Wireless Sensor Networks

flangeeasyMobile - Wireless

Nov 21, 2013 (3 years and 6 months ago)

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Wireless Sensor Networks

-

overview
-

Wireless Sensor Networks


Introduction


Terminology


Applications


Technical Challenges


Examples


Conclusion



Introduction


A Wireless sensor network (WSN) is a network that is formed
when a set of small sensor devices that are deployed in an ad hoc
fashion cooperate for sensing a physical phenomenon.




Wireless Sensor Network consists of base stations and a number
of wireless sensors.

Wireless Sensor Network

Introduction

-
basic features
-


Self
-
organizing capabilities


Short
-
range broadcast communication and
multihop routing


Dense deployment and cooperative effort of
sensor nodes


Frequently changing topology due to fading and
node failure


Limitation in energy, transmit power, memory,
and computing power

Terminology



Sensor: The device


Observer: The end user/computer


Phenomenon: The entity of interest to the
observer


Applications


General engineering


Agri
culture and enivronmental monitoring


Civil engineering


M
ilitary applications


H
ealth monitoring and surgery

Applications


-
general engineering
-


A
utomotive telematics (cars networked)


F
ingertip accelerometer virtual keybords


S
ensing and maintenance in industrial plants


A
ircraft drag reduction


S
mart office spaces


T
racking of goods in retail stores


T
racking of containers and boxes


S
ocial studies (human interaction and social
behavior)


C
ommercial and residential security

Applications


-
agr
iculture and
e
nvironmental
m
onitoring
-


P
recision agriculture (crop and livestock
management)


P
lanetary exploration (inhospitable environments)


G
eophysical monitoring (seismic activity)


M
onitoring of freshwater quality


Zebranet
project


H
abitat monitoring


D
isaster detection (forest fires and floods)


C
ontaminant transport

Applications

-
c
ivil
e
nginneering
-


M
onitoring of structures


U
rban planing (groundwater paterns, percent of
CO
2
cities are expelling,...)


D
isaster recovery (locating signs of life after
earthquake)

Applications

-
m
ilitary
a
pplications
-


A
sset monitoring and management


S
urveillance and battle
-
space monitoring


U
rban warfare (sensors in buildings, movement
of friend and foe, localizing snipers,...)


P
rotection (for sensitive objects)


S
elf
-
healing minefields

Applications

-
h
ealth
m
onitoring and
s
urgery
-


M
edical sensing (physiological data transmitted
to a computer o
r
physician, wireless sensing
bandages worn of infection, sensors in the blood
stream which prevent coagulation and
thrombosis)


M
icro
-
surgery (swarm of MEMS
-
based robots)


Technical challenges

-
performance metrics
-


Energy efficiency/System Lifetime


Latency


Accuracy


Fault tolerance


Scalability


Transport capacity/throughput


Production costs


Sensor network topology


Transmission media


Power supply


Communication architecture


Security



Technical challenges

-
sensor network topology
-


Hundreds of nodes require careful handling of topology
maintenance.


Predeployment and deployment phase


Numerous ways to deploy the sensors (mass, individual
placement, dropping from plane..)


Postdeployment phase


Factors are sensor nodes’ position change, reachability due to
jamming, noise, obstacles etc, available energy,
malfunctioning


Redeployment of additional nodes phase


Redeployment because of malfunctioning of units


Technical challenges

-

transmission media
-


In a Multihop sensor network nodes are linked by Wireless
medium


Radio Frequency (RF)


Most of the current sensor node HW is based on it


Do not need Line of Sight


Can hide these sensors


Infrared (IR)


License free


Robust to interference


Cheaper and easier to build


Require line of sight


Short Range Solution


Optical media


Require Line of sight


Technical challenges

-
power supply
-


Power

supply usually the limiting factor in terms
of size and cost and life time


Power sources can be classified as


Energy Reservoir (Energy storage in form of
chemical energy; batteries)


Power Distribution methods


Power Scavenging methods

Technical challenges

-
power supply (contd.)
-

Power distribution


Distribution of power to nodes from a nearby
energy rich source


Wires (defeats purpose of wireless communication)


Acoustic waves (very low power level)


Light or lasers (Directed laser beams to large number of
nodes very complicated )


Electromagnetic (RF) power


distribution


Example:
µ
-

chip developed

by Hitachi for RFID devices


Technical challenges

-
power supply (contd.)
-

Power Scavenging


Energy provided depends on how long the source is in
operation


Used usually to charge secondary batteries


Photovoltaic Cells


Temperature gradient


Human Power (average human body burns 10.5 MJ of energy
per day)


Wind / Air flow


Vibrations

Technical challenges

-

power consumption
-


Sensing


Communication


Data processing

Components of a sensor node

Technical challenges

-

power consumption (contd.)
-



Key to Low Duty Cycle
Operation:


Sleep


majority of the
time


Wakeup


quickly start
processing


Active


minimize work
& return to sleep

Technical challenges


-
Communication architecture
-


C
ombines power and
routing awareness,


Integrates

data with
networking protocols,


Communicates

power
efficiently through the
wireless medium


promotes cooperative
efforts of sensor nodes.

The sensor network protocol stack

Technical challenges


-
communication architecture (contd.)
-

Application layer


An application layer management protocol makes the

hardware and software of the lower layers transparent to

the sensor network management applications.


Sensor management protocol (SMP)


Task assignment and data advertisement protocol
(TADAP)


Sensor query and data dissemination protocol (SQDDP)

Technical challenges


-
communication architecture (contd.)
-

Transport layer


This layer is especially needed when the system
is planned to be accessed through Internet or
other external networks.


No attempt thus far to propose a scheme or to
discuss the issues related to the transport layer
of a sensor network in literature.

Technical challenges


-
communication architecture (contd.)
-

Network layer

Routing the data supplied by the transport layer.



Power efficiency is always an important consideration.


Sensor networks are mostly data centric.


Data aggregation is useful only when it does not hinder
the collaborative effort of the sensor nodes.


An ideal sensor network has attribute
-
based addressing
and location awareness.

Technical challenges


-
communication architecture (contd.)
-

Routing


Flooding
:


Broadcast based


-
High Overhead


-
Data aggregation to reduce the overhead


-
Less complex


Unicast:



Sensors can communicate with the observer directly or with the cluster
head using one to one unicast.


MultiCast:



Sensors form application
-
directed groups and use multicast to
communicate among group members.


Technical challenges


-
communication architecture (contd.)
-


Maximum available power (PA) route:
Route 2


Minimum energy (ME) route: Route 1


Minimum hop (MH) route: Route 3


Maximum minimum PA node route:
Route 3

S
elect
ing

an energy efficient route

Technical challenges


-
communication architecture (contd.)
-

Data link layer



The data link layer is responsible for the medium access and
error control. It ensures reliable point
-
to
-
point and point
-
to
-
multipoint connections in a communication network.


MAC (Medium Access Control)


Creation of the network infrastructure


Fairly and efficiently share communication resources between
sensor nodes


Error control


Forward Error Correction (FEC)


Automatic Repeat Request (ARQ).

Technical challenges


-
communication architecture (contd.)
-

Physical layer


The physical layer is responsible for frequency
selection, frequency generation, signal detection,
modulation and data encryption.


Technical challenges

-
security
-

Technical challenges

-
designed protocols
-


Examples


MIT d'Arbeloff Lab


The
ring sensor


Monitors the physiological
status of the wearer and
transmits the information to
the medical professional over
the Internet


Oak Ridge National
Laboratory


Nose
-
on
-
a
-
chip is a MEMS
-
based sensor


It can detect 400 species of
gases and transmit a signal
indicating the level to a central
control station


Examples

-

iButton
-


A 16mm computer chip armored in a stainless steel can


Up
-
to
-
date information can travel with a person or object


Types of i
-
Button


Memory Button


Java Powered Cryptographic iButton


Thermochron iButton

Applications


Caregivers Assistance


Do not need to keep a bunch of keys. Only one iButton
will do the work


Elder Assistance


They do not need to enter all their personal information
again and again. Only one touch of iButton is sufficient


They can enter their ATM card information and PIN
with iButton


Vending Machine Operation Assistance

Examples

-

Berkeley Motes
-


Small (under 1” square)
microcontroller


It consists of:


Microprocessor


A set of sensors for temperature,
light, acceleration and motion


A low power radio for
communicating with other motes


C compiler Inclusion


Development ongoing


Examples

-
iBadge


UCLA
-


Investigate behavior of children/patient


Features:


Speech recording / replaying


Position detection


Direction detection /estimation (compass)


Weather data: Temperature, Humidity, Pressure, Light

Conclusion


Wireless Sensor Networks are ideal for remote
sensing in various applications


Due to the severe power constraints there is a
need for a new set of protocols for WSN


Power consumption in hardware and OS must
be minimal


Data redundancy can be exploited to reduce
power consumption


Technology of the future!!!!