Introduction to Wireless Sensor Networks (WSN)

Wireless Sensor Networks
Prof. Ravindra Joshi
Department of Engineering Sciences
International Institute of Information Technology, I²IT
www.isquareit.edu.in

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Agenda
 Introduction to Wireless Sensor Networks (WSN)
 Wireless Sensor Networks and Mobile Ad-hoc
Networks (MANETs)
 Current Research in Wireless Sensor Networks
 Key Challenges
International Institute of Information Technology, I²IT, P-14, Rajiv Gandhi Infotech Park, Hinjawadi Phase 1, Pune - 411 057
Phone - +91 20 22933441/2/3 | Website - www.isquareit.edu.in | Email - info@isquareit.edu.in

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Wireless sensor networks
 Wireless sensor network is a distributed system
consisting of a large number of low-cost wireless
sensor nodes equipped with a small processor with
limited memory, RF trans-receiver, antenna, sensing
elements and are powered with small batteries and
solar cells.
 It’s a heterogeneous system, consisting of various types
of sensor nodes, actuators and operating systems.
 Sensor nodes operate under constraints of memory,
size, computational power, overall cost and limited
energy sources such as batteries / solar cells.

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Wireless sensor networks
 Main components are,
 Sensor nodes
 Sink nodes or base nodes
 Access points connecting WSN to the wired network
Sensor nodes
Sink nodes
Sink nodes
Sensor fields

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Components of Wireless sensor networks
 Sensor node is a basic component in any wireless
sensor network.
 It consists of sensing, computing and communication
capabilities and also has an “on-board” power source.
 After the field deployment, sensor nodes communicate with
each other with a multi-hop approach and collect information
using either continuous or event driven modes.
 Location and positioning information is also exchanged with GPS
or Local positioning algorithms.
 Global view of the phenomena or object is constructed after
processing the information collected from sensor nodes
 Once the battery get exhausted, sensor node can’t be used any
further.

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 Sink node (or base node) is another important
component in any wireless sensor network.
 They have enhanced capabilities such as more computational
power, memory, energy, storage and communication capabilities
 All sensor nodes within a sensor field communicate with this
base node periodically and to exchange the field information
 The processing capability of the individual node is limited but
the aggregate processing power of the entire network is sizable.
 Sink nodes are connected to wired network through access points
and act as interface between users and the sensor network.
 Users can inject queries and gather information of their interest
from the base nodes.
Components of Wireless sensor networks

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Communication between sensor nodes
(b) Self-configuration transition(a) Communication Hole (c) Final State
Help
Messages
Data Message
SinkSource SinkSource
Neighbor
Announcements
Messages
Data
Message
SinkSource
Active NeighborPassive Neighbor
 The nodes can be in active or passive state:
 Active nodes forward data packets (using a routing mechanism
that runs on the topology).
 Passive nodes do not forward packets but might sleep or
collect network measurements.
 10 to 1000 nodes, 5 m to 50 m spacing between the nodes

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Applications of wireless sensor networks
 Wireless Sensor Networks find numerous applications
in various areas as mentioned below,
 Environment monitoring and protection:
 Monitoring of seismic activities/ data collection
 Warning of earthquakes and floods
 Weather monitoring and forecasting
 Agricultural applications:
 Monitoring of soil humidity and temperature
 Detection of toxic levels in soil and water contamination
 Leakage in pipelines, risk of explosions for gas/oil pipelines
 Water pressure monitoring in dams and reservoirs
 Understanding of soil structure

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 Protection of buildings:
 Fire alarms
 Burglar alarms/ Intruder detection
 Structural condition assessment of buildings, bridges
 Military applications:
 Soldier tracking
 Battlefield tanks / vehicles tracking
 Invading remote and inaccessible areas
 Industrial applications:
 Inventory control
 Process automation

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 Automotive Engineering:
 Monitoring of engine parameters
 Noise and pollution measurements
 Structural condition assessment of vehicles
 Medical applications:
 Biomedical applications/ measurements
 Monitoring of human body with embedded sensors
 Space applications:
 Automatic positioning
 Sensing of humidity, gravitational force
 Marine Engineering:
 Study of marine life and water contamination

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Information Processing in Wireless sensor networks
Processor Platforms Radios Sensors
Operating Systems
Localization Time Synchronization Medium Access Calibration
Collaborative Signal Processing
Data-centric Routing Data-centric Storage
Querying, Triggering
Aggregation and Compression
Collaborative Event Processing
Monitoring
Security

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Hardware: Platforms, Radios & sensors
 Processors
– Atmel
– StrongARM
– X-Scale
 Radios
– Chipcon CC1000
– Bluetooth
– Zigbee
 Sensors
 Platforms
– Mica-2
– Stargate
– iMote

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Processor comparison
Atmel
ATMEGA128(L)
Strong ARM
SA1100
Intel XScale
Type Micro Controller Microprocessor Microprocessor
Architecture Harvard, 8-bit RISC Harvard 32-bit RISC Harvard 32-bit RISC
Speed 8MHz/16MHz 206MHz 200/300/400 MHz
Cache/
Memory
128KB programming
memory
4KB data memory
16KB instruction
cache
8KB data cache
32KB instruction cache
32KB data cache
Power Draw run mode: 16.5mW
sleep mode: < 60µW
run mode: 800 mW
idle mode: 210 mW
sleep mode: 50µW
run mode: 400 mW
idle mode: 160mW
sleep mode: 50µW
Example
Platforms
Mica2 mote Compaq iPAQ3700 Compaq iPAQ3900

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Radios
 Low power, short range
 Relevant criteria
– Frequency
– Modulation scheme
– Encoding scheme
– Data rates
– Frequency diversity
 Power considerations
– Receive power
– Transmit power
– For short range communication,
the two are comparable

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Sensors
 Small (coin, matchbox
size) nodes with
– Processor
• 8-bit processors to x86
class processors
– Memory
• Kbytes – Mbytes range
– Radio
• 20-100 Kbps
 Battery powered
 Built-in sensors

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Operating systems
 Depending the platform, various choices are available
 Tiny OS
 Embedded Linux
 -OS
 Tiny OS is most suitable
 Developed by University of California, Berkley
 Event driven execution, No polling, No blocking
 Concurrency intensive operation, multi-threads based
 Light weight
 Easy to integrate with hardware

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Hardware platforms using Tiny OS
Crossbow mica Crossbow mica 2 Intel Mote
CPU ATmega128L ATmega128L(4MHz) ARM core(12MHz)
Program
memory
128k Flash memory 128k Flash memory 512k Flash memory
Data
Memory
4K SRAM 4K SRAM 64K SRAM
Radio RFM TR1000 ChipCon CC1000 Bluetooth
Data rate 40 Kbps 76.8 K Baud 1 Mbps
Frequency 916.50 MHz 315/433/868/915MHz 2.4 GHz

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Wireless sensor networks & MANETS
 A mobile ad-hoc network (MANET) is a self-configuring
network of mobile routers and associated hosts connected
by wireless links.
 The mobile routers are free to move randomly and organize
themselves arbitrarily, hence the network topology may
change rapidly and unpredictably.
 This network may operate in stand alone manner or can
be connected to the Internet.
 It has less number of nodes compared to the wireless
sensor network. E.g. communication between vehicles
and roadside equipment (VANETS)

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Comparison of WSN & MANET
WSN
- More nodes are deployed (from
10 to 1000)
- Nodes have less processing power
- Nodes are miniature, low cost and
can not be easily replaced once
battery runs out, as they are
distributed over larger distances
- Nodes do not require human
interaction and can remain
unattended for a longer time
- Redundant information is collected
from neighboring nodes by the sink
MANET
- Less number of nodes are
deployed (from 10 to 100)
- Nodes have more processing
power and have less constraints
of memory, energy resources
etc.
- Nodes can be expensive
and can be replaced, if required
- Nodes are spread over less
distances
- Redundant information is not
collected by neighboring nodes

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Current research in wireless sensor networks
 Optimization of network lifetime:
 Requires less transmission power to be used
 Trade-off between network lifetime and reliability
 Minimize the battery consumption:
 Reduce the communication related and processing power
 Use of sleep/ inactive modes
 Routing algorithms:
 Transmission power is closely related to the route selection
 Algorithms for access control:
 They should consume minimum power

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Key technical challenges faced
 Scalability of network protocols:
 Since the number of nodes are large
 Designing simple, fast, efficient routing algorithms:
 Objective is to reduce the communication related power
 Optimum route selection between the available routes
 Fast convergence
 Less overheads
 Distributed signal processing:
 Mobility and security issues of the sensor nodes:

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 Designing simple algorithms for localization and discovery
of nodes, time synchronization.
 Media Access Control (MAC) layer issues:
 Collision avoidance
 Topology control for higher energy efficiency
 Trade-off between energy efficiency and latency, errors
 Bandwidth utilization
 Scalability in node density
 Reduce idle listening, collisions, control overheads, overhearing
 Improve physical/ radio layer performance

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 Fast information retrieval:
 Topology adaptation and control:
 Topology adaptation for higher node density, Environmental
changes, Redundant deployments
 Topology control schemes such as sharing workload within
cluster, removal of redundant links, data driven schemes

For further queries,
Kindly contact:
Prof. Ravindra Joshi
Associate Professor, Dept. of Engg. Sciences
International Institute of Information Technology (I2IT)
Email: ravindraj@isquareit.edu.in
Mobile: +91 9822021594

Introduction to Wireless Sensor Networks (WSN)

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