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GNSS Performance Monitoring GNSS PERFORMANCE Monitoring SiS AVAILABILITY PARAMETER DEfiNITION AND EVALUATION M. DE Groot Master THESIS Geoscience & Remote Sensing GNSS Performance Monitoring SiS availability parameter definition and evaluation by M. de Groot to obtain the degree of Master of Science at the Delft University of Technology, to be defended publicly on Wednesday September 27, 2017 Student number: 4089456 Project duration: May 1, 2016 – July 1, 2017 Thesis committee: Prof. dr. ir. R. F.Hanssen, TU Delft Graduation supervisor Dr. ir. H. van der Marel, TU Delft Daily supervisor Ir. A. van den Berg, CGI Daily supervisor Ir. W. J. F. Simons, TU Delft Co-reader An electronic version of this thesis is available at http://repository.tudelft.nl/. Preface This thesis forms the end of my period at the TU Delft. I enjoyed studying the bachelor of civil engineering and the master track of geoscience & remote sensing. The track contained several interesting topics in which GNSS had my attention from the start. Many people make use of GNSS on a daily basis without actually knowing how it works. Position, velocity and timing results are obtained using satellites at 20000 kilometres above the Earth. Good performance is usually taken for granted, but performance monitoring is essential for any system. Using a monitoring tool with substantiated parameters can give the system more trust and can lead to new insights. I would like to thank my daily supervisors, Axel van den Berg and Hans van der Marel, for introducing me to this topic. Both were really helpful with all their knowledge, experience and feedback. I would also like to thank the people of the space department of CGI the Netherlands with their input and for giving me a place to work on the project. I would like to thank Ramon Hanssen for being my graduation supervisor and Wim Simons for being the co-reader. M. de Groot Delft, July 2017 iii Abstract Nowadays, many people and organizations depend on Global Navigation Satellite Systems (GNSS) for nav- igation, positioning, timing and scientific applications. Monitoring of individual GNSS, such as the Amer- ican Global Positioning System (GPS) and the European Galileo system, is important to ensure the quality of GNSS measurements. The availability of the signals-in-space (SiS) is an essential part of the monitoring of GNSS, but it is not clear how availability is defined and standards for monitoring are lacking. The main research question for this thesis is therefore: Which are the key performance indicators related to availability that unambiguously describe sensor station and system performance in time, how can these be computed in an operational manner, and how can they be presented in a condensed form to the stakeholders? This includes a clear objective of defining unambiguous performance parameters for sensor station and system, and address the considerations related to the definition. A prototype software tool is created to study the algorithms and compute the key performance indicators. Availability is in the basis a binary operation: a signal is available or unavailable. When this is applied on daily measurements, daily statistics can be computed by dividing the amount of available observations by the amount of expected observations. A signal is considered available if the code, carrier phase and C/N0 measurements are present, and meet certain standards, which are discussed in the thesis. A signal is said to be expected if the satellite is expected to transmit that signal, the receiver is configured to receive that signal, and the signal is not blocked by objects in the signal’s path to the sensor station. For this it’s needed to define and compute an elevation mask for each station. The sensor station and system performance parameters are computed from a network of sensor stations, using observation and navigation files in the Receiver Independent Exchange format (RINEX) as input. The sensor station and system performance are each described by their own set of parameters. Four key per- formance indicators are defined for the sensor station performance. The Daily Station Availability describes the part of the day that the station is operational, the Daily Station Total Availability gives the percentage of available versus the expected observations, and the Effective Mean Elevation quantifies the elevation mask and thus the location of the sensor station. These three parameters are summarized into the Overall Station Quality parameter, which gives and overall performance class to the sensor station. For the system performance monitoring a satellite is considered available if all signals are received by a sen- sor station of the monitoring network and the health status is healthy. The satellite is considered unavailable if the signals are received by none of the monitoring stations, while expected by atleast two stations, or the health status is unhealthy. Two key performance indicators are defined for the system performance. The Daily GNSS Availability gives the percentage of the day that the satellite was available and the Daily Available number of Satellites tells how many satellites were available during the day. The parameters are computed for a period of 100 days. Results are presented using color codes and by show- ing only detailed information in case of anomalies or specific investigations. The results showed that no sensor station performs perfectly and some worse than others. During the testing phase of Galileo, several events took place. In the initial operational phase, which occupied 17 days of the test period, only a single Galileo event took place. The proposed key performance indicators showed to be very useful at pointing out good performances or anomalies. While SiS availability gives much insight in the performance, a monitoring tool can be improved when combined with other performance aspects. v Contents 1 Introduction 1 1.1 Motivation............................................1 1.2 Research Question........................................1 1.3 Objective.............................................3 1.4 Scope...............................................3 1.5 Outline..............................................3 2 LiterATURE REVIEW 5 2.1 Background on GNSS.......................................5 2.1.1 History...........................................5 2.1.2 Global Navigation Satellite Systems............................6 2.1.3 PVT algorithm.......................................9 2.1.4 Error sources........................................ 11 2.1.5 Position accuracy..................................... 14 2.2 GNSS performance monitoring.................................. 15 2.2.1 Sensor station performance................................ 15 2.2.2 System performance.................................... 17 2.2.3 Examples of GNSS performance monitoring groups.................... 17 2.2.4 Examples of GNSS performance monitoring software................... 20 2.3 Summary............................................. 23 3 AVAILABILITY 25 3.1 Stakeholders........................................... 25 3.2 Availability definition....................................... 26 3.2.1 Availability strategy.................................... 26 3.2.2 Main availability equation................................. 27 3.2.3 Availability monitoring................................... 27 3.3 Input data............................................. 28 3.3.1 RINEX observation files.................................. 28 3.3.2 RINEX navigation files................................... 30 3.4 Individual signal availability................................... 31 3.4.1 Code measurements.................................... 31 3.4.2 Carrier phase measurements................................ 33 3.4.3 Carrier-to-noise ratio measurements........................... 33 3.5 Expected signal definition..................................... 38 3.5.1 Sensor station and satellite configuration......................... 38 3.5.2 Mapping to elevation bins................................. 39 3.5.3 Elevation mask....................................... 40 3.5.4 Sensor station is receiving................................. 47 3.5.5 Satellite is transmitting................................... 47 3.6 Summary............................................. 48 4 Sensor STATION PERFORMANCE PARAMETERS 49 4.1 Daily Station Availability..................................... 49 4.2 Daily Station Total Availability.................................. 51 4.3 Effective Mean Elevation..................................... 54 4.4 Overall Station Quality...................................... 58 4.5 Alternative parameters...................................... 61 4.6 Summary............................................. 62 vii viii Contents 5 System PERFORMANCE PARAMETERS 63 5.1 Satellite availability........................................ 64 5.2 Monitoring network........................................ 65 5.3 Daily GNSS Availability...................................... 67 5.4 Daily Available number of Satellites................................ 69 5.5 Alternative parameters...................................... 70 5.6 Summary............................................. 71 6 Results 73 6.1 Presenting information...................................... 73 6.2 Sensor station results....................................... 73 6.2.1 Daily Station Availability.................................. 73 6.2.2 Daily Station Total Availability............................... 78 6.2.3 Effective Mean Elevation.................................
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