. "Monitoring and Assessment of GNSS Open Services--Jiao Wenhai, Ding Qun, Li Jian-wen, Lu Xiaochun, and Feng Laiping." Global Navigation Satellite Systems: Report of a Joint Workshop of the National Academy of Engineering and the Chinese Academy of Engineering. Washington, DC: The National Academies Press, 2012.
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Global Navigation Satellite Systems
Stepping into the 21st century, because of the successful launches of the BeiDou and the Galileo satellites, the GNSS is changing from the bipolar competition situation between GPS and GLONASS to a new situation of competition and cooperation among four systems. Obviously, the compatibility and interoperability of navigation signals have already been the main features during the period of GNSS development. Against this background, open signals, with the function of interoperability, are expected to bring GNSS services of higher quality and better performance to GNSS users, especially in such places as urban canyons and mountainous areas where visual airspace of satellite is limited. Open signals can bring a significant increase in the number of visible navigation satellites, improving the reliability and availability of navigation and positioning services (Yang, 2010). So far, the main existing and being designed signals of GNSS Open Services are as shown in Table 1.
At present, the four satellite navigation systems have issued or are planning to issue their own specifications on open service performance. However, because of the diversity in their respective conditions and knowledge, there may be large differences in those specifications, either in form or in performance. As a result, users will get confused when they are using and it will be inconvenient for them to use. In addition, there are no performance specifications on GNSS open service signals. 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 information for users when they are using its service, to minimize possible adverse effects and to improve quality of service. On the other hand, based on compatibility and interoperability, the GNSS system can bring not only a great leap in improved performance and quality of navigation service, but also large degradation due to signal interference problems between systems. Carrying on the monitoring and assessment of GNSS Open Services can help to deal with these problems. It can enhance the reliability of open service on one hand, and, on the other hand, from the standpoint of system monitoring and assessment on the comprehensive properties of multi-system open services, could improve compatibility and interoperability performance between each system, providing decision-support information for maintenance and management of the multi-system.