UNDERWATER ACUSTIC SENSOR NETWORKS (UW-

ASNs)

Daladier Jabba MolinaresDepartment of Computer Science and Engineering

University of South FloridaTampa, FL 33620

daladier@cse.usf.edu

UNDERWATER ACUSTIC SENSOR NETWORKS (UW-

ASNs) Introduction Communication architecture UW-ASN: Design challenges Principal layers

MAC Layer Network Layer Transport Layer

Clusters in Mobile Ad hoc Networks Minimum Cut problem applied to UW-ASN References Questions

INTRODUCTION

INTRODUCTION Group of sensors and vehicles deployed

underwater and networked via acoustic links, performing collaborative tasks

Equipment Autonomous Underwater Vehicles (AUVs) Underwater sensors (UW-ASN)

INTRODUCTION (Cont…) Objectives

UW_ASNs To exploit multi hop paths To minimize the signaling overhead for building

underwater paths AUVs

Rely on local intelligence Less dependent on communications from online

shores Control strategies (autonomous coordination obstacle

avoidance)

INTRODUCTION (Cont…) Applications

Environment monitoring Review how human activities affect the marine

ecosystem Undersea explorations

Detect underwater oilfields Disaster prevention

Monitoring ocean currents and winds (Tsunamis) Assisted navigation

Locate dangerous rocks in shallow waters Distributed tactical surveillance

Intrusion detection (Navy)

INTRODUCTION (Cont…)

Acoustic comms physical layer technology in underwater networks

High attenuation radio waves propagation problems

Links for underwater networks based on acoustic wireless communications (typically used)

INTRODUCTION (Cont…)

Challenges Available bandwidth is limited Propagation delayUnderwater=5 x Radio Frequency(RF)ground

High bit errors and temporary loss of connectivity Limited battery power Tendency of failure in the underwater sensors

because of corrosion

COMMS ARCHITECTURE

COMMS ARCHITECTURE Two-dimensional Underwater Sensor

Networks : for ocean bottom monitoring

Three-dimensional Underwater Sensor Networks : for ocean-column monitoring

Sensor Networks with Autonomous Underwater vehicles : for underwater explorations

COMMS ARCHITECTURE (Cont…)1. Static two-dimensional UW-ASNs for

ocean bottom monitoring Components:

*: not necessary

Gateway

COMMS ARCHITECTURE (Cont…)

Comms. Intra clusters (using CH)

Comms with the surface station

anchored

Acoustic link comms

RF comms

Satellite comms

Static two-dimensional UW-ASNs for oceanbottom monitoring (Cont…)

Problems Long distances between gateways and UW-ASNs

Power to transmit decay easy It is better multi hop paths

Bandwidth limitations Greater bandwidth for a shorter transmission distance

Increasing the UW-ASNs density generates routing complexity

Solving the problems Energy savings Increase network capacity

COMMS ARCHITECTURE (Cont…)2. Three-dimensional Underwater Sensor Networks

Components:

*: not necessary

COMMS ARCHITECTURE (Cont…)

anchored

RF comms

Satellite comms

Comms with the surface station

Acoustic link comms

Three-dimensional Underwater Sensor Networks (Cont…)

Problems If they are attached to a surface buoy

They can be easily detected by enemies Floating buoys are vulnerable to the weather and

pilfering ship navigations can be a problem

Increasing the UW-ASNs density generates routing complexity

Solving the problems Be anchored to the bottom of the ocean (to an

anchors by wires) Energy savings Increase network capacity

COMMS ARCHITECTURE (Cont…)3. Sensor Networks with Autonomous Underwater vehicles

Components:

*: not necessaryAUV

COMMS ARCHITECTURE (Cont…)

anchored

RF comms

Satellite comms

Comms with the surface station

Acoustic link comms

UW-ASN:DESIGN CHALLENGES

DESIGN CHALLENGES (Cont…) UWSNs vs Terrestrial Sensor Networks

Cost Terrestrial sensor networks will be cheaper and cheaper

with the time UWSNs are expensive

Deployment Terrestrial SNs are densely deployed UWSNs are generally more sparse

Power For UWSNs is higher

Memory Terrestrial sensors have less capacity

Basics of acoustic propagation in UWSNs Radio waves propagation for long distances

through sea water only at frequencies of 30-300 Hz

High transmission power Large antennas

Poor available Bandwidth

* In 802.11b : between 2.412 GHz to 2.484 GHz

DESIGN CHALLENGES (Cont…)

Some factors that affect the design Path loss

Attenuation provoked by absorption due to conversion of acoustic energy into heat

Because of the spreading sound energy as a result of the expansion of the wavefronts

Noise Man-made noise Ambient noise

High delay Propagation delayUnderwater=5 x Radio Frequency(RF)ground

DESIGN CHALLENGES (Cont…)

MEDIUM ACCESS CONTROL LAYER

Biomimetic Underwater Robot, Robolobster

MAC LAYER (Cont…) Multiple access techniques

Code Division Multiple Access (CDMA)

Carrier Sense Multiple Access (CSMA)

Time Division Multiple Access (TDMA)

Frequency Division Multiple Access (FDMA)

MAC LAYER (Cont…)

Proposed MAC protocols Slotted Fama

Applies control packets before starting transmission to avoid multiple transmissions at the same time

Issue: handshaking process can generate low throughput

Adapted MACA to underwater acoustic networks It uses CTS-RTS-DATA exchange and for Error detection STOP

and WAIT ARQ Retransmitting packets because of timeout in receiving ACK The source drops the communication after K trials

Problems

-Energy consumption because of repeating RTS several times before receiving a CTS

-Deadlock problems

Solutions

-To add a WAIT commands (destination tells that is busy)

-Add an assignment priority to every packet

MAC LAYER (Cont…)

MAC LAYER (Cont…) Clustering and CDMA/TDMA multiple

access For distributed UW-ASNs Communication intra cluster uses TDMA

(time slots) CDMA by each cluster using a different

code for transmission Problem

Number of code is limited Solution proposed

Reusable code (possible because the acoustic signal fades due to distance)

MAC LAYER (Cont…) Open research issues

Design access codes for CDMA taking into account minimum interference among nodes

Maximize the channel utilization Distributed protocols to save battery

consumption

NETWORK LAYER

NETWORK LAYER (Cont…)

Proactive routing protocols Dynamic Destination Sequenced Distance

Vector (DSDV), Optimizing Link State Routing (OLSR)

They are not suitable for UW-ASNs Large signaling overhead every time network

topology has to be updated All nodes are able to establish a path with others and

it is not necessary

NETWORK LAYER (Cont…)

Reactive routing protocols Ad hoc On Demand Distance Vector (AODV)

and Dynamic Source Routing (DSR) They are not suitable for UW-ASNs

It requires flooding of control packets at the beginning to establish paths (excessive signaling overhead)

High latency on establishment of paths Must of the reactive protocols rely in symmetrical

links

NETWORK LAYER (Cont…)

Geographical routing protocols Routing with Guaranteed Delivery in Ad Hoc

Wireless Networks (GFG) and Optimal local topology knowledge for energy efficient geographical routing in sensor networks (PTKF)

Establish source destination paths by leveraging localization information

A node selects its next hop based on the position of its neighbors and of the destination node

Problems They work with GPS (GPS uses waves in the 1.5 GHz band) It has not been improved the localization information in the

underwater environment

NETWORK LAYER (Cont…)

Solution proposed Network layer protocols specifically tailored to underwater

environment Example

A routing protocol was proposed that autonomously establishes the underwater network topology, control network resources and establishes the network flows using a centralized management

NETWORK LAYER (Cont…) Open research issues

Develop algorithms that reduces the latency Handle loss of connectivity using mechanisms

without generating retransmission Algorithms and protocols needs to improve the

way to deal with disconnections because of failures of battery depletion

How to integrate AUV with UW-ASNs and able communication among them

TRANSPORT LAYER

TRANSPORT LAYER (Cont…) Unexplored area It has to perform:

Flow control To avoid that network devices with limited memory

are overwhelmed by data transmissions Congestion control

To prevent the network being congested

TCP implementations are not suited The long Round Trip Time (RTT) in underwater

environment affect the throughput

TRANSPORT LAYER (Cont…) A transport layer for UW-ASNs requieres:

Reliability hop by hop In case of congestion, transport layer need to

be adapted faster to decrease the response time

Minimum energy consumption To avoid many feedbacks with the ACK

mechanism that can utilize bandwidth unnecessarily

TRANSPORT LAYER (Cont…) Open research issues

Flow control strategies to reduce not only the high delay but also delay variance of the control messages

Efficient mechanisms to find the cause of packet loss

To create solutions for handling the effect of losses of connectivity caused by shadow zones

Clusters in Mobile Ad hoc Networks

Clusters in Mobile Ad hoc Networks (Cont…)

Reduce the overhead in the network Reduce power consumption Different type of nodes

Cluster head Gateway Nodes in the cluster

Communication Intra cluster Inter cluster

Problems Hidden Terminal problem

Exposed Terminal problem

Clusters in Mobile Ad hoc Networks (Cont…)

A B C

A B C D

Clusters in Mobile Ad hoc Networks (Cont…)

Topology control (Cluster Initialization) LIDCA algorithm

lowest identifier HCCA algorithm

high connectivity Minimum cut problem (graph theory)

Contract nodes

Routing protocols Maintenance

Minimum Cut problem applied to UW-ASN (Network layer) To reduce interference

Challenge

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d e fX,a,b,c

D,e,f

Connectivity

References I. F. Akyildiz, D. Pompili, and T. Melodia. Underwater Acoustic Sensor

Networks: Research Challenges. Ad Hoc Networks (Elsevier), vol. 3(3), pp. 257–279, May 2005.

K. Kredo and P. Mohapatra. Medium Access Control in Wireless Sensor Networks. to appear in Computer Networks (Elsevier), 2006.

F. Salva-Garau and M. Stojanovic. Multi-cluster Protocol for Ad Hoc Mobile Underwater Acoustic Networks. In Proc. Of MTS/IEEE OCEANS. San Francisco, CA, Sep. 2003.

Hayat DOUKKALI and Loutfi NUAYMI. Analysis of MAC protocols for Underwater Acoustic Data Networks. 0-7803-8887-9/05. (c)2005 IEEE

Jim Partan, Jim Kurose Brian Neil Levine. A Survey of Practical Issues in Underwater Networks.

Borja Peleato and Milica Stojanovic. A MAC Protocol for Ad Hoc Underwater Acoustic Sensor Networks. WUWNet’06, September 25, 2006.

Ian F. Akyildiz, Dario Pompili, and Tommaso Melodia. State of the Art In Protocol Research for Underwater Acoustic Sensor Networks. WUWNet’06, September 25, 2006.

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Questions