antenna baseline measurement system 29 january 2010 mark phillips, research assistant ohio...
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Antenna Baseline Measurement System
29 January 2010
Antenna Baseline Measurement System
29 January 2010
Mark Phillips, Research AssistantOhio University, Athens OHResearch Intern Naval Research Laboratory
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OutlineOutline
• Common uses of differential systems
• What is ABMS
• Uses of ABMS
• System construction overview
• Conclusions
• Questions
Ohio University - Avionics Engineering Center
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Common Uses of Differential GPSCommon Uses of Differential GPS
• Wide Area Augmentation System (WAAS)
• Local Area Augmentation System (WAAS)
- First certified LAAS installed at Newark NJ
Ohio University - Avionics Engineering Center
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Wide Area Augmentation SystemsWide Area Augmentation Systems
38 Reference Stations
3 Master Stations
4 Ground Earth Stations
2 Geostationary Satellite Links
2 Operational Control Centers
• Currently Available in North America
• Reference Stations collect GPS Data
• Master Stations collect data from reference stations and creates correction message
• Correction Messages is Broadcast to the Geostationary Satellites • Satellite Orbits • Clock Drift • Atmospheric
• WAAS Capable GPS Receivers then Correct the GPS Message *FAA Eastern Services Area NAVAIDS Meeting March 2009
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Local Area Augmentation SystemLocal Area Augmentation System
• Designed to replace Instrument Landing Systems (ILS) for precision approach and Landing
• Composed of 3 subsystems
– Satellite
– Ground
– Airborne
• Navigation Performance requirements
– Must meet three-tiered structure of ILS Approach Services
– ICAO Ground Based Augmentation System Standardshttp://mmae.iit.edu/~gps/research/laas.html
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What is Antenna Baseline Measuring System? (ABMS)
What is Antenna Baseline Measuring System? (ABMS)
• Real time kinematic (RTK) System that uses the GPS technique of double differencing
• Measures precise distances between the phase center of two antennas.
• Can give a accurate relative frame of reference or given a surveyed point can give accurate positioning with respect to GPS coordinate system.
Ohio University - Avionics Engineering Center
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How the System WorksHow the System Works
• Components
- 1 Reference Box (REF)
- 1 Rover Box (ROV)
- 1 User computer with Matlab
• REF and ROV communicate observation files wirelessly to user computer. The user computer calculates the baseline between the antennas and displays result to the screen.
Ohio University - Avionics Engineering Center
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System Illustration System Illustration
Ohio University - Avionics Engineering Center
ROV REF
GPS Observation file1GPS O
bserva
tion fil
e 2
Computer Calculated Baseline
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Examples Of Uses To End UsersExamples Of Uses To End Users
• Precision local area coordinate frame measurements
- Precision surveying
- Precise position of array elements for radar
- Real time truth reference system
Ohio University - Avionics Engineering Center
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Example Application to Aviation Example Application to Aviation
• Precision Landing of UAV’s
Ability to calculate a precise 3D vector from aircraft to runway on approach
• Able to perform with very little ground based infrastructure or human input.
Ohio University - Avionics Engineering Center
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Potential in Flight ApplicationsPotential in Flight Applications
• Calculate and track multiple baselines once other system users come available. Giving each aircraft a ground based tracking system independent position of other aircraft relative to its position.
• If GPS reference stations were updated they could be used in differential GPS calculations.
Ohio University - Avionics Engineering Center
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UAV Relative In Flight PositioningUAV Relative In Flight Positioning
Ohio University - Avionics Engineering Center
Baseline 1Baseline 2Diff
eren
tial C
orre
ctio
ns
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What My Role Has Been?What My Role Has Been?
• Complete computer replacement on boxes
• Novatel OEM 4 and BeagleBoard hardware integration
• Miniaturization
• Act as an interface between Naval Research Lab (NRL) and Ohio University AEC department
• System testing
– Accuracy
– System Reliability
Ohio University - Avionics Engineering Center
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Miniaturization (Old System)Miniaturization (Old System)
Ohio University - Avionics Engineering Center
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MiniaturizationMiniaturization
What's been done?
• New smaller computer
• Removed Novatel OEM4 from factory case
• Integrated Novatel patch antenna ground plane in to top of the box
• Created a custom expansion and communication board for Novatel-computer communication
• Utilized external mobile power supply
Ohio University - Avionics Engineering Center
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Miniaturization (new system)Miniaturization (new system)
Ohio University - Avionics Engineering Center
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Stargate SpecificationsStargate Specifications
• 32-bit, 400 MHz Intel PXA255 XScale RISC processor.
• SA1111 StrongARM companion chip for multiple I/O access.
• 32 MB of Intel StrataFlash.
• 64 MB of SDRAM.
• Type II CompactFlash slot.
• 16-bit PCMCIA slot.
• 51 pin expansion connector
Ohio University - Avionics Engineering Center
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BeagleBoard SpecificationsBeagleBoard Specifications
• 600MHz ARM Cortex-A8 (>1GHz ARM11 MIPS)
• NEON and VFP extensions for additional acceleration
• Programming: gcc compiler for ARM CortexA8
• Programming: free, non-commercial TI compiler for C64x+
• Utilities: serial and USB boot-loader tools
Ohio University - Avionics Engineering Center
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AdvantagesAdvantages
• BeagleBoard is completely open source
• Not limited to Stargates Operating System
• Now running a full version of xUbuntu Linux
• Faster CPU
• Expandable and Upgradeable
– Current Revision C3
Ohio University - Avionics Engineering Center
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Future DevelopmentFuture Development
• Compile user computer Matlab code to C and let each ROV box calculate it’s own baseline
• Make system work with multiple ROV boxes
• Make user computer passive and able to select multiple boxes and view baselines between the multiple boxes
Ohio University - Avionics Engineering Center
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ConclusionsConclusions
• ABMS is a new form of differential GPS
• Potential applications are vast
• New system is robust and able to handle multiple applications
• Future work and implementations are being tested currently
Ohio University - Avionics Engineering Center