Download UnderWater Acoustic Sensor Networks

UnderWater Acoustic Sensor
Networks (UW-ASN)
-Xiong Junjie
-2009.2.10
Underwater applications
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Seismic 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
devices -> Wireless underwater networking
Use sound as the wireless communication medium.
Why using sound as communication
medium in UW-ASN?
 Radio waves propagate at long distances through
conductive sea water only at extra low frequencies (30-300
Hz), which require large antennae and high transmission
power.
 Optical waves do not suffer from such high
attenuation but are affected by scattering. Moreover,
transmission of optical signals requires high precision in
pointing the narrow laser beams.
Traditional approach for ocean-bottom monitoring
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Deploy underwater sensors to record data during the
monitoring mission, and then recover the instruments.
This approach has the following disadvantages:
Real time monitoring is not possible.
No interaction is possible between onshore control
systems and the monitoring instruments.
If failures or misconfigurations occur, it may not be
possible to detect them before the instruments are
recovered.
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 (memories, hard
disks, etc).
UW-ASN 2D Architecture for ocean bottom monitoring
UW-ASN 3D Architecture for ocean bottom monitoring
UW-ASN 3D Architecture with AUVs
Differences with Terrestrial Sensor Networks
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Higher Power Consumption.
Larger Memory.
Higher Cost.
Longer latency.
Sparser Deployment.
Few Spatial Correlation.
Challenges
 Battery power is limited and usually batteries can not be
recharged because solar energy cannot be exploited.
 The available bandwidth is severely limited.
 Channel characteristics, including long and variable
propagation delays, multi-path and fading problems.
 High bit error rates.
 Underwater sensors are prone to failures because of
fouling, corrosion, etc.
 A unique feature of underwater networks is that the
environment is constantly mobile, naturally causing the
node passive mobility.
 The ocean can be as deep as 10 km.
Current research result: multi-hop
 06 “Research Challenges and Applications for
underwater sensor networking” suggests to focus on
short-range communication to avoid the many
challenges of long-range transfer.
 Mobicom workshop WuWNet07 “A delay-reliability
analysis for multi-hop underwater acoustic
communication” proves that multi-hop is very useful in
shallow underwater acoustic networks
Current research result: cross-layer design
 WuWNet07 “State-of-the-Art in Protocol Research for
Underwater Sensor Networks” believes that the
underwater environment particularly requires cross-layer
design solutions that enable a more efficient use of the
scarce available resources
Current research result: drifter model
 07 “A drift-tolerant model for data management in ocean
sensor networks” uses real experiments to prove that a
fleet of drifters monitoring model is practical as long as
the deployment locations, deployment periods, initial
drifter location are well designed.
UW-FLASHR: Achieving High Channel Utilization
in a Time-Based Acoustic MAC Protocol
 The ratio of propagation delay to transmission delay is
high
 Channel utilization: Tdata/(Tdata+Tprop)
UW-FLASHR: Achieving High Channel Utilization
in a Time-Based Acoustic MAC Protocol
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Data packet delay:1
UW-FLASHR: Achieving High Channel Utilization
in a Time-Based Acoustic MAC Protocol
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TDMA-like
No precise clock synchronization
No knowledge of propagation delays
Completely decentralized operation
Utilizing acoustic propagation delay to design MAC
protocols for underwater wireless sensor networks
 This paper also utilizes the acoustic propagation delay,
but it has no schedule, and its ideas lie in nodes
deployment to avoid collision which are really simple.
My idea
In contrast with “UW-FLASHR: Achieving High
Channel Utilization in a Time-Based Acoustic MAC
Protocol” , I tentative improvement might be:
 TDMA, synchronization, propagation is easy to calculate
 Centralized or distributed (according to network size) ,
get a more compact schedule, reduce idle listening, add
sleeping period at the end of each TDMA
 Cross-layer, handle data direction, congestion
 Model or algorithm