scholarly journals Characteristics and Performance Evaluation of QZSS Onboard Satellite Clocks

Sensors ◽  
2019 ◽  
Vol 19 (23) ◽  
pp. 5147 ◽  
Author(s):  
Wei Xie ◽  
Guanwen Huang ◽  
Bobin Cui ◽  
Pingli Li ◽  
Yu Cao ◽  
...  
Keyword(s):  
Satellite System ◽  
Frequency Drift ◽  
Asia Pacific ◽  
Asia Pacific Region ◽  
Satellite Clock ◽  
Short Term ◽  
Performance Variation ◽  
And Performance ◽  
Clock Prediction ◽  
Clock Offset

In the Global Navigation Satellite System (GNSS) community, the Quasi-Zenith Satellite System (QZSS) is an augmentation system for users in the Asia-Pacific region. However, the characteristics and performance of four QZSS satellite clocks in a long-term scale are unknown at present. However, it is crucial to the positioning, navigation and timing (PNT) services of users, especially in Asia-Pacific region. In this study, the characteristics and performance variation of four QZSS satellite clocks, which including the phase, frequency, frequency drift, fitting residuals, frequency accuracy, periodic terms, frequency stability and short-term clock prediction, are revealed in detail for the first time based on the precise satellite clock offset products of nearly 1000 days. The important contributions are as follows: (1) It is detected that the times of phase and frequency jump are 2.25 and 1.5 for every QZSS satellite clock in one year. The magnitude of the frequency drift is about 10−18. The periodic oscillation of frequency drift of J01 and J02 satellite clocks is found. The clock offset model precision of QZSS is 0.33 ns. (2) The two main periods of QZSS satellite clock are 24 and 12 hours, which is the influence of the satellite orbit; (3) The frequency stability of 100, 1000 and 10,000 s are 1.98 × 10−13, 6.59 × 10−14 and 5.39 × 10−14 for QZSS satellite clock, respectively. The visible “bump” is found at about 400 s for J02 and J03 satellite clocks. The short-term clock prediction accuracy of is 0.12 ns. This study provides a reference for the state monitoring and performance variation of the QZSS satellite clock.

scholarly journals Precise Point Positioning Using the Regional BeiDou Navigation Satellite Constellation

2014 ◽  
Vol 67 (3) ◽  
pp. 523-537 ◽  
Author(s):  
Aigong Xu ◽  
Zongqiu Xu ◽  
Xinchao Xu ◽  
Huizhong Zhu ◽  
Xin Sui ◽  
...  
Keyword(s):  
Real Time ◽  
Precise Point Positioning ◽  
Satellite System ◽  
Convergence Time ◽  
Asia Pacific ◽  
Satellite Orbits ◽  
Navigation Satellite ◽  
Asia Pacific Region ◽  
Point Positioning

On 27 December 2012 it was announced officially that the Chinese Navigation Satellite System BeiDou (BDS) was able to provide operational services over the Asia-Pacific region. The quality of BDS observations was confirmed as comparable with those of GPS, and relative positioning in static and kinematic modes were also demonstrated to be very promising. As Precise Point Positioning (PPP) technology is widely recognized as a method of precise positioning service, especially in real-time, in this contribution we concentrate on the PPP performance using BDS data only. BDS PPP in static, kinematic and simulated real-time kinematic mode is carried out for a regional network with six stations equipped with GPS- and BDS-capable receivers, using precise satellite orbits and clocks estimated from a global BDS tracking network. To validate the derived positions and trajectories, they are compared to the daily PPP solution using GPS data. The assessment confirms that the performance of BDS PPP is very comparable with GPS in terms of both convergence time and accuracy.

Another Look at Short-Term Efficiency and Persistence: Evidence from the Asia Pacific Region

2021 ◽  
Author(s):  
Javier Vidal-García ◽  
Marta Vidal
Keyword(s):  
Asia Pacific ◽  
Pacific Region ◽  
Asia Pacific Region ◽  
Short Term

scholarly journals A New BDS-2 Satellite Clock Bias Prediction Algorithm with an Improved Exponential Smoothing Method

2020 ◽  
Vol 10 (21) ◽  
pp. 7456
Author(s):  
Ye Yu ◽  
Mo Huang ◽  
Changyuan Wang ◽  
Rui Hu ◽  
Tao Duan
Keyword(s):  
Forecast Accuracy ◽  
Satellite System ◽  
Exponential Smoothing ◽  
Normal Operation ◽  
Prediction Algorithm ◽  
Satellite Clock ◽  
Short Term ◽  
Error Learning ◽  
Satellite Clock Bias ◽  
New Algorithms

High-accuracy and dependable prediction of the bias of space-borne atomic clocks is extremely crucial for the normal operation of the satellites in the case of interrupted communication. Currently, the clock bias prediction for the Chinese BeiDou Navigation Satellite System (BDS) remains still a huge challenge. To develop a high-precision approach for forecasting satellite clock bias (SCB) in allusion to analyze the shortcomings of the exponential smoothing (ES) model, a modified ES model is proposed hereof, especially for BDS-2 satellites. Firstly, the basic ES models and their prediction mechanism are introduced. As the smoothing coefficient is difficult to determine, this leads to increasing fitting errors and poor forecast results. This issue is addressed by introducing a dynamic “thick near thin far (TNTF)” principle based on the sliding windows (SW) to optimize the best smoothing coefficient. Furthermore, to enhance the short-term forecasted accuracy of the ES model, the gray model (GM) is adopted to learn the fitting residuals of the ES model and combine the forecasted results of the ES model with the predicted results of the GM model from error learning (ES + GM). Compared with the single ES models, the experimental results show that the short-term forecast based on the ES + GM models is improved remarkably, especially for the combination of the three ES model and GM model (ES3 + GM). To further improve the medium-term prediction accuracy of the ES model, the new algorithms in ES with GM error learning based on the SW (ES + GM + SW) are presented. Through examples analysis, compared with the single ES2 (ES3) model, results indicate that (1) the average forecast precision of the new algorithms ES2 + GM + SW (ES3 + GM + SW) can be dramatically enhanced by 49.10% (56.40%) from 5.56 ns (6.77 ns) to 2.83 ns (2.95 ns); (2) the average forecast stability of the new algorithms ES2 + GM + SW (ES3 + GM + SW) is also observably boosted by 53.40% (49.60%) from 8.99 ns (16.13 ns) to 4.19 ns (8.13 ns). These new coupling forecast models proposed in this contribution are more effective in clock bias prediction both forecast accuracy and forecast stability.

scholarly journals Precision analysis for Compass satellite clock prediction based on a universal clock offset model

2015 ◽  
Vol 45 (7) ◽  
pp. 079502-079502 ◽  
Author(s):  
QunYang WANG ◽  
JiDong CAO ◽  
XiaoPing LIU ◽  
GuiFen TANG ◽  
XueQing XU
Keyword(s):  
Satellite Clock ◽  
Precision Analysis ◽  
Clock Prediction ◽  
Clock Offset

scholarly journals Corporate governance in the airline industry - evidence from the Asia-Pacific region

2016 ◽  
Vol 13 (2) ◽  
pp. 329-335
Author(s):  
Frank Scrimgeour ◽  
Rikkie Stevenson ◽  
Geeta Duppati
Keyword(s):  
Corporate Governance ◽  
Airline Industry ◽  
Poor Performance ◽  
Asia Pacific ◽  
Pacific Region ◽  
Asia Pacific Region ◽  
The Business Cycle ◽  
Four Levels ◽  
And Performance ◽  
Airline Performance

Globally airline performance has been variable with poor performance undermining the confidence of travelers, investors, Governments and other stakeholders. Airline corporate governance is a key determinant of airline performance. However, the relationships between governance and performance is complicated by the diversity of governance arrangements surrounding airlines. This study utilizes the four level model of Scrimgeour and Duppati (2014) to analyze the strengths and weaknesses of airline governance in the Asia Pacific region. Data from firm performance and firm behavior are analyzed for a 14-year period given governance and business choices occur at all stages of the business cycle and governance decisions have impact over multiple periods. Improving trust in the airline industry requires attention to all four levels of governance in a manner consistent with national and international business contexts

scholarly journals Single-Epoch Navigation Performance with Real BDS Triple-Frequency Pseudorange and EWL/WL Observations

2016 ◽  
Vol 69 (6) ◽  
pp. 1293-1309 ◽  
Author(s):  
Wang Gao ◽  
Chengfa Gao ◽  
Shuguo Pan
Keyword(s):  
Satellite System ◽  
Asia Pacific ◽  
Free Form ◽  
Asia Pacific Region ◽  
Frequency Signal ◽  
Beidou Navigation Satellite System ◽  
Triple Frequency ◽  
Wide Lane ◽  
Single Epoch ◽  
Navigation Accuracy

Triple-frequency signals of China's BeiDou navigation satellite system (BDS) are now accessible in the Asia-Pacific region. It is well understood that the third frequency signal will improve the navigation performance. Some literatures have described several navigation methods by using triple-frequency signals, and evaluated the performance. However the experiments were mostly implemented on simulated or semi-simulated observations. In this paper we investigate the navigation performance using real BDS triple-frequency observations. Apart from the pseudorange observations, carrier observations are also used, since the extra-wide-lane and wide-lane ambiguities can be reliably resolved with a single epoch. Several single-epoch navigation methods using BDS triple-frequency observations are described and the corresponding navigation accuracy and reliability are assessed. Results show that P3 has the highest accuracy among the three pseudorange observations. For carriers, the wide-lane and extra-wide-lane observations can be used to obtain much higher navigation precision compared with pseudorange observations. Besides, the two ambiguity-fixed extra-wide-lane and wide-lane observations can also be combined to ionosphere-free form, which can still obtain sub-decimetre and decimetre navigation accuracy in horizontal and vertical directions respectively.

scholarly journals An Improved Multi-Satellite Method for Evaluating Real-Time BDS Satellite Clock Offset Products

2020 ◽  
Vol 12 (21) ◽  
pp. 3638
Author(s):  
Zhimin Yuan ◽  
Changsheng Cai ◽  
Lin Pan ◽  
Cuilin Kuang
Keyword(s):  
Real Time ◽  
Product Evaluation ◽  
Satellite System ◽  
Earth Orbit ◽  
Satellite Clock ◽  
International Gnss Service ◽  
Accuracy Difference ◽  
Beidou Satellites ◽  
Biased Estimates ◽  
Clock Offset

Two methods are widely used for evaluating the precision of satellite clock products, namely the single-satellite method (SSM) and the multi-satellite method (MSM). In the satellite clock product evaluation, an important issue is how to eliminate the timescale difference. The SSM selects a reference satellite to eliminate the timescale difference by between-satellite differencing, but its evaluation results are susceptible to the gross errors in the referenced satellite clock offsets. In the MSM, the timescale difference is first estimated and then removed. Unlike the GPS, the BeiDou Navigation Satellite System (BDS) consists of three types of satellites, namely geosynchronous earth orbit (GEO), inclined geosynchronous orbit (IGSO), and medium earth orbit (MEO) satellites. The three types of satellites have uneven orbital accuracy. In the generation of satellite clock products, the orbital errors are partly assimilated into the clock offsets. If neglecting the orbital accuracy difference of the three types of BeiDou satellites, the MSM will obtain biased estimates of the timescale difference and finally affect the clock product evaluation. In this study, an improved multi-satellite method (IMSM) is proposed for evaluating the real-time BDS clock products by removing the assimilated orbital errors of the three types of BDS satellites when estimating the timescale difference. Three real-time BDS clock products disseminated by three different International GNSS Service (IGS) analysis centers, namely CLK16, CLK20, and CLK93, over a period of two months are used to validate this method. The results indicate that the assimilated orbital errors have a significant impact on the estimation of the timescale difference. Subsequently, the IMSM is compared with the SSM in which the referenced satellite is rigorously chosen, and their RMS difference is only 0.08 ns, which suggests that the evaluation results obtained by the IMSM are accurate. Compared with the traditional MSM, the IMSM improves the RMS by 0.16, 0.11, and 0.07 ns for CLK16, CLK20, and CLK93, respectively. Finally, three real-time BDS clock products are evaluated using the proposed method, and results reveal a significant precision difference among them.

scholarly journals Consensus Statement on the Use of Bone Turnover Markers for Short-Term Monitoring of Osteoporosis Treatment in the Asia-Pacific Region

2019 ◽  
Author(s):  
Chih-Hsing Wu ◽  
Yin-Fan Chang ◽  
Chung-Hwan Chen ◽  
E. Michael Lewiecki ◽  
Christian Wüster ◽  
...  
Keyword(s):  
Bone Turnover ◽  
Bone Turnover Markers ◽  
Consensus Statement ◽  
Osteoporosis Treatment ◽  
Asia Pacific ◽  
Pacific Region ◽  
Asia Pacific Region ◽  
Short Term ◽  
Turnover Markers ◽  
Term Monitoring

scholarly journals A Novel Long Short-Term Memory Predicted Algorithm for BDS Short-Term Satellite Clock Offsets

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Tailai Wen ◽  
Gang Ou ◽  
Xiaomei Tang ◽  
Pengyu Zhang ◽  
Pengcheng Wang
Keyword(s):  
Short Term Memory ◽  
Moving Average ◽  
Arima Model ◽  
Communication Link ◽  
Satellite Clock ◽  
Short Term ◽  
Term Memory ◽  
Long Short Term Memory ◽  
Galileo Satellite ◽  
Clock Offset

The satellite clocks carried on the BeiDou navigation System (BDS) are a self-manufactured hydrogen clock and improved rubidium clock, and their on-orbit performance and stabilities are not as efficient as GPS and Galileo satellite clocks caused of the orbital diversity of the BDS and the complexity of the space operating environment. Therefore, the existing BDS clock product cannot guarantee the high accuracy demand for precise point positioning in real-time scenes while the communication link is interrupted. To deal with this problem, we proposed a deep learning-based approach for BDS short-term satellite clock offset modeling which utilizes the superiority of Long Short-Term Memory (LSTM) derived from Recurrent Neural Networks (RNN) in time series modeling, and we call it QPLSTM. The ultrarapid predicted clock products provided by IGS (IGU-P) and four widely used prediction methods (the linear polynomial, quadratic polynomial, gray system (GM (1,1)), and Autoregressive Integrated Moving Average (ARIMA) model) are selected to compare with the QPLSTM. The results show that the prediction residual is lower than clock products of IGU-P during 6-hour forecasting and the QPLSM shows a greater performance than the mentioned four models. The average prediction accuracy has improved by approximately 79.6, 69.2, 80.4, and 77.1% and 68.3, 52.7, 66.5, and 69.8% during a 30 min and 1-hour forecasting. Thus, the QPLSTM can be considered as a new approach to acquire high-precision satellite clock offset prediction.

scholarly journals Elements and Performance Indicators of Integrated Healthcare Programmes on Chronic Diseases in Six Countries in the Asia-Pacific Region: A Scoping Review

2021 ◽  
Vol 21 (1) ◽  
pp. 3
Author(s):  
Kamilla Anna Pinter ◽  
Hanwen Zhang ◽  
Chang Liu ◽  
Bach Tran ◽  
Maulik Chokshi ◽  
...  
Keyword(s):  
Chronic Diseases ◽  
Scoping Review ◽  
Performance Indicators ◽  
Asia Pacific ◽  
Pacific Region ◽  
Asia Pacific Region ◽  
Integrated Healthcare ◽  
And Performance
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