any four will do1 interchangeability and cars bradford parkinson stanford university
TRANSCRIPT
Any Four Will Do 1
Interchangeability and CARS
Bradford ParkinsonStanford University
Any Four Will Do 22
What’s Next?
04/19/23
Any Four Will Do 304/19/23 3
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 (<$)
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International Augmentations
Differential GPS Networks
International GNSS Service Global Differential GPS System
Space-Based Augmentation Systems
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New Signals are On the Way
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Summary - Spectrum of Modernized GPS Signals
L5ARNS/RNSS Band
L1ARNS/RNSS Band
L2RNSS Band
P(Y)
C/A
L2C
M
L5
L1C
Earlier GPSDual Frequency w/ Semi-codeless P(Y)
Block IIR-MLaunch 2005Dual Frequency L1 C/A & L2C
Block IIF/IIR-M+Launch 2008Three Frequency L1 C/A, L2C, & L5
Block IIILaunch 2013L1C, L2C, L5, & L1 C/A Code
L5
New!
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GPS L2 GPS L1
1164
MH
z
Galileo E1 L1 E2Galileo E6Galileo E5A Galileo E5B
GPS L5 GLONASSG2
GLONASS G1
1188
MH
z
1214
MH
z12
17M
Hz
1239
MH
z
1260
MH
z12
61M
Hz
1300
MH
z
1559
MH
z
1563
MH
z
1587
MH
z
1591
MH
z15
93M
Hz
1610
MH
z
RNSS Band
Upper L-Band
RNSS Band
1151
MH
z
1237
MH
z
ARNS Band ARNS Band
RNSS BandRNSS Band
GLONASSG3 ?
Compass B6
B1Compass B5B
B2
Coming: a Plethora of Signals
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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
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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
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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
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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
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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
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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”
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CARS : GPS/Galileo ExampleFirst Step: Monitor the “other” constellation signals
GPS Control Segment
GPS
GPS GPS
GPS
Galileo
Galileo
Galileo
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 Constellation04/19/23
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GPS Control Segment
GPS
GPS GPS
GPS
Galileo
Galileo
Galileo
Galileo
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
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• 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
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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
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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?
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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
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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
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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