Presentation Title Propagation and Scattering Effects in Underwater Acoustic Communication Channel Team Members Students Name Reg No 1 V AISHWARYA ID: 930125
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Subject Name :WIRELESS COMMUNICATIONPresentation Title : Propagation and Scattering Effects in Underwater Acoustic Communication Channel
Team Members: Students Name Reg . No: 1.V. AISHWARYA 210617106002 2.S. BHAVANI SRUTHI 210617106019 3.J. DINU 210617106025 4.B. AKASH 210617106005 5.U. AKASH 210617106006 6.E. AMARAN 210617106008 7.R. VIJAY ANAND 210617106089
JEPPIAAR INSTITUTE OF TECHNOLOGY“Self-Belief | Self Discipline | Self Respect”Department of Electronics and communication Engineering
3/31/2020
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JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide2CONTENT Traditional approach for ocean bottom monitoring Sound as a wireless medium BW limitations Variations in speed of sound Multipath Propagation Noise Scattering Propagation speed Signal ProcessingUnderwater Applications Challenges3/31/20202JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide3Traditional approach for ocean bottommonitoringDeploy underwater sensors to record data during the monitoring mission, and then recover the instruments.Disadvantages :• Real time monitoring is not possible.• No interaction is possible between onshore controlsystems and the monitoring instruments.• If failures or misconfigurations occur, it may not be possible to detect them before the instruments arerecovered.• The amount of data that can be recorded during the monitoring mission by every sensor is limited by the capacity of the onboard storage devices.
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Slide4Use sound as the wirelesscommunication medium• Radio waves propagate at long distances through conductive sea water only at extra low frequencies (30-300 Hz), which require large antennae and hightransmission power.• Optical waves do not suffer from such high attenuation but are affected by scattering. Moreover, transmission of optical signals requires high precisionin pointing the narrow laser beams.3/31/20204JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide5UNDERWATER ACOUSTICCOMMUNICATION SYSTEM3/31/20205JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide6BANDWIDTH LIMITATIONS3/31/20206JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide7• Multipath structure depends on the channelgeometry, signal frequency, sound speed profile.•Models are used to obtain a more accurate predictionof the signal strength.• Ray model provides insight into the mechanisms ofmultipath formation:deep water — ray bendingshallow water — reflections from bottom.Multipath propagation3/31/20207JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide8Mechanisms of multipath formation• Deep water: a ray, launched at some angle, bendstowards the region of lower sound speed (Snell’slaw).Continuous application of Snell’s law à ray diagram (trace).
tx
Rays bend repeatedly towards the depth at which the sound speed is minimal.
Shallow water
: reflections at surface have little loss; reflection loss at bottom depends on the type (
sand,rock
, etc.), angle of incidence, frequency
.
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JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide9tx
rx
Multipath gets attenuated because of repeated reflection loss, increased path length
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JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide10Propagation speed
DOPPLER EFFECT tàt(1 v/c) fàf(1±v/c)Nominal: c=1500 m/s (compare to 3 x 108 m/s)Two types of problems:Motion-induced Doppler distortion (v~ few m/s for an AUV)
Long propagation delay.
3/31/202010
JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide11Signal processingBandwidth-efficient modulation (PSK, QAM)Phase-coherent detectionSynchronization
EqualizationMultichannel combining3/31/202011JEPPIAAR INSTITUTE OF TECHNOLOGY
Slide12Underwater applicationsSeismic monitoring,Pollution monitoring,Ocean currents monitoring,
Equipment monitoring and control,Autonomous Underwater Vehicles (AUV).To make these applications viable, there is a need to enable underwater communications among underwater devices3/31/202012JEPPIAAR INSTITUTE OF TECHNOLOGY