Tripod localization and sensing testbed
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Tripod Localization and Sensing Testbed. Lewis Girod. 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…

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Goals of this effort l.jpg
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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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

Mica2 Mote

USB 802.11 adaptor

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


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