China Satellite Navigation Conference (CSNC) 2018 Proceedings

Traditional troposphere tomography method cannot use the GNSS signals penetrating from the side face of research area, which not only decreases the utilization rate of GNSS observation but also leads to a low percentage of voxels crossed by rays. In order to overcome this issue, the GNSS signals penetrating from the model’s side face are also used to build the observation equation by introducing the truncation coefficient in this paper. Due to the fact that the tomography modeling is consists of various equations, including observation equation (using signals from the side and top faces of research area to build equations), horizontal and vertical equations, how to determine the weightings of different equations is a key to obtain the reliable tomographic result. Therefore, a method is proposed to determine the weightings of various equations based on the variance component analysis (VCA). The data from Satellite Positioning Reference Station Network (SatRef) of Hong Kong over the period of 27 days is selected for the tomography experiment. The tomographic result shows that the proposed method is of ability to obtain a good quality. Comparing to the traditional method, the utilization rate and number of voxels crossed by rays have been improved by 32.21 and 12.23%, respectively. When compared to the radiosonde data, the RMS error of the reconstructed integral water vapor (IWV) derived from the proposed method (4.2 mm) superior to that from the traditional method (5.2 mm). The comparison of water vapor profiles also shows that the proposed method with a RMS value of 1.30 g/m3, is smaller than that of traditional method with a value of 1.58 g/m3, and the accuracy of tomographic result based on the proposed method is increased by 17.7%.

In order to solve seamless positioning about indoor and outdoor, a SDS-TWR (Symmetric Double Side-Two Way Ranging) based wireless location system was proposed. The CSS (Chirp Spread Spectrum) signal, which has wide band characteristic, was used to obtain high-accuracy measurement of signal propagation delay. Least squares combining with linear Kalman filter algorithm was proposed in the positioning progress with linearization. Despite of increasing the complex of positioning algorithm, that improved the positioning accuracy, especially the stability of dynamic positioning situation. Finally, a hardware prototype system was exploited. And some tests were carried in the real indoor and outdoor environment. The results show that ranging error would not change significantly with distance increasing. And both of static and dynamic positioning accuracy are under one meter.

In order to improve the accuracy of slow deformation monitoring sequence, the smoothing filter is usually used. On the basis of weighted moving average method, a robust moving average method is proposed. An adaptive windowing method is developed and combined with ARMA time series analysis to improve the prediction precision of monitoring sequence. The experimental results show that, the robust moving average method can effectively weaken the error of the slow deformation monitoring sequence, and resist gross error efficiently. In addition, it can improve the accuracy and reflect the displacement trend of the slow deformation monitoring sequence more clearly with combination of ARMA method.

In order to solve the problem of remote monitoring and control of launch vehicles, this paper proposes that BeiDou navigation satellite system can achieve the real-time measurement and control of the launch vehicle, based on the analysis of the support of the space-based measurement and control system for the launch vehicle measurement and control tasks. And then proposes space-based measurement and control system schemes. According to the composing and task supporting ability of BeiDou navigation satellite system, the communication process of BeiDou navigation satellite system supporting the global launch vehicle space-based measurement and control is analyzed and applied. Then, according to the BeiDou global navigation satellite system, three kinds of constellation support communication schemes are designed and three networking constellations are proposed to support the space-based measurement and control tasks. Finally, the feasibility of the communication scheme is verified through simulation experiments, which provides a better solution for the space-based measurement and control system of the launch vehicle.

To achieve the best performance for a Kalman filter (KF) for global navigation satellite system (GNSS) positioning, a comprehensive measurement model is required. However, the GNSS observations suffer from unmodelled errors resulting from multipath, interference, etc. These errors are difficult (even impossible) to model using parametric models. Inspired by Gaussian process (GP) Bayes filters with measurement and dynamic models trained with non-parametric GP regression (GPR), the unmodelled errors in the GNSS observations can be trained online based on the GPR using the measurements residuals calculated by the KF. One of the problems in using the GPR for online modelling is its high computational cost. To reduce the computational complexity, more than one forward step sliding window for the input training points and the GPR model training can be used. Furthermore, to avoid the over-prediction using the online trained GPR model, a constraint on the query point was introduced. In this study a non-linear autoregressive model was used for the online GPR model training. To verify this algorithm, both static and kinematic experiments were evaluated. The results show that the online GPR-KF algorithm can effectively improve the deteriorated GNSS positioning accuracy caused by unmodelled errors in the GNSS observations. The effectiveness of the proposed algorithm was also validated using the measurement innovation statistical test.

It is very important to get precise positioning information continuously in the UAV RTK. However, the complex environment often degrades the observation quality or even introduces several gross errors which will seriously affect the accuracy and reliability of the results. In this paper, a new method of multi gross error detection with the constraint of epoch variation is put forward and validated by the UAV-PPK. The result shows that it can effectively detect multiple gross errors and handle the gross-errors and cycle-slips in a different way. Besides, it can also guarantee the stability of the filtering and significantly increase the ambiguity fixing rate and positioning accuracy. Thus, the reliable and precise positioning information can be continuously supplied for UAV RTK.

Global Positioning System Interferometric Reflectometry (GPS-IR) is a new remote sensing technique, and it can be used to estimate near surface soil moisture from signal-to-noise ratio data. Considering the advantages of multi-satellite convergence and the time and space scale of soil moisture, a multi-satellites fusion inversion model of soil moisture based on sliding window is proposed. Firstly, the direct and reflection signals of GPS satellites are separated by a low order polynomial fitting, and then the sinusoidal fitting model of reflection signals is established, the relative phase of the SNR interferogram is obtained. Finally, a sliding window is established to select the relative phases of the satellites effectively, and the best input variables of the inversion model are determined. Then, the soil moisture is retrieved by least square support vector machine. Based on the monitoring data provided by US Plate Boundary Observations Project, the feasibility and effectiveness of using single and different GPS satellites to sliding estimate soil moisture are compared and analyzed. The experimental results show that sliding window can effectively select GPS satellites and determine the best input variables for the model. The model fully takes the advantage of non-linear weight determination. The sliding type can achieve a longer time inversion. To a certain extent, this model improves the phenomenon that the inversion process is prone to jump when using single satellite inversion. Based on the inversion of more than four satellites, RMSE and MAE is less than 0.07 and 0.06, respectively, and R2 is increased by at least 21.9% compared with inversion result of a single satellite. Therefore, the inversion of soil moisture can be treated as nonlinear event, and multi-satellites fusion inversion is feasible and effective.

An ionospheric positive storm on 13 October 2016 was studied. The longitude effect of ionospheric storm along 40°N latitude region is studied with 23 GPS stations from 0°E to 360°E. Total electron content (TEC) was calculated with polynomial method, and TEC difference between the storm time and quiet time (ΔTEC) were calculated. The variations of TEC difference were different at different longitudes. There was a positive phase storm at the local time day side region, while the variations were not obvious at the night side longitudes. The maximum value of ΔTEC was about 25 TECU at 330°E at about 1400UT on 13 October 2016. Two Ionosonde data at EB040 (0.5°E, 40°N) and RL052 (51.5°N, 359.4°E) were also used to study the ionospheric storm. The ΔfoF2 of RL052 increased earlier that low latitude ionosonde of EB040. There was a second peak of ΔTEC at the local night time about 2000 LT on 13 October 2016. The latitude effect of ionospheric storm was also studied with 7 GPS stations at 0°E meridian. It was found that the positive storm was obvious at high latitude region, while it was weak at low latitude region. This phenomenon may be caused by the fountain effect. From high latitude to low latitude, ΔTEC gradually began to increase, and ΔTEC at higher latitude reached the maximum value earlier than the low latitude. These show that the positive ionospheric storm may be caused by the equatorward surge.

GPS interferometric reflectometry (GPS-IR) is a bistatic radar remote sensing technique that has the potential to retrieve environmental variables such as soil moisture, snow depth and vegetation parameters. The direct and reflected signals will be mixed by omni-directional geodetic GPS antenna and the interference patterns of the both signals are recorded in signal-to-noise ratio (SNR) data. The SNR metrics, which refer to the phase, amplitude and reflector height, are the key parameters in subsequent analysis and applications of GPS-IR. Lomb-Scargle periodogram (LSP) is commonly used to estimate the dominant frequency of the detrended SNR interferograms, and the dominant frequency is converted to an effective reflector height, while phase and amplitude are finally estimated with least-squares method. In this study, the SNR metrics are determined with an alternative approach which on the basis of the least squares spectral analysis (LSSA). The core of the procedure is detecting the underlying periodicity terms in the detrended SNR interferograms, and then confirming the statistically significant spectral peaks according to the criteria formulated with Fisher distribution. The performance of the approach is examined with eight satellite tracks at the P041 site, the residuals show a 0–38% reduction in the root mean square (RMS) value compared to the LSP method and better distribution.

With rapid development of technologies such as sensors and AI, smart construction machinery has gradually become research focus of construction machinery domain in recent years due to its high precision, low labor cost and high capability. As location-based services to be one of the important foundation of smart construction machinery, the design of a rigorous and convenient positioning and attitude determination algorithm has become an important foundation for the stable and agile operation of smart construction machinery. This paper combined back-hoe hydraulic excavator with GNSS positioning and orientation device and MEMS inclinometers, derived and verified a rigorous position and attitude calculation model of excavator upper structure and each part of working equipment according to the outputs of the two kinds of sensors. First, specialized algorithm to form attitude rotation matrix is deduced considering the effect characteristics of upper structure attitude on GNSS orientation baseline and output axis definition of dual-axis inclinometer, and with the GNSS antenna coordinate in topocentric coordinate system, the upper structure coordinate and attitude are obtained. Then, coordinate increment computation algorithm of key point on excavator working equipment in vehicle coordinate system considering upper structure attitude effect was deduced. Finally, by combining key point coordinate increment and upper structure coordinate and attitude, key point absolute coordinate was obtained. The correctness of this algorithm was verified by installation and test on real vehicle and comparison with result measured by RTK/total station. With rigorous derivation process, concise form and convenience of programming implementation, this algorithm has practical meaning in engineering.

In the satellite navigation and positioning process, the performance of the receiver directly impacts on the quality of observation data, and affects the positioning accuracy ultimately. Therefore, the receiver is sufficiently important for the whole navigation and positioning process. Deformation monitoring belongs to precise engineering survey and it often needs to reach the millimeter-level accuracy, so that the geodetic receiver with excellent performance and high price is often used in this survey. Under this background, improving the positioning accuracy of low cost receiver and applying it to deformation monitoring can effectively reduce the engineering cost, which has great practical significance and research value. This study is based on the low cost receiver EVK-M8T from ublox company. Firstly, the receiver performance is evaluated from signal to noise ratio (SNR), receiver clock and accuracy of standard point positioning (SPP) through comparing with geodetic receiver Trimble NetR9. Then through the experiment simulation of deformation monitoring, the feasibility of deformation monitoring using low cost receiver is analyzed. The numerical results show that the location accuracy of low cost receiver can basically keep in millimeter level when the observation period reaches more than 2 h, and it can correctly detect the movement of the point. Hence low cost receiver can be applied to the deformation monitoring under the premise of improving its stability.

It is of great importance to estimate zenith tropospheric delay (ZTD) and retrieve precipitable water vapor (PWV) using ground-based GNSS remote sensing technology. At present, the ground-based GNSS technology is usually studied based on single GPS system. In this paper, the precise point positioning technology for combined multi-GNSS is carried out using the observation data of 30 MGEX tracking stations for one month. The ZTD and PWV results obtained from individual GNSS and multi-GNSS are carefully compared and analyzed. The performance of multi-GNSS data for ZTD/PWV retrieval is also assessed and the accuracy is verified by CODE tropospheric products and Radiosonde observations. The statistical results show that: (1) There are significant differences in the PPP ZTD results obtained by different navigation systems, and the more stable ZTD results can be obtained from the multi-GNSS observations. (2) The ZTD series obtained from single GNSS and multiple GNSS show good agreement with CODE ZTD series. Compared with that of GPS, GLONASS, Galileo and BDS, the solution precision of combined GNSS is the highest, which is improved by 10.91, 19.04, 33.21 and 70.16% respectively. (3) The accuracy of atmospheric vapor in the PPP data processing can reach the meteorological requirements such as numerical weather prediction model. The performance of combined GNSS compared with sounding data is the best, the accuracy of which is improved than that of GPS, GLONASS, Galileo and BDS by about 3.45, 16.16, 16.45 and 41.78% respectively. Furthermore, the results reveal that the multi-GNSS combined PPP technology can significantly improve the accuracy and reliability of ZTD/PWV series, which can support for meteorological applications such as weather monitoring and forecasting.

In GPS meteorology, the pressure and temperature parameters of GPS station are very important when obtaining accurate precipitable water vapor (PWV). However, there are few GPS stations equipped with co-located sensors for these meteorological parameters. In order to solve the problem, two methods, which is Parameter Conversion Method (PCM) and Layer Interpolation Method (LIM), were analysed and compared in this paper. The mean sea level products and multi-level isobaric surface products provided by NCEP for the period from Mar to June 2017 were used to two methods, respectively. Based on 36 GPS stations around the world which contain meteorology file and co-located radiosonde data, the experiment verified the availability and accuracy of two methods in obtaining meteorological parameters and further, PWV. Results show that: (1) both LIM and PCM works well when station height below 1600 m, the average bias of LIM is 0.67 hPa and 1.12 K compared with 0.9 hPa and 1.65 K of PCM; (2) with increasing of the station height, the difference between observed values and calculated values of pressure become larger, while the LIM has better accuracy than PCM and the robustness is better, the RMS is 2.54 and 2.91 hPa, 3.53 and 4.69 K, respectively; (3) The experiment results and analysis shown the validity of LIM and PCM, and the estimated PWV shows a higher accuracy using LIM.

In GNSS real-time high-precision monitoring, the multipath spatial correlation is weak, it is difficult to eliminate the multipath error by double difference, and the traditional method based on the sidereal filtering in the coordinate domain to mitigate multipath error of MEO satellite will no longer be applicable. Aiming at the above problem, this paper storage single difference observation residuals after ambiguity resolved in real-time baseline resolution, where storage residual information for 1d in GPS, BDS GEO, IGSO, and BDS MEO satellite for 7d. When the residual information database initialization is complete, each satellite multipath error sequence model will be established from the residual database by using the low-pass filter method, then mitigating multipath error of the corresponding satellite carrier phase observations in real time. The measured data show that, based on the mitigating multipath of observation domain, the real-time monitoring accuracy of the 3D position can be improved by about 50% after mitigating multipath error in real-time.

With the rapid development of GNSS technology in the field of atmospheric and ocean remote sensing, especially the rise of GNSS remote sensing technology such as GNSS-R, which has promoted the wider application of coastal GNSS stations, such as crustal deformation, absolute sea level change, tide level changes monitoring, air-sea exchange and other fields. In view of the current research on the sea surface multipath and its impact on the precision of GNSS positioning is relatively few, in this paper, we selected the United States PBO network of coastal CORS station SC02 and its surrounding three PBO stations ALBH, P438 and P439 to analyze the characteristics of multipath effects of the coastal GNSS stations and their time series features. Then the stations are grouped and GAMIT is used for baseline solution. By setting different cutoff elevation angles, comparing the results of baseline solution and the residuals of multipath effects to explore whether the multipath effect of sea surface has a significant impact on the precision positioning of coastal GNSS stations. The result shows that when the cutoff elevation angle is selected from 10° to 15°, the result of the baseline solution is the best, and the effect of sea surface multipath on GNSS precision positioning is the least. Through the experimental, it is hoped to provide a reference for the future deployment of GNSS stations and GNSS for tide level real-time monitoring in coastal areas in the future, and to further promote the integrated application of coastal GNSS stations.

High precision GPS coordinate time series has become a rich source of data in many fields of research, such as studying the slow deformation of the earth’s surface, establishing and maintaining a regional or global reference frame, and studying the deformation process of earthquake pregnancy. In view of the current GPS time series analysis software in the processing of data is slow, inefficient, less choice of combination model, this paper studies and analyzes a new time series analysis software HECTOR. Firstly, the function and characteristics of HECTOR software are described in detail; Then, the software is used to obtain the periodic items and trend items in the three directions of the GPS time series, and compared with the parameters obtained by the CATS software. Secondly, the data of GPS time series in the study area are analyzed by using different noise models; Finally, BIC numerical analysis based on the maximum likelihood estimation and spectrum analysis are used to compare the results of different combinations of noise models. The results show that the HECTOR software can be used to obtain the parameters quickly and further. At the same time, GPS data for most of the selected study areas, white noise + power law noise for the optimal noise model. For GPS data of a few study areas, white noise + generalized Gaussian Markov noise, white noise + ARMA (5) noise are better noise models. Finally, it is found that the best noise model obtained in different directions of the same site is not the same, which can provide certain reference meaning for the future research in this direction.

The ground-based GNSS tomography technology can obtain three-dimensional distribution of water vapor. However, many voxels may not be passed through by satellite rays because of the limitation of satellite orbits and the topological distribution of ground GNSS stations, which results in the rank defect of tomography equations. In this paper, the geometric relationship between the elevation angle of the satellites and the satellite ray height intersecting with tomography boundary is deduced. The distribution of the GNSS satellite signals that can be used for the tomography at different stations is shown for the selected tomography area. In order to increase more usable GNSS rays and get stable and reliable results, the quad-constellation GNSS including GPS, GLONASS, Galileo and BDS (BeiDou navigation satellite system) systems are used simultaneously. Further, the Gaussian function is used as horizontal restriction while the mean value of three-day radiosonde profiles prior to the experiment is used as vertical restriction. To validate the four-constellation integrated tomography method, the raw GNSS observations were collected from 26 August, 2017 to 28 August, 2017 in Hong Kong to carry out the tomography experiment. During this period, there was a typhoon named Pakhar to pass the tomographic area, causing water vapor to vary dramatically. This process was descripted and captured by the presented tomographic technique. The result indicates that the current quad-constellation GNSS improves the tomographic accuracy by 5% compared with the GPS-only approach.

Snowfall as an important global freshwater resource, especially for Xinjiang Altai region in the snow all the year round, accurate and convenient snow thickness monitoring is particularly important, at present, the snow monitoring is divided into the time and space analysis of the macro snow cover and the micro snow depth monitoring. Macro monitoring are mainly composed of MODIS snow product, the micro snow depth monitoring from use of discrete meteorological point monitoring initially, laser detection, with the development of technology, satellite remote sensing monitoring has become the main trend. With the development of technology, satellite remote sensing monitoring has become a major trend. With the continuous improvement of GPS-MR snow remote sensing theory in recent years, in this paper, Altay GPS monitoring station as a demonstration using GPS-MR technology for snow monitoring research. Using the monitoring data from January 1 to March 31, 2017 for statistical analysis. The selection of satellite height Angle increase, due to the multipath effect will gradually reduce with the increase of altitude Angle, higher SNR ratio will lead to the inversion precision is decreased obviously. GPS data sampling rate has little effect on the inversion accuracy. Based on Altay GPS snow monitoring experimental station, Satellite elevation angle selection 5°–20°, the sampling rate is set to 15 s, the GPS-MR snow depth obtained is better than 0.027 m. Therefore, it is possible to make full use of the ground-based GNSS water vapor monitoring station for snow depth detection, GNSS remote sensing application potential will be brought into full play in the future environmental meteorological monitoring in our country.

With the continuous improvement of Global Navigation Satellite System (GNSS) theory, the signal-to-noise ratio (SNR) of a GNSS reflectometry signal can be applied to detect snow depth. However, there are still some issues, such as insufficient observation data, low detection precision, etc. To solve the above problems, this paper uses the SNR reflectometry data of GLONASS L1 and L2 to detect snow depth in Yellowknife, Canada, from July 2015 to June 2016. Then we analyzed the L1 and L2 SNR-derived snow depths and the average snow depths. The results show that snow depth detected using the two SNR signals can reach centimeter level. There is weak bias and strong correlation when comparing the detected snow depth based on which single-frequency SNR observations with in situ measurements are used. For L1 and L2 SNR-derived snow depths in a separate 365-day campaign, the former bias is superior to the latter. Both RMSE values are 4.5 and 2.6 cm. The stability of L2 SNR-derived snow depth was improved by over 40% than that of L1 SNR. The average snow depths detected using the two SNR signals have no significant improvement on the precision, but improve the spatial resolution because of more satellites. The experimental results show that the applications of GNSS technology can be further extended by GLONASS-MR technology based on L2 reflectometry signals.

The global navigation satellite system (GNSS) has the advantages of high precision, high temporal resolution and low cost. The total electronic content (TEC) can be calculated by GNSS observations. The TEC sequence can be used to reflect the disturbances of the ionosphere, and it can detect the ionospheric anomalies caused by strong convective weather which plays an important role in studying the coupling mechanism between the ionosphere and the troposphere. In this paper, the GNSS observations during a heavy rainfall at July 9, 2013 in Sichuan Province were selected, and the de-trend TEC sequence was obtained. It can be seen from the dTEC sequence that there are obvious anomalies in the ionosphere when the rainfall occurred, and the abnormal times between the different stations are slightly different which show the abnormal propagation process. In this paper, we argue that the ionospheric anomalies are related to the acoustic gravity waves (AGWs). Due to the special terrain of Sichuan, when the waves encountered the mountain, they would spread upward, and then reach the ionosphere and cause ionospheric anomalies. According to its propagation velocity, Sichuan Province is divided into uniform grid and the approximate location of the excitation AGWs can be found. Finally, based on the analysis of the heavy rainfall event, the coupling mechanism between ionosphere and troposphere is discussed.

Water level change is the crucial disastrous factor of reservoir deformation. This paper derives the water level changes of reservoir based on GNSS-R technology by using the multi-GNSS deformation monitoring observation data of Xikeng dam in Shenzhen, and compares the results with the artificial observation data. The numerical results show that the root mean square error (RMS) of GPS-R results is 7 cm with the accuracy of BDS-R and GLONASS-R is slightly lower than GPS-R, and the range of RMS is 8–10 cm. However, the changes are consistent with the artificial observation data, and the correlation coefficients between the experimental results of three system and the artificial observation data are better than 0.9. This research verifies the validity and reliability of GNSS-R technology used to water level changes measurement, and expands the application areas of the GNSS deformation monitoring system, which also indicates that multi-GNSS system can greatly improve the temporal resolution of single-system water level measurement.

In the calculation of high-precision GNSS data, solid tides, tides and atmospheric tides are not negligible factors in the solution process. In the present study, a large number of studies have been conducted on the effects of tidal load. The results show that the tide load The impact can reach the magnitude of cm. Relatively speaking, ATML is weak and there are few studies, but it is still a non-negligible interference factor, especially for the data calculation of national stations For example In this paper, GAMIT/GLOBK is used to solve the data of national stations in some provincial areas in 2017. The differences between ATML correction models and different stations are analyzed. The influence of ATML on the accuracy of GNSS baseline solution and station displacement is compared. The results show that the influence of ATML correction model on the baseline solution of regional GNSS is not related to the station location. ATML is insensitive to the influence of the baseline length, but it has an impact on station positioning and can bring about 1–2 mm, and mainly in the U direction, N, E direction of the small, can be ignored. The results also show that the impact of ATML on national stations in solving data is negligible, as is the case in engineering applications and in general scientific research, but corrections are necessary for solutions with higher precision requirements, however At present, there are few models of atmospheric mass load correction applied to baseline solution, so it is worth further study to determine the optimal correction model and eliminate its influence.

Location-Based Service (LBS) is an information service based on locations of mobile users and two-way interactions. Most LBS communications follow the client-server architecture which enables bidirectional communication between the server and a client. The paper examines the limitations of the current client-server LBS framework for time critical LBS application scenarios and their system requirements for networking and computing. It presents the publish/subscribe communication paradigm for unidirectional connections that support decentralised device-to-server and device-to-device data services with low-latency and high scalability. A lightweight publish/subscribe application protocol, namely Message Queue Telemetry Transport (MQTT), is also introduced for high-rate vehicle RTCM data exchanges for timely-critical connected vehicle applications. To prove the concept of the extended LBS, experiments are performed to demonstrate how well the MQTT can support real time location-based data transfer. Results show that the MQTT Broker overwhelmingly outperforms the NTRIP Caster in delivering RTCM correction data in terms of CPU usage of the network computer server and performs similarly well in latency and packet losses. MQTT is also tested for device to device GNSS data exchanges. Results show that two mobile devices can exchange RTCM v3 data with the reliability of 99% within the latency of 1 s under 4G cellular connectivity. The results also show that the MQTT Quality of Services mode 1 can support the 10 Hz data transfer at the latency of less than 100 ms and the reliability of above 99%, showing the potential in support of connected vehicle safety applications.

Since May 2016, QianXun Spatial Intelligence Inc. has launched its Beidou ground-based augmentation system (QX-GBAS) which supports high-precision GNSS positioning service within the national coverage. The user first sends its approximate coordinates to QX-GBAS in the NMEA $GPGGA format and subsequently receives 3D Cartesian coordinates of virtual reference station (VRS) and corresponding GNSS code/phase observations encoded in the format of RTCM. Unlike some operational province- and city-level GBASs whose VRS coordinates received by the user equal to those NMEA $GPGGA coordinates sent by the user, QX-GBAS does not always return VRS coordinate exactly equal to the user-sent NMEA $GPGGA coordinates. This study then investigated the pattern of QX-GBAS VRS coordinates in the RTCM message type 1005 and 1006, respectively. Numerical results showed that (1) the QX-GBAS RTCM1006 coordinates were equal to the user-sent NMEA $GPGGA coordinates within the range of 0.9 m (0.03″); (2) the QX-GBAS RTCM1005 coordinates were different from the user NMEA $GPGGA coordinates, but followed a 3′ × 3′ (latitude/longitude) grid pattern. The outcome of this study can be beneficial for both QX-GBAS, or other GBASs, server and users by providing more operational flexibilities and also, protect the homeland security from possible threats.

A number of indoor positioning systems based on WiFi fingerprinting were reported thanks to advantages of this method, such as low cost and extensive availability. The Bayesian fingerprinting method needs learn the radio map of probability distribution of WiFi signal strengths over the space of interest through a training phase. Traditionally, the histogram method was used for calculating probability distribution, and it required an adequate number of WiFi samples, which caused a long time taken in the training phase. This study first analyzes the temporal variation of WiFi received signal strength indication (RSSI) at a specific location, and proposes the Weibull signal model for representing the probability density of temporal variation of WiFi RSSI observables. Then, in the positioning phase, the Weibull-based probability density is utilized for Bayesian estimation to resolve the positioning solution. This method is proposed to reduce the required number of RSSI samples for learning probability distribution, and hence improve the efficiency of fingerprinting database training. This method is implemented on Android commodity smartphone, and is evaluated in office building environments. Experiment results show that this method reduces the work loading of fingerprinting training due to less samples required, and the positioning accuracy is enhanced by 21–35% up to different building environments, compared to the histogram based method even in which more samples are used.

This article first introduced the architecture, data processing flow, data processing strategies and data processing results of HNCORS GNSS online differential data processing system, and then analyzed the precision, repeatability and stability of the system by processing the GNSS data of datum stations and measured stations. Finally, based on the simulation deformation monitoring experiment, the feasibility of system application in deformation monitoring was discussed in this article. The experimental results showed that the repeatability and stability of the system is high, which can provide cm or mm level positioning services for Hunan Province GNSS users. What’s more, the system has broad application prospects in deformation monitoring.

Turn detection can be widely used in location navigation, user behavior identification, and scene awareness. Accurate real-time identification of pedestrian turns contributes to improving the accuracy of positioning navigation accuracy and scene awareness. Considering the problem of the insufficient accuracy and robustness of the existing turn detection algorithm, this paper proposes a turn detection algorithm based on periodic signal recognition, which effectively solves the misjudgment caused by the periodic swing of user walking. The algorithm collects the acceleration sensor and the gyro sensor data in real time and calculates the angular velocity of the rotation in the vertical direction by multiplying the vertical gravitational acceleration unit vector by the gyro sensor data. In this paper, fast Fourier transform (FFT) is used to identify and eliminate periodic interfering signals generated by user walking, only keeping the non-periodic signal generated by user walking (such as turning). By integrating the vertical angular velocity data in the sliding window to obtain the angle change value of the user walking within a certain period of time, and the threshold value is compared to realize the accurate identification of the turning behavior. In order to adapt to the user’s turn size and the turn speed, the algorithm also proposes a corner detection method based on multi-sliding window. The experiment results show that the proposed algorithm has higher accuracy and lower power consumption than other algorithms which based on GPS and electronic compass. The algorithm can realize the accurate identification of the turning behavior of the mobile phone in various positions of the user, and has good robustness. The accuracy of turning recognition can reach 93% and the average power consumption is about 60 mW.

Signal strength of indoor location is easily influenced by environment, multipath refraction and human disturbance. Considering the characters that long distance propagation of signals is more likely to be influenced by more reflection and multipath effects than short distance propagation, an anti-interference indoor localization algorithm is proposed in this paper. Firstly, the RSSI perturbation of long distance is filtered by setting threshold. Then, based on the principle of trilateration locating and selecting weight iteration (IGG), the coordinates are estimated. Finally, a practical example of indoor localization is given. The comparison test calculation is carried out by the positioning software developed independently on the Android platform. The results show that the method presented in this paper improves the location accuracy and has a certain anti-disturbance ability.

With the gradual progress of the urbanization process of modern society and the continuous improvement of residents’ living standard, people’s demand for IPS (Indoor Positioning System) is more urgent than that of the past, higher requirements for positioning accuracy, positioning robustness and positioning energy consumption are put forward. Low-power Bluetooth technology has the characteristics of low-cost, easy deployment and low power consumption, supporting all mainstream smartphone operating systems, and attracting extensive attention from academic and industry field. In this paper, aiming at the situation that current Bluetooth low energy positioning accuracy has large fluctuation under the circumstance of multipath propagation, external disturbance and other factors, and has poor user experience, a Bluetooth localization algorithm based on map path calibration and time series filtering is proposed (MCTF). This algorithm comprehensively utilizes a post-processing method based on the average sliding window, time-series based spatial restraint post-processing method and path information based location calibration method, effectively eliminating the large fluctuation of positioning results caused by multipath propagation and other external wireless signal interference in complex indoor environment. By using map information, based on the fact that position cannot be transient, utilizing feedback filtering, positioning results can get path correction and direction correction respectively, solving the problem that the positioning coordinates jump between adjacent narrow aisles and jump back and forth on the same path during the positioning process. Extensive experiments performed in shopping mall, building office, exhibition center and other typical indoor environments demonstrate that the average positioning error of the proposed algorithm is within 1.5 m, which has good robustness and ensures the smoothness, accuracy and stability of the positioning result.

In traditional indoor localization, fingerprint localization algorithm fully considers the influences of multipath signals and static obstacles but degrades in case of the changes of observation environment. Trilateration localization has the better robustness to the signal variations but its performance degrades for achieving a certain level of accuracy. In this paper, for the problems above, firstly, a weighted fusion algorithm based on fingerprint recognition algorithm and trilateration algorithm was proposed. Then, adaptive fusion is added to filter the error localization point. Finally, linear Kalman filtering which based on the constant velocity state model assumption is introduced to smooth Wi-Fi localization error. By using the algorithms above, the experimental platform is set up to carry out the localization test. The test result justify that our proposed algorithm has performed better and achieved a better level of accuracy.

With the rapid development of the self-determination navigation system in many countries, multi-band multi-mode GNSS integrated positioning has become the current research hotspot, which can overcome the limitations that the navigation based on single satellite system would be not continuous and reliable while GNSS signal is sheltered seriously. According to the development status of GNSS navigation positioning system in China in recent years, the paper intended to study on the performance of combined BDS/GPS-RTK with the application of products of iGMAS. The result of static experiment showed that the positioning accuracy of single GPS was better than single BDS and combined BDS/GPS in open area, combined BDS/GPS was better than single BDS and single GPS in enclosed area. The result of dynamic vehicle experiment showed that combined BDS/GPS could still provide continuous and stable positioning service although the positioning reliability was greatly affected when the observation environment was bad. The result of antenna movement experiment showed that the positioning accuracy of single GPS and combined BDS/GPS was almost the same in either vertical or horizontal direction in open area and single GPS was better than combined BDS/GPS in enclosed area.

Since the signal quality of global navigation satellite system (GNSS) is extremely vulnerable to the surrounding environment, the environment-aware adaptive positioning algorithm has drawn wide attention. In order to select the suitable positioning method in different types of environment, the receiver need to recognize the type of surrounding environment in real-time. Targeting on the vehicle positioning applications in the city, this paper divides the urban environment into six categories: canyon, downtown, suburb, viaduct-up, viaduct-down and boulevard, and proposes a novel environment recognition algorithm based on the navigation signal characteristics. Firstly, a five dimension signal feature vector is proposed to describe the quality of navigation signal. The vector elements are signal power attenuation mean, power attenuation standard deviation, signal blocking coefficient, DOP value expansion ratio and power fluctuation coefficient. Then, taking this vector as environmental attribute, this paper proposes an environment recognition algorithm based on the temporal filtering support vector machine (SVM). In the experiment, the raw navigation signal data are collected for more than 100 thousand epochs in six types of urban environment, with no less than 10 thousand epochs for each type. In order to verify the validity of the proposed recognition algorithm, the five cross validation method is used to train and test all the collecting data. The testing results show that the recognition accuracy of the algorithm are higher than 90% for all types of environment.

In recent years, due to the open access to raw GNSS measurements, it is possible to study other PVT algorithms to improve the positioning accuracy on smartphones. In this paper, we first give the analysis of the characteristics of the smartphone observations and measurement error sources, then focus on the continuous cycle slip of carrier phase with duty cycle mode. Then, we propose an improved Hatch filtering algorithm in order to use the carrier phase observations which have continuous loss of cycles to reduce the measurement noise of pseudoranges. Finally, we give a comparison of several pseudorange positioning algorithms, the model of pseudorange double difference algorithm and the parameter selection principle of Kalman filter. Experiments based on a real smartphone in the open sky environment and the post-processing of the collected data is discussed in detail later. The results show that the proposed carrier smoothing algorithm can effectively reduce the noise of pseudorange observations and the positioning accuracy of the pseudorange double difference algorithm with carrier smoothing technique is less than 5 m, which shows obvious improvement compared with the positioning accuracy of the traditional positioning method on smartphones.

UHF based single station RTK is widely used for auto-steering guidance of agricultural machinery in China currently. Too many reference stations in a region will cause serious interference of radio frequency. Moreover, the reliability is very low, since most of the stations were built on the residential buildings. Considering the above problems, we propose to construct the reference station on the communication tower because of the advantages including distribution density, infrastructure guarantee, high quality communication, and relative height compared with ordinary building. We select three communication towers for experiment in Beijing. The average baseline is 43.3 km. We place the GNSS antennas on the roof of communication equipment room, and put the reference receivers (PD318) in the room. An agri-CORS is constructed by using PowerNetwork software. We use 4G of China Mobile to transfer observation data and ephemeris data in real time. We put the antennas of UHF radio on the tower, which is nearly 50 m high. Results show that the data integrity of three reference stations are better than 99%. The signal-to-noise ratio of L1, L2, B1, B2, and B3 are greater than 46, 35, 44, 46, and 40% respectively. The multipath of all the bands are less than 0.50. The average accuracy of baseline after adjustment is better than 0.001 m. Both average internal accord accuracy of CORS and single station RTK are better than 0.01 m, and both average external accord accuracy of CORS and single station RTK are better than 0.025 m. Therefore, we get the basic conclusion that the selected communication towers are suitable for construction of GNSS reference station and the CORS and single station RTK meet the application requirement of auto-steering guidance of agricultural machinery.

The improvement of low-cost receiver performance and the development of Multi-GNSS will make high-precision dynamic positioning, which is for the general public, become the main growth point of GNSS applications gradually. However, under the complex road conditions of the city, there are apparent facts that seriously affect the continuity and reliability of GNSS positioning, like satellite occlusion, the multi-path effects and so on, and restrict the rapid development of GNSS mass navigation. In this paper, based on the static and dynamic data of dual system (GPS + BDS) acquired by ublox M8T module and ordinary ceramic patch antenna, an algorithm of phase smoothed pseudorange is used to improve the accuracy of pseudorange observations, the speed and direction of the receiver are constrained by doppler observations. The joint pseudorange and velocity pseudo-observations are used to establish the robust kalman filter for real-time dynamic positioning. The experimental results show that the proposed algorithm can guarantee the fast and reliable positioning of the low-cost receiver, under the open environment, the sub-meter level positioning accuracy can be basically achieved, and the reliable positioning within 2 m can be guaranteed effectively; in the complex environment, the positioning accuracy within 5 m can also be basically guaranteed.

The traditional satellite navigation and positioning technology uses a number of satellites to locate, for example, GPS and BDS use four satellites to locate. However, in some special cases, when GPS or BDS positioning device is invalid, it becomes very urgent to realize the positioning. In order to solve this problem, a single satellite positioning method and system based on the communication signals of the International Maritime Satellite (Inmarsat) Ground Earth Station (GES) is proposed in this paper. The standard rectangular space coordinate system is established with the center of the geocentric as the starting point, the flight path model of the aircraft is constructed, and all the possible flight paths of the aircraft are found by using the method of iterative analysis. Method to find out all the possible trajectories of the aircraft and visualize them by using the relevant data such as the Burst Timing Offset (BTO) provided by the GES to simulate, and determine the possible location of aircraft. Finally, the cubic spline interpolation is used to estimate the velocity components of the aircraft, combined with the Burst Frequency Offset (BFO) data formula to estimate the BFO value of each route, and compared with the standard BFO value to calculate the probability of each possible flight route, simulate the possible flight path. Taking the Beijing GES and the Asia-Pacific Satellite as an example, this paper analyzes. The research results of this paper will help to shorten the positioning time of the aircraft crash, find the aircraft as soon as possible.

Three QZSS satellites are launched in 2017, which implies that a four satellites regional system is to be established in 2018. There is no doubt that QZSS will play a more important role in the future global GNSS constellations. So it is quite necessary to investigate the importance of current QZSS constellation in positioning. In this paper, the number of visible satellite and PDOP (Position Dilution of Precision) value improvement by combining QZSS with the existing GPS and BeiDou system is analyzed among Asia-Pacific areas. 9 IGS stations are selected to evaluate the performance of SPP (Single Point Positioning) and PPP (Precise Point Positioning) using GPS, BeiDou and GPS + QZSS, BeiDou + QZSS system. Analysis results show that QZSS improves SPP performance for both GPS and BeiDou at different level. Especially when the satellite number is reduced, such as in urban areas or when the elevation cutoff is high, the positioning error will reduce after adding QZSS satellite and the availability of other GNSS systems will also improves. For kinematic PPP users, QZSS could also reduce the convergence period. Meanwhile, the dual frequency and single frequency RTK (Real Time Kinematic) positioning performance is compared after adding QZSS satellite into GPS and BeiDou. Kinematic car test in urban environment shows that when combining QZSS satellite with GPS and BeiDou, the rate of instantaneous ambiguity resolution will increase for both single and dual-frequency users.

Positioning precision of navigation satellite system can be measured by two indicators: the dilution of precision (DOP) and the user equivalent range error (UERE). As the DOP values are only related to the spatial distribution of navigation satellites, the reduction of UERE is the main approach to improve the positioning precision. Equivalent satellite clock (ESC) has been used by Beidou satellite system (BDS) to reduce the UERE and to improve the user’s positioning accuracy. In this contribution, both the pseudo-range and carrier-phase measurements of BDS are used to compute the ESC respectively, and the corresponding navigation positioning performance are also compared. It is shown that the UERE improvement based on phase observables is 50.1%, while 32.1% based on pseudo-range observables. Kinematic positioning experiments of 4 MEGX stations are performed respectively under the standard PNT service and wide area differential service (WADS). It is shown that horizontal, vertical and three-dimensional positioning results of WADS are better than that of the standard PNT service.

The development of multi-GNSS remarkably increased the number of available satellites, but how to solve the multi-dimensional ambiguity parameters quickly and accurately in network RTK technology is still an issue full of perplexity and significance. To ensure the virtual station have more available satellites under the occlusion environment, a fast ambiguity resolution method for base station based on ambiguity tight constraint was proposed in this paper. Firstly, the optimal subset of ambiguity is selected by partial ambiguity resolution (PAR) strategy, and then impose strong constraints on the ambiguities of these satellites. Finally, update the filter equation and assist in fixing the ambiguity of other satellites. The real measured baseline data which contain GPS, BDS and GLONASS from Tianjin CORS and Curtin University was used in the experiments, and the results illustrated that this method could significantly shorten the initialization time of ambiguity between base stations, accelerate the convergence speed of newly-arisen satellites, and increase the number of available satellites of RTK virtual observations (especially low-elevation angle satellites), that providing a reliable guarantee for high-precision positioning in the occlusion environment, such as the roads in cities.

Time transfer by precise point positioning has the defect of long latency resulting from IGR products. GPS common-view can be updated once every 16 min, but with a precision of about 3–5 ns. A real-time precise point positioning time transfer algorithm using IGS RTS (Real-time Service) products was proposed. It was proved to be practical through the time transfer experiments among 4 time laboratories in Western Europe. The time transfer results show that the accuracy of the new algorithm can be reach to 0.30 ns for RMS and 0.25 ns for STD. Moreover, the stability of the time transfer results is up to 2E−15 at 1 day averaging.

International time transfer experiment based on GPS- and BDS-precise point positioning (PPP) technique is carried out using final (ISC) and rapid (ISR) precise satellite clock products provided by iGMAS (international GNSS continuous Monitoring and Assessment System). As a comparison, the same processing is conducted by using COD products provided by the Center for Orbit Determination in Europe (CODE). Experimental data come from observation of seven stations from Multi-GNSS-Experiment (MGEX) and two stations including PT11 (PTB) and BRUX (ROB) from time keeping laboratory in 70 days from 5 August to 15 October 2017. With PTB as the center node, the solutions of 8 time-links are formed. In order to verify the type A uncertainty (uA) of time transfer based on GPS- and BDS-PPP by using iGMAS products, this paper compares the differences between GPS- and BDS-PPP results and GPS PPP results using IGR products. The experimental results demonstrate that uA of time transfer based on GPS- and BDS-PPP using iGMAS products are roughly equal to CODE products. For the results of time-links based on GPS- and BDS-PPP, the STD of one-day arc solutions can reach better than 0.1 and 0.8 ns for all of processing, while 0.1 and 1 ns were achieved for ten-day arc solutions, respectively. Since uA of GPS- and BDS-PPP time transfer using iGMAS products was up to sub nanosecond, therefore, the experiments can provide a reference for BIPM to use BDS PPP based on iGMAS products for International UTC/TAI comparison. Moreover, this also illustrates iGMAS products is reliable.

Passive hydrogen maser (PHM) has the advantages of high frequency stability and low frequency drift. It has been widely used in the navigation system and frequency calibration. Atomic transition signal amplitude of PHM directly determines the system signal to noise ratio, and thus affect system performance, which makes it one of the most important parameters of PHM. Straight solenoid is widely used in PHM to produce the C field for atomic transition. Due to restriction of structural of the physical package, there is improvement potential for homogeneity of magnetic field. This paper discusses the feasibility of multi-section coil for the C field of PHM. Simulation and optimization of the parameters of the multi-section coil is carried out, including length, number of sections, turns, spacing and diameter. Design of multi-section coil with better homogeneity of the C field can be given by the simulation software. Inhomogeneity of about 2% of the C field is realized comparing to about 10% of the straight solenoid. According to the simulation results, several multi-section coils are manufactured. Application and test of these multi-section coils in physical package of hydrogen maser are carried out. Experimental results show that atomic transition signal gain can be increased by about 10%, which is beneficial to the performance of PHM.

Analysing the mechanism of nonlinear variations in GPS stations coordinates time series is an effective way to improve the coordinates accuracy of GPS stations. The constellation design characteristic of GPS may cause the periodic variations of GPS stations coordinates and affect the precision of GPS stations coordinates. In order to analyze the systematic error of the GPS, the spectrum analysis was applied to detect the periodic terms of the GPS and VLBI vertical coordinates time series in the selected 6 amalgamated stations, the amplitude and initial phase of periodic terms were extracted. The annual terms were commonly found in the coordinates time series of GPS and VLBI, the annual terms’ changing trend of GPS and VLBI were basically same, and the systematic error was commonly found between GPS and VLBI. Meanwhile, it was also found that the systematic error of the semi-annual terms exist between the two technologies in some amalgamated stations, which may be related to the systematic error of GPS itself and the false periodic terms caused by the data’s quality problems.

Because of various factors, there are many abnormal situations in the atomic clock measurement data from time-keeping system, such as data lost, error data, phase jump. The abnormal data can not reflect the real status of atomic clock, it is necessary to correct the abnormal data caused by short-term external disturbances. In this paper, based on analyzing for frequently used algorithm objectively and combining multi-methods, an accurate and efficient detecting and correcting algorithm is put forward. At last, the algorithm is validated using the clock measurement data, the result shows that the algorithm can accurately locate the abnormal data, analyze abnormal type, the correction effect is satisfactory.

Each observation station in the VLBI has an independent hydrogen clock. In particular, on rare occasions the phase lock synthesizer loss phase lock on the signal from the hydrogen maser cavity resulting in a discontinuity in the clock time obtained from the maser, this phenomenon is referred to as a “clock break”. Clock breaks can be several hundred nanoseconds. In the VLBI data analysis and analysis to consider the special operation of the clock breaks. In the least squares solution method, it is necessary to reduce the influence of the clock break on the residuals of the observed data and the accuracy of the solution. The method of positioning the clock break is used to reduce the influence of the clock break by means of piecewise linearization. In the Kalman filter method, the stochastic model can not contain such a rapid clock time variation, but also the method of locating the clock break and then including the clock break in the state transition noise of the Kalman filter. Thus improve the accuracy of VLBI data solution.

An improved chi-squared test method used to detect frequency abnormity of atomic clock is presented. This method is independent of choice of reference value, which is applicable to the measure of data in pairs. The method may speed up the process of analysis and detection for frequency abnormity. The result shows that compared with the classical chi-squared test method, the detection performance of frequency abnormity of atomic clock are improved and the calculation procedure is simplificated.

GNSS timing receiver is widely used in various fields. Unfortunately, it has weak capability of anti-jamming and anti-spoofing, so an integrated processing technique based on joint verification of location and clock offset is proposed. The algorithm is verified by simulation with timing receiver data. Simulation results show that 95% probability of the spherical error of location result can be used as the threshold of the location to detect strong intentional or unintentional jamming signal efficiently. When the location check is passed, the clock offset checking is used to monitor the receiver clock offset anomaly, with processing error less than 0.2 ns. The joint verification of location and clock offset method can greatly improve the robust performance of timing receivers.

As an important load of BDS, the performance of satellite-borne atomic clock directly affects the service level of navigation system. Based on the requirements of navigation system on atomic clocks in orbit, the performance of BDS spaceborne atomic clocks has been studied in recent years. Precise clock products of two IGS analysis centers wum and gbm with sampling interval of 300 s from 2014 to 2017 were adopted. The BDS spaceborne atomic clocks were evaluated and analyzed from accuracy, drift rate and stability respectively. The results indicate that, overall, MEO satellite clock performance is the best, followed by IGSO satellite clock, the worst is GEO satellite clock;the accuracy, the daily drift rate and the 10,000 s stability fluctuate at 7 × 10−12–4 × 10−11, −3 × 10−13–3 × 10−13, 3 × 10−14–1.5 × 10−13 respectively. In terms of drift rate and the 10,000 s stability, the results of performance analysis of GEO satellite clock using two different precise clock products have great differences, while those of IGSO and MEO satellite clocks have little difference.

Laser detection avoid the limitation on cesium clocks’ lifespan due to electron multipliers. However, the laser inevitably induces light shift. By measuring the frequency shifts under various light powers, we study the light shift. The dependence of the light shift on the light power is 2 × 10−12/mW. The Allan deviation of the output power of the laser diode is 4.5 × 10−3 at 105 s under free running. The temperature coefficient of the clock is 1 × 10−12/℃. For a high-performance cesium clock, the light shift is one of the main restricts to accuracy and long-term stability. In order to improve the clock’s long-term frequency stability, accuracy and temperature coefficient, we propose a method for laser power stabilization. This method uses a liquid crystal variable retarder to tune the polarization of the light, in order to feedback control the light power with respect to the photoelectric detector. We theoretically analyze the method, and find that the drift of light power mainly results from the temperature drift of electronic elements. The temperature drift is below 1 × 10−5/℃, manifesting the theoretical feasibility. We build an experimental system and measure the light power for 20 days. The stability of light power is 6 × 10−5 at 10 s, and 3 × 10−6 at 105 s. Moreover, the temperature coefficient reduces to 2 × 10−13/℃ from 1 × 10−12/℃. Therefore, the method effectively improves the performance of the clock. Besides, it can be easily applied to other experiments that requires laser power stabilization.

Two Way Time Transfer (TWTT) is used in BDS to synchronize the time between satellite and ground system. Therefore, both Orbit Determination and Time Synchronization (ODTS) and TWTT can obtain BDS satellite clocks. For ODTS, satellite clock is estimated with satellite orbit, and the consistency of them is better, but estimation error of them cannot be separated. Compared with ODTS, satellite clock estimated by TWTT is less impacted by satellite orbit, because of the difference between uplink and downlink pseudo-ranges in TWTT processing. Consistency of ODTS satellite clock and TWTT satellite clock is of importance for the performance analysis of BDS satellite clock in orbit. Based on the satellite clocks estimated by ODTS and TWTT respectively, this paper analyzes the systematic, periodical and stochastic characteristics of BDS satellite clock, taking into account the characteristics of satellite clock data. The result can provide reference for BDS service performance optimization. It is shown that the performance of BDS satellite clock is approximately 5 × 10−12 τ−0.5 (WHFM, 103 s ≤ τ ≤ 104 s) + 4 × 10−14 (FLFM, τ > 105 s), while during the 104–105 s period, the orbital-period characteristics is notable.

A novel approximate analytical method is presented for calculating parameters of Whispering Gallery Mode (WGM) in a sapphire dielectric resonator (SDR). It is based on ray optics and wave theory. The frequency of WGM is computed with less computation time and the influence of sapphire’s parameters on the frequency is also analyzed. The Q value of SDR in the liquid helium temperature is optimized by adjusting the coupling coefficient and the surface roughness of the sapphire. According to the computed results, a SDR employing WGM at X-Band is fabricated. The loaded QL value reaches 4.0 × 108 and the eigen frequency is 9.205 GHz in the liquid helium temperature.

Delay errors will follow a biased distribution under the ionospheric anomaly or storms conditions, making it difficult to overbound effectively the delay errors with the estimated error bounds for SBAS. Gaussian-bounding theorem provides a way to test the effectiveness of ionospheric error bound estimate. With the theorem, various bound estimating methods and its overbounding capability were analyzed with observations during storms for China area where ionospheric anomaly persists. It also shows the strength of different estimations, in which the irregularity detector is an integral component to minimize the size of bound while maintaining the effectiveness, bound estimate with dynamic inflation factor outperforms over that of static inflating in system availability, and the undersampled threat model improves integrity margin in the bound at the cost of system availability, so diverse threat models are proposed to be constructed based on the ionospheric activities.

Ionospheric anomaly in south of China will degrade the performance of SBAS grid models severely. Characteristics of ionospheric delay errors are analyzed with observations from the mid and low latitudes area in China for various solar activities and ionospheric conditions. Results show the error distribution is symmetric, unimodal, and overbounded by a biased normal error distribution. The biased distributions would reduce the overbounding capability of the estimated bounds. Ionospheric anomaly contribute to the complicated spatial and temporal variations of the delay errors as storms, and even is the main influencing factors under certain condition.

With the huge potential of the GNSS market and thousands of LEO satellites in space in the future, a novel way is to use these LEO mega-constellations for positioning. In order to fulfil this purpose, the first step is to build a constellation that could be used for both communication and positioning. This paper discusses about some critical issues when designing LEO mega-constellations for positioning. By statistically analyzing from different perspectives, it is shown that in order to get a more uniform distribution of the number of visible satellites along latitude, the combination of different constellations together as a whole could be much more appealing. Meanwhile, in this paper, we did some preliminary work about how to determine some important parameters to get the most suitable combination. The selection of inclinations, orbit heights, number of combined constellations, and ratio of the number of satellites in each constellation will be discussed.

As an emerging commercial application, deliveries using Unmanned Aerial Vehicles (UAVs) have the advantages of low cost and flexibility over traditional logistic operations, and are therefore being increasingly adopted by logistics companies. In order to ensure the success of delivery missions, effective traffic management measures, including UAV safety or integrity monitoring, are essential. Currently, however, there is a gap in research on the concept and framework for the evaluation of integrity performance for the delivery application. This paper addresses the issue by proposing a UAV Navigation Monitoring Requirement (UNMR) specification for the monitoring of the accuracy and integrity performance of UAVs for use in delivery applications, based on the concept of Required Navigation Performance (RNP). The method used to determine the position accuracy requirement for en-route and terminal UNMR operations is based on the related factors in the context of UAV-borne delivery. This is represented by the width of the route and radius of the docking or landing spot. Simulation and initial field tests show that the flight technical errors and path definition errors should be considered for the total system error calculation for the UAV delivery. Effective application of the proposed framework for integrity performance evaluation has shown to be of potential benefits for the operational management of UAV deliveries.

In many areas such as safety of life application, the integrity of the navigation system is a very important indicator to indicate the trustworthiness of the system services. According to different scenarios, system integrity requirements are also different, but are usually in the order of 10−7 or even less. It is impossible to evaluate the performance by the traditional statistics which using the frequency of occurrence to simulate the probability. The Extreme Value Theory (EVT), which enables extrapolation of the observed error distribution’s tail into the misleading information domain, regardless of the underlying error distribution. In this paper, EVT is applied to the SBAS integrity evaluation field, which can effectively solve the problem of insufficient tail samples and realize a reasonable inference of extreme abnormal events. The paper first briefly introduces the basic concept of SBAS integrity and EVT, and then uses the mixture extreme model to solve the problem of threshold choosing. Finally, the paper uses EGNOS message data provided by EMS, and wtza station observation data to evaluate its integrity performance. The result shows that the EGNOS is compliant with LPV requirements in the vicinity of wtza station.

Advanced Receiver Autonomous Integrity Monitoring (ARAIM), based on multi-constellation and multi-frequency of global navigation satellites system, which can provide vertical navigation in terminal approach, has attracted more attentions. The ARAIM user algorithm is based on the multiple hypothesis solution separation within the Integrity Support Message. The total probability of the monitored fault modes subsets must meet the integrity budget. In ARAIM baseline algorithm, the fault mode determination is an independently sequential structure. The number of subsets determined by the maximum simultaneous faults number is redundant which increases computational burdens in fault-tolerant position. A refined subsets determination method is proposed to optimize the calculation. Instead of determining the maximum simultaneous faults number, the proposed method accumulates the fault mode in descending order according to the probability. The threshold for the integrity risk coming from the unmonitored faults is the only parameter to terminate this accumulation and determine the number of subsets. Every subset will be detected the observability and continuity further in this process to make sure that ARAIM can work normally. The structure is more compact and reasonable. The tests results shown that the proposed method is more rigorous as the accumulation processing can make sure the monitored subsets meet the threshold exactly and the accuracy of not monitored risk is increased by three orders of magnitude. The global 99.5% coverage under LPV-200 requirements can be up to 95.94%. The number of subsets is reduced more than 80% significantly without any impacts to the worldwide performance of ARAIM.

Beidou The pseudolites can be used as a backup signal source of the Beidou System on orbit while in the special geographical environment. It also provides foundation enhancement service for the Beidou system. When the ground-based satellite works on the ground, its observation is seriously affected by the multipath effect. At present, there are mainly signal methods and data processing methods to deal with the multipath in pseudolites pseudo range observation values. In this paper, the optimized AGC settings in signal processing methods and the improved CNMC method in data processing are selected for comparison and analysis. The comparative analysis of the results shows that the improved CNMC method is slightly better than the AGC location algorithm after the pseudolite pseudo range observation.

In the multi-constellation satellite navigation system, all the visible satellites are used for positioning, which will increase the computation amount of the receiver and affect the real-time positioning. How to quickly and effectively select visible satellites for positioning is a research topic. For this problem, a satellite selection algorithm based on Particle Swarm Optimization (PSO) is proposed. In this method, the visible satellite is numbered, random grouping, and each group as a particle; the velocity-displacement model in the PSO keeps the particles gradually close to the minimum value of the GDOP. Under a series of simulation experiments, the key parameters such as inertia weight factor, acceleration coefficient and maximum velocity of PSO are determined. Besides, local search based on chaos mechanism are introduced, which can avoid the results of PSO algorithm into local optimum. Finally, the performance of satellite selection with PSO is confirmed to be remarkable by the simulation experiments under different numbers of selected satellites. The results show that this method can quickly select satellites under BDS and GPS system, and the result meets receiver positioning accuracy.

The receiver autonomous integrity monitoring (RAIM) technology, which with the advantage of quick response and completed independent, plays an important role in the integrity monitoring system of GNSS. With the development of BDS and other navigation satellite systems, the dual-mode and the multi-mode satellite navigation receivers are paid more and more attention, which provide not only superior positioning accuracy, but also sufficient redundancy for RAIM. Among the fault detection algorithms, the “snapshot” detection methods show satisfied rapidity for detecting large fault in pseudorange measurement, while their abilities to detect a minor fault is poor. Although minor faults usually not serious enough to cause unavailable positioning of GNSS receiver immediately, but their influence on positioning error accuracy will accumulate with time to a significant level. In order to overcome the shortcoming of the traditional RAIM algorithm in detecting minor faults, an improved minor fault detection algorithm based on sliding-window accumulated parity vector is proposed in this paper. In the proposed algorithm, a new statistics for fault detection is obtained by accumulating the parity vector in a sliding window, so as to make an optimized fault diagnosis results online. A simulation system is established for validating the proposed algorithm. The simulation results show that the proposed algorithm could shorten the time delay in detecting minor faults.

The ionospheric delay model is a reliable method to reduce the influence of ionospheric delay. The phase smoothed pseudorange observations are always used to construct ionospheric delay model. However, the accuracy of the constructed ionosphere model is affected by precision of phase smoothed pseudorange observations and the number of base stations. This contribution presents a construction method of ionospheric delay model with combined BDS phase and range observation. The observations of ionospheric delay is constructed by precise point positioning (PPP) with original observations. At the same time, the polynomial model is used to ionosphere modeling. Finally, the validity of this method is verified using BDS and GPS data. The bias of ionosphere model is less than 1 m and the standard deviation is better than 0.4 m.

Integrity monitoring is an important means to guarantee the integrity of satellite navigation system. Receiver autonomous integrity monitoring (RAIM), as a client integrity monitoring method, has a lot of advantages such as not dependent on external equipment, low cost and easy to implement. Therefore, it is widely used in integrity monitoring. Traditional RAIM methods comprise RAIM algorithm based on Kalman filter and snapshot algorithm based on pseudorange observation. Compared with the snapshot algorithm, the Kalman filter innovation monitoring method is not limited to use the current measurement. Therefore it has advantages of independent detection and less calculation. It also can be used under the condition of few satellites. Unfortunately, the Kalman filter-based method is not sensitive to slowly varying pseudorange fault. Thus we propose an integrated algorithm combining the parity vector method based on the non-coherent accumulation with Kalman filter-based detection method. The result shows that, compared with the traditional parity vector method and the Kalman filter-based detection method, the proposed algorithm has a better result in fault detection and monitoring delay.

This paper established a constellation optimization model for global navigation enhancement, of which RAAN is non-uniformly distributed, aimed at GDOP (geometric dilution of precision) optimization of important cities around the world, using genetic algorithm to solve the constellation optimization problem and using STK to analyses the optimization results. The simulation results show, compared with the classic Walker constellation of which global uniformly distributed RAAN, the Leo constellation of global non-uniformly distributed RAAN not only finishes high precision worldwide global navigation, but reduce the number of satellite constellation, which is beneficial to reduce the cost and deploy rapidly.

Spoofing attack organized by generating fake navigation signal can precisely manipulate PNT output of target receiver. In this paper an authenticated augmentation message for GBAS is designed to obtain the authentication for both navigation message from satellites and augmentation message from GBAS broadcasters. The proposed navigation message authentication method has an advantage in efficiency and authentication delay compared with legacy schemes integrated into satellite signal while has an equally high security level as other schemes.

This paper focuses on the optimal design of the near space navigation network configuration concerning a specific target area. Optimal design not only ensure navigation service for specific area with high accuracy and low cost; but also enable all users in the target area to obtain a controlled precision. In this design, a double-layer Y configuration is adopted as the optimal basic unit. Adaptive algorithm and genetic algorithm are selected to detect the boundary of the configuration to realize the synchronization optimization of cost and accuracy. Combining with the working principle of aerostat in the stratosphere airspace, we design a platform dynamic trajectory and provide an algorithm optimization of layout for the partial users’ worse precision in dynamic scene. The simulation results show that the optimal design method proposed in this paper can meet the configuration design requirements of the dynamic navigation network based on near space with different size area and different precision requirement.

The estimate of Grid Ionospheric Vertical Delay (GIVD) and Grid Ionospheric Vertical Delay Error (GIVE) is the core content of ionospheric delay processing section in Satellite Based Augmentation Systems (SBAS). At present, WAAS and EGNOS respectively use Kriging method and Inverse Distance Weighting (IDW) method to estimate GIVD and GIVE. The existence of a fixed ionospheric abnormal zone at low latitudes south of the Yangtze River in China led to the advantages and disadvantages of the two algorithms in different regions of China. Aiming at this problem, this paper takes two mature methods of ionospheric grid correction as a reference, combined with the distribution characteristics of ionosphere in China, selected the measured data in China for simulation analysis. According to the comparative analysis of the simulation performance of the algorithm, this paper proposes an algorithm combination of strategies. This paper selects the measured data of 31 monitoring stations and 30 user stations from Crustal Movement Observation Network of China (CMONOC) for verification. Firstly, the spatial correlation characteristics of the ionosphere over China are analyzed and the applicability of the two algorithms to China is adjusted. Secondly, we compare the performance of the two mature algorithms. Finally, based on the comparative analysis, combined with the theoretical analysis of the use of two algorithms, this paper puts forward the combination strategy. In the area north of the Yangtze River, the ionospheric delay error model is stable and Kriging method is adopted to obtain a larger service area and better calibration performance. At the same time, in the area south of the Yangtze River, in order to counter the frequent occurrence of ionospheric abnormal, IDW method was chosen to ensure the integrity. The results show that compared with the IDW method alone, the combination accuracy is improved and the service area in the marginal area is expanded. Compared with the single plane Kriging method, the combined method ensures the integrity of the ionosphere active area in the south of the Yangtze River.

With the development of satellite navigation technology, the users’ demands for the integrity of GNSS are more and more intense. The ground based monitoring system can hardly report an alarm message to the GNSS users during the valid alarming period due to the satellite-earth propagation delay. It is beneficial to monitor the abnormal events and report the corresponding alarms in orbit. Through this way, which is an important branch of the future GNSS integrity monitoring, the time needed to give an alarm is shorter and the capability of system integrity service is strengthened. A new generation of BDS satellites has the capable of satellite autonomous integrity monitoring (SAIM). This paper presents the technology scheme of SAIM, and proposes the integrity monitoring method of navigation signals and clock on-board. The proposed method is verified based on the onboard test of the IGSO satellite. In addition, we analyze the integrity telemetry data from the new generation of BDS satellite, including the signal delay, power, carrier phase measurement, correlation peak, consistency of pseudo-code and carrier phase, clock phase and frequency step. The analysis results indicate that the quality of the data on orbit meets the requirements, and SAIM could monitor effectively the abnormal change of satellite clock and navigation signal, generate rapidly the alarm message, and transmit them to user. The alarm time is less than 6 s through the message, and 2 s through the non-standard code (NSC). In the end, we present the future work for improving the SAIM technology of BDS.