Antenna Baseline Measurement System 29 January 2010 Mark Phillips, Research Assistant Ohio...

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


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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

http://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.


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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.


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System Illustration System Illustration


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


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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.


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Precision LandingPrecision Landing


baseline

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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.


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UAV Relative In Flight PositioningUAV Relative In Flight Positioning


Baseline 1Baseline 2Diff

eren

tial C

orre

ctio

ns

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User ScreensUser Screens


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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


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Miniaturization (Old System)Miniaturization (Old System)


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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


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Miniaturization (new system)Miniaturization (new system)


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Stargate ComputerStargate Computer


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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


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BeagleBoard ComputerBeagleBoard Computer


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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


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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


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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


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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


www.ohio.edu/engineering

Questions

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