DESIGN AND EXPERIMENTATION WITH A SOFTWARE-DEFINED ACOUSTIC TELEMETRY MODEM

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DESIGN AND EXPERIMENTATION WITH A
SOFTWARE-DEFINED ACOUSTIC TELEMETRY MODEM
Department of Electrical and Computer
Engineering University of California, Santa
Barbara

• Daniel Doonan, Tricia Fu, Chris Utley,
• Ronald Iltis, Ryan Kastner, and Hua Lee

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Outline

• Motivation
• Summary of MP Algorithm and Aquamodem
  Implementation
• Direct Sequence vs. FSK
• Signaling Scheme
• Test Results wire, air, water
• Future work

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UC Moorea

• Ecological applications
• Collaboration MCR Moorea Coral Reef LTER

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Design Objectives
Target
Communication Range Communication Range 100 m
Operating Depth Operating Depth 20 m
Deployed Lifetime (without recharging) Deployed Lifetime (without recharging) 90 days
Allowable Multipath Spread Allowable Multipath Spread 10 ms
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MP Algorithm

• Run this whole process for each possible symbol m
  1, 2, , Ng.
• Run subsystems for k 2, , Nf.
• Store residual norms at step k Nf.
• Minimize over the Ng residual norms to determine
  symbol.
• Store channel estimate fm for corresponding
  symbol.

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MP Algorithm
Return Channel Estimate Vector fest
To rk Cancellation Substem fest(qk)
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MP Algorithm
Return Received Vector Residual Norm for a given
symbol.
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Direct Sequence vs FSK

• Direct Sequence Spread Spectrum (DSSS) offers
  frequency diversity gain over FSK in multipath.
• Implicit coding gain, 1 of 8 waveforms
  corresponds to a non-binary code.
• MP allows online channel sounding while
  communicating.

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Signaling Scheme

• 8-ary code orthogonal modulation

Fadc 96 kHz
Fchip 6 kHz
Chip Filter Root-raised-cosine, 30 excess bandwidth
Fcenter 24 kHz
Gold Code Length 8 binary symbols gt 56 chip sequences
Symbol Duration 9.333 ms
Time guard interval 9.333 ms (usually)
Fsym 53.57 baud 54 symbols/sec
Fbit 160.71 bps 161 bits/sec
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Hardware Implementation
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Hardware Implementation

• Spectrum Digital board with TI C6713B DSP
• Onboard audio CODEC (A/D, D/A, etc.)
• Sonatech custom built transducers horizontal
  omnidirectional coverage in 20 kHz 30 kHz range
• Commercial single-chip class D power amp,
  discrete matching network, automatic T/R switch,
  LNA, and VGA.
• Power supplies single 10V 25V rail from
  battery, mostly switching, linear for analog.

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Simulation

• Estimated MIP from simulations, with actual
  number of multipaths 10 and SNR -4 dB.
• Left 2 training symbols, SER 0.6645.
• Right 5 training symbols, SER 0.1023.

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Wire Test Results

• of Multipaths Actual 1, Estimated 1-3
• Estimated Doppler Spread 0.06 Hz
• 0 SER, as expected in high SNR environment

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Air Test in Lab Results

• of Multipaths Actual Unknown, Estimated 5-6
• Estimated Doppler Spread 0.104 Hz

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Air Test in Hallway Setup
Earlier Tests Later Tests
Range 67.5 ft 117 ft
NF Fixed Estimated
training symbols 2 5
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Air Test in Hallway Results
Trial SER Doppler Spread (Hz)
1 0.0233 0.173
2 0 0.1903
3 0 0.1557
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Air Test in Stairway Setup
Clockwise, from top left Transmitter setup on
3rd floor, view from middle of 4th and 3rd floor
stairway, receiver setup on 4th floor.
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Air Test in Stairway Results
Trial NF Guard time SER Doppler Spread (Hz)
1 20 9 0.0078 0.0069
2 20 11 0 0.0029
3 30 11 0.0078 0.0069
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Tank Test at MSI Setup
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Tank Test at MSINoisy Environment
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Tank Test Series A Video
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Tank Test Series AError Rates, Results
0.60 m range
12.7 m range
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Tank Test Series ADoppler Spread

• Doppler Spectrum Plots, at 0.6 m distance and
  12.7 m distance
• Doppler Spread 0.2 Hz vs 0.9 Hz

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Tank Test Series B

• 5 training symbols per sync, up from 2
• NF estimation code integrated
• Lower SNR due to Tx power amp problems (-1.0 dB
  vs. 6.1 dB)
• Only 0.60 m results collected

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Tank Test Series B Results

• Series A 6.1 dB vs. Series B -1.0 dB SNR
• Note weak path at 5 ms not as apparent in Series
  B MIP compared with Series A MIP.

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Pool Test 10/20/2006
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Pool Test 10/20/2006
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Future Work

• Additional MSI Tank Tests Pool Tests
• Tests off the Goleta Pier (and other exotic
  locales)
• Improvements to timing acquisition
• Incorporate sparse Bayesian Kalman filter in the
  modem.

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Acknowledgments

• UC Santa Barbara Marine Science Institute
• Keck Foundation
• Navy
• Sonatech