Performance Analysis of Real-time Gnss Data Distribution over the Internet

In this paper, the performance of real-time GNSS data distribution over a public packet switching network (such as the Internet) is assessed. It is expected that the provision of a suitable data format will allow users to take full advantage of the real-time GNSS data distribution system. Types of GNSS data supported, message sizes, data rates, data precision levels, hardware/software support, and possible future developments are investigated. A comparative review is carried out on commonly employed GNSS data format standards, highlighting the most suitable standard for each evaluation criterion. Version 1.0 of NTRIP is currently the most widely-used protocol for distributing realtime GNSS data over the Internet. Therefore data latency and integrity using NTRIP over the Internet are examined in order to identify their impact on users’ applications, such as the quality of real-time kinematic (RTK) positioning. The test data obtained from the SydNET CORS network were evaluated using both wired and wireless data networks. The results show that the performance of the real-time GNSS data distribution system satisfies the rigorous requirement of the end-user RTK application. The observed latency was less than two seconds during most of the test period and, within this range, there was little variation in the positioning quality. In several extreme samples the authors observed the latency threshold of approximately three seconds or above, for which the positioning algorithm could not provide optimal results (i.e. no fixed carrier phase ambiguity).