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KAIST
A Survey of Practical Issues in Underwater Networks
Jim Partan, Jim Kurose, and Brian Neil Levine, WUWNet’06
2007. 9. 20
Kim Taesung
Contents
Introduction
Underwater network operating regimes
Physical layer
MAC Protocols
Mobility and sparsity
Energy efficiency
Conclusions
A Secure Group Key Management Scheme for Wireless Cellular Network
Introduction
Highlight differences between terrestrial radio sensor networks and underwater acoustic sensor networks
Characteristics of Underwater networks
More expensive equipment, higher mobility, sparer deployments, different energy regimes.
Application of Underwater Networks
Environmental Monitoring
pollution monitoring (chemical, biological, etc.), monitoring of ocean currents and winds, improved weather forecast, detecting climate change.
Disaster Prevention
measure seismic activity from remote locations and provide tsunami warnings to coastal areas.
Assisted Navigation
Sensors can be used to locate dangerous rocks or shoals
Distributed Tactical Surveillance.
Mine Reconnaissance
Off-the-shelf oceanographic sensors
Conductivity, Temperature, and Depth (CTD):
$3k-$12k
Acoustic Doppler Current Profiler
(ADCP): $25k
Seismometer: $10k
Autonomous Underwater Vehicles
Anchored sensors AUV
Physical Layer
Underwater communication uses acoustics
10kHz ~ 1MHz
Speed of sound underwater is 1500 m/s
Large propagation delays
Multipath interference is common
Frequency-dependent is generally time-varying, causing fading.
Shadow zones where almost no acoustic signal exists
This effect cause network connectivity dropouts.
Technological Limitations
Communication is always half-duplex
Acoustic transducers cannot simultaneously transmit and receive.
AUVs can transmit at high data rates but harder for them to receive at high rates.
High data rate is 5k bits/sec at a range of 2Km
Low data rate is 80 bits/sec
Main reasons are the propulsion noise and difficulties in mounting receiver arrays.
The asymmetry in send and receive data rates
Star topologies with base stations.
MAC Protocols
J.Rice describe Seaweb
Seaweb have used hybrid TDMA-CDMA
Deployment takes more than a day.
Covering region of over 100km2
Freitag describe Mine Countermeasures(MCM)
A single hop, star-topology
1 hour deployment, 5km2
TDMA with low rate command and high rate data
Smith describe ad hoc network protocol based on CSMA/CD
Hidden terminal problem can be solved by MACA, MACAW and FAMA
Several people adopted these protocol in underwater networks
Park and Rodoplu adapt energy efficient protocol like S-MAC
CDMA in underwater networks
CDMA is a conflict-free multiple access
Each user is assigned a different spreading code
Users can transmit packets without considering other are doing
This solve many of MAC problems
Near-far problem
Received power for each users was equal.
Closed-loop power control update in CDMA-based cell phone.
Power control is a difficult and open problem
Underwater networks have a time-varying, half-duplex channel with a low propagation speed.
Mobility and Sparsity
Terrestrial sensor networks assume
Fairly dense, continuously connected coverage of an area using inexpensive, stationary nodes
Costs of underwater networks
Fabrication
An acoustic modem costs roughly $3K without sensors
The rugged construction required to survive storms.
Deployment
Research ships cost from $5k/day for a small coastal ship to $25k/day for a large ocean-going ship
Recovery
Since nodes are not disposable, recovery will remain a costly operation.
AUVs are a key element in most underwater network architetures
Due to the economics and flexibility
Contention between navigation and data signals
Autonomous mobile vehicle need navigation information
This cannot be supplied by GPS
It is supplied by acoustic transponders
Need to share the channel between network communication and navigation signals.
Freitag described results from passive navigation systems.
Ouimet described broadcast ping packet
ICoN prioritorize navigation and communication packet
AUVs receive adequate navigation information, yet are still responsive to command.
Energy Efficiency
Energy is limited in both terrestrial and underwater sensor networks
Communication energy costsTransmit power dominate
100 times more than receive power
50W for transmitting0.2W for listening and 2W for decoding
Range of 2 – 3Km at a 25kHz, 80bit/sec to 5kbits/sec
AUV Energy costPropulsion power dominates network communication power
As an example, REMUS AUV30W for hotel power load : non-propulsion
15W – 110W for propulsion power: 1.5m/s – 2.9m/s
For high speed AUV, communication energy can be neglected
Conclusions
Underwater network will be mobile and sparse than terrestrial network
Due to different energy and economic considerations
A Secure Group Key Management Scheme for Wireless Cellular Network
Time for
Any questions?
Thank you for listening !