.

Research on integrity fault monitoring performance based on GLS

ZHANG Jianjun, HAN Ming, LYU Zipeng, DENG Qi

2021, 46(5): 60-64, 91. doi: 10.12265/j.gnss.2021051001

[Abstract](329) [FullText HTML] (233) [PDF 2487KB](18)

Abstract:
As an advanced aviation new technology, the GBAS landing system (GLS) of satellite navigation plays an important role in providing signal correction and enhancement service for airborne precision approach in terminal area, and in realizing the function of high-precision departure and precision approach of the whole system. GLS integrity is an important parameter of terminal area approach and landing guidance application, which is an important basis for reliability. However, at present, ordinary users only pay attention to the accuracy of navigation and positioning, and do not consider the reliability of positioning results. The airborne of navigation field has high requirements for the reliability of positioning results. Therefore, this paper studies and analyzes the integrity fault monitoring performance. A clock error adjustment strategy is proposed, and the effectiveness of the method is verified by simulation, the influence of interity fault removed and non-removal on positioning accuracy and integrity is given. It is proved that integrity fault monitoring can ensure the system performance, operation ability and safety performance of GLS to meet the expected requirements.

Application of laser SLAM positioning method based on reflection target in port unmanned vehicle

WANG Kang, YANG Yongsheng, YAO Haiqing

2021, 46(5): 65-72. doi: 10.12265/j.gnss.2021032201

[Abstract](699) [FullText HTML] (229) [PDF 2969KB](50)

Abstract:
Facing the problem that in some specific scenarios in port, such as the shore work area and the container yard, the high-precision positioning of unmanned vehicles, this paper uses Cartographer simultaneous localization and mapping (SLAM) algorithm based on reflective targets to solve it. The reflective target parameters and layout method are designed and optimized, and the impact of key parameters inclucling speed and vibration, on the positioning accuracy of laser SLAM based on reflective targets is analyzed. A test system is designed and implemented, and extensive comparison tests are carried out to verify the trend of positioning accuracy. A large vibration can lead to the failure of laser SLAM, which is common in port. Therefore, the mechanism of positioning failure caused by large vibration is analyzed, and the composite positioning technology based on inertial measurement unit (IMU) and laser SLAM is implemented to suppress the positioning error of laser SLAM under a large vibration. The experimental results show that the proposed method improves the positioning accuracy and robustness of laser SLAM for unmanned vehicles in port.

Application of BDS in intelligent charging device of electric boat

CAO Yu, SONG Yuze, TANG Xiaobo, WANG Ning, LI Mengbo

2021, 46(5): 73-78. doi: 10.12265/j.gnss.2021033101

[Abstract](357) [FullText HTML] (203) [PDF 2952KB](23)

Abstract:
Marine electric ships have been widely used in marine scientific research activities, but their power supply mostly depends on shore-based charging equipment and manual recovery, which results in the low power supply efficiency. An intelligent charging device for electric boat powered by marine energy is designed, which can provide convenient charging for a surface electric boat by utilizing the complementary mode of wind energy and tidal current energy. The navigation and communication functions of the BeiDou Navigation Satellite System (BDS) are used to realize the positioning of the charging device and the real-time communication with the electric ship to guide it to the sea area where the charging device is located. The shore-based terminal realizes the information feedback of the working state of the device through BDS to obtain the real-time charging state of the electric ship. The device can improve the power supply efficiency of the electric boat with clean power source.

GNSS interference source detection and location technology based on unmanned aerial vehicle

SUN Xingxin, ZHEN Weimin, ZHANG Faxiang

2021, 46(5): 79-83. doi: 10.12265/j.gnss.2021040803

[Abstract](725) [FullText HTML] (217) [PDF 5824KB](66)

Abstract:
At present, the research on the detection of navigation interference sources based on unmanned aerial vehicles is mainly focused on the theoretical research and simulation implementation stage. In this paper, we designed a Global Navigation Satellite System(GNSS) interference source direction finding and positioning system based on a six-rotor unmanned aerial vehicle (UAV) platform, and it was tested in a certain field on the positioning accuracy of the interference source. The system is mainly composed of a six-rotor unmanned aerial vehicle, an interference source monitoring direction finding load, and a ground station. After the trial production of the system is completed, we selected an open environment to verify the positioning accuracy of the interference source system for different type of tnterference with different power.

Research on secure NTP method based on message digest encryption

CHEN Xi, ZANG Wenchi, MA Ming, GONG Hang, SUN Guangfu

2021, 46(5): 84-91. doi: 10.12265/j.gnss.2021072701

[Abstract](282) [FullText HTML] (141) [PDF 2953KB](21)

Abstract:
At present, the network time protocol (NTP) is the main time protocol used for time synchronization in wired networks. It can achieve a synchronization accuracy of more than ten milliseconds in wide area networks and a few milliseconds in local area networks. However, due to the openness of the protocol, there is no security protection. Under the circumstances, it is extremely vulnerable to network attacks, which brings potential risks to customers who need high security. The NTP protocol can increase security strategies to deal with possible security risks. The message digest algorithm 5 (MD5) and the secure hash algorithm (SHA-1) message digest algorithm is introduced into the NTP protocol algorithm, which is effective to verify data integrity and prevent data packets from being tampered with to ensure the security of time synchronization. Further, for these two types of algorithms, Hash encryption of key data frames of NTP packets is proposed, which can further improve the security of time synchronization while maintaining good synchronization accuracy. Experiments have compared the influence of the synchronization effect brought by the addition of the algorithm. The results show that after the message digest algorithm is added, NTP can still maintain millisecond-level synchronization performance, which is of great significance to the realization of the NTP secure time synchronization method.

Application of X-11-ARIMA model in post-processing of GNSS positioning data

KUANG Yulong, LEI Mengfei

2021, 46(5): 92-98. doi: 10.12265/j.gnss.2021051201

[Abstract](299) [FullText HTML] (165) [PDF 2329KB](19)

Abstract:
Positioning data analysis and post-processing is essential part in the application of Global Navigation Satellite System in S/M and geological hazard monitoring and forecast project. Generally, the smooth data obtained after the Kalman filter processes the positioning data can eliminate noise interference and obtain data close to the true value. However, in the case of a long-term span, the periodic interference is difficult to identify and filter out in a short time, which is reflected as a kind of lower frequency noise fluctuation. This paper assumes that the fluctuation interference is periodic, and uses the X-11 decomposition time series analysis method for data processing. After smoothing, the variance of the positioning data is reduced from 4.733 to 2.683, and the accuracy is increased by 43.3%. And perform autoregressive integrated moving average mode (ARIMA) modeling and prediction on the split data. When compare the restored data with the direct prediction data, we can draw the conclusion that the accuracy of the separate prediction and integration restoration is basically higher than that of the direct prediction by 5% to 10%, so as to deal with the problem of poor real-time smoothing.

Design of BDS / INS deep combination improved tracking loop based on B1C new signal

LI Zhongpan, HAN Peijun, ZHAO Dongqing, LIU Jiansong, LI Zheng

2021, 46(5): 99-103. doi: 10.12265/j.gnss.2021041101

[Abstract](326) [FullText HTML] (174) [PDF 2410KB](28)

Abstract:
Aiming at the BeiDou Navigation Satellite System/inertial navigation system (BDS/INS) deep integrated positioning system, a signal tracking algorithm using inertial nartgation system (INS) assisted B1C orthogonal component is proposed to solve the problem of lock-out of the deep integrated positioning system caused by weak signal in the positioning process. The algorithm uses the Kalman filter algorithm considering the inertial navigation data, at the same time, it uses the pilot component and data component to form a local code to track the signal. The algorithm is used to calculate the measured data, and compared with the traditional algorithm. It can be concluded that the tracking loop is more stable in the weak signal environment, the positioning accuracy is significantly improved, and the pseudo range also has a higher accuracy.

Airborne radar power line inspection based on multi-GNSS fusion precise single point positioning

MENG Hao, HAN Baomin, WANG Shengli, WANG Jin

2021, 46(5): 104-110. doi: 10.12265/j.gnss.2021042701

[Abstract](285) [FullText HTML] (249) [PDF 2392KB](23)

Abstract:
Through the power line inspection experiment of UAV equipped with light detection and ranging (LiDAR) measurement system, this paper proposes an airborne LiDAR power line inspection method based on multi-system precise single-point positioning. The article focuses on the analysis of the three processing strategies of base station differential, single-system precision single point positioning (PPP), and multi-system fusion PPP to generate POS data. The airborne LiDAR data are collected in the north-central part of Jiangsu Province and the results of manually placed control points for verification. The experimental results show that the root mean square error of the POS data obtained by the three methods are all within 0.016 m. Compared with the single-system PPP, the multi-system precision single-point positioning increases by 12% in the elevation direction and 21% in the east (E) direction. The north (N) direction has increased by 17%. The method proposed in this paper has high accuracy in generating three dimensional (3D) point cloud data, and the accuracy of the generated point cloud data meets the requirements of fine power line inspection.

The development and prospects of the earth orientation parameter measurement

CHEN Shaojie, GAO Yuping, SHI Chunlin, YIN Dongshan

2021, 46(5): 111-116. doi: 10.12265/j.gnss.2021031502

[Abstract](498) [FullText HTML] (198) [PDF 2072KB](71)

Abstract:
With the rapid development of space exploration engineering in China, the demand for the accuracy of earth orientation parameters is higher and higher. This paper introduces the measurement principle of earth orientation parameters (EOP), comprehensively describes the measurement principle and characteristics of the existing classical optical observation means and modern space geodesy means represented by VLBI, GNSS, Doris, LLR/SLR, etc, and make a prospect of the autonomous measurement and service of EOPs. It also provides data basis for the establishment of autonomous earth orientation parameters measurement system in China.

Research on water extraction method based on GF-5 hyperspectral feature analysis

SHEN Congying, GAN Shu, LI Xin’ao, FENG Hongneng

2021, 46(5): 117-122. doi: 10.12265/j.gnss.2021030901

[Abstract](706) [FullText HTML] (221) [PDF 2272KB](63)

Abstract:
In view of the spectral confusion between mountain water body, mountain shadow and bare land, a decision tree extraction model for mountain water body is constructed based on Gao Fen-5(GF-5) image data combined with hyperspectral feature analysis. First, perform hyperspectral feature analysis on the water body and related interference types to realize the selection of feature bands, apply single-band threshold method, multiple-band spectral relationship method, and NDWI method to extract experiments. By comparing the deficiencies of the above experiments, a single-band threshold is proposed. The decision tree water body extraction model combined with the constructed shadow water index (SWI) is used to evaluate the accuracy of the confusion matrix obtained by using Google Earth high-definition images as a reference and on-site sampling. The experimental results show that the single-band threshold method and NDWI method can easily identify mountain shadow as water body and are less affected by bare land; the multiple-band spectrum relationship method has a certain inhibitory effect on mountain shadow and is affected by small areas of bare land; decision tree model can effectively suppress the influence of mountain shadow and bare land to extract complete water body. The overall accuracy is 89.39%, and the Kappa coefficient is 0.82, which significantly improves the extraction accuracy of mountain water body.