Abstract: Factor graphs are widely used in the fields of coding, statistics, signal processing, and artificial intelligence as a modeling tool that represents factorization. The application of factor graphs in the navigation field is also gradually developed. The combination of multiple sensor information provides a more accurate and robust navigation state estimate than the information from a single sensor. However, various sensors have different error characteristics and these sensors usually operate at different frequencies. Considering that some sensors cannot supply the linear measurement information, and it brings the challenges to the design of the integrated navigation system. The navigation algorithm based on the factor graph model enables the system to have plug-and-play characteristics and achieve better results under nonlinear measurement conditions. The state estimation and information fusion problems in the navigation system can be represented by the factor graph model. Sum-product algorithm based on factor graph is the main method in navigation and positioning system.This paper summarizes the factor graph theory and its application in the navigation system, including: 1) Mathematical theoretical basis of factor graph and its related application fields 2) Development and application of factor graphs in the field of positioning and navigation.
Abstract: In the Ground-based Pseudolites System, near-field pseudolite signals may interfere and suppress the far-field signals since the existence of near-far effect, causing failure acquisition of the far-field signals. A SIC-based acquisition method anti near-far effect is proposed in this paper, aiming at the acquisition of time-hopping direct sequence spread spectrum (TH-DSSS) signal implemented in this system. Interferences of strong signals to weak signals are reduced by reconstructing local replica of the strong signal and interference cancellation. The proposed method is analyzed in theory and simulation. Simulation results indicate that the SIC-based acquisition method has the ability to reduce the influence of near-far effect, increase the detection probability of weak signals and enlarge the operating range of system without changing the pseudolite base station structure and the framework of corresponding receiver, which provides an effective guarantee for the receiver to capture, track and position in scenarios with strong near-far effect.
Abstract: The third-generation of Chinese BeiDou Satellite System (BDS-3) has been providing global service since the end of 2018. In order to evaluate the accuracy of BDS-2 and BDS-3 standard point positioning (SPP) as well as visible satellites and GDOP, 90 days of BDS-2 and BDS-3 data collected from 37 globally distributed International GNSS Service (IGS) Multi-GNSS Experiment network (MGEX) stations was used to perform data analysis. Results show that: 1) The geometry of BDS-3 is significantly improved when compared with that of BDS-2 by analyzing the visible satellites and GDOP. 2) The RMS of BDS-3 SPP error is 1.490, 2.610, 5.238m in the east, north and up directions, which is improved by 58％, 1％, and 24％ respectively when compared with that of BDS-2. 3) The RMS of combined BDS-2／BDS-3 SPP error is 1.45, 2.36, 4.90 m, which is improved by 59％, 11％ 29％ when compared with the BDS-2 results. 4) The RMS of combined BDS-2／BDS-3 SPP error is improved by 3％, 10％, 6％ when compared with the BDS-3 results. We also find that the combination of BDS-2 and BDS-3 weakens the marginal effect of BDS-2 SPP which is related to the geographical longitude.
Abstract: For GNSS navigation and positioning, ionospheric delay is one of the main error sources, and its influence can reach to several meters or even hundreds of meters. Therefore, it is necessary to study high-precision ionospheric model, especially regional ionospheric model establishment. In this study, a regional ionospheric model based on BeiDou foundation strengthening system is studied. By calculating the observation data of the three systems (GPS／BDS／GLONASS) of BeiDou foundation strengthening system and combining with the polynomial function model for modeling, the ionosphere model in China is obtained. The model precision was evaluated by direct comparison with CODG and indirect single frequency precision single point positioning results. The validations show that the accuracy of the regional ionospheric model based on the BeiDou foundation strengthening system is higher than of the ionospheric grid model published by CODG, and more consistent with the actual ionospheric spatial distribution.
Abstract: This paper analyzes the GPS power enhancement in the US-Iranian conflict in June 2019, and analyzes the power enhancement of GPS P(Y) code from receiver type, antenna type and satellite model. The analysis shows that the power enhancement values of the stations of different types of receivers are significantly different, while the power enhancement values of the stations using different types of antennas are not much different. In addition, in the case of the same receiver or antenna type, the same type of satellite power enhancement value comparison results of the same group of co-locaion-stations are consistent.
Abstract: Aerial triangulation, assisted by differential GNSS, is essential part of precise positioning of UAV image elements. As the sampling frequency of GNSS module usually does not exceed 50Hz, higher sampling frequency would be a serious problem for software and hardware of UAV. In this paper, 3D-coordinate interpolation for high dynamic positioning of UAV is realized based on cubic spline interpolation approach, whose applicability has been tested by real measurements. The experimental results show that clamped spline is more suitable for high dynamic interpolation of UAV. When the sampling frequency is higher than 5 Hz, plane interpolation accuracy is better than 1 cm and elevation interpolation is better than 2.2 cm.
Abstract: The Ground Based Augmentation System (GBAS) uses carrier phase smoothing pseudorange differential correction to achieve navigation aided positioning. The smoothing time constant is a key parameter affecting the accuracy of carrier phase smoothing pseudorange. To analyze the effects of ionospheric time gradient and spatial gradient on Hatch filtering under different smoothing times. Based on the analysis of the total error variance of the filtering caused by the ionospheric time-space gradient and multipath effect, the adaptive optimal smoothing time constant is derived. The positioning errors of GBAS static and dynamic environments are tested respectively. The experimental results show that the adaptive optimal smoothing time constant reduces the GBAS pseudorange measurement error, which enhances the positioning accuracy.
Abstract: GNSS is widely used at present, but GNSS signals are vulnerable to intentional and unintentional interference because of being extremely weak around the earth's surface and public of the format, which will affect the accuracy of GNSS positioning and timing. It is very important to localize and eliminate the interference source. The common way to localize the interference source is to use the direction finding equipment. However, it will take a long time to localize the interference source when there is no approximate location of the GNSS interference. If the coarse location of interference can be achieved by analyzing the output parameter of general receivers, it can provide the initial reference position and the approximate search range for direction finding equipment. As the GNSS receiver approaches the interference, it loses the position information, but as it is far away from the interference, it gets the position information again. To study the information of position loss and reacquisition of GNSS receivers can realize the interference localization. The simulation results show that the method can realize the localization of GNSS interference source, and provide position reference for further accurate location of interference.
Abstract: This paper presents a low-power anti-jamming processor for Global Navigation Satellite System (GNSS) smart antenna. By improving the design of mixer in GNSS anti-interference architecture, the digital high intermediate frequency mixer and filter are optimized. To further reduce the power consumption and resource occupation, an Output Double-Rate-Register(ODDR) scheme is introduced to realize the direct synthesis of high intermediate frequency signal. The experimental results show that the power consumption and hardware resources of this design are reduced by 11％ and 14％, which can be applied to GNSS smart antenna system.
Abstract: With the continuous development of China BeiDou Navigation Satellite System(BDS), it has entered the third stage of construction, and its positioning accuracy has always been a hot topic of global concern. Based on the multi-mode GNSS data of the IGS continuous tracking station on the 227th day of 2018, this paper dynamically processes the short baseline, analyzes the relative positioning accuracy of the BDS-3 system, and analyzes the relative positioning accuracy of the BDS-2. The results show that the relative positioning accuracy of the short-baseline of BDS-3 is better than 3 cm in the E direction, the N direction is better than 3.5 cm, and the U direction is better than 10 cm. The accuracy in the three directions is slightly higher than the short positioning accuracy of the BDS-2 short baseline.
Abstract: Power detection of spoofing signal is one of the most commonly used spoofing detection methods. However, the spoofing source can still achieve spoofing attack on the terminal in the ring by adjusting the power of the transmitted spoofing signal. In order to solve this problem, this paper proposes a spoofing detection method for mobile terminals based on signal power Variation. This method utilizes the essential attributes of distance difference between real satellite and deception source and terminal, it can detect spoofing jamming sources in close range effectively. In this paper, the power ratio model of mobile terminal signal is established, and on this basis, the binary hypothesis test for deception signal is given. Through theoretical analysis and simulation experiments, the validity of the proposed spoofing detection technology for mobile terminals based on signal power variation is verified. When the distance between the jammer and the terminal is less than 2000 meters, and the distance between the terminal and the terminal is more than 200 meters, the effective detection of spoofing attack can be realized under 1％ false alarm probability.
Abstract: China BeiDou navigation system is in the final stage of BDS-3 construction, and its positioning accuracy has been a hot topic at home and abroad. Based on the measured data of IGS continuous tracking station, this paper expounds the Beidou triple-frequency precise point positioning model, and compares and analyzes the observation data quality of BDS-2 and BDS-3 and the positioning precision. The research found that the data quality of BDS-3 is better, compared with BDS-2. The accuracy of precise point positioning using BDS-3 satellite is slightly worse than that of BDS-2, and the convergence time is slightly slower. Combined BDS-2 and BDS-3, the precision and the convergence time of the precise point positioning is greatly improved compared with the PPP result of BDS-2 only.
Abstract: GNSS height fitting is widely used engineering construction, different fitting methods have respective limitations. To improve the applicability, reliability and accuracy, this paper proposes a method to fit the height based on the EGM2008 and moving surface models, different experimental analysis shows that the method can effectively improve the precision of GNSS height fitting.
Abstract: In view of the traditional indoor localization algorithm based on BP neural network existing low precision and sconvergence speed. considering the sophisticated indoor environment, there is usually the multipath effect,in addition that the signal attenuation model unsuitable for accurate positioning, this paper proposes an improved artificial fish optimization WiFi fingerprint indoor localization algorithm of BP neural network. the foraging and searching methods of artificial fish are used to improve the speed and ability of global optimization, using the improved artificial fish algorithm (IAFSA) to optimize the selection of weights and thresholds of BP neural network, which effectively avoid the disadvantage that predicted value of traditional BP neural network is easily plunged into partial optimum, the signal is denoised by gaussian filter in advance.At the same time, the relationship between the signal strength value (RSSI) obtained by the sampling point and the position coordinate is established. Experimental results show that compared with the traditional BP neural network method, the proposed method of this paper reduces the average positioning error by 0.75m, and the average positioning accuracy is improved by about 32.2％. The algorithm of this paper improves the reliability of positioning and has better stability.
Abstract: In order to meet the requirement that the projection length deformation value of the high-speed railway line control network is not more than 10 mm／km, it is necessary to divide the line into multiple sections and establish their respective normal section meridian ellipses. For the adjacent connection problem of the ellipsoid, the method of the intersection point with same normal is proposed, the consistency of the intersection points after the ellipsoid transformation is realized, and the seamless connection problem of the lines is solved, thereby greatly enhancing the applicability of the normal section meridian ellipsoid theory in the bending property, complexity and length of the engineering line.
Abstract: Based on natural topography and urban characteristics, the Quasi-Zenith Satellite System (QZSS) has been basically built, with providing positioning enhancement services based on GPS. This paper introduces services and applications about QZSS, and gives the analysis of its signals, featured services, application modes and recommended product lists. QZSS promotes the use of terminal equipments, with taking advantages of manufacturing digital cameras and sport watches. Also, CLAS are expanded in industries such as railway, precision agriculture and construction. Those have certain reference meaning for promoting the applications of BeiDou Navigation Satellite System.
Abstract: With the rapid development of the radio and television industry, traditional TV signals based on SDI (Serial Digital Interface) baseband signals have been difficult to meet the needs of future technology development and business expansion. Thanks to the rapid development of modern communication technologies and the upcoming 5G era of the Internet of Everything, the radio and television industry will also adopt IP technology to build new network systems. In the transition period to the development of IP, there are still some urgent problems to be solved in the IP of radio and television. In order to solve the problem of requiring high-precision synchronization signals in the radio and television system network to complete time synchronization, this paper adopts PTP (Precision Time Protocol) time synchronization technology to complete time synchronization networking in private Ethernet, set up the test environment and analysis the test data. The test results shows, compared with the traditional NTP (Network Time Protocol) time synchronization technology, the accuracy of the output PTP signal can reach the order of sub-microsecond, which fully meets the high precision requirements of the time synchronization signal of the IP digital TV system in the radio and television industry.
Abstract: The principle of inversion of water level changes using GPS signal-to-noise ratio data is described in detail. Comparing the water level change with the signal-to-noise ratio of the Calcasieu Pass GPS station and the data monitored by the tide station, they show good consistency. The correlation coefficient is better than 0.96, and the RMSE is about 8 cm. The results further validate the feasibility and reliability of monitoring sea level changes based on GPS signal-to-noise ratio data. Through the test and analysis of different periods and time length, it is proved that the shore based GPS station can continuously monitor the water level.
Abstract: Based on the training of interference sources searching, this paper comprehensively evaluates the ability of locating and searching the interference sources of navigation signals. The analytic hierarchy process and Delphi method are used to solve three problems: one is to establish the evaluation index system; the other is to determine the weight of the evaluation index; the third is to determine the quantitative evaluation method, so as to provide an effective comprehensive ability evaluation method for the navigation signal interference sources search training, and ensure the scientificity and rationality of the training content setting, score distribution and quantitative score. It is helpful to accurately evaluate the ability to locate and search the interference sources of navigation signals.