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  • 1
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2014
    In:  Journal of Navigation Vol. 67, No. 6 ( 2014-11), p. 1109-1119
    In: Journal of Navigation, Cambridge University Press (CUP), Vol. 67, No. 6 ( 2014-11), p. 1109-1119
    Abstract: Fast high precision relative Global Navigation Satellite System (GNSS) positioning is very important to various applications and ambiguity resolution is a key requirement. It has been a continuing challenge to determine and fix GNSS carrier-phase ambiguity, especially for medium- and long-distance baselines. In past research, with dual-frequency band Global Positioning System (GPS), it is almost impossible for fast ambiguity resolution of medium- and long-distance baselines mainly due to the ionospheric and tropospheric effects. With the launch of the BeiDou system, triple-frequency band GNSS observations are available for the first time. This research aims to test the ambiguity resolution performance with BeiDou triple-frequency band observations. In this research, two mathematical models are compared: zenith tropospheric delay as an unknown parameter versus corrected tropospheric delay. The ambiguity resolution performance is investigated in detail with BeiDou observations. Different distance baselines are tested: 45 km, 70 km and 100 km and the performances are investigated with different elevation cut-off angles. Also the performance with BeiDou alone and combined BeiDou and GPS are compared. Experimental results clearly show that with practical observations of triple-frequency bands, ambiguity of medium- or long-distance baselines can be fixed. The results also show that: the performance of ambiguity resolution with an elevation cutoff angle of 20° is much better than that of 15°; The performance with tropospheric effect corrected is slightly better than that with tropospheric effect as an estimated parameter; Dual-frequency band GPS observations will benefit ambiguity resolution of integrated BeiDou and GPS.
    Type of Medium: Online Resource
    ISSN: 0373-4633 , 1469-7785
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2014
    detail.hit.zdb_id: 2015312-0
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  • 2
    In: Advances in Space Research, Elsevier BV, Vol. 52, No. 11 ( 2013-12), p. 1949-1958
    Type of Medium: Online Resource
    ISSN: 0273-1177
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2013
    detail.hit.zdb_id: 2023311-5
    SSG: 16,12
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  • 3
    Online Resource
    Online Resource
    MDPI AG ; 2021
    In:  Remote Sensing Vol. 14, No. 1 ( 2021-12-21), p. 13-
    In: Remote Sensing, MDPI AG, Vol. 14, No. 1 ( 2021-12-21), p. 13-
    Abstract: The network real-time kinematic (RTK) technique uses continuously operating reference stations (CORS) within a geographic area to model the distance dependent errors, allowing users in the area to solve ambiguities. A key step in network RTK is to fix ambiguities between multiple reference stations. When a new satellite rises or when maintenance happens, many unknown parameters are involved in the mathematical model, and traditional methods take some time to estimate the integer ambiguities reliably. The purpose of this study is the single-epoch ambiguity resolution on small-scale CORS network with inter-station distance of around 50 km. A new differencing scheme is developed to explore the full potential of multi-frequency Global Navigation Satellite System (GNSS). In this scheme, a differencing operation is formed between satellites with the closest mapping functions. With the new differencing scheme, tropospheric error can be mostly neglected after the correction, as well as the double-differencing operation. Numerical tests based on two baselines of 49 km and 35 km show that the success rate of ambiguity resolution can reach more than 90%. The single-epoch ambiguity resolution for reference stations brings many benefits to the network RTK service, for example, the instantaneous recovery after maintenance or when a new satellite rises.
    Type of Medium: Online Resource
    ISSN: 2072-4292
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2513863-7
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  • 4
    In: Sensors, MDPI AG, Vol. 18, No. 10 ( 2018-10-19), p. 3546-
    Abstract: The Chinese BeiDou Navigation Satellite System (BDS) has been an important constitute of the Global Navigation Satellite System (GNSS), and the combination of GPS and BDS shows significant improvements when compared with single GPS system for real-time kinematic (RTK) positioning, and improves on availability and fixing rates, especially in the East Asian area. While network RTK might have different types of receivers, both for global and regional networks, different types of receiver may adopt different internal multipath mitigation methods and other techniques that result in different pseudorange characteristics, especially for a multipath. Then, the performance of wide-lane ambiguity resolution (WL AR) is affected. In this study, we first analyze and compare the characteristics of BDS dual-frequency observations for different types of receivers, including Trimble, Leica, Javad, and Septentrio, based on multipath (MP) observables, and then we assess their influence on double-differenced (DD) WL AR. The numerical results show that an obvious low-frequency component exists in MP observables of BDS geostationary earth-orbit satellites (GEOs) for Leica receivers, while its high-frequency measurement noise is very small. For geosynchronous orbit satellites (IGSOs) and medium earth-orbit satellites (MEOs), a slight fluctuation can also be observed that is similar to that of GPS satellites, except for the satellite-included code bias. In Trimble, Javad, and Septentrio receivers, the MP series are dominated by high-frequency measurement noise, both for GEOs and non-GEOs, except for satellite-included code bias. Furthermore, the characteristic of Leica receivers for BDS GEOs seriously affects WL AR and, even for a short baseline, it takes a long time for WL ambiguities to converge, or not converge for many GEO-related DD WL ambiguities, while Trimble, Javad, and Septentrio receivers perform well for short and medium baselines. Then, a time-difference method is proposed to mitigate the multipath of BDS GEOs for a Leica receiver. After applying the proposed method, WL ambiguity fixing rates of GEO-related satellite pairs are improved significantly and the convergence time is shortened from several hours to ten minutes.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    Language: English
    Publisher: MDPI AG
    Publication Date: 2018
    detail.hit.zdb_id: 2052857-7
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  • 5
    In: Sensors, MDPI AG, Vol. 21, No. 1 ( 2021-01-04), p. 292-
    Abstract: Global navigation satellite systems (GNSS) can attain centimeter level positioning accuracy, which is conventionally provided by real-time precise point positioning (PPP) and real-time kinematic (RTK) techniques. Corrections from the data center or the reference stations are required in these techniques to reduce various GNSS errors. The time-relative positioning approach differs from the traditional PPP and RTK in the sense that it does not require external real-time corrections. It computes the differences in positions of a single receiver at different epochs using phase observations. As the code observations are not used in this approach, its performance is not affected by the noise and multipath of code observations. High reliability is another advantage of time-relative precise positioning because the ambiguity resolution is not needed in this approach. Since the data link is not required in the method, this approach has been widely used in remote areas where wireless data link is not available. The main limitation of time-relative positioning is that its accuracy degrades over time between epochs because of the temporal variation of various errors. The application of the approach is usually limited to be within a time interval of less than 20 min. The purpose of this study was to increase the time interval of time-relative positioning and to extend the use of this method to applications with a longer time requirement, especially in remote areas without wireless communication. In this paper, the main error sources of the time-relative method are first analyzed in detail, and then the approach to improve the accumulated time relative positioning method is proposed. The performance of the proposed method is assessed using both static and dynamic observations with a duration as long as several hours. The experiments presented in this paper show that, among the four scenarios tested (i.e., GPS, GPS/Galileo, GPS/Galileo/BeiDou, and GPS/Galileo/BeiDou/GLONASS), GPS/Galileo/BeiDou performed best and GPS/Galileo/BeiDou/GLONASS performed worst. The maximum positioning errors were mostly within 0.5 m in the horizontal direction, even after three hours with GPS/Galileo/BeiDou. It is expected that the method could be used for positioning and navigation for as long as several hours with decimeter level horizontal accuracy in remote areas without wireless communication.
    Type of Medium: Online Resource
    ISSN: 1424-8220
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2052857-7
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  • 6
    Online Resource
    Online Resource
    Elsevier BV ; 2017
    In:  International Journal of Antimicrobial Agents Vol. 49, No. 4 ( 2017-04), p. 427-436
    In: International Journal of Antimicrobial Agents, Elsevier BV, Vol. 49, No. 4 ( 2017-04), p. 427-436
    Type of Medium: Online Resource
    ISSN: 0924-8579
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2017
    detail.hit.zdb_id: 2011829-6
    SSG: 15,3
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  • 7
    Online Resource
    Online Resource
    Elsevier BV ; 2016
    In:  Information Sciences Vol. 363 ( 2016-10), p. 52-71
    In: Information Sciences, Elsevier BV, Vol. 363 ( 2016-10), p. 52-71
    Type of Medium: Online Resource
    ISSN: 0020-0255
    RVK:
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2016
    detail.hit.zdb_id: 218760-7
    detail.hit.zdb_id: 1478990-5
    SSG: 24,1
    SSG: 7,11
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  • 8
    Online Resource
    Online Resource
    Informa UK Limited ; 2019
    In:  Survey Review Vol. 51, No. 369 ( 2019-11-02), p. 525-532
    In: Survey Review, Informa UK Limited, Vol. 51, No. 369 ( 2019-11-02), p. 525-532
    Type of Medium: Online Resource
    ISSN: 0039-6265 , 1752-2706
    Language: English
    Publisher: Informa UK Limited
    Publication Date: 2019
    detail.hit.zdb_id: 2278647-8
    SSG: 19,1
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  • 9
    Online Resource
    Online Resource
    Elsevier BV ; 2018
    In:  Advances in Space Research Vol. 62, No. 9 ( 2018-11), p. 2454-2466
    In: Advances in Space Research, Elsevier BV, Vol. 62, No. 9 ( 2018-11), p. 2454-2466
    Type of Medium: Online Resource
    ISSN: 0273-1177
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2018
    detail.hit.zdb_id: 2023311-5
    SSG: 16,12
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  • 10
    Online Resource
    Online Resource
    Springer Science and Business Media LLC ; 2018
    In:  GPS Solutions Vol. 22, No. 1 ( 2018-1)
    In: GPS Solutions, Springer Science and Business Media LLC, Vol. 22, No. 1 ( 2018-1)
    Type of Medium: Online Resource
    ISSN: 1080-5370 , 1521-1886
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2018
    detail.hit.zdb_id: 2094351-9
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