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 !