acoustic technologies for underwater communication networks

7/29/2019 Acoustic Technologies for Underwater Communication Networks

1/39

Acoustic Technologies for Underwater

Communication NetworksBayan Sharif

http://www.ieccr.net


2/39

Sub-Sea Acoustic Communications

High data rate video/sonar: 16 Kbps @ 3 km

Low data rate command/control: 100 bps @10 km

Sensor data

http://www.naval-technology.com/projects/astute/index.html


3/39

Typical Applications

Command link

Very high integrity, low data rate: Control of valves, lights, pumps

Enable/disable functionsremotely

AUV navigation

Reverse link

High integrity and data-rate:

Video and sonar images

Monitoring of sensors: depth,

temperature, pressure Instrument data



4/39

Sensor nodes deployed

from helicopter or any

small vessel

Surface nodes provide acoustic

communication/tracking for

subsea nodes, GPS and

radio/satellite gateway to

central workstation

Wireless Sensor Network Potential Application Scenario

Movement with

Currents

Active buoyancy

Sensor Payload: Chemical or biological



5/39

Main Technologies

Acoustic Communications

Point-to-point

Mobility

Low Power

Other Electromagnetic

Optical

EM Acoustic

Acousto Optical



6/39

Why ~Kbps and not ~Mbps?

~Mbps can be achieved using EM

propagation, however, seawater ishighly conductive and signal

attenuation is therefore very high.

Feasible distances can only beachieved by acoustic propagation,

but only at low frequenciestherefore limiting achievable

bandwidth, hence ~Kbps.

~10 dB/m

~.001 dB/m

Joseph Hansen, Nav al Postgraduate School

Channel Range (km) Bandwidth (kHz)

Very Short < 0.1 >100

Short 0.1-1 20-50

Medium 1-10 10

Long 10-100 2-5

Very Long >100


7/39

Challenges to Acoustic Receivers

1803-1853

Mulltipath Noise Doppler

Low speed ofacoustic waves

(1500m/s) cause

Doppler effects up

to 1% for moving

underwater targets.

Sampling

clock

Transmit

waveform

Receive

waveform

Acoustic Speed



8/39

Other System-related Limitations

Battery life

Transducer frequency response roll-off Fouling/corrosion

Half-duplex transmission

Sound speed depends on depth,

temperature, salinity, etc.

http://../AppData/Local/Temp/HZ$D.928.685/HZ$D.928.686/vert1.mpg


9/39

Deployment Cost

$5000

$10000

$15000

$20000

Deployment Method

DailyCost



10/39

More about the Underwater Channel- Multipath, Doppler and Noise



11/39

Multipath: Shallow Water Channel (1 km)

Short-Term VariationLong-Term Variation

http://../AppData/Local/Temp/HZ$D.928.685/HZ$D.928.686/D1_T1_F1_C1_CH1_IR.avi


12/39

Multipath Spread and Coherence Bandwidth

14 ms, 250 Hzrms coh

rms

B

=

FFT,



13/39

Coherence time and Doppler Bandwidth

FFT

Hz4.0dBs5.21

=d

cohB

T

,

4 ms 0.4 Hz 0.0016 1rms dB =


14/39

7

3 54

2

8

1

3 m

3 m

3 m

3 m

Side view

1 m

Junctionbox

Transducer Array

Ambient Noise

http://../AppData/Local/Temp/HZ$D.928.685/HZ$D.928.686/noise8.wavhttp://../AppData/Local/Temp/HZ$D.928.685/HZ$D.928.686/noise1.wav


15/39

Adaptive Receivers

Doppler Compensation

Acoustic Receiver Structures



16/39

Adaptive Receiver with Phase Recovery

Chirp(Doppler tolerant)

BPSK-modulatedPN Sequence

QPSK-modulatedInformation Bits

Training Sequence DataChannelEstimation

ReceiveElement

Down-

conversionUnit

TimingUpdate

)(nPhaseUpdate

)( nje

AdaptiveAlgorithm

)(ny)( n

fw

MMSEFilter

DataDecisionDevice

)(nd

)(nd

)(ne

)( nb

w

FeedbackFilter

TrainingSequence

FeedforwardFilter



17/39

2D-Rake Receiver Architecture (Temporal Combiner)

From otherreceive

elements

l

)( 1 nlw

lK

Data

)(nd

)(nd

)(ne

TrainingSequence

DecisionDevice

AdaptiveAlgorithm

CarrierPhaseUpdate

)( nje

MMSE

Flter

MMSE

Flter

MMSE

Flter

MMSE

Flter

)( 2 nlw )( nlKw)( 1 nlKw

)(1 nyl )(2 nyl )(1 nylK )(nylK

)(nyls )(nz

)(1 nyl

1l

)(nrl )( 1ll nr )( lKl nr



18/39

2-D Rake Multi-channel Receiver

User 1 User 2

Channel Impulse Responses



19/39

2-D Rake Multi-channel Receiver

1x2-AC Rake:

SINRo = 10.46 dB1x1-AC Rake:

SINRo = 9.31 dB

Performance for User 2

1x4-AC Rake:

SINRo = 13.43 dB1x3-AC Rake:

SINRo = 12.51 dB



20/39

Multichannel Receiver (Spatial-Temporal Combiner)

ReceiveArray

Elements

AdaptiveAlgorithm

AdaptiveCorrelators

1

2

K

)( 1 ncw

)( 2 ncw

( )K ncw

)(1 ny

( )Ky n

)(2 ny

Data

)(nd

)(nd

)(ne

TrainingSequence

)( nb

w

FeedbackFilter

)(nz

DecisionDevice

CarrierPhaseUpdate

)( nje

)(nys

1( )x n

( )Kx n

2( )x n

0.00 0.05 0.10 0.15 0.20 0.25

time (ms)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.00 0.05 0.10 0.15 0.20 0.25

time (ms)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.00 0.05 0.10 0.15 0.20 0.25

time (ms)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22


The Sub Sea Acoustic Channel


21/39

Array Configuration

1 2

3 4

5 6

The Sub-Sea Acoustic Channel

(2km)


The Sub Sea Acoustic Channel


22/39

Array Configuration

1 2

3 4

5 6

The Sub-Sea Acoustic Channel

(2km)

Significant temporal fluctuations

during single packets implies

requirement for adaptive

techniques

Relatively little separation

between elements (a few

wavelengths) results in low spatial

correlation between fluctuations

in channel response


2 D Rake Multi channel Receiver


23/39

2-D Rake Multi-channel ReceiverPerformance for User 2

1x4-AC Rake:

S INRo

= 13.43 dB

1x3-AC Rake:

S INR o = 12.51 dB1x2-AC Rake:


S INR o = 9.31 dB

Combining Gain

6x4-AC Rake:

S I NR o = 17.91 dB6x3-AC Rake:



S INR o = 13.64 dB



24/39

Adaptive Receivers Doppler Compensation

Acoustic Receiver Structures

http://www.naval-technology.com/contractors/electrical/saft/


25/39

Conventional Adaptive Receiver Structure

with both Phase and Timing Recovery

)( nw

MMSEFilter

ReceiveElement

Down-conversion

Unit

TimingUpdate

)(nPhaseUpdate

)( nje

)(ny

DataDecisionDevice

TrainingSequence

)(nd

)(nd

)(ne

AdaptiveAlgorithm

)(nz



26/39

Doppler-Shift in Wideband Communications

Doppler shift () modelled as a time scaling:

Equivalent (for a discrete-time sampled system) to scaling of the samplingperiod (interpolation or decimation):

Then, inverse time-scaling will remove carrier/symbol shift:

Which corresponds to a scaling of the sampling frequency:

])1([][ ss TnsnTr +=

+= ss T

nrnTs

1][

ss ff )1(' +=

)()( )1( tstr +=



27/39

Doppler Compensation Methods

Block-based:

Closed-loop:

Interpolator

(1+)input

signalReceiver

/demodulator

Block Doppler

estimator

Interpolator

(1+)inputsignal

Receiver

/demodulator

Cost

function



28/39


29/39

Adaptive Doppler Compensation

Interpolation Factor

where kp is a proportional constant.

npnn kII +=+ .1*.arg nnn dy=

Down-converter

(I-Q)

Linearinterpolator(s I.s)

RxSignal Forward fil ter

h0(N taps)

SFeedback

filterg(M taps)

x0

y

Training

Sequence

d

UpdateAlgorithm

Single element structure

Element 1

ElementK

For significant Doppler shift variations arising from vehicle acceleration, a more

robust alternative would be adaptive closed loop Doppler compensation.



30/39

Block vs. Adaptive Doppler Compensation



31/39

Multichannel Receiver with Doppler Compensation

ReceiveArray

Elements

AdaptiveAlgorithm

Adaptive

Correlators

1

2

K

)( 1 ncw

)( 2 ncw

( )K ncw

)(1 ny

( )Ky n

)(2 ny

Data

)(nd

)(nd

)(ne

Training

Sequence

)( nb

w

FeedbackFilter

)(nz

DecisionDevice

CarrierPhaseUpdate

)( nje )(nys

1( )x n

( )Kx n

2( )x n

LinInterpolate

DownConvert

Down

Convert

DownConvert

Lin

Interpolate

LinInterpolate



32/39

Emerging Technologies



33/39

MIMO-OFDM

OFDM Processing efficiency

PAPR Doppler tracking

MIMO Increased throughput Processing complexity

Size constraints(e.g. ~1.5m spacing @ 10kHz)


Acoustic Networks


34/39

Acoustic Networks

Seaweb Network,

D. J. Grimmett,

Oceans 2007Challenges

Node energy sustainability Network optimisation



35/39

Physical Layer Network Coding

Without a relay the transmission power must be increasedand there is also a greater delay in exchanging messages.



36/39

PNC for Underwater Relay Networks

PNC

Mapping-1

SISO

Decoder

ModulatorEncoder

Without a relay the transmission power must be increasedand there is also a greater delay in exchanging messages.

A shorter distance means reduced transmissionpower. Employing PNC at the relay reduces thedelay in receiving messages.

Deinterleaver

Interleaver


Scheduling & Fault Tolerance


37/39

Node 5

(3km)

Scheduling & Fault Tolerance

Half-duplex communications and severe latency

Node 1

(750m)Master

Node

Node 3

(2.25km)

Node 2

(1.5km)

Node 4

(3km)

~20% throughput if all nodes are polled for data

~ 70% throughput by multi-cast data request, selecting nodes to avoid

collisions and hence exploit the channel latency.

Adaptive scheduling is vital to create an efficient subsea network

However, complexity increases with multi-hop routing and dynamic nodes. Redundant nodes can maintain connectivity and coverage in the event of

node or communication failure.

Node 5

(3km)



38/39


39/39

Thank You

Sh ifh // i

acoustic technologies for underwater communication networks

Documents