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Welcome!. United States Coast Guard Command and Control Engineering Center (C2CEN) Portsmouth, VA, USA. U. S. Coast Guard. Engineering the USCG Differential System for Sub-meter Performance. LT Mike Parsons, USM GPS Workshop 17 March 2004. Introduction. INTRODUCTION HISTORY

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  1. Welcome! United States Coast Guard Command and Control Engineering Center (C2CEN) Portsmouth, VA, USA

  2. U. S. Coast Guard Engineering the USCG Differential System for Sub-meter Performance LT Mike Parsons, USM GPS Workshop 17 March 2004

  3. Introduction • INTRODUCTION • HISTORY • IFRASTRUCTURE • RECAP • eDGPS • CONCLUSION

  4. Introduction • Original DGPS Requirements • 285-325kHz • <10 meters (8-20 H/HA) • 200 bits/sec • Max 450km Range • Early Requirements • Based on removal of S/A • Achieved with Relative Ease • 2 May 2000 S/A was set to zero

  5. Introduction (cont) 0400Z (2400 EST) 02 MAY 00

  6. DGPS System History • Maritime System • 1991: Proof of concept • 1999: FOC Achieved • Nationwide System • 1997: Policy and Implementation Team (PIT) • 2003: Installations continue • Current System Status • 86 Sites • 95% Single Coverage • 45% Double Coverage

  7. History

  8. History

  9. Standard Site Configuration • All site utilize similar RS and IM suite • Ashtech Z-12-R Reference Station • Trimble IM-4000 Integrity Monitors • Similar communications equipment • Transmitters and Backup Power System • Maritime sites are configured as (V1) and (V2) • Nationwide sites are configured as (V2) and (V3)

  10. Current Configuration CURRENT CONFIGURATION

  11. Standard Site Configurations

  12. System Infrastructure

  13. System Infrastructure

  14. Standard Site Configurations • Recent System-wide Upgrades • Nationwide Control Station (NCS) • Frame Relay (FR) Wide Area Network (WAN)

  15. System Block Diagram

  16. Recap

  17. Antenna Study Ashtech Choke Ring Leica AT503 Choke Ring Novatel Pinwheel GPS-702 Trimble Zephyr Geodetic

  18. Antenna Improvements • Concerns • Existing Tower • Patch antennas • Choke Rings • New Technology • Proposals • Stability • Single Antenna • Center on Mast

  19. Antenna Improvements (cont)

  20. Type 15 Messages • DGPS has 80cm accuracy at the REFSTAs • Decorrelates to 300cm at fringe of coverage • Primary cause of decorrelation is Iono • Turn on RTCM 15 messages to allow user to back out IONO portion of DGPS correction and use rover observed value

  21. Enhanced Almanac • RTCM SC-104 is developed an RTCM Type 27 • RTCM 27 is an enhanced beacon almanac message • Receivers intelligently choose beacons • Receivers will seamlessly shift to best beacon

  22. Reference Station Architecture • Open Architecture • PC platform • Software based components • Flexible configuration • TCP/IP controlled comms • Multiple GPS/DGPS receivers connected to a single antenna

  23. Proof of Concept PHASE ONE CONFIGURATION

  24. RECAP CONFIGURATION

  25. Timeline March 2004: Software delivered & testing begins May 2004: Prototype installed for testing at C2CEN September 2004: Ethernet configuration installed for testing at C2CEN January 2005: Recap configuration installed & monitored at prototyped field sites August 2005 – July 2007: Full configuration installed system wide January 2006 – July 2007: Replace Ashtech & Trimble receivers as needed October 2007 – January 2009: Replace all Ashtech & Trimble receivers

  26. eDGPS

  27. eDGPS Symposium • 17-19 June 2003 hosted by C2CEN • Manufacturers • Academia • Government agencies • Industry leaders • Major CGcommands • Standardscommittees

  28. Introduction • eDGPS Goals • Commercial products • Reverse & forward compatibility • Open Architecture • Performance, reliability, & functionality • Partner with service providers • Strengthen radio navigation partnerships • Safeguard legacy users eDGPS

  29. eDGPS Goals • eDGPS Goals • Continue & Improve the differential signal • Make RTK style solutions available • Incorporate NOAA atmospheric model • Improve GPS antennas • Leverage dedicated network • Improve (redefine) Receiver Architecture • Increase datalink throughput to 1000 baud • Broaden bandwidth of datalink hardware

  30. Enablers • New Modulation Format • NOAA Tropo Model & Network Synergy • RS/IM Recapitalization Project • Datalink Hardware Improvement Project • Coverage Study • Alternatives to traditional datalinks

  31. NOAA Atmospheric Correction • Large file (20-200Kb) • Troposphere • Valid 30 minutes • Single layer • 20KM grid • Ionosphere • Valid 15 minutes • 2-3 layers • 111 km grid • 10-30cm accuracy

  32. Leveraging the Network • Networked Reference Stations • Shared Corrections • Build Continental Models • Support other Services • National Notification

  33. Coverage Analysis • Evaluate WAAS, DGPS, and GPS performance in harbor and harbor approach environments • Questions • What is the absolute accuracy of DGPS? • How does it compare to WAAS & GPS? • How does the DGPS accuracy vary with distance? • How does the beacon signal strength vary over distance? • What more can be done to improve the datalink?

  34. Datalink Format Study Discrete multi-tone • Ideal Capacity • Compact RTK • Compression • Modulation Formats • Second Data Channel • Sub Carrier Phase Trellis Overlay

  35. Datalink Hardware Engineering • “150e” Tower • adverse weather compatible • 6 Top Loading Elements (TLE) • TLE lengths of 150 feet each • Improved Coupler • Improved Ground System • Benefits • Wider bandwidth • Stronger usable signal • Greater reliability

  36. The Approach • Build a hybrid datalink capable of accommodating both legacy and new data channels… • 200 baud low rate channel intact for legacy • New high rate channel providing: • RTK style observables • Detailed NOAA Tropo & Iono models • Precise orbit data • DHS emergency messaging

  37. High Rate Data Channel • Characteristics • Utilize same carrier frequency • Minimal impact on legacy signal • 1000baud throughput speed • Compact message format • May employ compression • Support message intended for other uses • Compatible with fielded hardware

  38. RS/IM Architecture • Open Architecture • PC platform • Software based components • Flexible configuration • TCP/IP controlled comms • Multiple GPS/DGPS receivers connected to a single antenna

  39. Alternatives to Traditional Datalink • Internet delivery of corrections • Cellular data devices are small & user friendly • Internet delivery is gaining in wide spread acceptance • Bandwidth no longer an issue with high speeds of the internet

  40. So, what will it look like? • PC based • PC • GPS • DSP • COTS Software • Non-proprietary Hardware • 2 Modulation Formats • Forward Compatible • Comms over a LAN • Infinitely Configurable • Soft Fail ?

  41. The sky is the limit FINAL CONFIGURATION

  42. How will eDGPS perform? • Single frequency low rate DGPS: .8 mtr decorrelating to 3mtr • Dual freq low rate DGPS: .8 mtr – no decorrelation • Dual freq high rate DGPS: 10-30 cm

  43. Conclusion • Where are we now? (FY03 effort) • Proof of concept RS Software nearing completion – delivery Mar 04 • University studies completed – delivery Jan 04 • Stanford • Calgary • USCGA w/JJMA • C2CEN to begin hardware testing • R&D Focus shifting to enhanced capabilities

  44. Conclusion • Where are we going? (FY04 effort) • Finalize RS/IM hardware configuration • Contract Antenna Study • Propose a 1000 Baud Datalink Format • Propose Datalink Sharing Approach • Integrate the Atmospheric Correction • Explore Benefit of Precise Orbit Data • Develop a Standards Proposal • ION-NTN and RTCM Conf Presentations

  45. Conclusion • FY05 • Delivery of eDGPS prototype • Examine current signal spec definitions • ID a GPS receiver to mate with the unit • Finalize system architecture • Modify Standards • Pull Compression algorithm into public domain • Participate with other service providers • Continue to push datalink improvements • Continue follow-on Studies

  46. Conclusion • Fy06 • Field Prototype • Modify signal specification • HQ / NAVCEN / C2CEN Acceptance • FY07 • Upgrade Bridge Products • FY08 • Continue Recap on remaining sites

  47. Nationwide DGPS C2CEN Thank you!

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