Longxia Xu

A new timing method based on common-view

GPS one-way timing is the simplest and most commonly used method for users to acquire precise time. However, it has inferior accuracy in performance as most errors due to satellites and in the path from satellites to users can not be canceled. Common-view time transfer is seen as the improvement of one-way technique and its accuracy is typically in the 1 to 10 ns range. Without exception, common-view time transfer also has limitations. For instance, it is real-time limited and can not be used simultaneously for broad users.

Research on position differential method of dual-satellites TDOA and FDOA in passive location system

Combining with the principle of dual-satellite TDOA and FDOA in passive location system, a position differential method basing on dual-satellite TDOA and FDOA in passive location is put forward, which derives solution position of known and unknown radiation source by using conventional location algorithm method of TDOA and FDOA location, then position correction is achieved by subtracting the exact position and solution position of known radiation source to correct the solution position of unknown radiation source. Simulation results show that, according to similar Geometric Dilution of Precision(GDOP) principle, the known and unknown radiation source at a distance of several hundred kilometers are selected for differential, which can greatly improve location precision. This method develop positioning system of dual-satellite TDOA and FDOA, which has important value for improving its availability and the reliability of positioning result.

Two Methods of Processing System Time Offset in Multi-constellation Integrated System*

Two methods on how to deal with the time offset in multi-constellation navigation systems are discussed in this paper. One approach is disposing time offset in receiver end (DRE) and another disposing in system level (DSL). Comparisons and analysis in different aspects of these two methods are involved. Simulation results indicate that the positioning accuracy of multi-constellation navigation systems is affected more obviously by the method of DSL than DRE. When the error of broadcasted time offset is 5ns, it is more advisable to process time offset use the method of DRE.

Analyzing Prediction Methods and Precision of GNSS System Time Offset Using End-Point and Kalman Filter

GNSS compatibility and interoperability is one of the most significant problems in multi-system navigation and position. The precise prediction of system time offset is one of the most important problems for application of GNSS compatibility and interoperability. To increase the prediction precision of system time offset and meet the requirement of multi-system users, this essay studies the prediction algorithm of system time offset. First, based on research on the prediction principle of end-point (EP) and Kalman filter, the feature of GNSS system time offset is analyzed. The initial values of Kalman filter parameters are determined to reduce the uncertainty and error caused by it. In addition, the real-time measurement data is provided by a platform that monitors GNSS system time offset at National Time Service Center (NTSC). It verifies the applicability of two methods to predict the system time offset and compares the precision of EP and Kalman filter. The result shows that for any type data of system time offset, when real-time precision prediction is required, Kalman filter provides higher precision and will be influenced less significantly by other factors: For GPS data, precision is about 1 ns and for GLONASS data, it is 2 ns. It is 0.5 times higher than that of EP. In other cases, EP is more precise.

Measurement and Correction Method of the System Time Offset of Multi-mode Satellite Navigation

Multi-mode satellite navigation is an important development direction of Global Navigation Satellite Systems (GNSS). Because of each satellite navigation system owing an independent and stable operating system time scale, one of key issues that must be solved to implement multi-mode navigation is to determine the system time offset between two satellite navigation systems. National Time Service Center (NTSC) keeps our country’s standard time (UTC (NTSC)). It is an available resource for us to monitor the system time offset of satellite navigation systems by means of receiving signal-in-space using the geodetic time receiver. The monitoring principle and main measurement errors are discussed. The correction method of system time offset measuring results is studied with the IGS precise orbit ephemeris. In order to test rationality of the measurement method, circular T bulletin data published by Bureau International des Poids et Mesures (BIPM) is applied to compare with the monitoring data and revised data. Data Processing results are given and shown that this monitoring method is practical and can be applied to multi-mode navigation.

System Time Offset Based RAIM in Combined GPS/Beidou Navigation System

Compatibility and interoperability of Global Navigation Satellite System (GNSS) are becoming the main trend of future navigation. However, each navigation system has a time scale. When users positioning with not only one system, the time offset between them must be considered. There are several ways to acquire system time offsets. By adding unknown variables in the combined position equation to solve this variable is the commonly used way. For positioning with multi-constellations, system time offsets are some kind of burden which must be taken into account. This paper takes full use of the obtained offsets and proposes a new fault detection method for Receiver Autonomous Integrity Monitoring (RAIM). Simulations are made to estimate the ability of this new method. This new method takes the high stability of system time offsets of GPS/Beidou system and applies it to assistant fault detection. This method has no additional requirements for navigation system and is fit for applied in receivers. It can be expected this method will be one means of RAIM for Beidou navigation system when integrated with other GNSS in future.

A New Algorithm for Receiver Integrity Monitoring with Receiver Clock Error Auxiliary

The receiver integrity monitoring technology is one of the important technologies to reflect the GNSS integrity. It can be divided into receiver autonomous integrity monitoring (RAIM) and auxiliary autonomous integrity monitoring. Apart from the redundant observations of the receiver are used for RAIM, there are various parameter information provided form receiver and the receiver clock error is one of them. As the stability of the receiver oscillators to 10–10/s, this makes it possible to make short-term predictions. In this paper, the receiver clock error is introduced and the receiver clock error auxiliary GNSS integrity monitoring method is proposed. In this paper, the principle of the method is introduced and the algorithm flow is established firstly. Then the key steps involved in the method are discussed, including receiver clock error prediction method, threshold value determination method, fault detection method and fault identification method. Among these key steps, threshold determination method are fully discussed and validated. Results show that the threshold determination method is proper in the method. Finally, the performance and feasibility of the proposed algorithm are evaluated. The results show that the proposed method can effectively detect and identify the faulty satellites. This method makes full use of the historical clock error information, and provides a simple and effective method for the receiver integrity monitoring.

Transmission delay measurement for converter

This paper presents two various methods of transmission delay measurement for converter. One is group delay measurement method for multi-lever converter by means of high performance vector network analyzer. The other is envelope method used to determine the absolute delay of a converter using fast sampling scope. A scheme and key technologies of group delay measurement are described. A good measurement example is given and measurement results and their uncertainty are analyzed. It can not represent the real delay when modulation signals pass though the converter, Because the group delay curve measurement is performed by a vector network analyzer which needs the input of sweep frequency stimulation signal. Therefore, the characterization of BPSK modulation signal is analyzed. Transmission delay measurement method of BPSK modulation signal which passes though the converter is researched. Finally, the two measurement results obtained using two methods mentioned above are compared.