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Interchangeability and CARS

Interchangeability and CARS. Bradford Parkinson Stanford University. What’s Next?. 12/20/2019. 2. PNT to Explode with Opportunities. GLONASS – (Russia). Galileo (European). The Five Design Keys (& Barriers to Entry) The CDMA signal (PRN or Spread spectrum)

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Interchangeability and CARS

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  1. Interchangeability and CARS Bradford ParkinsonStanford University Any Four Will Do

  2. What’s Next? 12/20/2019 Any Four Will Do 2

  3. PNT to Explode with Opportunities GLONASS – (Russia) Galileo(European) • The Five Design Keys (& Barriers to Entry) • The CDMA signal (PRN or Spread spectrum) • Van-Allen qualified atomic clocks • Orbit prediction to a few meters (URE) in 20,000 miles of travel • Spacecraft that lasted about ten years (cost of ownership) • User Equipment that could (eventually) be miniaturized (<$) GPS(USA) Compass (Beidou China) QZSS(Japan) 12/20/2019 Any Four Will Do 3

  4. International Augmentations Differential GPS Networks Space-BasedAugmentationSystems Global Differential GPS System International GNSS Service 4 12/20/2019 Any Four Will Do

  5. New Signals are On the Way 12/20/2019 Any Four Will Do 5

  6. Summary - Spectrum of Modernized GPS Signals L5 Earlier GPSDual Frequency w/ Semi-codeless P(Y) C/A P(Y) Block IIR-MLaunch 2005Dual Frequency L1 C/A & L2C New! L2C M Block IIF/IIR-M+Launch 2008Three Frequency L1 C/A, L2C, & L5 L5 Block IIILaunch 2013L1C, L2C, L5, & L1 C/A Code L1C L5ARNS/RNSS Band L2 RNSS Band L1ARNS/RNSS Band 12/20/2019 Any Four Will Do 6

  7. Coming: a Plethora of Signals Upper L-Band ARNS Band ARNS Band RNSS Band RNSS Band RNSS Band RNSS Band Galileo E5B Galileo E5A Galileo E1 L1 E2 Galileo E6 GLONASSG2 GLONASSG3 ? GPS L2 GLONASS G1 GPS L1 GPS L5 B2 B1 Compass B6 Compass B5B 1593MHz 1217MHz 1591MHz 1610MHz 1260MHz 1300MHz 1559MHz 1563MHz 1587MHz 1151MHz 1214MHz 1164MHz 1237MHz 1188MHz 1239MHz 1261MHz 12/20/2019 Any Four Will Do 7

  8. Latest Signal Verified – L5 • L5 spectrum captured by Stanford 45.7m dish antenna. • Antenna gain as high as 52 dB, • L5 signal high above the noise floor in frequency. • Clear L5 spectrum - both main lobe and two side lobes 12/20/2019 Any Four Will Do 8

  9. Levels of Cooperation - New Systems:Can’t we just get along? Degrees of “Getting Along” Compatible Lets not hurt each other Interoperable I’ll try yours, you can try mine Interchangeable Any four will do 12/20/2019 Any Four Will Do 9

  10. GPS and Galileo/Compass/GLONASS-The Users Viewpoint Real Measure: Interchangeability“Mix and Match” with the same ranging accuracy Enabled by L1C - defined, implemented, and operable – including all details Seamless WAAS/EGNOS/+ ? True clock Synchronization (Common Clock)and common grid Payoff – Availability, Accuracy and Robustness for Worldwide Users 12/20/2019 Any Four Will Do 10

  11. Achieving Interchangeability Simplest: Common Clock and Geodetic System Probably Implies a common Control System Nationalistic Resistance A New Proposal – Cross-Augmentation Reference System (CARS) Each Satellite Broadcasts WAAS like Corrections to allow it to be seamlessly operated as a part of the “other” constellation 12/20/2019 Any Four Will Do 11

  12. Three levels of “WAAS-like Corrections” • Correction for ephemeris and specific satellite clock • Implies frequent upload capability • Correction for satellite clock alone • Geodetic correction assumed constant • Intersystem time calibration (sub-nano-second) • Assumed very slowly changing In addition some form of Integrity Message could be included Any Four Will Do

  13. GPS/Galileo CARS Example–Cross Augmentation Reference System GPS Monitor Stations track Galileo satellites (L1C) Form WAAS-like Corrections for GPS satellites to operate as Galileo Ranging sources (Clock and Position – Include integrity?) Include corrections as part of the GPS message Result: GPS satellite is seamlessly useable as a part of the Galileo Constellation ANY Four Satellites will do: A step beyond Interoperable-CARS is truly “interchangeable” 12/20/2019 Any Four Will Do 13

  14. CARS : GPS/Galileo ExampleFirst Step: Monitor the “other” constellation signals GPS GPS GPS Galileo Galileo Galileo Galileo GPS GPS Control Segment • GPS Reference Receivers Monitor all L1C signals • GPS Master Control Calculates a WAAS/EGNOS type correction for each GPS satellite (or for inter-system time) –for operation in the Galileo Constellation 12/20/2019 Any Four Will Do 14

  15. CARS : GPS/Galileo ExampleSecond Step: Send Augmentation Corrections to Each “own” satellite to allow it to be “seen” (used) as a member of the other constellation GPS GPS GPS Galileo Galileo Galileo Galileo GPS GPS Control Segment • Thus, any GPS satellite can operate as full member of the other constellation • Note: • Corrections are slowly changing (low data rate) • Each GPS satellite either • only broadcasts its own correction to the Galileo reference • Broadcasts inter-system time difference and time-difference rate • Each constellation controls this use 12/20/2019 Any Four Will Do 15

  16. And Galileo would do the same for GPS (etc. for other GNSS Systems) Advantages: Satellites are truly Interchangeable Avoids issue of which time or which Geodetic System Very Low Rate message, low overhead Very efficient – corrections broadcast only for the satellite being used Each Satellite Provider has some control over use of their system User can have highly accurate PNT in coordinates of their choosing 12/20/2019 Any Four Will Do 16

  17. Unintended Consequences? • Each Constellation forced to be smaller? • Still need core capability to operate alone? • Military cannot use for “Fire” clearance – Sky impaired warrior not helped • Next Gen (FAA) still needs MOPS – May take a long time with Galileo • Misleading Information • Cross Augmentation Bit in message? Any Four Will Do

  18. Implementation of CARS Bi-Lateral Agreements Could be done experimentally on a unilateral basis Technical Working Group to adapt WAAS or EGNOS-like format for message Which level and frequency of update? Include Integrity? Ionospheric correction probably not necessary 12/20/2019 Any Four Will Do 18

  19. Conclusion We are entering an era with incredible opportunities in Worldwide PNT With a concerted effort of cooperation, all users should receive benefits: economic, safety and convenience The ultimate goal is interchangeability CARS would enable this 12/20/2019 Any Four Will Do 19

  20. Notes • Time only: Phi, Phidot, and tzero • System to system time only • Saves a calibrating satellite • Unintended consequences • Need less satellites? • Military • Next Gen • Limited Upload Capability Any Four Will Do

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