UNDERWATER SENSOR NETWORK

BY ADEEBA KHAN MTECH CT

General Idea

Sensor A Device that receives and respond to a signal

or stimulus. As human we perceive the world via

senses( we can hear, taste, touch, see and smell).

Machine senses through sensors like temperature sensors ,pressure sensors and light sensors.

Sensor Network Sensor networks are dense wireless networks of small, low-cost

sensors, which collect and disseminate environmental data.

Architecture of Sensor Network

Internet, Satellite, etc

Sink

TaskManager

AB

CD

EF

Sensor Node

Sensor Field

Key Technologies that enable sensor network:

Micro electro-mechanical systems (MEMS) Wireless communications Digital electronics

Terrestrial sensor network It typically consist of hundreds to thousands of inexpensive

wireless sensor nodes deployed in a given area ,either in ad hoc or in a preplanned manner.

INTRODUCTION Underwater sensor network have the

potential to enable unexplored applications and to enhance our ability to observe and predict the ocean .

Unmanned or Autonomous Underwater vehicles (UUVs, AUVs),equipped with underwater sensors are also envisioned to find application in exploration of natural underwater resources and gathering of scientific data in collaborative monitoring missions.

INTRODUCTION Underwater sensor network have the

potential to enable unexplored applications and to enhance our ability to observe and predict the ocean .

Unmanned or Autonomous Underwater vehicles (UUVs, AUVs),equipped with underwater sensors are also envisioned to find application in exploration of natural underwater resources and gathering of scientific data in collaborative monitoring missions.

APPLICATIONS It enable abroad range of application:

Ocean Sampling network Environmental monitoring Undersea Explorations Disaster prevention Seismic Monitoring Equipment monitoring Assisted Navigation Distributed Tactical Surveillance Mine Reconnaissance

CHALLENGES IN DESIGN OF UNDERWATER NETWORK

The available bandwidth is severely limited. The underwater channel is impaired because of multipath and

fading. Battery power is limited and usually batteries cannot be

recharged. Underwater sensors are prone to failures because of fouling

and corrosion.

DIFFERENCES WITH TERRESTRIAL SENSOR NETWORKS

Underwater Sensor Network has to take care of living beings that exist in Oceans and to protect their life while using autonomous vehicles and sensors . Thus these network has to be developed based on the challenges posed by the underwater environment.

Beyond that underwater sensor network is different from terrestrial sensor network in terms of :

Cost Deployment Power Memory Spatial Correlation

UNDERWATER SENSOR NETWORK COMPONENT

For realization of these networks we need different components as:UNDERWATER SENSORS The typical internal architecture of an underwater sensor is shown:

The controller receives data from the sensor and can store the data in the on-board memory, process them, and send them to other network devices by controlling the acoustic modem.These devices include sensors to measure the quality of water and to study its characteristics.

• Examples of Underwater Sensors Node:

(a) (b)

• (a) Aquacomm underwater modem • (b) LinkQuest underwater sensor nodes.

AUTONOMOUS UNDERWATER VEHICLES Autonomous Underwater Vehicles (AUVs) are programmable,

robotic vehicles that, depending on their design, can drift, drive, or glide through the ocean without real-time control by human operators.

In addition to static sensor nodes, several types of AUVs exist as experimental platforms for underwater experiments.

Examples of existing AUVs : Odyssey-class AUVs developed at MIT (small scale submarines )

Odyssey AUV

Drifters and gliders are oceanographic instruments often used in underwater exploration(simpler devices that do not encompass such sophisticated capabilities).

View of a drifter from above (left) and from below (right)

Spray glider.

COMMUNICATON ARCHITECTURE The network topology is in general a crucial factor in

determining the energy consumption, the capacity, and the reliability of a network.

The network capacity is also influenced by the network topology. Since the capacity of the underwater channel is severely limited, a it is very important to organize the network topology in such a way that no communication bottleneck is introduced.

Static 2-D UWSNs for ocean bottom monitoring Static 3-D UWSNs for ocean-column monitoring The 3-D networks of AUVs

Static 2-D UWSNs for ocean bottom monitoring:• These are constituted by sensor nodes that are anchored to the

bottom of the ocean.• Typical applications may be environmental monitoring, or

monitoring underwater plates in tectonics.• Components used :

Architecture for 2-D UWSNs.

Static 3-D UWSNs for ocean column monitoring• These include networks of sensors whose depth can be

controlled by means of various techniques.• May be used for surveillance applications or monitoring of

ocean phenomena (ocean bio/geo/chemical processes, water streams, pollution).

• Components:

Architecture for 3-D UWSNs.

3-D Networks of AUVs• These include networks of sensors whose depth can be

controlled by means of various techniques.• May be used for surveillance applications or monitoring of

ocean phenomena (ocean bio/geo/chemical processes, water streams, pollution).

AUV

The integration and enhancement of fixed sensor networks with AUVs is an almost unexplored research area which requires new network coordination algorithms such as:

• Adaptive sampling: This includes control strategies to command

the mobile vehicles to move to places where their data will be most useful.

• Self-configuration: This includes control procedures to automatically detect connectivity holes due to node failures or channel impairment and request the intervention of an AUV. Furthermore, AUVs can be used either for installation and maintenance of the sensor network infrastructure or to deploy new sensors.

Sensor network protocol stack Physical Layer :Until the beginning of the last decade, due to the

challenging characteristics of the underwater channel, underwater modem development was based on non-coherent frequency Shift Keying (FSK) modulation, since it relies on energy detection and thus does not require phase tracking, which is a very difficult task mainly because of the Doppler-spread in the UW-A channel. In FSK modulation schemes developed for underwater, the multi-path effects are suppressed by inserting time guards between successive pulses to ensure that the reverberation, caused by the rough ocean surface and bottom, vanishes before each subsequent pulse is received.

Data Link Layer :Channel access control in UW-ASNs poses additional challenges because of the peculiarities of the underwater channel, in particular limited bandwidth, and high and variable delay.

Frequency Division Multiple Access (FDMA) is not suitable for UW-ASNs due to the narrow bandwidth in UW-A channels and the vulnerability of limited band systems to fading and multi-path.

Time Division Multiple Access (TDMA) shows a limited bandwidth efficiency because of the long time guards required in the UW-A channel. In fact, long time guards must be designed to account for the large propagation delay and delay variance of the underwater channel.

Carrier Sense Multiple Access (CSMA) prevents collisions with the ongoing transmission at the transmitter side. To prevent collisions at the receiver side, however, it is necessary to add a guard time between transmissions dimensioned according to the maximum propagation delay in the network. This makes the protocol dramatically inefficient for UW-ASNs.

Network Layer :The network layer is in charge of determining the path between a source (the sensor that samples a physical phenomenon) and a destination node (usually the surface station). In general, while many impairments of the underwater acoustic channel are adequately addressed at the physical and data link layers, some other characteristics, such as the extremely long propagation delays, are better addressed at the network layer.

The existing routing protocols are usually divided into three categories, namely proactive, reactive and geographical routing protocols.

Transport Layer :A transport layer protocol is needed in UW-ASNs to achieve reliable transport of event features, and to perform flow control and congestion control. Most existing TCP implementations are unsuited for the underwater environment since the flow control functionality is based on a window-based mechanism that relies on an accurate estimate of the Round Trip Time (RTT). The long RTT, which characterizes the underwater environment, would affect the throughput of most TCP implementations. Furthermore, the variability of the underwater RTT would make it hard to effectively set the timeout of the window-based mechanism, which most current TCP implementations rely on.

Application Layer :Channel access control in UW-ASNs poses additional challenges because of the peculiarities of the underwater channel, in particular limited bandwidth, and high and variable delay.

The purpose of an application layer is multi-fold: i) provide a network management protocol that makes hardware and software details of the lower layers transparent to management applications; ii) provide a language for querying the sensor network as a whole; iii) assign tasks and advertise events and data.

SOURCES Underwater Acoustic Sensor Network -edited by Yang Xiao http://nopr.niscair.res.in/bitstream/123456789/6203/1/IJMS%

2038%283%29%20267-273.pdf Wireless Sensor Networks By Ian F. Akyildiz, Mehmet Can Vuran https://www.google.co.in/url?

sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0CDIQFjAF&url=http%3A%2F%2Fwww.ece.rutgers.edu%2F~pompili%2Fpaper%2Fpompili_dario_200708_phd.pdf&ei=yPdAVbSLKcbauQT1mYHoDg&usg=AFQjCNFTfU1ebFGjgxlnhN0PgeAsOb06Xw&sig2=_-zC3vVa5TZW98TyGFxRmA&bvm=bv.92189499,d.c2E

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