The Usefulness of Internet-based (NTrip) RTK for Navigation and Intelligent Transportation Systems

Current fast and reliable Internet services provide many advantages for worldwide GNSS users. Development of techniques using the Internet for streaming RTK/DGPS corrections allows mobile users to achieve high-accuracy positioning over both short and long baselines. Applications like GNSS Internet Radio are used for distributing raw GPS data and real-time corrections of GPS observations via RTCM protocols. NTrip (Networked Transport of RTCM via Internet Protocol), developed by the German Federal Agency for Cartography and Geodesy (BKG), is one of these Internet-based applications used for high-accuracy positioning and navigation. It enables streaming of GNSS data for stationary and mobile users by using the latest mobile communication technologies such as GPRS or UMTS in any area covered by a cell-phone network. A particular NTrip-delivered stream can be accessed simultaneously by many clients using laptops, mobile phones or PDAs giving this approach enormous potential for supporting mass usage. Since NTrip became the leading standard protocol for GNSS data streaming, it has become popular in various public and private sectors. In the near future, dual-frequency GNSS receivers will be available at a moderate price, and therefore NTrip/RTK activities will be focused on dissemination of GNSS corrections for applications requiring greater accuracy like intelligent vehicle navigation systems and automatic machine guidance and control systems. One of the topics that has long been a subject of research is improving the safety and efficiency of automobile transportation. Because GNSS/RTK techniques have great potential (enabling positioning to centimeter accuracy), researchers are developing tools to put them to practical use for controling vehicle motion for driver assistance. The combination of high-accuracy positioning information obtained from NTrip/RTK with high-precision INS sensors can support the latest concepts in vehicle-control systems (detection of relative vehicle position on a highway or collision avoidance). In this paper, we focus on evaluating the performance of NTrip/RTK solutions for accurate and precise car navigation. Our approach is based on field experiments and the analysis of both the accuracy and availability of RTK data using mobile wireless transmissions. We investigate the advantages and disadvantages of each component in the navigation system. Car experiments were conducted on test routes under different driving conditions. To demonstrate the versatility of mixedreceiver systems, both NovAtel and Trimble mobile receivers were connected via a CDMA network to an NTrip broadcaster hosted by a Trimble NetR5 reference station receiver. Additional tests were performed using an