Global Navigation Satellite Systems Report of a Joint Workshop of the National Academy of Engineering and the Chinese Academy of Engineering (2012) / Chapter Skim
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Monitoring and Assessment of GNSS Open Services--Jiao Wenhai, Ding Qun, Li Jian-wen, Lu Xiaochun, and Feng Laiping
Monitoring and Assessment of GNSS Open Services--Jiao Wenhai, Ding Qun, Li Jian-wen, Lu Xiaochun, and Feng Laiping
Pages 105-118
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From page 105... ...
This paper begins to illuminate the elements and methods for monitoring and assessing GNSS Open Services. Then according to the requirements, the architecture of an international GNSS Monitoring and Assessment System (iGMAS)
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To ensure the safety of the usage and achieve the ultimate goal of interoperability of GNSS Open Services signals, it is essential for us to research the monitoring and assessment of GNSS Open Services. Monitoring and assessment of GNSS Open Services could provide third-party information on performance for a single system and reliable decision-support TABLE 1 Signals of GNSS Open Services Global Navigation Center Frequency Modulation Interoperable Satellite Systems Frequency (MHz)
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Stanford and the DLR have already formed the cooperation mechanism for joint monitoring and assessment of GPS and Galileo signals. ELEMENTS AND METHODS FOR MONITORING AND ASSESSING GNSS OPEN SERVICES The work of monitoring and assessing of GNSS Open Services can be divided into the following layers: constellation state layer, spatial signals layer, navigation information layer, and service performance layer.
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Monitoring and assessment of the constellation state include the following content. Constellation State Constellation state refers to the working state of a single satellite or that of each satellite in GNSS constellation at a particular moment.
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Spatial Signals To assess the quality of GNSS spatial signals, relative assessment experiments should be taken from time domain, frequency domain, modulation domain, and correlation domain. Time Domain Characteristics To obtain baseband signals, those digital intermediate frequency signals col lected by a high-gain antenna should be conducted by quadrature carrier stripping and Doppler removing using a software receiver.
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We can also see its stability by rootmean-square deviation calculated by this analyzer. Correlation Domain Characteristics Correlation domain characteristics of received signals are analyzed mainly from aspects such as the correlation curve, correlation loss, curve symmetry, code delay, and S curve deviation of DLL discriminator, etc., by offline analysis soft ware (Lu and Zhou, 2010)
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And its accuracy will directly affect the PVT calculating precision for various GNSS user equipments, especially for timing equipments. So monitoring GNSS time deviations has more requirements for equipment to get more reliable external accuracy.
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In addition, HMI probability refers to the dangerous probability when the current measured value falls in the range of alarm threshold. Continuity Service continuity refers to the time percentage when a satellite navigation system can continuously meet required service precision in a period of time and specified service area.
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Equipment for monitoring and data collecting mainly includes anti-multipath omnidirectional antennas, multi-beam antennas that can receive all GNSS signals in the visible world (with equivalent diameter of 2.4 m and gain of 28 dB)
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That means comprehensive analysis of GNSS signals and information to assess its service performance. For example, analyzing constellation characteristics such as the number of visible satellites, constellation state, and constellation DOP; analyzing navigation signal properties from time domain, frequency domain, modulation domain, and correlation domain; verifying the validity of navigation information, such as navigation mes sage, accuracy of ionosphere delay correction, accuracy of GNSS time deviations, validity of time deviation parameters between different frequencies; and assessing the precision, availability, integrity, and continuity of GNSS Open Services.
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The basic unit of iGMAS is called a node. Nodes can have five functions of data collecting and monitoring, data transmitting, data storing, data analyzing, and information release.
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116 GLOBAL NAVIGATION SATELLITE SYSTEMS FIGURE 2 Optimal design of 1-overlap coverage stations. Jiaoetal_Fig2.eps bitmap FIGURE 3 Optimal design of 4-overlap coverage stations.
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Obtained results showed that this system could achieve some deeper tasks of GNSS signal-quality monitoring and assessment using many standard measuring instruments, monitoring receivers, high-speed data collecting equipments, and offline analysis software. At present, two key technologies of GNSS signal-quality monitoring and assessment, that is, offline technology for analyzing signal performance based on correlation curve and channel calibrating technology, have strived to make important technological breakthroughs, while the anti-interference technology has also made much progress.
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From page 118... ...
There is sufficient evidence to show that the iGMAS proposed in this paper is technically feasible. For example, the pre liminary exploration of BeiDou in its open services monitoring and assessment, the long-term successful operation of IGS, and achievements in navigation signal monitoring and assessment made by Stanford University and DLR, etc.
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