underwater counderwater coommunications · 2009-10-31 · back zbs in electrical and cobs in...
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Underwater CoUnderwater Co
Ballardbjblair@April 19
WHOIE Adviser: James Preisig
April 19, 2007 Underwater CoBallard
ommunicationsommunications
9, 2007
MIT Adviser: Art Baggeroer
ommunicationsd Blair
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Back
BS in Electrical and CoBS in Electrical and CoCornell university 2002
MS in Electrical and CoJ h H ki 2005Johns Hopkins 2005
Hardware Engineer, JH
PhD Candidate, MIT/WApril 19, 2007 Underwater Co
Ballard
kground
omputer Engineeringomputer Engineering, 2
omputer Engineering,
HUAPL 2002-2005
WHOI Joint Programommunicationsd Blair
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Introduction
O 0% f l• Ocean covers 70% of plan• 11,000 meters at deepest p
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and Motivation
netpoint
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Underwate
WHOApril 19, 2007 Underwater Co
Ballard
WHO
r Technology
OI 2006ommunicationsd Blair
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OI, 2006
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Comm
S t kSensor networks
Autonomous underwate
Gliders
Manned VehiclesManned Vehicles
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unication
er vehicles (AUV)
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Current A
ScienceScience− Geological / bathymetric su
Underwater archeology− Underwater archeology− Ocean current measuremen
Deep ocean exploration− Deep ocean explorationGovernment
Fish population manageme− Fish population manageme− Costal inspection
IndustryIndustry− Oil field discovery maintena
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Applications
rveys
nt
ntnt
ance WHOI, 2005
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Applications plann
Ocean observation systemOcean observation system− Costal observation
MilitaryMilitary− Submarine communications
Shi i ti− Ship inspectionNetworking
M bil t k (DA− Mobile sensor networks (DAVehicle deployment
− Multiple vehicles deployed s− Resource sharing among ve
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ned / in development
mm
s (covert)
ARPA)ARPA)
simultaneouslyehicles
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Example Comm
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munication System
PLUSnet/Seaweb
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Technology fo
RF (~1m range)RF ( 1m range)− Absorbed by seawater
Laser (~100m range)( g )− Hard to aim/control− High attenuation except for blue/g
Ult L F ( 100 kUltra Low Frequency (~100 km− Massive antennas (miles long)− Very narrowband (~50 Hz)y ( )− Not practical outside of navy
Cable− Expensive/hard to deploy mainta− Impractical for mobile work sites
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r communication
green)m)
in
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Acoustics is
Fairly low powerFairly low power− ~10-100W Tx − ~100 mW Rx100 mW Rx
Well studied− Cold war military funding
Compact− Small amount of hardware n
Current Best Solution
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s the solution
WHOI Micromodem
needed
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Acoustics
A ti iAcoustic wave is compthrough water medium
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Background
i t liression wave traveling
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Sound
S d f d 1500Speed of sound ~ 1500
Deep water profile
Schmidt, Computational Ocean Acoustics
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d Profile
0 /0 m/s
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Global Oc
Schmidt, Comput
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cean Profile
tational Ocean Acoustics
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Shallow w
Schmidt, Comp
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water profile
putational Ocean Acoustics
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Speed of Sou
V ti l d d fi• Vertical sound speed profi• the characteristics of the• the amount and importan• the amount of bottom int• the location and level of
• Horizontal Speed of SoundN li i i i h• Nonlinearities in channe
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und Implications
l i tle impactse impulse responsence of surface scatteringteraction and lossshadow zones
d impactsll response
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Propaga
Schmidt, C
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ation Paths
Computational Ocean Acoustics
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Mul
Mi lti th d tMicro-multipath due to Macro-multipath due top
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tipath
h frough surfaceso environment
Sea surfaceSea surface
TxRx
seabed
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Time vary
Time variation is due to:Time variation is due to:− Platform motion− Internal waves− Surface waves
Effects of time variabilityEffects of time variability− Doppler Shift
cuff cd =
− Time dilation/compression of the
Channel coherence times often
c
Channel coherence times oftenChannel quality can vary in < 1
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ying channel
received signal
n << 1 secondn << 1 second. 1 second.
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Acoustic FocusingTime-Varying Channel Impulse Response
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Time (seconds)
g by Surface WavesDynamics of the first surface scattered arrival
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Multipath and Time V
Ch l t ki dChannel tracking and q− Equalizer necessary an
Coding and interleavingCoding and interleaving
In networks, message r
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Variability Implications
lit di ti i it lquality prediction is vitalnd beefy
gg
routing
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Shado
Sometimes there is no direct path two points. All paths are either suno paths.pProblem with communications be
instruments in upwardly refractingwater, deep water).Problem with communications be
surface in a downwardly refractingwater and deep water).
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w Zones
Clay and Medwin, ,“Acoustical Oceanography”
(unscattered) propagation between urface or bottom reflected or there are
etween two bottom mounted g environment (cold weather shallow
etween two points close to the g environment (warm weather shallow
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Shadow Zone Exa
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amples (Deep Water)
ommunicationsd Blair
22Figures from J. Preisig
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Ambie
• Ambient noise• Ambient noise – Passing ships, storms, breaking wav– p.s.d. decays as 20dB/decade ->N(f)
Primary natural sources− bubbles, rain, and biologic sources such
BubblesCan cause communications channel to di− Can cause communications channel to di
− Can increase surface scattering losses (u
− Attenuation in bubble cloud can be 20dB/
F d d t tt ti ( k 3− Freq dependent attenuation (peak near 3
− Can persist for minutes
− Cause sound (noise)
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ent Noise
ves, seismic events )= 1010 f-2 Watts/Hz re 1μPa
as snapping shrimp
isappearisappear
up to 10dB per bounce)
/meter
30kH )30kHz)
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No
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oise
Figure from:
Stojanovic, j ,WUWNeT'06
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Bubble Clou
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ud Attenuation
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25Figures from J. Preisig
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Band
C t f t iCenter frequency typica
Typical Bandwidth ~ 5-
Channel is inherently by− Modulation essential for
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dwidth
ll d 10 30kHally around 10-30kHz
15kHz
band-limitedr high rate communications
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Path loss an
P th LPath Loss− Spherical Spreading ~ r− Cylindrical Spreading ~
Absorption ~ α(f)-r
Thorp’s formula (for sea− Thorp s formula (for sea
410044
111.0)(log10 2
2
2
2
++
+=
ff
fffα
41001 ++ ff
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nd Absorption
r -1
r -0.5
a water):a water):
(dB/km) 003.0 000275.0 22 ++ f
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Short Rang
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e Attenuation
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28Figures from J. Preisig
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Long Rang
SNR( f ) =171+10log(P) − r α( f ) − 20log(h /2
60
70
80
90
1 km
30
40
50
SN
R (d
B) 10 km
50 km
-10
0
10
2050 km
100 km
0 5 10 15 20 25-20
f (kHz)
Figure courtesy of Costas
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Figure courtesy of Costas
ge Bandwidth
⎛ ⎞2) −10log(r − h /2) −10log N( f )df
f −df / 2
f +df / 2
∫⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ dB
Source: 20 Watts
h 500h = 500 m
30 35 40
s Pelekanakis
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s Pelekanakis
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Attenuation of S
Schmidt CApril 19, 2007 Underwater Co
Ballard
Schmidt, C
Sound in Seawater
Computational Ocean Acousticsommunicationsd Blair
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Computational Ocean Acoustics
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Bandwidth
M d l ti fModulation frequency m
System inherently wide
Frequency curtain effecq y− Form of covert commun
Might help with network− Might help with network
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Implications
t b k t lmust be kept low
e-band
ctnicationsk routingk routing
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Latency
P ti f dPropagation of sound s− Feedback might take se− Channel changing faste
Most underwater nodesC i ti T− Communications Tx pow
− Retransmissions costly
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and Power
l th li htslower than lighteveral seconder than feedback
s battery powered( 10 100W)wer (~10-100W)
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Example
Power A
WHOI Micromodem
DSP Tex10
Transmit Power
10 Typ
Receive 80 Power Wh
Data Rate 805 pFS
Daughter Card / Co-processor
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FS
e Hardware
Amp
Micromodem in action
Micromodem Specifications xas Instruments TMS320C5416 0MHz low-power fixed point processor
Watts pical match to single omni-directional ceramic transducer.
milliwatts hile detecting or decoding an low rate FSK packet.
-5400 bps packet types supported. Data rates higher than 80bps SK i dditi l d t b i d
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SK require additional co-processor card to be received.
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Conc
C i ti i thCommunicating in the oce− Time varying channel− Inconsistent noise− Shadow zones− Bubbles− Latency
Many questions still left to − Communications is not well− Many opportunities for adva
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clusions
i diffi ltan is difficult
be answered researched
ancesommunicationsd Blair
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Acknowle
I ld lik t th k thI would like to thank thehelping me with this pre
− Jim Preisig− Costas Pelekanakis− Henrik Schmidt− Milica StojanovicMilica Stojanovic− WHOI Acoustic team
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edgements
f ll i l fe following people for esentation:
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My Re
C di f th dCoding for the underwa
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esearch
t h later channel
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