Elec6076 wireless sensor networks

Nadège Barrage Nadège Barrage -- [email protected]@soton.ac.uk

ELEC6076ELEC6076

DefinitionNetwork topologiesStandardsApplicationsConclusion

2 Nadège Barrage – ELEC6076 – Wireless Sensor Networks

3

A wireless sensor network (WSN) = various wireless nodes communicating with base stations via radio link.

It is an ad-hoc network: nodes act as forwarder, relaying data to a base station.

Nadège Barrage – ELEC6076 – Wireless Sensor Networks

4

Each node is equipped with:

One or two sensors

A wireless commu-nications device

A small micro-controller

An energy source

The sensors can measure various conditions: temperature, sound, vibration, pressure, motion, pollutants…


5

Main functions of the microcontroller:Managing data collection from the sensorsPerforming power management functionsInterfacing the sensor data to the physical

layerManaging the radio network protocol

Nodes are really cheap. Their interface and their components are very basic, so they don’t need a lot of resources (which is not the case for base stations).


6

Star Network:Star Network:

One base stationThe remote nodes can only send

or receive a message from the base station

Advantages: simple, minimum power consumptionDisadvantages: the base station must be within radio transmission range of all individual nodes


7

Mesh Network:Mesh Network:

Any node can transmit to any other node (if the node is within its radio transmission range): multihop communications

Advantages: redundancy, scalabilityDisadvantages: power consumption higher for the nodes implementing the multihop communications (battery life limited)


8

Hybrid Star-Mesh Network:Hybrid Star-Mesh Network:

The lowest power sensor nodes cannot forward messages

The other nodes are enabled with multihop capability so that the messages can be forwarded from the low power nodes to other nodes on the network

Robust and versatile network, power consumption minimum.


9

Standards → interoperability among multiple companies networks

Predominant standards for WSN communication:Wi-Fi (IEEE802.11):Wi-Fi (IEEE802.11): for local area and high

bandwidth data transfer between computers and other devices. Data transfer rate rangesData transfer rate ranges: 1 Mbps-50 Mbps Typical transmission range:Typical transmission range: 300 feetDisadvantages: power requirements quite high

Bluetooth (IEEE802.15.1 and .2):Bluetooth (IEEE802.15.1 and .2): PAN lower power than Wi-Fi using a star network topology.Disadvantages: can only support 7 nodes and relatively high power for a short transmission range


10

Zigbee (IEEE802.15.4):Zigbee (IEEE802.15.4): specifies the IEEE802.15.4 as the physical and MAC layer. It can support both star and hybrid star-mesh networks. IEEE802.15.4 is specifically designed for the requirement of wireless sensing applications. The hardware is designed to allow for the radio to be put to sleep.

Transmission frequencies: Transmission frequencies: 868 MHz/902-928 MHz/2.48-2.5 GHz

Data rates:Data rates: 20 Kbps, 50 Kbps and 250 Kbps

WirelessHART:WirelessHART: used for industrial environments, it adopts the IEEE802.15.4 as the physical layer but defines its own time-synchronized MAC layer. It uses self-healing mesh network and meets the stringent requirements of industrial control.


11

Area monitoring:Area monitoring:Common application of WSNsNodes are deployed over a region where a

phenomenon needs to be monitoredEvent detected (pressure, vibration…) → a base

station receives the information and can take appropriate action


Environmental monitoring:Environmental monitoring:Landslide detection:

WSNs used to detect the slight movements of soilData gathered by the base station → the occurrence

of landslides can be known long before it actually happens

12

Environmental monitoring:Environmental monitoring:Greenhouse monitoring:

WSNs used to control the temperature and humidity levels in greenhouses

Fall of temperature or humidity below a specific level → information transmitted by the node to the base station which can send a notification to the greenhouse manager

WSNs easy to move → ideal for this kind of application

Glacsweb:Project at the University of Southampton using

WSNs to monitor glacier behaviour.Nodes are placed on and under glaciers in Norway.


13

Industrial monitoring:Industrial monitoring:

Structural health monitoring:Sensors embedded into machines, structures and

previously inaccessible locations → condition-based maintenance

Expensive method but can prevent the cost of catastrophic failure of one of the machine or structure.

WSNs can also be used for health monitoring of large civil structures, using strain gauges.


14

Industrial Industrial monitoring:monitoring:

Industrial automation:

Use of wired sensors too cumbersome for a production line environment

Example of use: measurement of gaps where rubber seals are to be placed


15

Smart home:Smart home:

A future application !It could control almost everything in a house!



Wireless sensing networks are very versatile.Widespread development of WSNs in the futureLow power system absolutely necessary ; it is one of

wireless sensor networks’ main challenges right now

Internet:Internet:http://en.wikipedia.org/wiki/Wireless_sensor_networkhttp://www.ece.ncsu.edu/wireless/wsn.htmlhttp://microstrain.com/white/Wilson-chapter-22.pdfhttp://www.cs.utexas.edu/~shan/paper/rtas08.pdfhttp://envisense.org/glacsweb/index.html

Books:Books:Lewis, F.L., « Wireless Sensor Networks », Smart Environ-ments: Technologies, Protocols, and Applications ed. D.J. Cook and S.K. Das, John Wiley, New York, 2004.


18

Technology

Elec6076 wireless sensor networks