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GUS Type 1 Maintainer Training

GUS Type 1 Maintainer Training. Purpose of the WAAS. Satellite Navigation. GPS. GPS Satellites constantly orbit the earth; at least four should be visible anywhere on Earth. 12-hour orbit (11,000 nm altitude, in view for up to 6 hours)

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GUS Type 1 Maintainer Training

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  1. GUS Type 1 Maintainer Training Purpose of the WAAS

  2. Satellite Navigation

  3. GPS • GPS Satellites constantly orbit the earth; at least four should be visible anywhere on Earth. • 12-hour orbit (11,000 nm altitude, in view for up to 6 hours) • 6 orbital planes, located 60 ° apart in right ascension and inclined at 55° to the equator. • Broadcast signals include: Ranging, Ephemeris (own orbit), Time, Almanac (other orbits), Health and Status

  4. Distance Point A Point B Range Navigation • Distance measured as mi or km • Or distance measured using time Distance = Time X Velocity

  5. Ionospheric Delay Changes the Speed of the signal • GPS signal isn’t traveling in a straight line through a vacuum • Ionosphere’s electron content causes a curved path and a propagation delay • Causes a range error because signal takes longer to arrive • Can be determined by measuring two different freq L1 and L5

  6. GPS Error Sources Type of Error Definition Amount Drift, short-term and long-term, that prevents satellite broadcasts from being perfectly synchronized Clock 3 meters 4 meters Ephemeris Error in measurement and calculation of satellite’s orbit Troposphere Effects of lower (ground to 8-13 km) atmosphere’s temperature, pressure, and humidity on signal propagation 2.4-25 meters Ionosphere Effect of upper (50 km to 500 km) atmosphere’s free electrons on signal propagation 10-30 meters Multipath Error caused by signals reflected from surfaces near the receiver’s antenna (such as buildings); these reflections interfere with or are mistaken for the primary signal 2-100 meters

  7. The Theoretical View • Satellite orbits are perfect, so the satellite position is absolutely correct. • Ranging signals from all satellites are perfectly synchronized, so receiver offset is a constant • Broadcast signals are not distorted by passing through the atmosphere

  8. The Realistic View • Satellite orbits are out of date, so the satellite position is uncertain. • Ranging signals from all satellites are out of step, so receiver offsets are all different • Broadcast signals are delayed by the ionosphere and troposphere; noise is present everywhere

  9. The “Cylinder” View of Protection and Alarms

  10. Using Differential GPS to reduce GPS errors • Receiver is placed at very accurately surveyed location • Position is measured using GPS satellites • Range correction is calculated by base, since it knows exactly where it is • Correction is transmitted to neighboring receivers More info at: http://www.trimble.com/gps/dgps.html

  11. WAAS Functions

  12. WAAS Functions • Measures pseudoranges to satellites and verifies the GPS satellites are giving valid data. • Measures and models atmospheric effects (signal delays) • Calculates corrections (pseudorange, satellite position, satellite clock, Ionospheric delay) • Determines residual errors (uncertainty) in the corrections

  13. WAAS Functions - Continued • Broadcasts the corrections and associated residual errors using geosynchronous satellites • Monitors, configures, and directs repair - both automatically and manually

  14. Safety Is Paramount • Hazardously Misleading Information (HMI) must be avoided • Indicated error more than true error, pilot won’t land with GPS/WAAS , even though it’s safe—misleading but not hazardous • Indicated error less than true error, pilot will land with GPS/WAAS, but it’s not safe—misleading and hazardous.

  15. Two System Modes • Continuous Service • All algorithms performed • All messages broadcast • Military Emergency • All algorithms performed (as in Continuous Service) • Fast Correction message altered; range correction = 0 and UDRE = maximum, to deny full accuracy to enemy

  16. WAAS Architecture

  17. GEO Satellite GPS Satellites GCCS GEO Satellites GUS (3) GUS Primary GUS Backup GUST Primary GUST Backup WRS (38) (3) Correction and Verification Subsystem WRS = 3 WREs Operations and Maintenance Subsystem WAAS/GCCS System Diagram TCN WMS (5) (3 C&V Capable) O&M (2)

  18. WAAS/GCCS Architecture • Three GEO satellites (CRE/AMR/CRW) and six GUSTs (BRE, WBN, HDH and SZP, APC, and LTN). • A primary and a redundant GUSTs are implemented with a dedicated GEO satellite. • The two GUSTs are operationally independent and geographically separated. • Mitigate simultaneous loss due to natural disasters. • Redundant GUST radiates into a dummy load while receiving GEO and GPS satellite signals. • A GUST consists of the SGST, RFU, antennas, and supporting equipment.

  19. WAAS Block Diagram

  20. Terrestrial Communication Network (TCN) • Private Network • Two Independent Rings with diverse paths • 10.20x.1.xxx and 10.20x.2.xxx • Four Communication Nodes - ZLA (Palmdale, CA), ZDC (Leesburg, VA), ZAU (Chicago, ILL), ZTL (Hampton, GA) • One Distribution Node – ZSE (Seattle, WA) • Each Site connects to two different Communication Nodes.

  21. Wide-area Reference Station (WRS) • Contains three identical Wide-area Reference Equipment (WRE) subsystems • With three independent measurement threads • Each WRE: • Collects and validates data • Independently transmits measurements to the three WMSs with C&V cabability (ZDC, ZTL, and ZLA)

  22. Wide-area Master Station (WMS with C&V capability) • Selects independent wide-area reference equipment (WRE) data streams • Calculates corrections for each space vehicle (SV) • Determines residual errors • Ensures proper safety bounding of user position error; adjusts user differential range error (UDRE), grid ionospheric vertical error (GIVE) • Schedules and formats messages to users • Sends messages to all ground uplink stations type 1 (GUSTs) for broadcast to GEO • Automatically controls GUST switchovers

  23. GEO Uplink Subsystem Type 1 (GUS Type 1) • Relay WAAS transmission from WMS to the WAAS satellites • Transmit combined WAAS message and ranging signal • Generate proper C/A code ranging signal • Provide closed loop control to maintain a “GPS like” WAAS Signal-in-Space (SIS) • Validate GEO message transmission • Monitor and report GUST status to WMS

  24. O&M Subsystem • Monitors all WAAS/GCCS subsystems • Displays alarms and alerts • Allows operator to reconfigure subsystems • Change operating mode • Download software • Allows operator initiated corrective maintenance procedures.

  25. Summary Purpose of WAAS • Satellite Navigation • WAAS Functions • WAAS Architecture

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