Differential GPS integrity monitor

Government provided DGPS service is currently planned for all coastal waters of the US. The Harbor/Harbor Approach (HHA) requirement from the Federal Radionavigation Plan will be met by the Coast Guard´s DGPS service. Commercial shipping will rely heavily on the DGPS service for maneuvering in harbors and constrained waterways. Therefore, the Coast Guard has developed a requirement for real time integrity monitoring of the DGPS service. In order to fulfil this requirement, the United States Coast Guard R&D Center has been conducting research regarding integrity monitoring of Differential GPS (DGPS). The research is currently focused on the development of a prototype integrity monitoring system. This paper describes this DGPS integrity monitor and the specific DGPS quantities monitored. These include the radiobeacon signal, the quality of the RTCM SC-104 message stream and the accuracy of the positioning performance using the DGPS corrections. Algorithms are described for all quantities measured. Details of the software design and implementation, including the use of standard RTCM SC-104 and NMEA-0183 data interfaces are included