Developing carrier-phase differential global positioning system networks with partial derivative algorithms

Centimeter-to-decimeter-level positioning accuracy from the global positioning system (GPS) requires the use of carrier-phase measurements. The system is generally operated in a double differential mode in which a nearby reference station is used to calibrate for errors in the satellite differential measurements. For large-scale applications, a network of multiple differential reference stations is necessary. This paper describes the major errors affecting differential GPS (DGPS) applications, how a network of reference stations can be used to estimate these errors, and one method of implementing carrier-phase network differential GPS (CP-NDGPS) using partial derivative algorithms (PDAs). PDAs can be implemented by a network service provider and are used to estimate spatial and nonspatial signal errors that cannot be measured by a single GPS reference station. For networks having numerous reference stations, a PDA is an efficient method of transmitting information though a data link to the network users. Such a system is also capable of reducing DGPS errors. Of the networks studied during this project, DGPS errors were reduced 30 to 90%.