asp term paper ppt1

8/10/2019 ASP Term Paper Ppt1

1/20

ADVANCED ADAPTIVE SIGNAL

PROCESSING TECHNIQUE FORUNDERWATER ACOUSTIC

COMMUNICATION

LOKENDER SINGH SHEKHAWATVISHWA KELAIYA


2/20

CONTENT

1. UNDERWATER ACOUSTIC COMMUNICATION

2. WHY ACOUSTIC COMMUNICATION

3. CHALLENGES

4. DOPPLER

5. MULTIPATH PROPAGATION

6. SIGNAL PROCESSING7. DECISION FEEDBACK EQUALIZER

8. CONCLUSION


3/20

UNDERWATER ACOUSTIC

COMMUNICATION

Underwater Acoustics is the study of propagation of sound in

water & interaction of mechanical waves that constitute with

water & its boundaries.

Typical frequencies associated with Underwater Acoustics are

10Hz to 1MHz.

The propagation of sound in the ocean at frequencies lower

than 10 Hz is not possible.

Frequencies above 1 MHz are rarely used because they are

absorbed very quickly.

Underwater Acoustics is also known a HYDROACOUSTICS.


4/20

UNDERWATER ACOUSTIC

COMMUNICATION


5/20

WHY ACOUSTIC COMMUNICATION

Radio waves propagate at long distances through conductivesea water only at extra low frequencies (30-300 Hz), which

require large antennae and high transmission power.

Optical waves do not suffer from such highattenuation but are affected by scattering. Moreover,transmission of optical signals requires high precision in

pointing the narrow laser beams.

Acoustic waves are the single best solution for communicatingUnder water.


6/20

PARAMETER VARIATION IN

DIFFERENT UNDERWATER LAYERS


7/20

CHALLENGES

Multipath Propagation

Doppler Effect

Time Variation of the Channel

Bandwidth Limitation

Signal Attenuation


8/20

DOPPLER

There are two aspects to cause the Doppler:The motion of sea surfaces and currents and

The relative motion between transmitter and receiver.

Doppler frequency shift is estimated byusing cyclic prefix and compensated by

resampling the received signal.


9/20

Multipath structure depends on the channelgeometry, signal frequency, sound speed profile.

Models are used to obtain a more accurate prediction

of the signal strength.

Ray model provides insight into the mechanisms of

multipath formation:

Deep water Ray bending

Shallow water Reflections from bottom.

MULTIPATH PROPAGATION


10/20

MULTIPATH INTERFERENCE UNDER

WATER COMMUNICATION


11/20

TIME STRUCTURE

Multiple paths as visible in the envelope of real time

domain signal.

Approximate dimensions: water depth 90m,

horizontal range 1000 m, source depth 15m, receiver

depth 83 m


12/20

12

Bandwidth-efficient modulation (PSK, QAM)

Phase-coherent detection

Synchronization

Equalization

Multichannel combining

SIGNAL PROCESSING


13/20

DECISION FEEDBACK EQUALIZER

(DFE)

DFE is a non-linear equalizer

Feedback filter: ISI cancellation using previous

receiver decisions

Feed-forward filter: ISI cancellation on the

transmitted symbols

Advantages:

Performance comparable to the optimum

demodulator but with much lower

computational complexity

Low noise enhancement


14/20

DFE BLOCK DIAGRAM

+Feed-forward

Filter

Feed-back

Filter

DecisionDevice

yN(t)

_

SN(k)N(k)

ISI(N-1)(t)


15/20

CHANNEL ESTIMATOR AND

EQUALIZER IMPLEMENTATION

Two major possibilities for implementing the

channel estimator and the equalizeradaptively are : -

1. Fixed Channel Estimate/Adaptive Equalizer

2. Adaptive Channel Estimate/Adaptive

Equalizer


16/20

TAP SELECTION

Three Major Approaches : -

1. Optimally Sparsed Filter

2. Approximation of the Optimization Criterion

3. An Ad Hoc Method


17/20

MULTICHANNEL CASE

Pre-combiner.

..Equalizer 1

Equalizer 2

Decision

Channel estimation &Post cursor ISIcomputation

PhaseCorrection

e(n)

To parameterupdate

trainingsequence

1()

()

d(n)

Datadecision

-

--

+


18/20

CONCLUSION


19/20

REFERENCE


20/20

The End

Questions?

Thank You!

asp term paper ppt1

Documents