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Author

Gang Zhao

Bio: Gang Zhao is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Orbit determination & Satellite. The author has an hindex of 1, co-authored 1 publications receiving 32 citations.

Papers
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Journal ArticleDOI
TL;DR: In order to improve the orbit determination accuracy for BDS, a new orbit determination strategy is proposed, in which the satellite clock measurements from TWSTFT are fixed as known values, and only the orbits of the satellites are solved.

50 citations


Cited by
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Journal ArticleDOI
TL;DR: An integrated indoor positioning system (IPS) combining IMU and UWB through the extended Kalman filter (EKF) and unscented Kalmanfilter (UKF) to improve the robustness and accuracy and two random motion approximation model algorithms are proposed and evaluated in the real environment.
Abstract: The emerging Internet of Things (IoT) applications, such as smart manufacturing and smart home, lead to a huge demand on the provisioning of low-cost and high-accuracy positioning and navigation solutions. Inertial measurement unit (IMU) can provide an accurate inertial navigation solution in a short time but its positioning error increases fast with time due to the cumulative error of accelerometer measurement. On the other hand, ultrawideband (UWB) positioning and navigation accuracy will be affected by the actual environment and may lead to uncertain jumps even under line-of-sight (LOS) conditions. Therefore, it is hard to use a standalone positioning and navigation system to achieve high accuracy in indoor environments. In this article, we propose an integrated indoor positioning system (IPS) combining IMU and UWB through the extended Kalman filter (EKF) and unscented Kalman filter (UKF) to improve the robustness and accuracy. We also discuss the relationship between the geometric distribution of the base stations (BSs) and the dilution of precision (DOP) to reasonably deploy the BSs. The simulation results show that the prior information provided by IMU can significantly suppress the observation error of UWB. It is also shown that the integrated positioning and navigation accuracy of IPS significantly improves that of the least squares (LSs) algorithm, which only depends on UWB measurements. Moreover, the proposed algorithm has high computational efficiency and can realize real-time computation on general embedded devices. In addition, two random motion approximation model algorithms are proposed and evaluated in the real environment. The experimental results show that the two algorithms can achieve certain robustness and continuous tracking ability in the actual IPS.

150 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a derivation approach to the satellite clock offsets and the geometric distances from TDMA dual one-way measurements without a loss of accuracy, where the derived clock offsets are used for time synchronization, and the derived geometry distances are used by the satellite for autonomous orbit determination.
Abstract: Autonomous orbit determination is the ability of navigation satellites to estimate the orbit parameters on-board using inter-satellite link (ISL) measurements This study mainly focuses on data processing of the ISL measurements as a new measurement type and its application on the centralized autonomous orbit determination of the new-generation Beidou navigation satellite system satellites for the first time The ISL measurements are dual one-way measurements that follow a time division multiple access (TDMA) structure The ranging error of the ISL measurements is less than 025 ns This paper proposes a derivation approach to the satellite clock offsets and the geometric distances from TDMA dual one-way measurements without a loss of accuracy The derived clock offsets are used for time synchronization, and the derived geometry distances are used for autonomous orbit determination The clock offsets from the ISL measurements are consistent with the L-band two-way satellite, and time–frequency transfer clock measurements and the detrended residuals vary within 05 ns The centralized autonomous orbit determination is conducted in a batch mode on a ground-capable server for the feasibility study Constant hardware delays are present in the geometric distances and become the largest source of error in the autonomous orbit determination Therefore, the hardware delays are estimated simultaneously with the satellite orbits To avoid uncertainties in the constellation orientation, a ground anchor station that “observes” the satellites with on-board ISL payloads is introduced into the orbit determination The root-mean-square values of orbit determination residuals are within 100 cm, and the standard deviation of the estimated ISL hardware delays is within 02 ns The accuracy of the autonomous orbits is evaluated by analysis of overlap comparison and the satellite laser ranging (SLR) residuals and is compared with the accuracy of the L-band orbits The results indicate that the radial overlap differences between the autonomous orbits are less than 150 cm for the inclined geosynchronous orbit (IGSO) satellites and less than 100 cm for the MEO satellites The SLR residuals are approximately 150 cm for the IGSO satellites and approximately 100 cm for the MEO satellites, representing an improvement over the L-band orbits

77 citations

Journal ArticleDOI
TL;DR: The performance of orbit determination has been increased about 37–76% for different satellites in orbit-only signal-in-space range error (orbit-only SISRE).
Abstract: The BeiDou Navigation Satellite System is expected to provide a global positioning and navigation service by 2020. To achieve this goal, the new-generation navigation satellites that have been launched since March 2015 are equipped with inter-satellite links (ISLs), with the objective of testing new navigation signals and the ISLs themselves. Using these new-generation navigation satellites and several ground facilities in China, a combined orbit determination experiment was carried out during August 2016. The orbit mechanical model, orbit determination method, and accuracy evaluation method used in this experiment are presented here. The accuracy of the combined orbit determination method is evaluated, and the performance-related improvements resulting from the ISLs are analyzed. The performance of orbit determination has been increased about 37–76% for different satellites in orbit-only signal-in-space range error (orbit-only SISRE).

61 citations

Journal ArticleDOI
TL;DR: In this article, the frequency stability, clock prediction accuracy and clock rate variation characteristics of the third generation of Beidou Satellite Navigation System (BDS3) experimental satellites were analyzed using the high-precision clock values obtained by satellite-ground and inter-satellite measurement and communication systems.
Abstract: Various types of onboard atomic clocks such as rubidium, cesium and hydrogen have different frequency accuracies and frequency drift rate characteristics. A passive hydrogen maser (PHM) has the advantage of low-frequency drift over a long period, which is suitable for long-term autonomous satellite time keeping. The third generation of Beidou Satellite Navigation System (BDS3) is equipped with PHMs which have been independently developed by China for their IGSO and MEO experimental satellites. Including Galileo, it is the second global satellite navigation system that uses PHM as a frequency standard for navigation signals. We briefly introduce the PHM design at the Shanghai Astronomical Observatory (SHAO) and detailed performance evaluation of in-orbit PHMs. Using the high-precision clock values obtained by satellite-ground and inter-satellite measurement and communication systems, we analyze the frequency stability, clock prediction accuracy and clock rate variation characteristics of the BDS3 experimental satellites. The results show that the in-orbit PHM frequency stability of the BDS3 is approximately 6 × 10−15 at 1-day intervals, which is better than those of other types of onboard atomic clocks. The BDS3 PHM 2-, 10-h and 7-day clock prediction precision values are 0.26, 0.4 and 2.2 ns, respectively, which are better than those of the BDS3 rubidium clock and most of the GPS Block IIF and Galileo clocks. The BDS3 PHM 15-day clock rate variation is − 1.83 × 10−14 s/s, which indicates an extremely small frequency drift. The 15-day long-term stability results show that the BDS3 PHM in-orbit stability is roughly the same as the ground performance test. The PHM is expected to provide a highly stable time and frequency standard in the autonomous navigation case.

59 citations

Journal ArticleDOI
TL;DR: Time synchronization of new-generation Beidou Navigation Satellite System (BDS) satellites equipped with an ISL payload was conducted using L-band Two-way Satellite Time Frequency Transfer (TWSTFT), and system errors in the ISL measurements were calibrated by comparing the derived clock offsets with the TWSTFT.

52 citations