Paul Boughton
C-Nav’s international Satellite Based Augmentation System (SBAS) is a Precise Point Positioning capability with worldwide reach. The latest upgrades have improved real-time positioning accuracy at the decimetre level and include additional layers of security, quality control, resilience and assured access to provide a unique solution to the industry’s need for self-regulating (autonomous) independent solutions.
Unlike traditional DGPS, where accuracy and precision is a function of reference station geometry, C-Nav corrects at the source of the errors: the GPS satellites’ clock and orbital parameters. Through the advanced proprietary development of NASA’s Jet Propulsion Laboratory’s Real-Time GIPSY (RTG) suite, the result is a single set of globally valid corrections for all GNSS satellites. The correction stream is broadcast to the user community through six high-power L-Band communication satellites.
The C-Nav ground segment comprises of a dense network of ground tracking stations around the world. Typically, up to seven stations will each track the same GPS satellites. The C-Nav tracking stations have dual frequency receivers operating through a common IGS-style choke ring antenna; these stations are further augmented with tracking stations of the NASA/JPL network. The SBAS system is controlled through two independent, geographically separated, Processing Centres. Each centre receives the full complement of reference station data with a latency of less than two seconds. With hot primary and secondary production layers at each Processing Centre, four sets of orbit and clock correction values are generated.
The six geostationary high-power communication satellites provide global, L-Band distribution between about 75° north and south latitudes. The satellite constellation is uplinked through six land earth stations, each equipped with primary and secondary layers of equipment. Each layer receives the corrections from both Processing Centres. The satellite constellation is configured as C-Nav NET-1 and C-Nav NET-2 with the satellites’ monitored by the Processing Centres to ensure service continuity and data quality.
In the user domain, Kalman filtering solves for satellite and receiver channel biases and a least squares solution calculates the position based on phase-smoothed refraction and bias-corrected code observables. The Precise Point Positioning (state-space) technique is so refined as to include corrections for distorting Earth-tides and ocean loading (and other geodetic effects) through an algorithm accessing the proprietary Sinko Earth-tide model.
It was to meet the demands of C-Nav’s government and private sector customers that the real-time positioning of the C-Nav SBAS system was set at typically 10cm level (in term of ITRF) with a vertical accuracy of 15cm. This level of precision enables the widest range of GNSS users to benefit. The user community includes the maritime and on-shore sector, the oil and gas industry, RTK augmentation, airborne platform and autonomous robotic vehicle operators and naval charting.
However, it was to address the growing need for autonomous assured independence in solution integrity, quality assurance and confidence, that the latest upgrades to C-Nav were instigated. The C-Nav's service is based on a worldwide over-determinate tracking network and enjoys the exclusive benefit of generating and applying the satellite orbit and clock correctors in a tightly modelled integrated RTG solution. The vulnerability of system failure is mitigated by redundancy through route diversity and system backups. This robust structure provides redundancy at each layer.
* The tracking network has a 6:1 excess ratio; stations can be removed from the solution without affecting system performance.
* The two Processing Centres each determine two independent RTG solutions which are compared for veracity before broadcast.
* The communication satellite NET-1 and NET-2 configuration provides independent communication delivery between the hubs and user community.
* All C-Nav tracking stations have dual racks of equipment. In the event that a performance flag identifies an anomaly, a rack can be excluded without impacting the solution.
* Each C-Nav tracking station has multiple communication links to the Processing Centres. In the event of a communications failure, an alternate method of communication is automatically put on line.
* Each system user may employ multiple and/or differing C-Nav receivers.
* The C-Nav GPS receivers can be configured to operate with either NET-1 or NET-2 correction signals or with both Networks for maximum reliability and technical redundancy.
* The NET-1 and NET-2 configuration provides for independent delivery over each ocean region
Customers’ have a choice of receivers. The 26-channel Nav2050 dual-frequency receiver with integrated L-Band receiver and tri-band antenna delivering typically 10cm horizontal and 15cm vertical accuracy. The C-Nav1010 L1 receiver, in common with all C-Nav receivers, integrates C-Nav correctors as well as WAAS / EGNOS data and provides sub-metre accuracy and is designed to maximise precision and stability in noisy and hostile environments. The C-Nav2000 is a ‘smart-antenna’ design with an integrated dual-frequency GPS, L-Band demodulator, and a tri-band antenna in one package.
Enquiry details
Edwin Danson FRICS FInstCES is a Business Consultant with C&C Technologies Inc, Lafayette, USA. www:cctechnol.com
Unlike traditional DGPS, where accuracy and precision is a function of reference station geometry, C-Nav corrects at the source of the errors: the GPS satellites’ clock and orbital parameters. Through the advanced proprietary development of NASA’s Jet Propulsion Laboratory’s Real-Time GIPSY (RTG) suite, the result is a single set of globally valid corrections for all GNSS satellites. The correction stream is broadcast to the user community through six high-power L-Band communication satellites.
The C-Nav ground segment comprises of a dense network of ground tracking stations around the world. Typically, up to seven stations will each track the same GPS satellites. The C-Nav tracking stations have dual frequency receivers operating through a common IGS-style choke ring antenna; these stations are further augmented with tracking stations of the NASA/JPL network. The SBAS system is controlled through two independent, geographically separated, Processing Centres. Each centre receives the full complement of reference station data with a latency of less than two seconds. With hot primary and secondary production layers at each Processing Centre, four sets of orbit and clock correction values are generated.
The six geostationary high-power communication satellites provide global, L-Band distribution between about 75° north and south latitudes. The satellite constellation is uplinked through six land earth stations, each equipped with primary and secondary layers of equipment. Each layer receives the corrections from both Processing Centres. The satellite constellation is configured as C-Nav NET-1 and C-Nav NET-2 with the satellites’ monitored by the Processing Centres to ensure service continuity and data quality.
In the user domain, Kalman filtering solves for satellite and receiver channel biases and a least squares solution calculates the position based on phase-smoothed refraction and bias-corrected code observables. The Precise Point Positioning (state-space) technique is so refined as to include corrections for distorting Earth-tides and ocean loading (and other geodetic effects) through an algorithm accessing the proprietary Sinko Earth-tide model.
It was to meet the demands of C-Nav’s government and private sector customers that the real-time positioning of the C-Nav SBAS system was set at typically 10cm level (in term of ITRF) with a vertical accuracy of 15cm. This level of precision enables the widest range of GNSS users to benefit. The user community includes the maritime and on-shore sector, the oil and gas industry, RTK augmentation, airborne platform and autonomous robotic vehicle operators and naval charting.
However, it was to address the growing need for autonomous assured independence in solution integrity, quality assurance and confidence, that the latest upgrades to C-Nav were instigated. The C-Nav's service is based on a worldwide over-determinate tracking network and enjoys the exclusive benefit of generating and applying the satellite orbit and clock correctors in a tightly modelled integrated RTG solution. The vulnerability of system failure is mitigated by redundancy through route diversity and system backups. This robust structure provides redundancy at each layer.
* The tracking network has a 6:1 excess ratio; stations can be removed from the solution without affecting system performance.
* The two Processing Centres each determine two independent RTG solutions which are compared for veracity before broadcast.
* The communication satellite NET-1 and NET-2 configuration provides independent communication delivery between the hubs and user community.
* All C-Nav tracking stations have dual racks of equipment. In the event that a performance flag identifies an anomaly, a rack can be excluded without impacting the solution.
* Each C-Nav tracking station has multiple communication links to the Processing Centres. In the event of a communications failure, an alternate method of communication is automatically put on line.
* Each system user may employ multiple and/or differing C-Nav receivers.
* The C-Nav GPS receivers can be configured to operate with either NET-1 or NET-2 correction signals or with both Networks for maximum reliability and technical redundancy.
* The NET-1 and NET-2 configuration provides for independent delivery over each ocean region
Customers’ have a choice of receivers. The 26-channel Nav2050 dual-frequency receiver with integrated L-Band receiver and tri-band antenna delivering typically 10cm horizontal and 15cm vertical accuracy. The C-Nav1010 L1 receiver, in common with all C-Nav receivers, integrates C-Nav correctors as well as WAAS / EGNOS data and provides sub-metre accuracy and is designed to maximise precision and stability in noisy and hostile environments. The C-Nav2000 is a ‘smart-antenna’ design with an integrated dual-frequency GPS, L-Band demodulator, and a tri-band antenna in one package.
Enquiry details
Edwin Danson FRICS FInstCES is a Business Consultant with C&C Technologies Inc, Lafayette, USA. www:cctechnol.com
