Presentation on theme: "DGPS Services Group C&C Technologies, Inc., (Lafayette, La) Globally Corrected GPS (GcGPS): C-Nav GPS System."— Presentation transcript:
DGPS Services Group C&C Technologies, Inc., (Lafayette, La) Globally Corrected GPS (GcGPS): C-Nav GPS System
GPS Space Segment Comprises of a nominal network of 24 GPS satellites in orbit around the globe. Nominal orbit height of 20,200 Kilometers. Initial 24Hr operational capability was declared on 8 December, Full 24 Hr operational capability was declared after testing on 17 July, Selective Availability signal degradation was removed in May, 2000.
GPS Space Segment
GPS User Segment The user segment is comprised of the GPS receivers that have been designed to decode the signals transmitted from the GPS satellites for the purposes of determining position, velocity and time. There are two types of service available to GPS users - the SPS (Civilian) and the PPS (Military). SPS - Standard Positioning Service is the positioning accuracy that is provided by GPS measurements based on the single L1 frequency C/A code. PPS - Precise Positioning Service is the highest level of dynamic positioning accuracy that is provided by GPS measurements based on the second L2 frequency P-code.
GPS is a one way TIME BASED measurement system. Full three dimensional (3D) navigation or positioning uses a minimum of four range measurements to four satellites. With these pseudorange measurements the user is able to solve time, and then the three-dimensional coordinates (x, y, z) of their GPS receiver antenna electrical phase center. Over determined solution calculations (>4 SVs) provide redundant measurements that provide for better positioning and also the ability to determine any possible erroneous conditions in calculating the final 3D surface position. Positioning With GPS
GPS Error Sources User Independent User Dependent Ephemeris Data - Errors in the transmitted location of the GPS satellite Satellite Clock - Errors in the transmitted clock (including SA) Ionosphere - Errors in the corrections of the measured pseudorange caused by ionosphere signal path effects or delays Troposphere - Errors in the corrections of pseudorange caused by troposphere signal path effects or delays Multipath - Errors caused by reflected signals entering the receiver antenna from local surfaces (longer travel times) Receiver - Errors in the GPS receiver's measurement of range caused by thermal noise, software accuracy, and inter-channel biases User – Errors caused by the operator of the GPS receiver
GPS Errors (Diagram) The User
What Does This Mean? The accuracy and stability of real-time corrected GPS navigation solutions are dependant on:- –How well the GPS corrections are computed and measurements are applied by the GPS user –The location of the GPS antenna to reduce signal blockages and multi-path effects –The quality of the GPS receiver and its operation to reduce noise and operator errors
Differential (RTCM) GPS
The C-Nav Methodology Does not use the traditional (RTCM) measurement and/or position domain correction methodology Uses a state-space, precise point positioning solution (Wide Area dGPS) whereby the actual physical properties that comprise each of the errors in pseudorange observations are computed (the User Independent Errors) –similar to SatLOC and WAAS, EGNOS etc… C-Nav is a further development from existing WADGPS solutions in that the use of Dual Frequency GPS receivers to compute the local user ionospheric pseudorange observation errors (differencing of the L1/L2 code derived pseudorange measurements) is employed
dGPS Corrections Account for?? User Independent User Dependent Ephemeris Data - Errors in the transmitted location of the GPS satellite Satellite Clock - Errors in the transmitted clock (including SA) Ionosphere - Errors in the corrections of the measured pseudorange caused by ionosphere signal path effects or delays Troposphere - Errors in the corrections of pseudorange caused by troposphere signal path effects or delays Multipath - Errors caused by reflected signals entering the receiver antenna from local surfaces (longer travel times) Receiver - Errors in the GPS receiver's measurement of range caused by thermal noise, software accuracy, and inter-channel biases User – Errors caused by the operator of the GPS receiver R T C M One combined correction to the GPS psuedorange observation W A S Individual Orbit & Clock Corrections plus a regional Iono/Tropo Model RTG Individual Orbit Corrections and Individual Clock Corrections for each GPS satellite WCT One combined Orbit and Clock Correction value for each GPS satellite The C-Nav unit computes its own Iono/Tropo corrections from the L1/L2 measurements
dGPS Corrections Account for?? RTCM (1) = Combined (Ephemeris + Clock + Iono + Tropo) S.B.A.S (3) = Independent (Ephemeris) + (Clock) [WAAS / EGNOS] + Combined (Iono + Tropo) Model/Grid RTG (2)** = Independent (Ephemeris) + (Clock) to the broadcast GPS SV almanac information WCT (1)**= Combined (Ephemeris + Clock) ** C-Nav GPS Engine calculates, from the GPS L1 and L2, DUAL FREQUENCY, signal measurements, the local user area Atmospheric delays for each GPS observation to correct for the Ionosphere delay errors.
WCT US Network Frame Relay with backup ISDN
Global Reference Network Reliability based on redundancy –Two independent/redundant Network Processing Hubs –Redundant communication links (Frame Relay, ISDN) –Dual modulation racks at each LES uplink facility –Redundant Reference Receivers at WCT sites –Redundant Reference Sites (more than minimally required) Dual frequency GPS reference receivers –Refraction corrected pseudoranges observations –Extended smoothing to minimize multipath measurement –Phase tracking to aid with C/A code measurement processing
Real Time Gipsy Corrections Worldwide Global GPS Network (GGN) reference stations transmit all of their RAW GPS dual frequency observations to three Network Processing Hub locations (SF & JPL) via TCP/IP and the Internet. The NPHs performs the task of breaking down the GPS range error sources into their component, User Independent, parts in real-time. Independent Refraction Corrected Orbit and Atomic Clock Offset corrections (to the broadcast ephemeris) for all GPS satellites are computed (by the NPH), and transmitted via Land Earth Stations for uplink over StarFire L- Band communication satellites. The user requires a Dual-Frequency GPS receiver to be used at their remote location so that computation of the local Refraction Corrected pseudorange observations can be obtained. The GPS receiver applies the received RTG Orbit and Clock corrections along with the internally computed, Refraction Corrected, GPS Satellite pseudorange observations to compute a 3D surface position.
RTG Reference Sites Global GPS Network (30+) Brewster, USA / Cordoba, Argentina / Christiansted, Virgin Islands / Fairbanks, USA / Galapagos Island, Ecuador / Greenbelt, USA / Goldstone, USA / Dededo, Guam / Krugersdorp, South Africa / Bangalore, India / JPL Pasadena, USA / Kokee Park, USA / Robledo, Spain / Ross Island, Antarctica / Mauna Kea, USA / Moscow, Russia / Franceville, Gabon / Norilsk, Russia / Lamont, USA / Quezon City, Phillipines / Bishkek, Kryghystan / Santiago, Chile / Tidbinbilla, Australia / USNO, USA / Usuda, Japan / Yakutsk, Russia / plus others… ( see JPL Live Demo WEB Site at )
WCT Reference Sites North America (8) Redondo Beach, CA / Portland, OR / Fargo, ND / Kansas City, MO / WestLaCo, TX / Moline, IL / Belleglade, FL / Syracuse, NY Europe (4) Tampere, Finland / Madrid, Spain / Goonhilly, U.K. / Zweibruken, Germany Australia (5) Perth (2 sites) / Sydney / Brisbane / Melbourne South America (3) Rosario, Argentina / Horizontina, Brazil / Catalao, Brazil
C-Nav Global Positioning Both RTG and WCT corrections are optimized for dual frequency GPS user equipment. The GPS SV Orbit and Clock corrections for the RTG process are globally uniform. One set of RTG corrections for all GPS SVs worldwide. WCT corrections provide back-up, secondary positioning in regional areas. SBAS corrections provide regional tertiary positioning.
C-Nav GPS Receiver Design Multi-function L-Band antenna 12 channel dual-frequency, geodetic grade GPS engine L-Band communications receiver and embedded microprocessor Patented multi-path reduction signal processing capability and P code recovery algorithm Dual-frequency code and carrier phase measurement are used to form smooth refraction corrected code pseudoranges Compact size and integrated package design
C-Nav[RM] GPS Receiver Multi Function Antenna L-Band Comms. Receiver Dual- Frequency GPS Engine Fully Ruggedized, Masthead Mounted, Sealed Package for the Marine Environment Waterproof 8-Pin Connector that provides DC Power and External Data Interfaces (RS- 232 and CAN Bus)
C-Nav Block Diagram Ground Ign. On D.C. In CAN Bus RAW GPS Corrections 1PPS L-Band Communications Downconvertor GPS Receiver Engine A/D Converter Cct. DSP / CPU Processor DC to DC Power Supply Cct. L1 L2 Internal Tri-Freq. Antenna Front End RF Signal Board Downconverter Board GPS ModuleDigital Board Subcon Connector Pin #1 Pin #2 Pin #3, #4 Pin #5, #6 Pin #7 RS232 I/F
C-Nav[RM] GPS System C-Nav GPS Receiver Interconnect Cable C-Nav Control Display Unit (CnC D.U.)
C-Nav[RM] GPS User System Basic System Hardware Bundle –1 x C-Nav GPS Receiver –1 x 30m Interconnect Cable –1 x C-Nav Control Display Unit (CnC D.U.) –1 x C-Nav GPS Receiver Data and Power Y-Cable –1 x DC Power Cable –1 x C-Nav Operations Manual –1 x Qa/Qc and Application Software Utilities
C-Nav[RM] GPS System Options Options –15m Interconnect Cable –60m Interconnect Cable –Universal a.c. to d.c Power Supply –RS-232 to RS-422 In-line Amplifier/Converter System –19 inch Rack Mount C-Nav Control Display Unit –Rugged Transport / Shipping Case
DP Vessel Hardware C-Nav integrated mast-head unit 19inch Rack-Mount CnC D.U. Desk-Top-Mount CnC D.U. Interconnect Cable can be any length required RS-232/422 Inline Amplifier / Converter Pair (Option) (Optional Master/Slave Assy shown)
C-Nav GLOBAL Service The C-Nav correction service is available in the following regions: –North & Central America (RTG, WCT, and WAAS) –Western Europe & Mediterranean Sea (RTG, WCT, and EGNOS) –Australia (RTG & WCT) –South America (RTG) –Eastern Europe, Mediterranean & Black Sea (RTG) –African Continent (RTG) –Middle East, & Asian Continent (RTG) –Atlantic, Indian and Pacific Oceans (RTG)
C-Nav Features Global corrected GPS Positioning ( RTG, WCT & S.B.A.S. ) NMEA Data Msgs ( GGA, GLL, GSA, GST, RMC, VTG, ZDA ) - 1Hz Proprietary NMEA Data Msgs ( SATS, NAVQ, RXQ, NETQ ) RTCM Output ( Standard RTCM Type 1 Message Format – 5 seconds ) Dual Frequency, Geodetic GPS Engine to resolve local Ionospheric delay observation errors Multipath Mitigation Algorithm Rugged and waterproof Single Integrated Package Low Power Consumption ( <= 10 Watts ) Optional 5Hz positioning and data output ( w/o CnC Display Unit ) Automatic Restart based on last operating configuration
Example SA Plots May 2000 Mode: Autonomous - L1 Period: 30mins 95% ~ 47.2 meters Mode: DGPS - L1 Period: 52mins 95% ~ 0.5 meters
Applications Offshore applications for the C-Nav GPS equipment and the Global correction signal services include: –Hydrographic surveying –Oceanographic surveying –Dynamic Vessel positioning –Jacket and Template positioning –Work Boat operations –Dredging operations and surveying –Geophysical, Geotechnical, and Geodetic surveying –Offshore construction surveying –Pipeline construction, maintenance, and route surveying –ROV support positioning –Commercial diving support positioning –Underwater cable route, installation, maintenance surveying
Conclusion The RTG correction service and C-Nav GPS System provides real-time, 24-hour accurate, stable, and precise user positioning solutions. C-Nav and the RTG corrections are a truly Globally corrected GPS solution and provides decimeter performance to all C-Nav users between 72deg North and 72deg South.. The C-Nav GPS equipment is rugged, reliable and able to withstand the offshore environment. The C-Nav GPS system provides industry standard NMEA sentence messages and can also provide RINEX L1/L2 code and phase observations. Comprehensive QA and QC is available from the C-Nav GPS System to enable the user to monitor the navigation solution performance. The WCT corrections provide sub-meter performance and are available on a regional basis – North America, Western Europe, and Australia (S.America) and is a backup positioning source to RTG. S.B.A.S signals are also available (where applicable) for tertiary backup.