Back to Articles

C-Nav®: A Globally Corrected DGPS System

September 18, 2001 - Abstract

C & C Technologies, Inc., GPS Services Group has embarked on a program to provide globally corrected GPS (GcGPS) positioning services for the hydrographic and offshore oil field exploration, survey and construction industries.

To achieve this goal, C & C Technologies has partnered with NavCom Technology Inc., a wholly owned subsidiary of John Deere & Co., to provide both a continental implementation of a Wide Area Differential GPS (WADGPS) system which provides a new level of accuracy across continental distances, and also by use of technology from the Jet Propulsion Laboratory to implement a worldwide GPS positioning solution with accuracies of the order of a few decimeters. These systems are designed for dual frequency GPS signal operations and are based on several key technical developments:

* Low-cost, high-quality, dual frequency GPS receivers were developed for use as both reference receivers and mobile receivers;
* Special dual frequency extended smoothing techniques were developed which allow the use of refraction corrected measurements for both the reference and mobile receivers, resulting in removal of ionosphere as an error source, and in significant reduction in errors due to multipath - two of the largest error sources in a WADGPS system;
* A new L-band satellite communication receiver was developed which uses a single, multi-function antenna designed to receive both of the GPS frequencies (L1 and L2) and the Inmarsat L-band communication frequencies (1525-1565MHz);
* Wide area Correction Transform (WCT) correction algorithms were developed which exploit the dualfrequency architecture of the system to generate a single set of corrections uniformly accurate across any continental region resulting in lower bandwidth requirements and more centralized processing; redundant subsystems and monitoring equipment are utilized to provide a high degree of system reliability, availability and service integrity;
* The Real-Time correction algorithms were developed by JPL, and implemented in their Real Time GIPSY software (RTG). RTG exploits the dual-frequency architecture of the system to generate a single set of corrections uniformly accurate across the entire world, which also results in lower bandwidth requirements and centralized processing. Redundant subsystems and monitoring equipment are utilized to provide a high degree of system reliability, availability and service integrity;

The paper reviews errors in GPS measurements, the StarFire system architecture, infrastructure, GPS performance, and user equipment. Surface navigation positioning examples are provided for the current operational system and the future directions that are planned for the systems continued implementation is outlined.

 Click to view the paper in PDF format
 Click to view the handouts in PDF format

Contact: info@cctechnol.com