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Design and Development of a Design and Development of a Software-Defined Underwater Software-Defined Underwater Acoustic Modem for Sensor Acoustic Modem for Sensor Networks for Environmental Networks for Environmental and Ecological Research and Ecological Research 

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

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OutlineOutline

Summary of MP Algorithm and Summary of MP Algorithm and Aquamodem ImplementationAquamodem Implementation

Comparison w/ other Acoustic Comparison w/ other Acoustic ModemsModems

Hardware ImplementationHardware Implementation Test Results: wire, air, tankTest Results: wire, air, tank Future ideas (in the works)Future ideas (in the works)

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Design ObjectivesDesign Objectives

Operating range: >= 100 mOperating range: >= 100 m Operating depth: up to 20 mOperating depth: up to 20 m 90-day deployed lifetime90-day deployed lifetime Handle multipath spread of Handle multipath spread of

several ms (up to 11.2 ms)several ms (up to 11.2 ms) What else to add here?What else to add here?

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MP AlgorithmMP Algorithm

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MP Algorithm: SimulationMP Algorithm: Simulation

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Simulated MIP, 5 Training Symbols, SNR = -4 dB, Estimated NF = 5 to 16

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Simulated MIP, 2 Training Symbols, SNR = -4 dB, Estimated NF = 3 to 17

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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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Matching Pursuits vs Matching Pursuits vs FSKFSK Direct Sequence Spread Spectrum Direct Sequence Spread Spectrum

(DSSS) preferred over frequency (DSSS) preferred over frequency hopping when channel exhibits hopping when channel exhibits deep, narrow fades so that signal deep, narrow fades so that signal energy spread over wide bandwidth.energy spread over wide bandwidth.

MP produces channel estimates MP produces channel estimates during symbol demodulation during symbol demodulation process.process.

Add – check Iltis paper.Add – check Iltis paper.

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Signaling SchemeSignaling Scheme

8-ary code orthogonal modulation8-ary code orthogonal modulation 56-chip Gold sequences, 6000 chips/sec56-chip Gold sequences, 6000 chips/sec Chip sequences applied to root-raised-Chip sequences applied to root-raised-

cosine filter, 30 % excess bandwidthcosine filter, 30 % excess bandwidth 24 kHz center frequency24 kHz center frequency Guard interval, normally same length as Guard interval, normally same length as

symbol duration.symbol duration. At Fs = 96 kHz rate, symbol rate is ~ 54 At Fs = 96 kHz rate, symbol rate is ~ 54

Hz, bit rate ~ 161 bps.Hz, bit rate ~ 161 bps.

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Hardware Hardware ImplementationImplementation Texas Instruments’ C6713 DSP BoardTexas Instruments’ C6713 DSP Board Sonatech custom built transducers: Sonatech custom built transducers:

horizontal omnidirectional coverage in horizontal omnidirectional coverage in 20 kHz – 30 kHz range20 kHz – 30 kHz range

System power: alkaline primary cellsSystem power: alkaline primary cells Commercial single-chip class D power Commercial single-chip class D power

amp driving matching network, amp driving matching network, automatic transmit/receive switch.automatic transmit/receive switch.– Tx transducer also connected to low-noise Tx transducer also connected to low-noise

variable gain amplifier when power amp variable gain amplifier when power amp not operating.not operating.

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Hardware Hardware ImplementationImplementation Blah need djd input!Blah need djd input!

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Wire Test: resultsWire Test: results

Multipath Intensity Profile, NF MAX = 5

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Doppler Spread, Wire Test

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Air Test in Lab: resultsAir Test in Lab: results

Multipath Intensity Profile, NF MAX = 20

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Delay (in ms) 25 50 75 100

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Doppler Spread, In-Lab Air Test

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Air Test in Hallway: Air Test in Hallway: setupsetup

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 : Air Test in Hallway : resultsresults

Multipath Intensity Profile, NF MAX = 30

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Doppler Spread, Hallway Air Test

TrialTrial SERSER Doppler Spread (Hz)Doppler Spread (Hz)

11 0.02330.0233 0.1730.173

22 00 0.19030.1903

33 00 0.15570.1557

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Air Test in Stairway: Air Test in Stairway: setupsetup

Clockwise, from top left: Receiver 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: Air Test in Stairway: resultsresults

Multipath Intensity Profile

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Doppler Spread, Stairway Test 2, w/ extended guardband 11*ns

TriaTriall

NFNF Guard Guard timetime

SERSER Doppler Spread Doppler Spread (Hz)(Hz)

11 2020 99 0.0070.00788

0.00690.0069

22 2020 1111 00 0.00290.0029

33 3030 1111 0.0070.00788

0.00690.0069

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Tank Test at MSI: Tank Test at MSI: setupsetup

Need better pic from Chris (get Need better pic from Chris (get Friday)Friday)

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Tank Test at MSI: Tank Test at MSI: noisy environmentnoisy environment

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Tank Test Series A: Tank Test Series A: videovideo To get from Chris (20-30 sec) on To get from Chris (20-30 sec) on

Friday.Friday.

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Tank Test Series A: error Tank Test Series A: error rates, resultsrates, results

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Tank Test Series A: Doppler Tank Test Series A: Doppler SpreadSpread

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Doppler Spread, 12.7 m distance

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Doppler Spread, 0.6 m distance

•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 BTank Test Series B

5 training 5 training symbols per symbols per sync, up from 2sync, up from 2

NF estimation NF estimation code integratedcode integrated

Lower SNR due to Lower SNR due to Tx power amp Tx power amp problems (-1.0 dB problems (-1.0 dB vs. 6.1 dB)vs. 6.1 dB)

Only 0.60 m Only 0.60 m results collectedresults collected

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Tank Test Series B: Tank Test Series B: resultsresults

Series A: 6.1 dB vs. Series B: -1.0 dB SNR Series A: 6.1 dB vs. Series B: -1.0 dB SNR Note weak path at 6 ms not as apparent in Series B Note weak path at 6 ms not as apparent in Series B

MIP compared with Series A MIP.MIP compared with Series A MIP.

Test Series A: Multipath Intensity Profile, 0.6 m distance, NF = 5

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Test Series B: Multipath Intensity Profile, 0.6 m distance, NF = 1-2

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Doppler Spread PlotsDoppler Spread Plots

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AcknowledgmentsAcknowledgments

MSI, Keck Foundation, Navy, MSI, Keck Foundation, Navy, Sonatech, blahSonatech, blah