Tripod Localization and Sensing Testbed

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Tripod Localization and Sensing Testbed

• Lewis Girod

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Goals of this effort

• Develop a system to calibrate locations of
  field-deployed motes
• Turnkey system
• Deploy, use, and take down in a day
• Minimize restrictions on deployment
• Provide a convenient platform for
• testing and evaluating new ranging techniques
• Acoustic channel measurement?
• Other kinds of sensing experiments?

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Mote Localization Problem
Motes
Tripods
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Tripod Design

• Resource un-constrained design
• Runs on batteries for 6 hours
• Four audio channels
• 4 fixed microphones
• Omni-directional, 15Hz-30KHz
• 1 fixed speaker with a reflector
• 96 KHz / 24 bit samples
• CPU
• 1 GHz P3, 256 MB, 20GB Hard drive
• Runs on 12V
• Network
• 802.11 for inter-tripod network
• MoteNIC to talk to mote network
• 3-axis orientation sensor

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More detail
USB 802.11 adaptor
Mica2 Mote
Reflector
Car stereo speaker
3-axis orientation sensor from MicroStrain. May
be dropped due to cost if found unnecessary.
Behringer ECM8000 microphone, intended for
acoustic testing. Very flat response from 15Hz
to 20KHz
2x Audiobuddy 2 channel microphone preamp,
feeding to M-Audio Delta-44 4 channel 96/24 PCI
sound card.
30 cm inter-mic spacing
CPU Currently a ruggedized industrial PC from
littlePC.com
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Questions

• Would this kind of platform be helpful to your
  group?
• Are there additional / unnecessary features?
• Is 96 KHz / 24 bit useful to you?
• Microphone spacing?
• Microphone preamps
• Need phantom power
• The one I selected runs off 9V AC ?
• Rather have it run off a (noisy) DC supply

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Mote Localization in More Detail
Relative locations of motes more poorly
constrained

• Inter-mote ranging.. Why not?
• Additional hardware and software constraints
• Resource consumption
• Emitter only is low-cost
• How important is it?
• Bi-partite geometry may leave locations of motes
  poorly determined
• Other constraints
• Bearing estimates?
• Mote connectivity?

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Tripod System in more Detail
After motes in blue region are located, move
tripods to cover green region

• Grounding the coordinate system
• Locate one tripod at origin position, define it
  as the origin
• Will another fixed point be needed?
• System feedback to user
• System can ask tripods to be moved to improve
  constraints
• System indicates when all motes in region are
  located
• Cover more ground by moving tripods

Origin
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Experimental Ranging TechniquesLeveraging Four
Channels

• Bearing estimates
• Add constraints to multilateration
• May be helpful to address bi-partite topology
• Angular inconsistencies across nodes might detect
  obstructed signals
• Computed based on detected ranges to each
  microphone
• More sophisticated analysis might correlate mic
  signals

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Multipath Bearing Estimation

• Bearing estimates of multipath components?
• Distribution of incoming paths (angle and
  intensity)
• Might provide clue about whether path is
  obstructed
• Cases with LOS should have much stronger direct
  path
• Deduce location of sender in some cases?
• Estimation using model of reflectors