1. Any Four Will Do1 Interchangeability and CARS Bradford Parkinson Stanford University

2. Any Four Will Do22 What’s Next? 8/9/2015

3. Any Four Will Do38/9/20153 GLONASS – (Russia) PNT to Explode with Opportunities Galileo (European) GPS (USA) Compass (Beidou China) QZSS (Japan) The Five Design Keys (& Barriers to Entry) 1.The CDMA signal (PRN or Spread spectrum) 2.Van-Allen qualified atomic clocks 3.Orbit prediction to a few meters (URE) in 20,000 miles of travel 4.Spacecraft that lasted about ten years (cost of ownership) 5.User Equipment that could (eventually) be miniaturized (<$)

4. Any Four Will Do44 International Augmentations Differential GPS Networks International GNSS Service Global Differential GPS System Space-Based Augmentation Systems 8/9/2015

5. Any Four Will Do5 New Signals are On the Way 8/9/20155

6. Any Four Will Do66 Summary - Spectrum of Modernized GPS Signals L5 ARNS/RNSS Band L1 ARNS/RNSS Band L2 RNSS Band P(Y) C/A L2C M L5 L1C Earlier GPS Dual Frequency w/ Semi-codeless P(Y) Block IIR-M Launch 2005 Dual Frequency L1 C/A & L2C Block IIF/IIR-M+ Launch 2008 Three Frequency L1 C/A, L2C, & L5 Block III Launch 2013 L1C, L2C, L5, & L1 C/A Code L5 New! 8/9/2015

7. Any Four Will Do77 GPS L2 GPS L1 1164MHz Galileo E1 L1 E2 Galileo E6 Galileo E5A Galileo E5B GPS L5 GLONASS G2 GLONASS G1 1188MHz 1214MHz 1217MHz 1239MHz 1260MHz 1261MHz 1300MHz1559MHz1563MHz1587MHz 1591MHz 1593MHz 1610MHz RNSS Band Upper L-Band RNSS Band 1151MHz 1237MHz ARNS Band RNSS Band GLONASS G3 ? Compass B6 B1 Compass B5B B2 Coming: a Plethora of Signals 8/9/2015

8. Any Four Will Do8 Latest Signal Verified – L5 8 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 8/9/2015

9. Any Four Will Do99 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 8/9/2015

10. Any Four Will Do10 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 8/9/2015

11. Any Four Will Do11 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 8/9/2015

12. Any Four Will Do12 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

13. Any Four Will Do13 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” 8/9/2015

14. Any Four Will Do14 CARS : GPS/Galileo Example First Step: Monitor the “other” constellation signals GPS Control Segment GPS Galileo 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 8/9/2015

15. Any Four Will Do15 GPS Control Segment GPS Galileo CARS : GPS/Galileo Example Second Step: Send Augmentation Corrections to Each “own” satellite to allow it to be “seen” (used) as a member of the other constellation 8/9/2015 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

16. Any Four Will Do16 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 8/9/2015

17. Any Four Will Do17 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?

18. Any Four Will Do18 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 8/9/2015

19. Any Four Will Do19 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 8/9/2015

20. Any Four Will Do20 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