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About this book

China Satellite Navigation Conference (CSNC 2020) Proceedings presents selected research papers from CSNC 2020 held during 22nd-25th November in Chengdu, 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 13 topics to match the corresponding sessions in CSNC2020, 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

Satellite Navigation Application

Frontmatter

High-Speed Railway Track Comprehensive Measurement System Based on GNSS/INS Multi-sensor

Track measurement is an importantly basic and preliminary work to ensure high-speed, safe and smooth operation of trains. In the stages of design and construction, the high-speed railway track measurement at least includes the layout and measurement of all control networks, the subgrade deformation monitoring, and the track irregularity measurement. However, there are several problems such as long retest period, high labor cost, and low detection efficiency, which cannot fully meet the needs of large-scale high-speed railway tracks rapid detection in the stages of operation and maintenance. So, a set of track comprehensive measurement methods of high-speed railway based on GNSS/INS multi-sensor are proposed, and the corresponding system is developed. It has been applied to the actual track fine adjustment engineering, and compared with the Amberg track geometry measurement system based on total station coupled with level, and the results show that the proposed system has realized the integration of track subgrade deformation monitoring and track geometry absolute measurement and relative measurement, which fully meets the requirements of the Code for Engineering Survey of High-Speed Railway, and significantly improves the measurement efficiency.

Qi Li, Zhengdong Bai, Bobo Chen, Haohao Xin, Yuhang Cheng, Qiang Zhang

Research on Application of Improved S Transform in High Frequency GNSS Data Processing Results During Earthquake

The high-frequency GNSS data at the time of earthquake was obtained by dynamic single-epoch positioning solution, and the GNSS displacement results were obtained. However, the seismic-time GNSS displacement result after dynamic single-epoch solution contains a lot of noise. It has a great impact on the analysis and research of the displacement during the earthquake, in order to minimize the noise impact in the results and improve the accuracy of dynamic positioning. Traditionally, the S transform denoising method is used to denoise the processing results, but the denoising effect is affected because its time resolution is limited.This paper improves the S-transform method and improves its time-frequency resolution. The principle of S-transform and improved S-transform is introduced. The improved S-transform is used to denoise the high-frequency GNSS single-epoch dynamic positioning results after earthquake processing by GAMIT/TRACK, which greatly removes the noise of displacement results and improves The analysis and research of the dynamic positioning accuracy and the high-frequency GNSS displacement results during the earthquake are made to more accurately determine the time when the GNSS seismic wave arrives at the observation station. Finally, based on the characteristics of high-frequency GNSS acquisition of seismic instantaneous deformation information, this paper proposes an improved S-transform method combined with a trend term denoising method, which can minimize the effect of positioning errors of long-period low-frequency displacement signals, which is more conducive to the in-depth study of GNSS Seismology.

Jingyu Shen, Yun Shi, Kangkang Wu, Lu Zhang, Fan Tian, Kan Zhao

Inversion of Soil Moisture by GPS-IR Combined with Wavelet Analysis and LS-SVM

The research on the inversion of soil moisture by Global Navigation Satellite Signal-Interferometer and Reflectometry (GPS-IR) has become a hot research field in recent years. In the past few years, ground-based experiments using the US Panel Observation Program (PBO) have confirmed that GPS receivers primarily used for measurements can be used to measure changes in surface physical parameters. In this paper, we study the improvement of the separation model of satellite reflected signal in GPS signal to noise ratio (SNR) observation, and the inversion model of GPS-IR remote sensing soil moisture. Firstly, wavelet analysis is used to effectively separate satellite reflected signals. Further use Least squares support vector machine (LS-SVM) rolling predictive model for estimating soil moisture. Soil moisture was estimated using the GPS SNR provided by the P038 station of the PBO observation network. Comparative analysis of the feasibility and effectiveness of single- and multiple-GPS satellites for soil moisture rolling estimation. Theoretical analysis and experiments show that wavelet analysis can effectively improve the separation accuracy of satellite reflected signals. The LS-SVM rolling estimation results are highly consistent with the soil moisture verification data. This model fully exploits the advantages of LS-SVM and effectively integrates the satellites. Performance, improved the use of a single satellite for soil moisture estimation, the results are prone to abnormal jumps; the model requires less modeling data, the use of rolling can achieve long-term estimation, the estimation error is more stable.

Zhigang Zhang, Chao Ren, Yueji Liang, Yalong Pan

Bare Soil Freeze/Thaw Process Detection Using GNSS-R/IR Techniques: A Case Study in Alaska, USA

GNSS-IR is a new emerging remote sensing technique, and it utilizes the interference signal of direct and reflected signals for geophysical parameters retrieval. Nowadays, its application include soil moisture, snow depth, vegetation water content and sea level detection. This paper has extended its application to monitor soil freeze/thaw process. Mixed material dielectric constant model is employed to get the dielectric constant change as soil freeze/thaw process occurs. Forward GPS multipath model is used to establish the quantitative relationship between GPS multipath observables and soil freeze/thaw process. One open GPS site and a corresponding SNOTEL soil climate site are analyzed to get the relationship between multipath SNR and soil temperature (as soil freeze/thaw process occurs). To take the effect of receiver temperature into consideration, multipath data at higher elevation angles are analyzed. In-situ measurement data indicate that there is a good relationship between soil temperature and GPS multipath data and there is a bright potential for soil freeze/thaw process detection using GNSS-IR.

Xuerui Wu, Sharula, Xuanran Li, Lei Yang

High Temporal Resolution of PWV Acquisition Method and Its Preliminary Application in Yunnan

Rapid variation of atmospheric water vapor is important to the regional hydrologic cycle and climate change. Due to the lack of high temporal resolution precipitable water vapor data, it is tough to monitor the rapid change of water vapor. This paper focuses on the hourly PWV data calculated by using the GNSS ZTD from CMONOC and meteorological parameters in ERA5 datasets from ECMWF and the application of PWV in ENSO event is also studied. This paper first verifies the pressure (P) and temperature (T) data in ERA5 datasets. Then, ZHD is calculated based on the atmospheric pressure data, and ZWD is obtained by using GNSS ZTD of CMONOC, and then PWV data of the Yunnan area is calculated based on Tm obtained by improved IGPT2w model from 2011 to 2017 and verified it. At last, the research on the abnormal daily variation of PWV during ENSO and the monitoring of ENSO events is carried out. The results show that: (1) The average RMS and bias of P/T are 3.33 hPa/1.20 K and 0.86 hPa/−0.15 K, respectively. (2) The average RMS and Bias of PWV difference from ERA5 and ERA-interim are 1.98 and 0.83 mm, respectively. (3) Based on the analysis of PWV daily variation during EI Niño Events in 2015–2016, it is found that the PWV daily variation in 2016 is significantly higher than that in 2015. (4) Combining temperature and SSTa index, a new index (ENSO Monitor Index, EMI) of ENSO events is proposed. The correlation between the index and SSTa is 0.59. Therefore, the results of this paper are considerable significance to the study of water vapor distribution and climate monitoring.

Pengfei Yang, Qingzhi Zhao, Wanqiang Yao

Soil Moisture Inversion Based on Beidou SNR and Carrier Phase Combinations

Soil moisture is a very important variable in the study of terrestrial water and energy cycle, traditional soil moisture monitoring methods have great limitations for high resolution large area monitoring. Soil moisture monitoring based on Global Navigation Satellite System Interferometry and Reflectometry (GNSS-IR), which also known as signal-to-noise ratio (SNR) method or interference pattern technique (IPT), can be used to overcome those shortcomings, so that it receives more and more attention in recent researches. However, previous studies mostly used the observed data of Global Positioning System (GPS) to estimate soil moisture. With the maturity of the Beidou system, application of Beidou system is the focus of future research. This paper studies the soil moisture inversion methodology using the signal-to-noise ratio (SNR) data of Beidou B1, B2, and also proposes a novel method of soil moisture inversion based on geometry-free linear combinations of carrier phase on Beidou B1, B2. It also presents the soil moisture inversion model as well as the relevant signal processing flow. Moreover, an in-situ experiment campaign is performed for verification. The results show that the soil moisture obtained by the proposed models is significantly correlate to the ground truth data. The signal-to-noise ratio method achieves slightly higher accuracy than the carrier phase combinations method, which proves that both the two methods can realize a continuous long-term in-situ observation of soil moisture.

Bo Sun, Lei Yang, Xuerui Wu, Chengyi Wang, Xiumei Guo, Liguo Zhang

An Improved Method of ZTD Model in Yunnan Province Based on GPT2w Model

The GPT2w model is one of the currently disclosed high-precision empirical models of tropospheric key parameters. The model can provide a variety of meteorological parameters, and the ZTD can be calculated using the model parameters. However, when using the GPT2w model to calculate ZTD directly, its accuracy is reduced, and there is a specific regional. In order to obtain higher precision ZTD parameters, this paper proposes a ZTD model that improved GPT2w(IGPT2w). The model uses the ZTD calculated by the GPT2w as the initial value of the IGPT2w and calculates the ZTD residual for the ZTD actual value and the GPT2w. The difference was fitted to obtain a ZTD residual fitting model. Finally, the IGPT2w model consists of the initial value calculated by the GPT2w and the residual estimated by ZTD residual model. Taking Yunnan, China, as an example, this paper selects 27 GNSS stations in Yunnan from 2015–2017 to establish the IGPT2w model and verify its accuracy. Firstly, MSSA and LS methods are used to analyze the characteristics of the ZTD residual and determine the periodic signals and establish a ZTD residual model considering annual, semiannual, and seasonal period, and then establish the IGPT2w in combination with the GPT2w. The IGPT2w model was established based on GNSS data from 2015–2016 and applied to ZTD estimation in 2017; The result shows that the IGPT2w estimates that the external RMS and MAE (2.4/1.8 cm) of the ZTD are lower than the GPT2w (2.8/2.3 cm). Compared with the GPT2w, the average accuracy of ZTD was improved by 13.4%. The above results show that the IGPT2w model is superior to the GPT2w model in the Yunnan province of China.

Zheng Du, Qingzhi Zhao, Wanqiang Yao

Inclusion of Side Signals on GNSS Water Vapor Tomography with a New Height Factor Model

GNSS tomography has bloomed into an efficient tool for sensing the high spatiotemporal variations of tropospheric water vapor. Presently, GNSS signals passing from the top boundary are selected as effective rays to tomography system in the most studies. However, a number of side signals penetrating from the side of tomography area are eliminated, which reduces the utilization of GNSS rays and aggravates the morbidity of tomographic observation equations. In this paper, the integration of top signals and side ones for GNSS water vapor tomography system is explored and developed. The sectional slant wet delay (SWD) corresponding to part signals, regarded as the key for utilizing side rays, is accurately estimated by a new height factor model (HFM). In addition, dynamic top boundary of tomography area is analyzed and determined based on the same radiosonde data. Three experimental schemes are carried out using 31 days observation data from the Satellite Positioning Reference Station Network (SatRef) and Radiosonde in Hong Kong. The experimental results show that the average number of effective signals increased by 66.29% and the average utilization rate of GNSS signals is enhanced by 31.86% with side signals absorbed into the tomography system. Furthermore, with the proposed method, the statistics suggest that the mean RMSE is reduced from 1.59 g/m3 (Scheme I) to 1.08 g/m3 (Scheme III), and the accuracy is remarkably improved by 32.08%. On the other hand, compared to the present approach for modeling side rays, the improved model proposed in this paper has a better retrieval capability.

Wenyuan Zhang, Nan Ding, Shubi Zhang

Real-Time Attitude Estimation for High-Speed UAV in High-Frequency Environmental Dithering Based on AMCF

Attitude Measurement System (AMS) that comprised of the low-cost Micro-Electro-Mechanical System (MEMS) based Inertial Measurement Unit (IMU) is usually used as the backup equipment for high-speed Unmanned Aerial Vehicle (UAV) in high-frequency environmental dithering condition. However, both the large-amplitude acceleration during UAV high-speed taxiing and the high-frequency environmental dithering caused by the propeller are important reasons decreasing the real-time attitude measurement precision of the UAV. Furthermore, there is no any other aiding sensors could be used to correct the measurement errors except for the gyroscopes and accelerometers in MEMS IMU. In this paper, an Adaptive Mahony Complementary Filter (AMCF) is used to estimate the real-time attitude of oil-powered single-propeller industrial-grade UAV with low-cost MEMS AMS. Meanwhile, the AMCF based on interference acceleration compensation is proposed to compensate the external disturbance acceleration and the dynamic tuning PI parameters of AMCF. Moreover, the attitude angle is updated by the quaternion updating algorithm to improve the real-time performance and reliability of the AMS. Finally, the UAV high-speed taxiing and flight experiments are included to verify the practical measurement accuracy of low-cost MEMS AMS when it compared with the high-precision and expensive reference system. The flying experimental results demonstrated that the statistical RMS errors of AMS by low-cost MEMS IMU do not exceed 0.882° in pitch and 0.864° in roll when installed in the aviation UAV with high-speed and high-frequency dithering environments. These results not only provide powerful supports for UAV developers but also provide useful method for low-cost MEMS AMS developing and application.

Zebo Peng, Lianwu Guan, Xu Xu, Jianhui Zeng, Yanbin Gao, Jie Yang

Modeling and Simulation of GNSS-R Signals with Ocean Currents

In recent years, with the development of Global Navigation Satellite System (GNSS), GNSS reflectometry (GNSS-R) has become a new method in the field of remote sensing. And the simulation of the GNSS-R research is very important. The simulation of GNSS-R signals mostly uses wind-driven wave spectrum, which ignoring other factors in the real ocean environment, such as the currents. Therefore, this paper proposes a method for modeling GNSS-R signal with considering currents. The influence of currents on the wave spectrum is simulated, and the wave spectrum model of the wind and currents is established. The Kirchhoff approximation-geometric optics is used to calculate the composite scattering coefficient. Finally, with the newly built model, the delay waveform (DW) and the Delay-Doppler maps (DDM) obtained from the simulation in the space-borne scene are analyzed. The results show that ocean currents of different speeds and directions have different effects on the simulation of GNSS reflected signals. The simulation results of the proposed model have good consistency with the theoretical waveform, and the correlation coefficient between DWs is raised to 0.9999. It is proved that the proposed model of GNSS-R signals considering the influence of currents is feasible and effective. And it made the simulated reflected signal more realistic.

Bowen Li, Baoguo Yu, Lei Yang, Dongkai Yang, Hua Han

Coastal GNSS-R Code Delay Altimetry Using GPS L5 Signals

In recent years, with the gradual completion of different GNSS constellations, the available L-band navigation signals have become more abundant. Not only can they be used for PNT (Positioning, Navigation, and Timing), but the reflected signals can also be used for retrieving a variety of geophysical parameters such as sea surface height. Coastal GNSS-R (Global Navigation Satellite System Reflectometry) code delay altimetry obtains the path delay measurements between reflected signal and corresponding direct signal based on ranging code. And the height from sea surface to antenna can be calculated according to the geometric relationship of sea surface altimetry. In order to achieve path delay with higher accuracy, we performed coastal GNSS-R altimetry experiment on a trestle using GPS L5 signals with high ranging code rate. The digital IF (intermediate frequency) data at 25 MHz sample rate were collected during the experiment. Then, self-developed software-defined receiver was used to process the IF data. As the code modulation methods of in-phase (I component) and quadrature-phase (Q component) on GPS L5 carrier are different, we tested the accuracy of I and Q component for sea surface altimetry, separately. In addition, considering different coherent integration time have a certain impact on the accuracy, 1 ms and 10 ms coherent integration time are adopted to compute the path delay based on I and Q component. The results show: for 1 ms coherent integration, the RMSE of I and Q component are 0.70 m and 0.61 m, respectively; while the coherent integration time is 10 ms, the RMSE of I and Q component are 0.54 m and 0.43 m, respectively. To sum up, increasing coherent integration time can improve the accuracy; the altimetry accuracy of the Q component signal is better than that of I component signal.

Xinyue Meng, Fan Gao, Tianhe Xu, Yunqiao He, Ti Chu, Nazi Wang

An Improved Height Rate Correction Method Based on Robust Regression for Sea Level Estimation in GNSS Interferometry Reflectometry

Global Navigation Satellite System-Interferometry Reflectometry (GNSS-IR) sea level altimetry, which is based on analysis of GNSS signals reflected from the sea surface, has demonstrated unique advantages for sea level monitoring. The signal-to-noise ratio (SNR) of a geodetic GNSS receiver can be used to estimate the distance between antenna and sea surface called reflecting height (RH), and subsequently to retrieve sea level. The classical SNR analysis method uses the multipath frequency of the SNR to estimate RH by assuming the sea is static within a limited period. Then, the bias caused by the moving sea surface is corrected by the height variation rate $$ \dot{h} $$ from the dynamic surface and by the elevation angle variation rate $$ \dot{e} $$ from the dynamic satellite. However, this method cannot correct this height rate error completely because $$ \dot{h} $$ cannot be calculated accurately from the raw RH series. Recently, a dynamic SNR method has been developed that can estimate $$ h $$ and its variation rate $$ \dot{h} $$ concurrently from the variational multipath frequency based on the least square method. However, this method has no ability to avoid error, leading to many outliers in retrieval series. So, we introduced the robust regression method to improve this method to avoid errors. The different performance of the classical SNR method and the improved dynamic SNR method is firstly analyzed and compared, using the SNR data from the Kachemak Bay GPS site. The results showed the retrievals of improved dynamic method based on robust regression achieves a higher accuracy than that of classical method. And it has the potential for short-term monitoring (waves and individual days when an event such as a large storm surge might occur).

Xiaolei Wang, Jie Wang

Application Research and Error Analysis of GNSS-MR Technology in Snow Depth Measurement

As a part of global fresh water resources, the change of snow storage has an important impact on the earth’s ecological environment, climate change and human development. Recently years, with the continuous development of Global Navigation Satellite System, GNSS Multipath Reflectometry technology has become one of the emerging means of snow depth measurement because of its all-weather, low cost, high spatial-temporal resolution and other advantages. Based on the study of the basic principle of snow depth measurement by GNSS-MR technology, this paper uses the observation data of p351 station in the PBO network of the United States to retrieve the local snow depth. And then the retrieved snow depth is compared with the measured snow depth of 490 station in the SNOTEL network of the United States. The results show that the correlation coefficient between the two is about 0.98, and the Root Mean Square Error is about 0.1 m, which has a good consistency. On this basis, this article analyzes GNSS-MR snow depth measurement error from three aspects: azimuth, elevation angle and snow depth, and finds that there is a certain quantitative relationship between the negative error generated by GNSS-MR snow depth measurement and the snow depth. Aiming at different error characteristics and error sources, the weakening methods are proposed and verified in practice, which provides a reference for the error correction of GNSS-MR technology in snow depth measurement and other environmental monitoring.

Zheng Li, Peng Chen, Naiquan Zheng, Hang Liu, Lixia Liu

Tide Height Inversion and Accuracy Analysis Based on GNSS-MR Technology

The tide height of offshore waters is an indispensable marine geographic information data for marine traffic, offshore environmental management, and marine disaster warning and forecasting. Recently years, with the advantages of low power consumption and low cost, the Global Navigation Satellite System Multipath Reflection (GNSS-MR) technology has become an emerging technical method of tide height measurement. In this article, the observation files of SC02 station in 2018 in Washington state of United States is used to retrieve the distance in vertical direction from antenna phase center to sea surface by using the change of signal-to-noise ratio (SNR) caused by the multipath effect of navigation satellite signal. Afterwards, the elevation based on International Terrestrial Reference Frame (ITRF) is converted to the elevation based on the Mean Lower Low Water (MLLW). And then the tide height of each inversion time relative to MLLW is obtained. Finally, the retrieved tide height is compared and analyzed with the tide height offered by the tide gauge station named FRIDAY HARBOR. The results show that the mean error of the two is about −12 cm, the root mean square error is about 15 cm, and the correlation coefficient is about 0.98. Overall, the retrieved tide height agrees well with the measured tide height. Hence, the tide height retrieved by GNSS-MR technology can make up for the lack of ocean observation data in the coastal waters and plays an important role in marine scientific research.

Naiquan Zheng, Peng Chen, Zheng Li, Yongchao Ma, Lixia Liu

Research on Sea Surface Height Measurement Based on GNSS-IR Dual Frequency Data Fusion

It is an important application of GNSS in marine remote sensing to measure sea level by using Global Navigation Satellite System Interferometry Reflectometry (GNSS-IR), which provides a new direction for global sea level change research. At present, the accuracy of sea level retrieved from GNSS single-frequency observations needs to be further improved. In order to solve this problem, this paper proposed a new retrieval method based on the peak weighting scheme of integrating the respective sea level retrieved from signal-to-noise ratio (SNR) data of two single frequency L1 and L2 of the Global Positioning System (GPS). The peak weighting method takes the peak power of the spectral analysis of the observed signal-to-noise ratio as the weight, thereby integrating dual-frequency data for sea level retrieval. In order to verify the validity of the mentioned method, the continuous multi-day dual-frequency SNR observation data of two coastal GPS stations were processed and analyzed. At first, the Lomb-Scargle Periodogram (LSP) spectral analysis method was used to obtain the peak oscillation frequency. Then the peak weighting method is used to fuse the two-frequency sea level retrieval results. At last, the sea level results obtained from the single-frequency observations are compared with that of the double-frequency observations, and the proposed weighting method is verified by comparing with tide gauge. The results show that the accuracy of the retrieval results using the peak weighting method is better than that of the GPS single-frequency observations when sea condition is good, while the accuracy improvement is not obvious when the sea surface is rough.

Jie Wang, Tianhe Xu, Nazi Wang, Yunqiao He, Fan Gao

Application of Fitting of Moving Quadric Surface to Height Anomaly Fitting in the Band-Shaped Area

Global Navigation Satellite System (GNSS), which can provide high-precision coordinates in the global geodetic framework, is able to replace most geodetic surveying, but it is difficult to replace conventional leveling surveying due to height anomaly. The Fitting of Moving Quadric Surface (FMQS) is based on the known points in the circular region with the center of the point to be fitted and a specific radius. In this paper, the method of FMQS is used to fit the height anomaly of Nanjing section of Yangtze River and the downstream, and the results show that the fitting accuracy of the 226 points evenly distributed along the river is 1.86 cm; At the same time, the fitting of GNSS height determination using this set of data can replace the fourth order leveling that the leveling line more than 3.46 km at 95.5% confidence interval. Benchmarks data collected in the field show that the difference between the height of National Vertical Datum 1985 obtained by geodetic height fitting with Jiangsu CORS and the height of National Vertical Datum 1985 obtained by third order leveling is within 2 cm.

Puyu Sun, Chengfa Gao, Xinde Zhai, Yongsheng Liu

Instant PPP with Low-Cost Multi-constellation Dual-Frequency GNSS Chipset

With increased measurement quality of low-cost Global Navigation Satellite System (GNSS) receivers, Precise Point Positioning (PPP) becomes feasible using a low-cost multi-constellation single-frequency GNSS receiver. Profound Instant PPP (IP3), for example, is a real-time fast convergence PPP technology that offers world-wide 50-cm circular error probability (CEP) PPP solution using a low-cost GNSS chipset. IP3 is able to output precise positioning solutions within seconds, which makes it suitable for various emerging applications such as self-driving cars, UAV and smartphones. With strong demand on higher accuracy by those applications, several low-cost dual-frequency GNSS chipset products (e.g. u-blox F9P, Broadcom BCM47755, etc.) have been released to market. The availability of GNSS observations at the second frequency can further improve the positioning accuracy with low-cost GNSS chipsets. Compared to single-frequency PPP, a dual-frequency PPP system not only increases the redundancy of the positioning system but also helps mitigate the ionospheric effect, leading to more accurate and robust positioning solutions. This paper describes the development of a dual-frequency based Instant PPP system (DF-IP3) using low-cost multi-constellation dual-frequency GNSS chipsets. This system is able to output precise positioning solutions at 30 cm CEP within a few seconds and can be applied to support a wide range of applications.

Fei Liu, Hongzhou Yang, Yang Gao

Preliminary Research on GNSS Multipath Interpret the Process of Vegetation Growth

Vegetation is a significant link between soil, moisture, organisms and the atmosphere. Recording vegetation changes has important significance in climate change. Traditional remote sensing has the drawback with low temporal resolution in monitoring vegetation, while GNSS multipath can provide a more complete vegetation growth process. Firstly, the multipath characteristics of GNSS are analyzed, and then basic principles and processes of multipath interpret vegetation growth are introduced in detail. Finally, GNSS continuous tracking stations P476 and P542 deployed in California are used for analysis. The preliminary results show that, at P476, the correlation coefficient between multipath and Normalized Difference Vegetation Index (NDVI) is 0.64 (When the lag time is considered, the correlation can reach 0.88), and similar results are obtained at P542. The results show that GNSS multipath interpret vegetation growth process is effective. In phenology, GNSS multipath estimated phenology variables have later growth season start time and peak time, and shorter season length, mainly affected by lag time.

Jilun Peng, Shuangcheng Zhang, Jingjiang Zhang, Qi Liu, Tao Wang

Calibration and Error Analysis of the BF-1 Demonstration GNSS-R Satellites

The reflection signal of Global Navigation Satellite System can be applied to the research of Remote Sensing Applications (GNSS-Reflectometry, GNSS-R), which shows such advantages as all-time, all-weather, light weight, small volume and low cost. As the first generation of GNSS-R microwave remote sensing satellite in China, BF-1 demonstration satellite is capable to produce high spatial and temporal resolution wind speed observation results, which plays an significant complementary role in the measurement of global wind speed, with the continuous observation of typhoon in particular. In this paper, an introduction is made of the calibration process from the metadata of payload output to the normalized bistatic scattering cross section (NBRCS) of wind speed retrieval. The entire process involves two steps. Firstly, the metadata of payload is calibrated using the calibration load and temperature information, and then it is calibrated according to the geometry of transmitter and receiver. The errors introduced in the process of calibration are analyzed by formula derivation, based on which the total error of the calibration result is obtained as 0.74 dB. This term demonstrates the accuracy and validity of the data processing results regarding BF-1 test satellite, in addition to providing a reference for the design of the next-generation GNSS-R microwave remote sensing satellite.

Bei Wan, Xinliang Niu, Cheng Jing, Bochi Lei, Chong Han

Application and Technology of Bufeng-1 GNSS-R Demonstration Satellites on Sea Surface Wind Speed Detection

GNSS-R microwave remote sensing technology has increasingly become an important branch of satellite navigation applications. In June 2019, China successfully achieved the deployment of BuFeng-1 A/B satellites by Chinese first time sea platform launch. BuFeng-1 is mainly to conduct GNSS-R on-orbit tests of sea wind field detection and its applications. In the processing method, the power self-calibration method is introduced to eliminate the influence of the GNSS-R load receiving link changes by the space environment. Then, the GNSS-R observation geometric change by the GNSS-R geometry is corrected. Finally, DDMs with power self-calibration and geometric correction can directly show an agreement with the sea surface wind speeds. On-orbit results show that the detection accuracy is of 2.63 m/s up at 30 m/s of wind speeds by European Centre for Medium-Range Weather Forecasts (ECMWF) and 1.97 m/s at 20 m/s compared with ASCAT observations, which are accorded to the pre-design requirements of 2 m/s or 10%.

Xinliang Niu, Feng Lu, Yuanhua Liu, Cheng Jing, Bei Wan

Study on the Correlation Between GNSS Vertical Time Series and the Space-Time Distribution of Groundwater in California

The agriculture in California mainly depends on irrigation, but it is one of the regions that suffer serious groundwater loss in the world. The authors obtain the four-year data of 48 survey stations uniformly distributed by PBO network in California and the vertical time series of each station based on GAMIT/GLOBK software. Based on the time series, the contour map of surface elevation variation in California from 2014 to 2017 can be obtained, and it is found that there is an obvious subsidence funnel in southern California. In order to analyze the cause of subsidence funnel, the authors introduce the burial depth data, which shows that the groundwater depth in this area decreases 25.65 cm annually in the past four years. The groundwater loss caused by agricultural irrigation is the main reason for the formation of settlement funnel in this area, while rainfall can effectively alleviate the exploitation of groundwater for agriculture. Through analyzing the TRMM rainfall data of this area, the authors find that the cumulative rainfall in northern California from 2014 to 2017 is significantly higher than that in the south. The maximum reaches about 6000 mm, but the minimum rainfall occurs in the south, less than 1000 mm. According to the GPS vertical time series, TRMM rainfall data and groundwater depth analysis, there is a high correlation between the P566 survey station with severe surface subsidence and the groundwater depth data of nearby wells. In addition, the rainfall data shows that the rainfall in southern California is significantly lower than that in the north. The experimental results indicate that the time series of the surface elevation change acquired by the GPS can effectively reflect the groundwater timing change; the ground surface settlement monitored by the GPS is highly correlated with the measured groundwater depth data, which proves that the surface settlement of the southern California is mainly caused by the exploitation of the underground water; the loss of groundwater in the southern region can not be effectively alleviated due to inadequate rainfall, which further demonstrates that the surface settlement in California is mainly caused by the excessive exploitation of groundwater.

Xiaoguang Pang, Yong Luo, Shaodong Jing, Shuangcheng Zhang, Kunchao Lei

Suspension Cable Bridge Deflection Determination Using Kinematic PPP with High-Rate GPS Satellite Clock Corrections

Many previous studies have utilized the advantages of GPS for structural health monitoring however high data rate (higher than 1 Hz) is required for structures’ vibration detection using GPS. This paper investigates the advantages of utilizing high-rate satellite clock in a kinematic PPP processing strategy specifically applied to the detection of bridge displacement. Global distributed IGS stations high rate observations were used for GPS satellite clock estimations. The Uncalibrated Phase Delay (UPD) and the Zenith Total Delay (ZTD) parameters were firstly estimated using PPP in static mode. The GPS satellite clock product with 1 Hz sampling rate were successfully estimated by applying the UPD and tropospheric delays as compensations to the carrier phase. The deformation of the suspension cables (20 Hz datasets) and towers (10 Hz datasets) were estimated using both the kinematic PPP, using the 1 s, 30 s, 300 s clocks, and the DD data processing method. The 1 s GPS satellite clock gave the most precise and stable solution when compared with the 30 s and 300 s clocks obtained from IGS. Correlation coefficient of PPP solution and DD solution reflects bridge displacement waveform using 1 s PPP is more consistency and accuracy. The 1 s PPP is an alternative method for suspension cable bridge deflection determination, particular in the scenario that DD is impossible due to failure of reference station.

Xu Tang, Fei Guo, Craig Matthew Hancock, Huib de Ligt

Radiosonde-Based New Spatiotemporal Modelling for the Construction of Temperature Profiles for GNSS Applications

In order to construct temperature profiles over a GNSS station of interest, a series of spatiotemporal models for determining the ratio of the zenith dry delay (ZDD) for 40 selected pressure levels were established using a harmonic function and 18 years radiosonde data from 92 stations distributed in East Asia. The ZDD over a site is defined by the integral of the temperature profile and the dry pressure profile over the site. In the case that neither the temperature profile nor the dry pressure profile is available, a method for the ZDD obtained from precipitation water vapor (PWV) and zenith hydrostatic delay (ZHD) is derived in this study. Then, the ZDD value at a dry pressure level, named ZDD-lev, was obtained by multiplying the above ZDD with the ratio of the ZDD interpolated from the above mentioned spatiotemporal model for the level. The ZDD-lev and the dry pressure were used to determine the temperature of the level. The temperature profile was composed of the temperature values at all the dry pressure levels. The temperature profiles constructed at 10 IGS stations during a 8-year-period were evaluated using the observed ones as the references. The results indicated that the mean root-mean-square error (RMSE) and mean bias of the temperature profiles at 10 IGS stations was 3.24 K and 0.5 K, respectively.

Longjiang Li, Zhen Shen, Qimin He, Mofeng Wan, Kefei Zhang, Suqin Wu

Analysis of Temporal and Spatial Variation of Crustal Strain Around Longmenshan Fault Based on GNSS Observation

The Longmenshan fault zone is located in the transition zone between the eastern margin of Qinghai-Xizang Plateau and Sichuan Basin. It is an important part of the north-south seismic belt in China, and the tectonic activity is frequent, and the 2008 Wenchuan earthquake and the 2013 Ya’an earthquake are all on the tectonic fault. In this paper, the coordinates’ time series and velocity fields in the region with high precision are obtained based on GAMIT/GLOBK. The strain parameters in the region are calculated by using the strain model and the high-precision dynamic model of the fault zone and the surrounding crust are constructed, and the time-space distribution of the abnormal information of the fault zone is extracted and analyzed with the reference of the earthquake such as Wenchuan and Ya’an. The study in this paper can be used as a reference for the analysis of crustal movement characteristics and the assessment of geological hazards in Sichuan-Yunnan region.

Huijuan Liu, Xianchun Chen, Caiya Yue, Qiang Yang

Design and Research of Missile-Borne High Dynamic Satellite Navigation Device

A design scheme of the missile-borne high dynamic satellite navigation device is given for the requirements of the trajectory correction projectile for the measurement system, analyzing the dynamic stress characteristics of the trajectory correction projectile. In order to solve the problem of the signal’s lock-lose of the trajectory ascending section, the strategy of the carrier tracking loop is improved. Finally, the effectiveness of the improved strategy is verified by the simulation scenario test.

Feiping Lu, Wen Xue

Navigation and Location-Based Service

Frontmatter

Detecting Community Structure of Urban Hotspot Regions

The travel behavior of residents is influenced by environment factor such as urban transportation system and administrative division. In turn, users equipped with navigation devices act as sensors detecting the environmental dynamics. The long-term accumulation of navigation big data contains massive valuable spatio-temporal information. We propose to detect the spatio-temporal distribution and community structure of urban hotspot regions from navigation big data. A framework including data preprocessing, hotspot region detection, urban spatial discretization, and community structure detection is designed in this work. Hotspot regions are detected by kernel density estimation and density-based clustering on origin-destination (OD) points of navigation trajectories. The hotspot regions are discretized into Voronoi polygon grids based on the spatial distribution of OD points. Finally, we analyze the complex network formed by hotspot region grids and employ Louvain algorithm to detect the community structure of hotspot region network. This framework is implemented on the taxi dataset of Chengdu. The experimental results reveal the spatio-temporal distribution and community structure of urban hotspot regions in different periods of weekdays and weekends. The urban hotspot regions and the community structure are influenced by inherent geographical environment and dynamically evolve with time. The spatio-temporal characteristics of urban hotspot regions are proved to be the result of coaction of environment and human activities. Findings of this work could provide decision-making support for transportation system optimization, city layout plan, and smart city construction etc.

Rui Chen, Mingjian Chen, Wanli Li, Naikun Guo

FM and DTMB Signal Fingerprinting Positioning System Based on Multi-peak Gaussian Distribution Model

With the rapid development of wireless communication technology and the popularization of smart devices, all walks of life are constantly exploring location-based services in recent years. This paper proposes a combination of Frequency Modulation (FM) signal and Digital Television Terrestrial Multimedia Broadcasting (DTMB) signal to improve the indoor positioning accuracy of the new method for the disadvantages of partial positioning technology. The signal intensity of FM and DTMB is taken as the position fingerprint. The multi-peak Gaussian distribution model is used to fit the signal intensity, and then the probabilistic positioning matching algorithm is used to achieve high-precision positioning in the room. We verified the feasibility of the method through actual measurements in the indoor environment. Compared with the existing positioning technology, this method has the advantages of large coverage, high stability, low cost and high precision. The accuracy of the joint positioning of two signals is higher than that of the FM signal alone. It is verified that the positioning error of this system can reach 1.20 m when the multi-peak Gaussian distribution model is used. Compared with the single-peak Gaussian distribution model, the positioning accuracy is improved by about 0.80 m, which has certain reference significance in the field of indoor positioning.

Hongyu Qiao, Hong Wu, Menghuan Yang, Hongzhao Peng, Haixiao Yang, Bin Zhao

Kinematic Positioning Algorithm Based on the Grey Prediction Model for Urban Navigation

Lack of visible satellites in urban environment will have an adverse impact on positioning and navigation. The kinematic positioning will have a degrading accuracy and even fail to gain the consequences of positioning when in serious conditions. In view of the shortage of observable satellites, this paper, based on the grey prediction model, respectively uses the pseudo-range observation values of the latest epochs and the estimation vector of state parameters to forecast the pseudo-range observation values and state parameters of the current epoch. The experimental results show that it is feasible to use the grey prediction model to predict the state value as the navigation and positioning result or pseudo-range observation value for positioning in the epochs with insufficient observable satellites. The actual calculation example shows that the accuracy of predicted observation values in the absence of available satellites in the field is improved by 61.9%, 53.6% and 18.9% respectively in the ENU direction, and the predicted state parameters are improved by 38.1%, 18.1% and 11.3% respectively in the ENU direction. Obviously, the algorithm proposed in this paper can effectively solve the problem that the kinematic positioning accuracy is reduced or even cannot be located when the signal is blocked for a short time in urban environment, and improve the accuracy and reliability of the kinematic positioning.

Tianhang Gao, Xianqiang Cui, Xun Wang

A New Adaptive Estimation Algorithm Based on CT Model and Ellipsoid Constraint

Kalman filtering algorithm is frequently used in the kinematic measurement of Global Navigation Satellite System (GNSS) for positioning calculation. The vehicle often appears maneuvering turns in GNSS navigation and positioning with randomness and unpredictability, which makes it impossible to be described with an accurate models. If the Kalman filtering algorithm based on Constant Velocity (CV) or Constant Acceleration (CA) model is still applied for navigation solution, the accuracy and reliability of the filtering results will be significantly reduced. Aiming at the problem that the current dynamic model has a large error under the maneuvering turns, this paper combines the Coordinated Turn (CT) model and the fixed elevation algorithm to estimate the horizontal turning rate of the vehicle in real time, and limits the deviation of Z direction through the ellipsoid constraint, which ameliorates the impact of the dynamic model deviation on navigation solutions. Experiments show that no matter in left turn, right turn or compound road section, the adaptive filtering algorithm proposed in this paper can better control the influence of dynamic model deviation, and effectively improve the positioning accuracy and reliability of the vehicle during maneuvering turns.

Xun Wang, Xianqiang Cui, Tianhang Gao

Fault-Tolerant Navigation Method for Unmanned Aerial Vehicle Based on Heterogeneous Pseudorange Augmentation

With the increasing application field of unmanned aerial vehicles, the integrity guarantee capability of satellite navigation system is constantly challenged by complex environments. The introduction of multi-source auxiliary information is an effective mean to enhance the availability of satellite navigation. As a method of land-based long-range radio navigation, Loran-C navigation system has good stability and can provide pseudorange auxiliary measurement information in specific areas to assist satellite receiver in fault detection. Aiming at the problems that the protection level provided by satellite navigation alone may not meet the requirements and the accuracy and reliability of fault detection result may reduce in complex environments, this paper proposed a fault-tolerant navigation method for unmanned aerial vehicle based on pseudorange augmentation. This method introduces the augmented pseudorange information of Loran-C system to assist the inertial/Beidou integrated navigation in integrity detection. Considering the difference of pseudorange measurement characteristics between Loran-C system and Beidou navigation system, this paper uses the weighted least square method to overcome heteroscedasticity and establishes the Loran-C/Beidou augmented pseudorange observation model. Based on this model this paper studies the augmented pseudorange system integrity protection level algorithm when introducing the Loran-C information, and constructs the fault detection and system fault-tolerance algorithm on this basis. The simulation results show that, compared with traditional satellite navigation, this method can effectively improve the integrity guarantee level of system and enhance the fault-tolerance ability of the system under the condition of partial limitation of satellite navigation.

Xin Chen, Rong Wang, Zhi Xiong, Jianye Liu, Weixing Qian, Junnan Du

A Method for PPP Ambiguity Resolution Based on Bayesian Posterior Probability

After the corrected by the uncalibrated hardware delay fractional part (FCB) product, the integer characteristic of precise point positioning (PPP) ambiguity can be recovered, which can significantly shorten the convergence time. However, the incorrectly fixed ambiguity seriously affects the accuracy of the results. In the convergence stage of PPP, the traditional method based on ratio test is prone to miss detection and fixed ambiguity incorrectly, which brings an extremely deviation to the results at the user end. Therefore, we propose a step-by-step PPP ambiguity resolution method based on Bayesian posterior probability. The method is deduced from the rigorous mathematical theory, which is guaranteed by the confidence level and can be adjusted according different scenarios. 116 global MGEX stations are selected as the server end to generate two kinds of FCB products, i.e., ionosphere-free combined FCB and undifferenced and uncombined FCB products, and another 50 stations are selected as the user end to test the proposed method. Compared with the traditional method, the success rate of the new method increases from 95.0% to 99.5% in static condition, and the missing detection rate detection reduces from 6.5% to 0.2%; the success rate of the new method increases from 82.9% to 95.9% in kinematic condition, and the missing detection rate detection reduces from 13.1% to 1.9%.

Zhenqiang Du, Hongzhou Chai, Xiao Yin, Chunhe Liu, Mingchen Shi

Convergence Analysis on Iterative Algorithm in Ultra-Wideband Positioning Under Ill-Conditioned Configuration

Since the functional model of UWB positioning is nonlinear, iterative algorithms are often considered for solving the localization problem. With a rough initial value, we can obtain the optimal solution by the way of continuous iteration. However, in the UWB indoor positioning, the positioning system is prone to become ill-posed. It resulting in iterative algorithm cannot easily converge to a global optimal solution. In this paper, the convergence on iterative algorithm is analyzed. First of all, the nonlinear least-squares solution of distance equations in UWB positioning is given, then, four optimization iterative methods are presented. Finally, the four methods are applied to UWB static and dynamic positioning under ill-conditioned positioning configuration, the convergence property of the four methods are compared. For the iteration, three types of initial values are selected, and the three cases represent bad, general and good initial value respectively. Experimental results are given to demonstrate that although the barycenter method can converge correctly, it is inefficient with too more iterations. In addition, with a good initial value, the Gauss-Newton method can converge effectively, its iterations increase a lot with a general initial value, and this method rarely converges successfully, and sometimes converges to a false local optimization solution when selecting a bad initial value. Moreover, both the regularized Gauss-Newton method and closed-form Newton method work and converge to the global optimum effectively under the three types of initial values, and the closed-form Newton method has fewer iterations. The study shows that the closed-form of Newton method has higher efficiency of convergence than the other methods in Ultra-wideband positioning under ill-conditioned configuration.

Chuanyang Wang, Jian Wang, Hang Yu, Yipeng Ning, Feng Xu

Comparison of RDSS Timing for BD-2 and BD-3 System

With the launching of BD-3 satellites, Beidou navigation satellite system is going to the global service operation. Therefore, this paper study the RDSS timing principle of BD-2 and BD-3 systematically. By analysing the one-way and two-way timing precision, we have the conclusions: for RDSS one-way timing, the precision of BD-2 is less than 30 ns, and its RMS is less than 6.81 ns, the precision of BD-3 is less than 20 ns, and its RMS is less than 4.26 ns; for RDSS two-way timing, the precision of BD-2 is less than 20 ns, and its RMS is less than 3.60 ns, the precision of BD-3 is less than 10 ns, and its RMS is less than 2.09 ns. The results reflect timing performance for Beidou regional and global system.

Dongxia Wang, Rui Guo, Tianqiao Zhang, Zhijun Liu, Jie Xin

A Multi-constellation Positioning Method Based on Optimal Stochastic Modelling

Recent years, with the continuous improvement of positioning requirements, the inherent deficiency of single constellation positioning is increasingly magnified, the number and distribution of satellites seriously restrict the positioning effect, which impair the availability of the navigation system. In view of this phenomenon, the space-time unification of multi-constellation is carried out to realize the orbit determination error analysis. The weighted least square algorithm is combined with Helmert variance component estimation method to optimize stochastic model, single-constellation dynamic positioning and multi-constellation dynamic positioning are realized respectively in the scene of opening and sheltering. The error and accuracy of the two positioning methods are compared and analyzed to verify the improvement of multi-constellation. The experimental results demonstrate that the orbit errors of the broadcast ephemeris within 10 m. Compared with the traditional single constellation positioning method, the multi-constellation positioning method based on optimal modelling can effectively increase the number of visible satellites, ameliorate the geometric distribution of satellites and improve the positioning accuracy.

Jian Wang, Zijian Zhou, Wei Jiang, Baigen Cai, Wei Shangguan

BDS-3/GNSS Data Quality and Positioning Performance Analysis

Since November 2017, China has launched 24 Beidou-3 (BDS-3) navigation satellites. So far, China’s independently developed Beidou satellite navigation system has officially entered the global service stage. Compared with the Beidou-2 satellite navigation system (BDS-2), the MEO satellite of the Beidou-3 satellite navigation system (BDS-3) adds two new signals, B1C and B2a. The quality of the original observation data can directly affect the navigation and positioning system. Positioning accuracy and service performance. This paper selects the original 182-day raw observation data of 23 tracking stations of the International GNSS Monitoring and Assessment System (iGMAS), and analyzes the data quality from four aspects: data integrity rate, signal-noise ratio, cycle slip ratio and multipath effect. The quality of the observed data of GLONASS and GALILEO is compared, and finally combined with the point positioning accuracy of each system for comprehensive evaluation. The results show that in terms of data integrity rate, the data integrity rate of BDS-3 is comparable to that of GPS, GLONASS and GALILEO, and can reach more than 80%. In terms of signal-to-noise ratio, the new BDS-3 satellite The signal strengths of the signals B1C and B2a are not much different from those of the old signals. Compared with other systems, the signal strength of the new BDS signals is better. In terms of the cycle-to-hop ratio, the cycle-bounce ratio of the new signal B2a of the BDS is higher than that of other signals. High, and superior to GPS and GLONASS, it is equivalent to GALILEO’s E5b signal; in terms of multipath effect, the multipath RMS value of each signal of the four systems is within 0.5 m, and the multipath error of BDS-3 satellite B2a signal is slightly the multipath error below B1I and B3I is about 0.1 m. In terms of pseudo-single point positioning and precise single-point positioning, the BDS-3 has a slightly lower positioning accuracy than GPS and GALILEO, but is superior to GLONASS. The results of this paper have certain reference value for the location and maintenance of iGMAS observatory, GNSS data processing and product generation, the development of Beidou GNSS receiver and the positioning performance of Beidou satellite navigation system.

Renhai Mu, Yamin Dang, Changhui Xu

A BEIDOU Short Message Based Method for Position Information Distribution of Reentry Vehicles

The traditional reentry vehicles, including recoverable satellites, vehicles for deep space mission and manned spacecrafts, utilize the way of transmitting typical beacon signals to the ground part to realize positioning. However, it usually takes long time for seeking as only direction information is available, which may push the risk to a high level. In this paper, a novel method depending on BEIDOU short message communication is proposed. Firstly, the reentry vehicles are capable of acquiring self-position information by receiving and analyzing signals from GPS or BEIDOU system. After that, BEIDOU short message communication chain is utilized to broadcast the accurate position information to the ground. Compared with the traditional method, the efficiency of seeking procedure will be significantly improved as more accurate position information is now available. Meanwhile, the risk of seeking will be reduced as well. The paper consists of three parts. In the first part, the whole information flow including the space part and the ground part is introduced. Then, the design of the system and the key instruments onboard is illustrated, as well as the feasibility in a typical application. At last, the verification results of the method proposed in an experiment are displayed. By comparing with the traditional method, the prospects and potential applications are concluded.

Yuanqing Zhao, Luyuan Wang, Xiangyu Li, Haogong Wei, Gang Chen, JingShuang Cheng

A Two-Dimensional Point Cloud Matching Method Based on ICP Improvement

The indoor map is the basis of indoor navigation and positioning. The core problem of indoor map construction by using two-dimensional lidar is to solve the matching problem between different point clouds. The standard ICP algorithm is easily affected by the initial position and interference points, so this paper proposes an improved algorithm based on ICP for 2D point cloud matching. This paper proposes a dynamic initial value matching method based on the highly correlated characteristics of the transformation parameters of adjacent point clouds. Then set the radius threshold to filter out the corresponding points to be matched to provide more ideal data input for the ICP algorithm. In this paper, the indoor parking lot with an area of about 2500 m2 can be collected by using the vehicle 2D lidar equipment, which takes about 85 s to collect. And the global map can be obtained by using the improved ICP algorithm, which takes about 100 s to process the data. Experimental results show that this method has the remarkable characteristics of low cost and high efficiency. Compared with the total station measurement, the method can meet the requirements of the plane map with decimeter accuracy required by the navigation and positioning of the indoor parking lot, and it has a better matching effect in the practical application.

Huchao Xu, Letao Zhou, Yinghao Zhao, Zheng Yuan

DTMB and FM Signals Indoor Fingerprint Positioning System Based on Compressive Sensing

Location-based services have become an indispensable part of people’s daily lives. GNSS can provide favorable outdoor location services, but it cannot meet the needs of indoor positioning. This paper proposes an indoor localization fingerprint system using DTMB and FM signals, which consists of offline and online stages. In the offline stage, the Received Signal Strength of the Reference Points is measured in the experimental area, and the data acquisition amount is reduced by Compressive Sensing theory. In the online stage, the coordinates of Test Points are reconstructed by using Compressive Sensing algorithm. The experiments show that the average positioning accuracy of the DTMB and FM signal indoor positioning system based on Compressive Sensing is about 2.14 m. The proposed system has larger coverage and lower cost, which can meet the actual indoor positioning requirements.

Menghuan Yang, Hong Wu, Hongzhao Peng, Zhuo Chen

Daily Climatological Fields Based on GNSS Radio Occultation Measurements: A Feasibility Study

GNSS Radio occultation (RO) technique can provide high-quality measurements of the Earth’s atmosphere. Monthly (or seasonly) RO climatological fields have been widely used in climate and weather studies. However, the low temporal resolution makes it difficult in resolving the rapid variations in the atmosphere. Here we established the daily climatological fields by GNSS RO measurements from the Constellation Observing System for Meteorology, Ionosphere, and Climate. By applying a “point” strategy, RO profiles are assimilated into a 3°×3° longitude-latitude global grid through the Gaussian weighting function. By comparison between the RO climatological fields and European Centre for Medium Range Weather Forecasts reanalysis, the differences display distinctive features in different layers of the Earth’s atmosphere. The overall differences are about 2 K, 1.5% and 40 m (temperature, density, and geopotential height) in the lower troposphere; 1 K, 0.5% and 40 m in the upper troposphere and lower stratosphere region; and 2 K, 1% and 100 m in the upper stratosphere. The results have demonstrated that the observation-based RO climatological fields are reliable in both northern and southern hemispheres.

Zhen Shen, Qimin He, Longjiang Li, Kefei Zhang, Suqin Wu

Stochastic Modeling of BeiDou Double-Difference Observation and Impact Analysis

Double-difference integer ambiguity resolution (IAR) is playing the vital part in the high precision GNSS positioning and navigation. The IAR success rate depends on three factors: the functional model, the stochastic model and the chosen method of the integer ambiguity estimation. Stochastic model plays an important role in parameter estimation of global navigation satellite system (GNSS). Only a correct stochastic model can be used to obtain the reliable integer ambiguity, the accurate positioning and the reliable baseline precisions. In this paper, a stochastic model with significantly sophisticated structure is designed, and the MINQUE method is utilized to estimate the cross correlations between different types of observations at arbitrary frequency and the time correlations for phase and code observations per frequency. In assessing the stochastic model, the short-length baseline and zero-length baseline with sampling frequency of 1 s are processed to analyze the impact of the realistic stochastic model considering the cross and time correlations on the IAR success rate and positioning. The results confirm that compared with the empirical stochastic model ignoring the cross and time correlations, the more realistic stochastic model can significantly improve the IAR theoretical and practical success rate, especially for single-frequency data, the practical success rate increases by 5%. The baseline precision that ignores cross and time correlation has a large difference from the theoretical ones. Namely, the baseline precision ignoring physical correlations is too optimistic and unrealistic. On the contrary, the baseline precision that considers physical correlation match the theoretical ones more well.

Zhongzhi Wang, Weikai Miao, Yunzhong Shen

Research on Key Performance of BeiDou Global Short Message Communication Service

By carrying global message communication payloads on some satellites of the BeiDou Global System, a two-way link between a user terminal and a ground control center can be constructed by using inter-satellite links and satellite-ground links. At the same time as providing PNT services, BeiDou system provides global short message communication service. On the basis of designing the system scheme, this paper analyzes the key performance of the global short message service, the coverage characteristics, and the system capacity through simulation.

Xin Nie, Jun Xie, Tianxiong Liu, Chonghua Liu, Kanglian Zhao

An Algorithm of Passive Location About Satellite Navigation Disturb Source Based on Combat Platforms Networking

Focusing on the problem that the satellite navigation and positioning of the combat members in the future electronic confrontation is disturbed, a solution for passive location of the interference source is proposed. Under the condition of members networking, the interference source is located accurately using least - square according to the measurement information of each member so that the weapon systems can be guided to implement over - the - horizon strikes. Finally, the simulation results show that the solution proposed in this paper can effectively locate the disturb source and reduce the number of false results. At the same time, this solution is small in calculation and suitable for engineering applications.

Linxu Wu, Jiang Li, Xiaoyu Wang

Satellite Navigation Signal and Signal Processing

Frontmatter

Real-Time Parallel Generation Method of Weil Code and Its Implementation in New GNSS Signal

Pseudo-codes with good autocorrelation properties and cross-correlation properties play a very important role in CDMA satellite navigation systems. For the navigation signal with the code length of 10230, the Weil code based on the Legendre sequence has better correlation characteristics than the traditional gold code. Therefore, in the new system signal, the GPS L1C and the BDS B1C frequency point both use the Weil code as the ranging code. The generation method of Weil code is complicated, and the calculation amount is large, which is difficult to generate in real time. Therefore, in the past, most of the receivers use a storage table to store the Weil code. This method is simple and easy to implement, but consumes a large amount of storage resources. Based on the generation method of Weil, this paper proposes a real-time parallel generation method of Weil code, which can not only generate Weil code in real time, but also can be used to generate Weil code in parallel for multiple channels. The method only needs to store the Legendre sequence with length N, which occupies less resources, and has high engineering application value in the receiver tracking channel.

Zhiqin Xue, Kun Liu

Pseudorandom Code Error Monitoring Method for GNSS Signal

Pseudorandom code error of GNSS signal could degrade user receiver’s data demodulation and ranging performance, it is usually caused by unexpected behaviour within the logic circuits of navigation signal generation in satellite payload. Due to the complexity of modernized GNSS signal structure, real-time pseudorandom code error monitoring has become an important and challenging issue. A novel method is proposed in this paper, by appending several calculation steps into conventional receiver’s signal tracking loop and with the external aid of navigation message, rapid detection of GNSS single spreading code error can be realized. The simulation result shows that by taking this method, accidental pseudorandom code error can be instantly detected regardless of various code chip waveforms and multiplexing schemes, and it’s applicable for both public and authorized signals. This method can be applied to the design of Satellite Autonomous Integrity Monitoring (SAIM) payload.

Yi Yang, Lin Chen, Yuqi Liu, Shaobin Guo

Research on MPSK Modulation Based GNSS Signals with High Data Rate

With the increase of the requirement on the fast time-to-fix and precise message, the high data rate becomes on the key feature of GNSS signals. The most existing GNSS signals are the DSSS signals with BPSK or BOC modulation. Thus, to increase the data rate would cause two results. One is that the spreading spectrum gain decreases and the equivalent PRN code length shortens. The other is that the PRN code rate increases while keeping code length unchanged, so the signal bandwidth increases. The CSK modulation can modulate data using the PRN code phase, and change flexible the data rate. Meanwhile, the PRN code length and code rate maintain constant. Due to the above advantages, CSK modulation has been applied in QZSS L6 signal. However, CSK is usually used to demodulate data information, and difficult to measure range. Aiming at this problem, this paper proposes the MPSK modulation based GNSS signals for broadcasting high rate data and ranging. Firstly, the MPSK modulation is introduced, and the scheme of MPSK modulation applied in GNSS signals is analyzed. Secondly, taking 8PSK as an example, the demodulation performance, code/carrier tracking schemes, and tracking performance are analyzed. On this basic, the advantages and disadvantages comparing MPSK modulation and CSK modulation are discussed. Then, the constant envelope multiplexing method combining the existing GNSS signals and MPSK modulation signal is studied. Finally, an application example of MPSK modulation based GNSS signals is presented, and the performance is analyzed with the help of simulation. The results verify the effectiveness of MPSK modulation as a candidate of GNSS signals with high data rate.

Tao Yan, Ying Wang, Xiao Liu, Lang Bian, Yansong Meng

The Base Stations’ Networking Scheme and Spreading Code Optimization Strategy of TC-OFDM

In order to achieve large-scale positioning by the ground positioning base station network, the mode of co-address and co-frequency broadcasting between the positioning base station and the existing communication base station can be considered. Under this circumstance, in order to meet the need of ultra-dense networking of integrated communication and navigation system, an optimized cellular positioning networking scheme is proposed in this paper. In the outdoor complex transmission environment, the boundary conditions that the proposed cellular network model needs to meet are analysed for the TC-OFDM system. Besides, based on the greedy algorithm of quadratic optimization, the spreading codes with better performance are selected for the reuse of cellular network modules. Theoretical analysis and simulation results show that the optimized cellular network model can well meet the large-scale positioning requirements of integrated communication and navigation system, and the selected spreading code has better performance.

Ke Han, Jiabing Yin, Zhongliang Deng, Jieshu Dong, Shihao Tang, Zhiyuan Ma

Frame Synchronization Method for BDS B2a Signal Under the Constraint of Non-binary LDPC Code

Low-Density Parity-Check (LDPC) Code has become one of the best coding technologies at present because of its low complexity iterative decoding algorithm and its performance with further close to the Shannon limit. Non-binary LDPC codes designed in high order Galois fields have shown better potential than binary LDPC codes with the same code length and code rate, therefore it was applied for the navigation message encoding in BeiDou satellite navigation system (BDS). The navigation message contains time information, ephemeris parameters, clock correction terms and so forth, which is necessary for navigation solution. As the synchronization head was not encoded, it is hard to deal with data synchronization and navigation data decoding when the navigation receiver works at a low Signal-to-Noise Ratio (SNR). Aiming at this problem, we present a synchronization scheme for BDS B2a signal by utilizing the information from the process of decoding. The synchronizer is based on syndrome checks using the decoding result of the Extended Min-Sum (EMS) algorithm. Ratios of satisfaction of all check restrictions are computed firstly, and then the boundary value is obtained through MonteCarlo method. Simulation results show that the proposed algorithm performs well at relatively low SNR compared with traditional method.

Bowen Jiang, Lin Chen, Hongchen Pan, Yuqi Liu, Jiangyu Chen, Shaobin Guo

Quality Analysis of Signal for BDS-3 Basic System

The BeiDou-3 basic system consisting of 19 new-generation BeiDou global satellites (BDS-3) was officially put into operation on December 27, 2018. In addition to B1I and B3I signals, the BDS-3 also transmit several new navigation signals, namely B1C, B2a and B2b, the performance of basic navigation services has been greatly improved. It is necessary to make a comprehensive evaluation for the quality of its observation data. In this paper, the real multi-GNSS data of 8 iGMAS tracking stations with 4 receiver types from 18 March to 31 March, 2019 are selected for quality analysis in terms of data integrity, SNR, multipath effect, ionospheric delay and cycle slip. By comparing with overlap frequencies from BDS-2 MEO B1I/B3I signals, GPS L1/L5 signals and Galileo E1/E5a signals, the performance of the current BDS-3 satellite signal and the receiving capability of the iGMAS stations are obtained. The results show that, the data integrity rate of each signal of BDS-3 satellite is slightly lower than that of the overlap frequency of BDS-2/GPS/Galileo satellite, but it can meet the daily positioning needs. The pseudorange multipath error and ionospheric delay error are comparable to the overlap frequency of BDS-2/GPS/Galileo satellite. The SNR and CSR are better than the overlap frequency of BDS-2/GPS/Galileo satellite. Therefore, BDS-3 basic system satellite maintains the excellent performance of BDS-2 B1I/B3I signals, and the observation data quality of B1C and B2a signals is comparable to that of GPS L1/L5 and Galileo E1/E5a signals, which can meet the normal working requirements of BDS, lay a solid foundation to establish the BDS-3 global system.

Yilei He

Subcarrier Periodic Shifting BOC Modulations

Designing the modern satellite navigation signals is essential for modernizing global navigation satellite systems (GNSS). For satisfying the diverse user requirements, more superior receiving performance is one of the urgent problems solved for GNSS. This paper proposes an improved BOC modulation technique, called subcarrier periodic shifting BOC (SPS-BOC) modulations. The spreading code delay is used as the time interval to form the SPS-BOC modulations by periodically shifting the phase of the subcarrier. The simulation shows that the high-frequency components of the SPS-BOC modulations are larger than traditional BOC modulations. By comparing with traditional BOC signals, the receiving performances of low-order SPS-BOC signal are superior to BOCs signals. Especially, the quality factor of matching interference is 50% more than BOCs. When the filter bandwidth is 10 MHz, Gabor bandwidth of low-order SPS-BOC signal is 26% more than BOCs, and the multipath error envelop is reduced by 34%. Therefore, the SPS-BOC modulation proposed in the paper has superior receiving performance and can be used as a new option for low-order components in MBOC signals and designing next-generation navigation signals.

Xin Zhao, Xinming Huang, Jingyuan Li, Ke Zhang, Guangfu Sun

Analysis of Multipath Error Characteristics of BeiDou Navigation Signal

Pseudorange multipath error is one of the main error sources of BeiDou Navigation Satellite System (BDS), all precise applications which use code measurements are severely affected. In view of the current situation that BDS lacks comprehensive assessment of multipath error characteristics, this paper analyzes time and frequency domain characteristics of multipath error and its relationship with elevation angle, following with its performance under different signal modulation systems, correlator intervals and RF bandwidths. By way of tri-frequency pseudorange and carrier phase combination method, the results demonstrate that three types (MEO, GEO, IGSO) of satellites’ multipath error all reflect low frequency characteristics, and the multipath error elevation-dependence of BDS-3 MEO satellites is significantly lower than that of BDS-2. Compared with signal B1I with 4 M modulating bandwidth, the multipath error fluctuation of B2I, B3I and B2a (single sideband reception) with 10 M bandwidth are smaller. For the new system broadband modulation system, signal using TMBOC(6, 1, 4/33) modulating method has better anti-multipath performance than BOC(1, 1). In addition, increasing RF bandwidth or reducing correlator interval can both impair multipath error. The research results would have certain guiding significance for the performance evaluation of the new Beidou navigation signal system and the system design for Beidou navigation receiver.

Yi Lu, Zhibin Xiao, Yaoding Wang, Shaojie Ni

A Coherent Processing Technique with High Precision for BDS B1I and B1C Signals

The smooth transition constraint and constant envelope restriction of the Beidou Navigation Satellite System (BDS) make the legacy regional system B1I signal and new global system B1C signal, which are located at different center frequencies, coexist in the BDS-3 B1 band. Therefore, new modulation and multiplexing techniques need to be adopted to meet these system constraints. More specifically, single-sideband complex binary offset carrier (SCBOC) modulation and constant envelope multiplexing via intermodulation construction (CEMIC) techniques are used in B1 band to construct a multicarrier constant-envelope composite navigation signal. In particular, the SCBOC modulation technique is introduced into the B1I signal to move its main energy from the global system B1 frequency to the regional system B1 frequency. However, as of now, the SCBOC modulation has only been regarded as a means to achieve the smooth update of the BDS, whose high-precision ranging potential has not been fully understood and utilized. To solve this problem, this paper proposes a high-precision coherent processing technique, which makes full use of the coherence between B1I and B1C signals. The proposed algorithm can not only exploit the ranging performance brought by high-frequency complex subcarriers without loss, but also greatly simplify the implementation complexity of the receiver. The experimental results of live BDS-3 signals verify the effectiveness and correctness of the proposed method. This paper provides a new solution for the high-precision application of the BDS B1 composite signal and has great reference value for receiver designers.

Yang Gao, Zheng Yao, Mingquan Lu

Preliminary Analysis of BDS-3 and Galileo Compatible Interoperable Positioning Performance

In this paper, using the BDS-3 and Galileo observation data collected by compatible interoperable receivers, the signal-to-noise ratio (SNR), multipath, pseudorange and phase noise, single point positioning performance of B1C, B2a, E1, E5a and BDS-3 SBAS positioning accuracy are compared and analyzed. The results show that the SNR of B1C/B2a are 2–3 dB-Hz higher than E1/E5a. The average of pseudorange multipath of 4 frequencies are between from 0.4 m to 0.8 m. The pseudorange noises of 4 frequencies are all better than 8 cm and phase noises are better than 0.006 cycle. The interoperable positioning accuracy is improved by 11.5%–59.8% compared to BDS-3 single system. Compared with B1C + B2a dual-frequency positioning, the accuracy of BDS-3 dual-frequency SBAS positioning is improved by 5.6%–15.2%.

Wenjun Zhao, Wei Wang

Robust GNSS Triple-Carrier Joint Estimations Under Strong Ionosphere Scintillation

In this paper, we proposed a tri-frequency joint estimation algorithm to address the loss of lock issues during strong ionospheric scintillations. This algorithm utilizes the frequency dependency to assist the GNSS tri-frequency signal tracking. The tri-frequency measurements are combined in a joint estimator for Doppler estimations so as to perform inter-frequency aiding from uncompensated signals to the interfered signals and mitigate the strong amplitude attenuations. However, as the tri-frequency estimations are coupled together, the bad measurements will deteriorate the strong signal tracking performance. We upgrade the tri-frequency joint estimator with a real time weighting adjustment according to the observed signal strengths on three frequency bands to address the issues. In addition, the algorithm adopts independent tracking on carrier phase, while joint tracking on carrier frequency. Therefore, the phase fluctuation features on each frequency can be preserved for the ionospheric scintillation characterizations and detections. The performance of the proposed algorithm is verified by the simulations. The results show that the tri-frequency joint estimator can effectively suppress tracking errors and recover carrier parameter estimations during strong ionospheric scintillations.

Rong Yang, Xingqun Zhan, Jihong Huang

Research on Enhancement Scheme of GPS Occultation Open-Loop Tracking Strategy

GPS radio occultation detection technology is a new application technology, mainly using GPS for edge detection of the atmosphere and ionosphere. In the low troposphere, it is difficult to track the low tropospheric part (about below 10 km) of the rising occultation using the closed-loop mode. The open-loop mode can effectively overcome the limitations of the closed-loop mode, improving the quality and quantity of low tropospheric occultation observations. The traditional open loop tracking is L1C guided L1P capture, and then L2P capture. The overall design is a serial design, and L2P tracking takes too long. In order to improve the available duration of dual-frequency, this paper optimizes the L2 capture strategy. Through the open-loop prediction, the model pseudo-range placement channel is obtained to get code phase, which directly guides L2P code capture and tracking. At the same time, L1P and L1CA are made into a synchronous code loop, and the L1P code acquisition and tracking process is eliminated to shorten the L2P code acquisition and tracking time, thereby solving the problem of long time to track L2. This article compares the availability of in-orbit data and inversion results of the two tracking schemes, and concludes that the new tracking strategy has increased the available time of dual-frequency data by about 20 s, while increasing the atmospheric dry temperature and dry pressure index profiles below 10 km, which provides effective data support for the low tropospheric atmosphere detection, and at the same time provides verification of tracking algorithms for the development of GNSS occultation receivers.

Lu Zhang, Xiaojiang Yang, Qijia Dong, Juanjuan Dong, GenJin, Xianyang Liu, YanCheng, Lijing Pan

Policies, Regulations, Standards and Intellectual Properties

Frontmatter

Patent Analysis Reveals the Development Route of the Indoor High-Accuracy Positioning Technology

As an important part of PNT system (Positioning, Navigation and Timing), indoor positioning technology can solve the vulnerability problem of space-based navigation system in the presence of occlusion and interference and provide users with completed services such as indoor positioning, navigation, query, identification and event inspection. The analysis of a large number of patents related to indoor positioning technology indicates that the relevant patents are relatively concentrated in China, the United States, Korea, Japan and other countries and a large-scale patent layout has been carried out all around the world. It is of great significance for us to track the development route of PNT technology to understand the technological development trend of foreign countries, to optimize the technological development route, and to make full use of the supporting role of patents in technological forecasting.

Huiying Li, Jinping Yu, Qingyi Gao

Research on Legal Protection Mechanism of BeiDou Related Names and Marks

The development of BeiDou system contains the hard work and unremitting struggle of several generations of scientific researchers, has accumulated a strong social attraction and appeal, and is a heavyweight national business card for China’s high-tech exploration. The names and marks of “BeiDou” have high social recognition, wide influence and great commercial value. However, due to the lack of relevant regulations, there are some confusion in them use. In view of the practical need to standardize the use of BeiDou’s related names and marks, this paper systematically analyzes the multiple mechanisms of trademark law, anti-unfair competition law and special legal protection under the current legal framework, and puts forward suggestions for the improvement of legal protection in order to promote the construction of “BeiDou ruled by law”.

Lin Su, Jingfan Yang

Quantitative Research of Satellite Navigation Industry Policy Based on Text Analysis

Satellite navigation industry policy modernization depend upon systematic, standardized satellite navigation industry policy. Applied with the method of policy text analysis, this paper construct three-dimensional framework based on object including satellite navigation industry policy tools, satellite navigation industry process, satellite navigation industry policy targets. This paper analyzed 25 satellite navigation industry policy samples, analyzed satellite navigation industry policy by three-dimensional framework, as well as conclusion: policy tool genres appear uneven, policy targets appear even. Then carry out quantitative analysis research on satellite navigation industry policy hot spot, collaborating following aspects: policy text hotspot, policy publisher, policy publish date and policy text key words, thus obtain satellite navigation industry policy key words: reinforce infrastructure, develop core technologies edge, broaden application range. The research result is meant to provide reference for optimize satellite navigation industry policy.

Xinran Peng, Xiaosong Li, Mingxing Yuan

Development Strategy of Chinese Satellite Navigation Technology: A Research Based on SWOT Method

In recent years, western countries have been strengthening their containment of China’s technology development in an all-round way, and the scope of technical restrictions has involved satellite navigation and other strategic emerging industries. As an important support for national security, China’s science and technology security in the field of satellite navigation is facing major challenges. The purpose of this paper is to make a comprehensive analysis of the advantages and disadvantages of China’s satellite navigation technology security and what opportunities and challenges it will face, and to make a qualitative analysis of all combined strategies, then to put forward suggestions for the development of China’s satellite navigation. The analysis based on the SWOT shows that, in order to prevent from major risks in the field of science and technology, and break through the West’s “encirclement” of science and technology, the optimal choices are the “SO” strategies of distinctive advantages, independent innovation, international cooperation, and industrialization. Also, a torsion strategy requires an in-depth analysis of the challenges and weaknesses. To accelerate the construction of an monitoring and pre-alarming system for science and technology security in the field of satellite navigation is a feasible solution.

Wenbo Chen, Xiaole Li

Technologies for Navigation of Autonomous Systems

Frontmatter

Integrated Error Compensation Method for Three-Axis Magnetometer in Geomagnetic Navigation

In the process of geomagnetic field measurement, the three-axis magnetometer is affected by various interference factors and produces various errors, which have an impact on the measurement accuracy. In this paper, the joint estimation iterative algorithm is used to calibrate the three-axis magnetometer, and the performance of the method is compared with the EKF algorithm and the nonlinear least squares algorithm. The simulation results show that in the three methods, the error average and the standard deviation of the joint estimation iterative algorithm are the least and the convergence rate is the fastest, which proves that the method is effective and usable. The experimental results show that the joint estimation iterative algorithm reduces the mean average of the measured value of the three-axis magnetometer from 69.5211nT to 9.241nT, the standard deviation is reduced from 122.0014nT to 19.941nT, and the suppression ratio reaches 86.71%. The result suggest an effective way for the calibration of three-axis fluxgate magnetometers.

Binfeng Yang, Run Wang, Huan Sun

Azimuth Error Suppression Method Based on the Rotation Modulation and Acoustic Navigation Assistance for Polar Grid SINS

The grid strapdown inertial navigation system (SINS) can conquer the orientation problem caused by the meridian convergence in the polar region, but azimuth errors of the grid SINS still exist. The navigation error characteristic is analyzed based on the grid SINS mechanization. According to the error analysis, the azimuth error of the grid SINS will accumulate with time and it is hard to be estimated in polar regions because of the low observability. To improve the orientation accuracy, an azimuth error suppression method based on the rotation modulation and acoustic navigation assistance is proposed in this paper. The grid SINS mechanization is modified to update without longitude and avoid the influence from the longitude error amp. As the latitude increased, the compass effect decreased, which leads to the reduction of azimuth errors observability. So the rotation modulation, which chooses the azimuth axis as rotation axis, is employed to restrain the azimuth errors caused by the horizontal inertial measurement devices, and simultaneously improve the observability of azimuth errors. Then the azimuth errors accumulate with time and will increase the nonlinearity of system, and together with the velocity and position navigation information from acoustic measurement units, the nonlinear filter model is designed to further estimate and suppress the azimuth errors. Finally the simulation results show that with the rotation modulation and acoustic navigation assistance the proposed method in this paper can suppress the accumulated azimuth errors of the grid SINS effectively when working in the polar regions, and prove that the scheme has practical engineering application value.

Yingyao Kang, Lin Zhao, Jianhua Cheng, Mouyan Wu

X-Ray Pulsar-Based Navigation Method Verification by Insight-HXMT Satellite Data

X-ray pulsar-based navigation is a novel spacecraft autonomous navigation method. At present, pulsar-based navigation technology has entered the stage of space experiment verification. In recent years, many countries are carrying out X-ray pulsar-based navigation experiments. China’s first large-scale X-ray astronomical observation satellite—Insight-HXMT also regards the X-ray pulsar-based navigation technology verification as one of its scientific research tasks. Its X-ray sensors’ total effective area is near 1 m2 in an energy range from 1 to 250 keV. Therefore it could be used to verify X-ray pulsar-based navigation methods. The Insight-HXMT satellite has been sent into space for 2 years, and part of observation data has been open to researchers. This paper processed the raw observation data from the satellite’s high-energy X-ray telescope and the navigation results are present. At the same time, the results are compared with the external measurement values, so the accuracy of the experiment is analyzed.

Dapeng Zhang, Yidi Wang, Wei Zheng, Mingyu Ge

High Precision Integrated Navigation Algorithms for Weak Observation of Quasi-One-Dimensional Application and on Track Test

The intelligent and safe operation requirements of rail application put forward higher requirements to navigation and positioning technology. For example, strong multipath, weak signal and fast scene-switching, tunnel scene, occlusion scene in the station and so on. In the application of integrated navigation, rail application belongs to the issue of weak observation (slow acceleration and deceleration), rapid environment change (need adaptive modelling), quasi one-dimensional motion. At the same time, the application of rail application requires strict reliability and maintenance free. The above factors have blocked the application of integrated navigation system in rail application for a long time. In this paper, an integrated navigation algorithm based on adaptive modelling is proposed for the application under the weak observation and quasi one-dimensional constraints. By modelling the IMU signal, combined with the quasi one-dimensional motion constraints, the automatic initial alignment under the condition of weak observation is realized. Through the real application of train on operation, the model parameters are trained and tested. From the results of on track test, under the condition that the hardware platform of commercial MEMS devices with gyro stability less than 20º/h and accelerometer stability less than 30 mg without wheel speedometer and other auxiliary signals, the algorithm can achieve better than 3% * distance error accumulation under the conditions of insufficient visible satellites, no satellites and weak signals. Furthermore, the algorithm is expected to achieve 0.1% * distance error accumulation when the subsequent high-precision MEMS devices are used. The research results of this paper can be popularized in China’s rail application, including railway, subway, rail mine transportation, rail port transportation and other fields.

Peng Li

Design and Verification of Long-Term Reliable Autonomous Navigation System of Navigation Satellite

Beidou-3 global navigation satellite system (GNSS) has the capability of autonomous navigation. Without the support of the ground system for a long time, it uses the pre-recorded ground auxiliary data, with the help of intersatellite/satellite-ground measurement, intersatellite/satellite-ground data exchange and the processing of the satellite autonomous navigation software to ensure the autonomous and stable operation of the navigation system. Autonomous navigation service is built on the complex dynamic network system of satellite and ground station, involving diverse system equipments and complex information process. In order to ensure the long-term, high-precision and reliable service capability of autonomous navigation, it is necessary to adopt various means in the design of satellite autonomous navigation to improve the reliability and robustness. In this paper, the profile analysis of autonomous navigation long-term operation scenario is carried out, and the on-board realization of autonomous navigation satellite system is designed by combining the working mode, adaptive data processing, intelligent start synchronization and other technologies, the design of the autonomous navigation system on the satellite was researched. Also the autonomous navigation reliable operation ability was validated based on long-term tasks, abnormal interactions between satellites, constellation refactoring conditions.

Weisong Jia, Qiuli Chen, Ying Wu, Haihong Wang

Research on the Verification of Autonomous Navigation Technology Based on Inter-satellite Link of BDS Satellite

Up to now, the new generation of BDS-3system has nearly completed the global networking. Different from the BDS-2 satellite, the BDS-3 satellite has the inter-satellite ranging function supported by the inter-satellite link. The introduce of inter-satellite link and inter-satellite ranging enables that BDS-3 system has autonomous navigation function by autonomous orbit and clock difference determination, which has less or no dependence on ground systems. Taking the BDS-3 satellite as an example, this paper evaluates the autonomous navigation results based on inter-satellite and satellite to ground ranging. the influence of the different ranging data to satellites orbits and clock errors was analyzed. The precision of autonomous navigation of BDS-3 system based on inter-satellite ranging has been given.

Qiuli Chen, Ying Wu, Haihong Wang, Weisong Jia

Research on Inter-satellite Link Network Routing Algorithm Based on Multi-objective Optimization

In view of the problem that the inter-satellite link network routing planning algorithm adapts to the single business scenario and has poor generalization ability, this paper proposes a multi-objective optimized inter-satellite link routing model based on the breadth-first routing algorithm. In this model, the optimization objects are the data transmission performance and connectivity of the time-varying inter-satellite network, the inputs are the point-to-point path hop threshold, the preferred path number threshold, and the node load weight in the route planning algorithm, and the evaluating indicators are data transmission delay, satellite node load, and network connectivity. In this paper, the fast non-dominated sorting genetic algorithm with elite strategy (NSGA-II) is used to solve the model. In addition, this paper establishes a data transmission model based on the STDMA communication protocol of the satellite navigation system to obtain the data transmission delay in each iteration, which is composed of 24 MEO, 3 GEO and 3 IGSO satellites. Finally, the Pareto solution set of point-to-point path hop threshold, the preferred path number threshold, and the node load weight is determined when the data transmission performance and network connectivity performance of inter satellite link are optimal. According to the Pareto solution set obtained in this paper, it can effectively modify the key parameter settings of the routing planning algorithm and improve the generalization ability of the algorithm in multi service scenarios.

Sixin Wang, Qi Wang, Hao Yin, Yu Zhou

Pedestrian Autonomous Positioning System Based on Inertial Navigation

Under the background of mobile Internet era, the application requirements of indoor positioning technology is increasingly urgent, and accurate positioning information has become an important prerequisite and guarantee for the successful completion of various tasks. Since GNSS faces problems such as wireless signal attenuation and positioning accuracy degradation in a complex indoor environment, an autonomous positioning system based on the strapdown inertial navigation principle has become an important way to obtain position information in complex environments. Aiming at the requirements of wearable, miniaturization and accurate positioning of the autonomous positioning system, this paper carried out the structure and autonomous positioning algorithm design. An algorithm structure combining complementary filtering attitude solution, zero-speed detection and zero-speed update was proposed, the system miniaturization structure design and low-power power management strategy were also studied. The system can complete all-weather, full-area, high-concealment three-dimensional real time positioning. Experimental results show that the system’s autonomous positioning accuracy is within 6‰ of the walking distance.

Bowen Xing, Haonan Jia, Pengfei Liu, Guoju Ma, Xiaonan Li

Integrated Precise Positioning System for Autonomous Level II Driving Offering Lane Level Accuracy

Precise Point Positioning (PPP) has become an attractive topic as consumer low-cost receivers are able to provide raw observations and signals with multiple frequencies and support multiple GNSS systems. Generally, PPP can provide sub-meter level accuracy in favorable environments. However, such an accuracy degrades in challenging environments where the GNSS observations are attenuated or blocked. In order to reach seamless and reliable navigation performance, in this research, PPP is designed to integrate with a low-cost IMU which runs the Inertial Navigation System (INS) algorithm on it. A low-cost Profound-IP3/DR (dead reckoning) integrated navigation system targeted for precise vehicular navigation is proposed. The integrated system is accessed through various road tests which cover good LOS GNSS environments, sub-urbans, short-term GNSS outages, and complete GNSS outages. The results indicate that the Profound-IP3/DR is able to maintain sub-meter RMS accuracy in open-sky and sub-urban areas. For complete GNSS outages and challenging downtown environments with severe multi-path and signal blockages, the Profound-IP3/DR shows robust long-term performance with decimeter to meter-level accuracy. The high positioning accuracy supports Profound-IP3/DR to be a key player in continuous and precise vehicular navigation applications such as asset tracking and car navigation. Moreover, such accurate navigation performance shows the potential and readiness to be integrated with other sources of update such as vision, LiDAR, radar and digital maps to fully benefit the technologies for navigation of autonomous systems.

Haiyu Lan, Hongzhou Yang, Yashar Balazadegan Sarvrood, Fei Liu, Ahmed Wahdan

Reliable Localization Using Multi-sensor Fusion for Automated Valet Parking Applications

Multi-sensor fusion is the key to enabling reliable and accurate localization for automated valet parking (AVP) systems that can autonomously navigate in highly structured indoor environments. The current state-of-the-art in AVP systems depends on light detection and ranging (LiDAR) systems, visible-light cameras, or infrastructure-based solutions. LiDAR systems can provide high positioning accuracy across a variety of operating conditions. However, they are generally more expensive, have moving parts that create more room for error, and the processing of its 3D point cloud is computationally demanding. As for cameras, the performance of any camera-based localization system is susceptible to variations in lighting conditions and fail altogether under degraded visual environments. This paper presents a real-time, radar-based localization library developed by Profound Positioning Inc. (PPI). PPI’s localization library utilizes a multi-sensor fusion approach for real-time vehicle localization in structured environments such as underground parking lots. PPI’s algorithm integrates the onboard motion sensors, a set of mid-range automotive radars, and two-dimensional (2D) high definition (HD) maps. PPI’s radar-based localization library is capable of maintaining a decimeter-level accuracy, and it is validated and evaluated using real-life scenarios in an indoor parking lot.

Mostafa Sakr, Adel Moussa, Walid Abdelfatah, Mohamed Elsheikh, Naser El-Sheimy

Backmatter

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