1. Wireless Sensor Networks

2. Introduction to Wireless Sensor Networks Basic Features of WSNs
Outline
Introduction to Wireless Sensor Networks
Basic Features of WSNs
Applications
Factors Influencing WSN Design
Localization and Coverage Issues
Topology Control
Security of Sensor Networks
Data management
7/2009 (L. Ni)

3. Sensor Networks: Purpose: Introduction
Composed of a large number of low-cost, low-power, multifunctional sensor nodes, densely deployed either inside the phenomenon or very close to it.
Sensor node consists of sensing, data processing, and communicating components
The positions of sensor nodes need not be engineered or pre-determined
Purpose:
To monitor, combine, analyze and respond to the data collected by hundreds (thousands) sensors distributed in the physical world in a timely manner.
7/2009 (L. Ni)

4. Self-organizing capabilities
Basic Features of WSNs
Self-organizing capabilities
Short range broadcast communication and multi-hop routing
Dense deployment and cooperative effort of sensor nodes
Frequently changing topology due to fading and node failures
Limitation in energy, transmit power, memory and computing power
7/2009 (L. Ni)

5. Applications（1）：Military
Monitoring friendly forces, equipment and ammunition
Reconnaissance of opposing forces and terrain
Battlefield surveillance
Battle damage assessment
Nuclear, biological and chemical attack detection
Battlefield surveillance
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Urban warfare

6. Applications（2）：Environmental
Great Duck Island Ecosystem Monitoring
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7. High-speed Wireless LAN (WLAN)
Applications（3）：Home
Sensors Modules
High-speed Wireless LAN (WLAN)
WLAN-Piconet
Bridge
Piconet
WLAN Access
Point
Sensor Management
Sensor Fusion
Speech
Recognizer
Database
& Data Miner
Middleware Framework
Wired Network
Network Management
Networked Toys
Sensor Badge
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Smart Kindergarten Project: Sensor-based Wireless Networks of Toys

8. Factors Influencing WSN Design
Fault tolerance
Scalability
Production costs
Operating environment
Sensor network topology
Hardware constraints
Transmission media
Power consumption
7/2009 (L. Ni)

9. Fault tolerance（1）
Failures:
lack of power
physical damage in harsh environment
Interference by other objects (e.g. radios) and other sensors.
Fault tolerance: the ability to sustain sensor network functionalities without any interruption due to failures
The environment is important to the fault tolerance of algorithms and protocols
7/2009 (L. Ni)

10. Density also depends on the applications.
Scalability（2）
Number of sensors
hundreds, thousands, to millions, depending on the type of applications.
Good scalability
Architecture and protocol design should have very good scalability
Density also depends on the applications.
7/2009 (L. Ni)

11. Per node cost is important for large sensor networks.
Costs（3）
Per node cost is important for large sensor networks.
It has to be kept low.
Bluetooth radio system:
$5 now, but still too expensive for sensors, targeted to be < 50c.
More challenging, with large amount of functionalities
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12. Unique Hardware Constrains（4）
Low computational power
Current mote processors run at < 10 MIPS
No enough horsepower to do real signal processing
Limited memory
Poor communication bandwidth
Current radios achieve about 10 Kbps per mote
(Zigbee) radios now available at 250 Kbps
But with small packets, real data rate is about 25 kbps
Limited energy budget
2 AA motes provide about 2850 mAh
Coin-cell Li-Ion batteries provide around 800 mAh
Solar cells can generate around 5 mA/cm2 in direct sunlight
7/2009 (L. Ni)

13. Sensor network topology（5）
Topology maintenance a challenging task
# of nodes, failures, dynamics etc
Pre-deployment and deployment phase
no careful planning: the installation cost, no need for any pre-organization and pre-planning, the flexibility of arrangement, and better self-organization and fault tolerance.
Post-deployment phase
topology changes are due to change in position, reachability (due to jamming, noise, moving obstacles, etc.), available energy, malfunctioning, etc
How to maintain the topology change?
Re-deployment of additional nodes phase
Adding new sensors
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14. Diverse transmission media
Wireless communication, formed by radio, infrared or optical media
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15. Sensing, communication, and data processing
Power Consumption（7）
Sensing, communication, and data processing
Communication
A sensor node expends maximum energy in data communication, the active power + the start-up power consumption
Data processing
Much less, local data processing is crucial in minimizing power consumption in a multi-hop sensor network.
7/2009 (L. Ni)

16. Localization and Coverage Issues
Finding locations of sensors without GPS
One-hop or multi-hop time synchronization (important for scheduling of sensor nodes).
Placement of data-sinks for efficient data collection or network throughput.
Network connectivity (or area coverage) and node density.
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17. Dynamic, distributed (localized), and efficient.
Topology Control
QoS topology control
Dynamic, distributed (localized), and efficient.
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18. Security of Sensor Networks
Light-weight cryptographic primitives
Light-weight security protocols for key distribution / key management / authentication
Intrusion detection / intrusion tolerance
Secured routing (lack of security infrastructure)
7/2009 (L. Ni)

19. Data management
Data Aggregation a key enabler for efficient networking
Other options – data storage, broadcasting aggregates – also well supportable
7/2009 (L. Ni)