Self-Assisted First-Fix Method for A-BDS Receivers with Medium- and Long-Term Ephemeris Extension

As a sensor for standalone position and velocity determination, the BeiDou Navigation Satellite System (BDS) receiver is becoming an important part of the intelligent logistics systems under rapid development in China. The applications in the mass market urgently require the BDS receivers to improve the performance of such functions, that is, shorter Time to First Fix (TTFF) and faster navigation signal acquisition speed with Ephemeris Extension (EE) in standalone mode. As a practical way to improve such functions of the Assisted BDS (A-BDS) receivers without the need for specialized hardware support, a Self-Assisted First-Fix (SAFF) method with medium- and long-term EE is proposed in this paper. In this SAFF method, the dynamic Medium- and Long-Term Orbit Prediction (MLTOP) method, which uses the historical broadcast ephemeris data with the optimal configuration of the dynamic models and orbit fitting time interval, is utilized to generate the extended ephemeris. To demonstrate the performance of the MLTOP method used in the SAFF method, a suit of tests, which were based on the real data of broadcast ephemeris and precise ephemeris, were carried out. In terms of the positioning accuracy, the overall performance of the SAFF method is illustrated. Based on the characteristics of the medium- and long-term EE, the simulation tests for the SAFF method were conducted. Results show that, for the SAFF method with medium- and long-term EE of the BeiDou MEO/IGSO satellites, the horizontal positioning accuracy is about 12 meters, and the overall positioning accuracy is about 25 meters. The results also indicate that, for the BeiDou satellites with different orbit types, the optimal configurations of the MLTOP method are different.

Download Full-text

The evaluation of the positioning accuracy of the EGNOS and DGPS systems based on the long-term measurements in the years 2006–2014

Polish Cartographical Review ◽

10.1515/pcr-2015-0006 ◽

2015 ◽

Vol 47 (2) ◽

pp. 99-108 ◽

Cited By ~ 1

Author(s):

Mariusz Specht

Keyword(s):

Global Positioning System ◽

Satellite System ◽

Differential Gps ◽

Positioning Accuracy ◽

Gps Positioning ◽

Global Positioning ◽

Constant Improvement ◽

Long Term Measurement ◽

Measurement Campaigns

Abstract The DGPS (Differential GPS) and EGNOS (European Geostationary Navigation Overlay Service) systems belong to a group of systems supporting the global satellite system GPS (Global Positioning System). These systems have significantly better navigation performance than GPS and, therefore, they are widely used in the maritime, civil and air navigation. The analysis of the positioning accuracy of GPS leads to the conclusion: from year to year the accuracy of the positioning determination increases. The effect of the permanent increasing of the GPS positioning accuracy is the parallel increasing of the positioning accuracies of all the supporting systems. In connection with the constant improvement of the precision characteristics of the above mentioned systems on one hand and the fact, that the users do not possess the current information about the actual status of these characteristics on the other hand, it is reasonable to conduct the periodical research in this area. For that purpose the long-term measurement campaigns were realized in the years 2006-2014; the values of measures, describing the positioning accuracies obtained by both systems, were determined on the basis of those campaigns.

Download Full-text

Performance analysis of SBAS ephemeris corrections and integrity algorithms in China region

Satellite Navigation ◽

10.1186/s43020-021-00045-z ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Biao Jin ◽

Shanshan Chen ◽

Dongjun Li ◽

Yuechen Wang ◽

Elhadi Takka

Keyword(s):

Variance Estimation ◽

Real Data ◽

Satellite System ◽

Minimum Variance ◽

Civil Aviation ◽

Navigation Satellite ◽

Chi Square ◽

Positioning Accuracy ◽

Global Ionosphere Map ◽

Global Navigation Satellite

AbstractSatellite Based Augmentation Systems (SBASs) improve the positioning accuracy and integrity by broadcasting to the civil aviation community the corrections and integrity parameters. A snapshot algorithm based on the minimum variance estimation is investigated in this study to calculate the satellite clock and orbit corrections. A chi-square test is performed on the remaining errors in the corrected ephemeris to guarantee the integrity. User Differential Range Error (UDRE) and scaling matrix contained in Message Type 28 are derived using the covariance information based on the assumption that one of the reference stations failed. A software package is developed and applied in the real data collected at 26 stations. International GNSS (Global Navigation Satellite System) Service (IGS) precise clock and orbit products are taken as the references to assess the accuracy of corrections. For both Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS), the range accuracy of 0.10 m can be achieved with the employment of the derived corrections. No obvious performance difference between GPS and BDS is found. UDREs for all visible satellites are generated with the maximum index of 12 and minimum index of 3. The geometric range differences calculated with IGS precise products and broadcast ephemeris are employed to assess the integrity of UDRE. It is found that the UDRE is able to bound the residuals with 99.9% confidence which meet the requirement of aviation users. With ionospheric delay corrected by Global Ionosphere Map (GIM), the positioning accuracy of 0.98 m with GPS corrections and 0.80 m with multi-constellation augmentation can be achieved which indicates a significant improvement of GPS standalone results.

Download Full-text

Design of rural water systems using dynamic models

Water Science & Technology ◽

10.2166/wst.1999.0209 ◽

1999 ◽

Vol 39 (4) ◽

pp. 221-231

Author(s):

A. H. Lobbrecht

Keyword(s):

Dynamic Models ◽

Water System ◽

Design Procedure ◽

Real Data ◽

Water Systems ◽

Design Methods ◽

Water Quality Criteria ◽

Rural Water ◽

Rural Water Systems ◽

The Way

The properties of main water ways and infrastructure of rural water systems are often determined by very general design methods. These methods are based on standards that use only little information of the actual water system. Most design methods applied in the Netherlands are based on land use and soil texture. Standards have been developed on the basis of generalized properties of water systems. Details of the actual layout of the water system and the way in which that system is controlled, are usually not incorporated. Present-day dynamic simulation programs and the computer power currently available enable more detailed modeling and incorporation of location-specific data into models. Such models can be used to design the water system and can include real data. A model-based design method is introduced, in which the actual situation of the water system is taken into consideration as well as the way in which the water system is controlled. Stochastics concerning the operation and availability of controlling infrastructure are included in the method. Models can be evaluated by including real data. In this way the actual safety of the water system, for example during floods, can be determined. Water-quantity design criteria can be incorporated as well as water-quality criteria. Application of the method makes it possible to design safe water systems in which excess capacities are avoided and in which all requirements of interest are met. The method, called the ‘dynamic design procedure’, can result in considerable savings for water authorities when new systems have to be designed or existing designs have to be reconsidered.

Download Full-text

Single-epoch RTK performance assessment of tightly combined BDS-2 and newly complete BDS-3

Satellite Navigation ◽

10.1186/s43020-021-00038-y ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Wanke Liu ◽

Mingkui Wu ◽

Xiaohong Zhang ◽

Wang Wang ◽

Wei Ke ◽

...

Keyword(s):

Performance Assessment ◽

Success Rate ◽

Ambiguity Resolution ◽

Satellite System ◽

Asia Pacific ◽

Single Frequency ◽

Navigation Satellite ◽

Short Baseline ◽

Positioning Accuracy ◽

Single Epoch

AbstractThe BeiDou global navigation satellite system (BDS-3) constellation deployment has been completed on June 23, 2020, with a full constellation comprising 30 satellites. In this study, we present the performance assessment of single-epoch Real-Time Kinematic (RTK) positioning with tightly combined BeiDou regional navigation satellite system (BDS-2) and BDS-3. We first investigate whether code and phase Differential Inter-System Biases (DISBs) exist between the legacy B1I/B3I signals of BDS-3/BDS-2. It is discovered that the DISBs are in fact about zero for the baselines with the same or different receiver types at their endpoints. These results imply that BDS-3 and BDS-2 are fully interoperable and can be regarded as one constellation without additional DISBs when the legacy B1I/B3I signals are used for precise relative positioning. Then we preliminarily evaluate the single-epoch short baseline RTK performance of tightly combined BDS-2 and the newly completed BDS-3. The performance is evaluated through ambiguity resolution success rate, ambiguity dilution of precision, as well as positioning accuracy in kinematic and static modes using the datasets collected in Wuhan. Experimental results demonstrate that the current BDS-3 only solutions can deliver comparable ambiguity resolution performance and much better positioning accuracy with respect to BDS-2 only solutions. Moreover, the RTK performance is much improved with tightly combined BDS-3/BDS-2, particularly in challenging or harsh conditions. The single-frequency single-epoch tightly combined BDS-3/BDS-2 solution could deliver an ambiguity resolution success rate of 96.9% even with an elevation cut-off angle of 40°, indicating that the tightly combined BDS-3/BDS-2 could achieve superior RTK positioning performance in the Asia–Pacific region. Meanwhile, the three-dimensional (East/North/Up) positioning accuracy of BDS-3 only solution (0.52 cm/0.39 cm/2.14 cm) in the kinematic test is significantly better than that of the BDS-2 only solution (0.85 cm/1.02 cm/3.01 cm) due to the better geometry of the current BDS-3 constellation. The tightly combined BDS-3/BDS-2 solution can provide the positioning accuracy of 0.52 cm, 0.22 cm, and 1.80 cm, respectively.

Download Full-text

Time-Based Corporate-Social-Responsibility Evaluation Model Taking Chinese Listed Forestry Companies as an Example

Sustainability ◽

10.3390/su13147971 ◽

2021 ◽

Vol 13 (14) ◽

pp. 7971

Author(s):

Xinfei Li ◽

Baodong Cheng ◽

Heng Xu

Keyword(s):

Corporate Social Responsibility ◽

Social Responsibility ◽

Evaluation Model ◽

Rapid Development ◽

Entropy Method ◽

Static State ◽

Different Types ◽

Normative Constraints ◽

Corporate Social

With the rapid development of the economy, corporate social responsibility (CSR) is receiving increasing attention from companies themselves, but also increasing attention from society as a whole. How to reasonably evaluate the performance of CSR is a current research hotspot. Existing corporate-social-responsibility evaluation methods mostly focus on the static evaluation of enterprises in the industry, and do not take the time factor into account, which cannot reflect the performance of long-term CSR. On this basis, this article proposes a time-based entropy method that can evaluate long-term changes in CSR. Studies have shown that the completion of CSR in a static state does not necessarily reflect the dynamic and increasing trend of CSR in the long term. Therefore, the assessment of CSR should consider both the static and dynamic aspects of a company. In addition, the research provides the focus of different types of forestry enterprises in fulfilling CSR in the long term, and provides a clearer information path for the standard identification and normative constraints of different types of forestry enterprises CSR.

Download Full-text

The Pice Effects of Competition from Parallel Imports and Therapeutic Alternatives: Using Dynamic Models to Estimate the Causal Effect on the Extensive and Intensive Margins

Review of Industrial Organization ◽

10.1007/s11151-021-09834-x ◽

2021 ◽

Author(s):

David Granlund

Keyword(s):

Dynamic Models ◽

Causal Effect ◽

The Other ◽

Causal Effects ◽

Parallel Imports ◽

Extensive And Intensive Margins ◽

Price Effects ◽

Short And Long Term ◽

Therapeutic Alternatives

AbstractThis paper studies responses to competition with the use of dynamic models that distinguish between short- and long-term price effects. The dynamic models also allow lagged numbers of competitors to become valid and strong instruments for the current numbers, which enables studying the causal effects using flexible specifications. A first parallel trader is found to decrease prices of exchangeable products by 7% in the long term. On the other hand, prices do not respond to the first competitor that sells therapeutic alternatives; but competition from four or more competitors that sell on-patent therapeutic alternatives decreases prices by about 10% in the long term.

Download Full-text

Investigation of GIM-TEC disturbances before M ≥ 6.0 inland earthquakes during 2003–2017

Scientific Reports ◽

10.1038/s41598-020-74995-w ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Fuying Zhu ◽

Yingchun Jiang

Keyword(s):

Rapid Development ◽

Science Research ◽

Satellite System ◽

Statistical Investigation ◽

Electron Content ◽

Total Electron ◽

Spatial And Temporal Distributions ◽

Before And After ◽

Global Ionosphere Map ◽

Global Navigation Satellite

Abstract With the rapid development of the Global Navigation Satellite System (GNSS) and its wide applications to atmospheric science research, the global ionosphere map (GIM) total electron content (TEC) data are extensively used as a potential tool to detect ionospheric disturbances related to seismic activity and they are frequently used to statistically study the relation between the ionosphere and earthquakes (EQs). Indeed, due to the distribution of ground based GPS receivers is very sparse or absent in large areas of ocean, the GIM-TEC data over oceans are results of interpolation between stations and extrapolation in both space and time, and therefore, they are not suitable for studying the marine EQs. In this paper, based on the GIM-TEC data, a statistical investigation of ionospheric TEC variations of 15 days before and after the 276 M ≥ 6.0 inland EQs is undertaken. After eliminating the interference of geomagnetic activities, the spatial and temporal distributions of the ionospheric TEC disturbances before and after the EQs are investigated and compared. There are no particularly distinct features in the time distribution of the ionospheric TEC disturbances before the inland EQs. However, there are some differences in the spatial distribution, and the biggest difference is precisely in the epicenter area. On the other hand, the occurrence rates of ionospheric TEC disturbances within 5 days before the EQs are overall higher than those after EQs, in addition both of them slightly increase with the earthquake magnitude. These results suggest that the anomalous variations of the GIM-TEC before the EQs might be related to the seismic activities.

Download Full-text

A long‐term broadcast ephemeris model for extended operation of GNSS satellites

Navigation ◽

10.1002/navi.404 ◽

2020 ◽

Author(s):

Oliver Montenbruck ◽

Peter Steigenberger ◽

Moritz Aicher

Keyword(s):

Broadcast Ephemeris ◽

Extended Operation

Download Full-text

A Novel Deep Learning Approach for Machinery Prognostics Based on Time Windows

Applied Sciences ◽

10.3390/app9224813 ◽

2019 ◽

Vol 9 (22) ◽

pp. 4813 ◽

Cited By ~ 2

Author(s):

Hanbo Yang ◽

Fei Zhao ◽

Gedong Jiang ◽

Zheng Sun ◽

Xuesong Mei

Keyword(s):

Time Windows ◽

Remaining Useful Life ◽

Sensor Data ◽

Time Interval ◽

Kernel Module ◽

Initial Stage ◽

Research Task ◽

Consecutive Time ◽

Useful Life

Remaining useful life (RUL) prediction is a challenging research task in prognostics and receives extensive attention from academia to industry. This paper proposes a novel deep convolutional neural network (CNN) for RUL prediction. Unlike health indicator-based methods which require the long-term tracking of sensor data from the initial stage, the proposed network aims to utilize data from consecutive time samples at any time interval for RUL prediction. Additionally, a new kernel module for prognostics is designed where the kernels are selected automatically, which can further enhance the feature extraction ability of the network. The effectiveness of the proposed network is validated using the C-MAPSS dataset for aircraft engines provided by NASA. Compared with the state-of-the-art results on the same dataset, the prediction results demonstrate the superiority of the proposed network.

Download Full-text

BeiDou Satellite Unhealthy States and the Impact on System Performance

Sensors ◽

10.3390/s18124196 ◽

2018 ◽

Vol 18 (12) ◽

pp. 4196 ◽

Cited By ~ 1

Author(s):

Caibo Hu ◽

Chuang Shi ◽

Jinping Chen ◽

Yidong Lou ◽

Fei Wang

Keyword(s):

System Performance ◽

Satellite Orbit ◽

Service Area ◽

The Other ◽

Classification Method ◽

Positioning Accuracy ◽

General Classification ◽

Broadcast Ephemeris ◽

Beidou System ◽

The Impact

The BeiDou system satellites may be unhealthy due to many reasons, affecting system performance in different ways. Therefore, it is important to analyze the causes and characteristics of the satellites’ unhealthy states. In this study, these states are classified into five types based on the broadcast ephemeris. Three criteria are presented, based on which a general classification method is proposed. Data from July 2017 to June 2018 are analyzed to validate the method, from which we know that the average unhealthy duration due to satellite maneuvers is much longer than the duration of unhealthy states related to satellite orbit or clock anomalies, and the other unhealthy states may be caused by inbound or outbound satellites. Statistics show that most of the time, the number of unhealthy satellites is no more than two and the average positioning accuracy in the service area will decrease by no more than 0.75 and 1.2 meters when one or two BDS satellites are unhealthy, respectively.

Download Full-text