1. Wireless Sensor Network
17년 4월 22일 17시 54분 4초
Wireless Sensor Network
Dr. Monir Hossen
ECE, KUET
Department of Electronics and Communication Engineering, KUET
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2. Agendas of This Lecture
Introduction
Differences with ad hoc networks
Applications
Characteristics
Challenges
Future
Motes
Hardware Setup Overview
Department of Electronics and Communication Engineering, KUET

3. Introduction
Wireless Sensor Networks (WSNs) are networks that consists of sensor nodes which are distributed in an ad hoc manner
WSN consisting of spatially distributed autonomous devices using sensors to cooperatively monitor physical or environmental conditions:
- Temperature
- Sound
- Pressure
- Home automation
- Traffic control
- Healthcare application
Main Devices of WSN
Sensor Nodes and PANC
Department of Electronics and Communication Engineering, KUET

4. Characteristics of Wireless Sensor Networks
Wireless Sensor Networks mainly consists of sensor nodes. Sensor nodes are -
Low power device
Consist of limited memory
Energy constrained due to their small size.
Wireless networks can also be deployed in extreme environmental conditions and may be prone to enemy attacks.
Although deployed in an ad hoc manner they need to be self organized and self healing and can face constant reconfiguration.
Department of Electronics and Communication Engineering, KUET

5. Design Challenges of WSN (1/2)
Heterogeneity
=> The devices deployed maybe of various types and need to collaborate with each other.
Distributed Processing
=> The algorithms need to be centralized as the processing is carried out on different nodes.
Low Bandwidth Communication
=> The data should be transferred efficiently between sensor nodes.
Department of Electronics and Communication Engineering, KUET

6. Design Challenges of WSN (2/2)
Large Scale Coordination
=> The sensors need to coordinate with each other to produce required results.
Utilization of Sensors
=> The sensors should be utilized in a ways that produce the maximum performance and use less energy.
Real Time Computation
=> The computation should be done quickly as new data is always being generated.
Department of Electronics and Communication Engineering, KUET

7. Operational Challenges of WSNs
Energy Efficiency
Limited storage and computation
Low bandwidth and high error rates
Errors are common
Wireless communication
Noisy measurements
Node failure are expected
Scalability to a large number of sensor nodes
Survivability in harsh environments
Experiments are time- and space- intensive
Department of Electronics and Communication Engineering, KUET

8. The Growth of Sensor Networks
WSNs grown from simple point-to-point networks with simple interface protocols providing sensing and control information
The sensor node has increased onboard intelligence and processing capabilities thus providing it with different computing capabilities
The development of the Manufacturing Automation Protocol (MAP), reduced the cost of integrating various networking schemes into a plant wide system
The development of other communication protocols allowed simultaneous analog and digital communications created a sensor network
Department of Electronics and Communication Engineering, KUET

9. Enabling Technologies
Embed numerous distributed devices to monitor and interact with physical world
Network devices to coordinate and perform higher-level tasks
Networked
Exploit collaborative
Sensing, action
Embedded
Control system w/
Small form factor
Untethered nodes
Sensing
Tightly coupled to physical world
Exploit spatially and temporally dense, in situation of sensing and actuation
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10. Future of WSN Smart Home / Smart Office
Sensor nodes controlling appliances and electrical devices in the house.
Better lighting and heating in office buildings.
The Pentagon building has used sensors extensively.
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11. Biomedical / Medical Health Monitors Glucose Heart rate
Cancer detection
Chronic Diseases
Artificial retina
Cochlear implants
Hospital Sensors
Monitor vital signs
Record irregularities
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12. Military
Remote deployment of sensors for tactical monitoring of enemy troop movements.
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13. Industrial & Commercial
Numerous industrial and commercial applications:
Agricultural Crop Conditions
Inventory Tracking
In-Process Parts Tracking
Automated Problem Reporting
RFID – Theft Deterrent and Customer Tracing
Plant Equipment Maintenance Monitoring
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14. Traffic Management & Monitoring
Future cars could use wireless sensors to:
Handle Accidents
Handle Thefts
Sensors embedded in the roads to:
=> Monitor traffic flows
=> Provide real-time route updates
=> Monitor the speed of a car
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15. Typical Multi-hop WSN Architecture
WSN Normally Constitutes an Multi-hop Wireless Network
Since area of u-City is increasing:
Diameter of WSN is increased (> 10 Km)
Number of sensor nodes are increased ( > multi-decades of thousands)
Number of wireless hopes are increased (>15)
Reverse time delay is increased
Department of Electronics and Communication Engineering, KUET

16. Limitations of Multi-hop WSNs
The Multi-hop WSN Possess the Following Limitations:
- Large Time Delay
- Huge Traffic Overcrowding
- Data Repetition Multiple Times
- Huge Energy Loss
- Difficult to Protect The Failure of a Node
- Large Time for Fault Analysis
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17. Data Transmission Protocol in WSN
Two Types of Data Transaction Exist:
PANC Sensor Node
Sensor Nodes PANC DS US
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18. Routing Protocols in WSNs
Traditional Routing
Current Routing
Flooding
Gossiping
Flat-Based
Hierarchical-Based
Location-Based
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19. Flooding Protocol
A classical mechanisms to relay data in sensor networks without the need for any routing algorithms and topology maintenance. It broadcasts data.
Drawbacks:
Implosion (duplicate packet may receive)
Overlap  (two sensors send a packet and at the same time)
Resource blindness (without checking node’s status it transmits packets)
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20. Gossiping Protocol
A slightly enhanced version of flooding where the transmitting node sends the packet to a randomly selected neighbor which picks another neighbor to forward the packet to and so on.
Advantage: avoid the collapse
Drawback: Transmission delay
Department of Electronics and Communication Engineering, KUET

21. Flat-Based Routing Protocols (1/2)
All the nodes are treated equally and have the same functionality
1. Sensor Protocol for Information Negotiation (SPIN):
Sending meta -data to neighboring nodes, instead of data
Requesting for the desired data
Avoid redundant data transmission
Adaptation to remaining energy increase network lifetime
2. Directed Diffusion:
BS continuously sends query to the neighboring nodes
Node with the desired data transmit all the way back to BS
Saving energy by selecting the optimal return path
Not practical for continuous data demand cases
Department of Electronics and Communication Engineering, KUET

22. Flat-Based Routing Protocols (2/2)
3. Rumor Routing:
Variation of Directed Diffusion
Each node has an event table
Event agent flooding instead of
query flooding
Significant energy saving
Good for when number of events is less than queries
4. Minimum Cost Forwarding Algorithm (MCFA):
Each node knows the least cost path between itself and BS
Least cost path can be acquired via initialization
Saving energy by selecting the optimal return path
Good for small networks
Department of Electronics and Communication Engineering, KUET

23. Hierarchical Routing (1/3)
Higher energy nodes for transmission, lower energy nodes for sensing
Two layer routing
Increasing the life time
1. Low Energy Adaptive Clustering Hierarchy (LEACH):
Random and variation Cluster Head (CH) selection
Compression and transmission of arriving data at CHs
Constant monitoring applications
Good for small networks
Extra overhead because of clustering
Department of Electronics and Communication Engineering, KUET

24. Hierarchical Routing (2/3)
2. Self Organizing Protocol (SOP):
Mobile sensors to probe the environment
Stationary nodes as the routers
LML algorithm for routing
Energy consumption is less than SPIN
3. Virtual Grid Architecture
Symmetric, non-overlapping clusters with optimal CH
Local and global data aggregation
Hard to find the optimal global aggregators
Department of Electronics and Communication Engineering, KUET

25. Hierarchical Routing (3/3)
4. Hierarchical power-aware routing
Proximate nodes form zones
Routes through the zones which has maximum minimum residual energy
Extra algorithm can be exploited
Department of Electronics and Communication Engineering, KUET

26. Location-Based Routing
Sensor nodes are addressed based on their location
Location are acquired by GPS or via coordination among nodes
1. Geographical Adaptive Fidelity (GAF):
Network divided into zones
Only one node is awake in each zone, the rest sleep
Conserves energy by turning off unnecessary nodes
Increases the network life time
2. SPAN:
Some nodes are selected as coordinators based on their positions
Enough coordinators such that network is three-hop reachable
Not energy efficient as the others
Department of Electronics and Communication Engineering, KUET

27. Routing Protocols Based on Protocol Operation
1. Multipath routing
Increases fault tolerance
Sophisticated case: have back up paths
2. Query-based routing
Query transmitted and the date is sent back
3. Negotiation-based routing
High-level data description
Elimination of redundant data transmission
4. QoS-based routing
Balance between data quality and energy consumption
Department of Electronics and Communication Engineering, KUET

28. Hidden Terminal Problem
Hidden terminals
A and C cannot hear each other.
A sends to B, C cannot receive A.
C wants to send to B, C senses a “free” medium (CS fails)
Collision occurs at B.
A cannot receive the collision (CD fails).
A is “hidden” for C.
Solution?
Hidden terminal is peculiar to wireless (not found in wired)
Need to sense carrier at receiver, not sender!
“virtual carrier sensing”: Sender “asks” receiver whether it can hear something. If so, behave as if channel busy. A B C
Department of Electronics and Communication Engineering, KUET

29. Exposed Node Problem
Exposed node problem occurs when a node is prevented from sending packets to other nodes due to a neighboring transmitter. 
If a transmission between S1 and R1 is taking place, node S2 is prevented from transmitting to R2 as it will interfere with the transmission by its neighbor S1
However note that R2 could still receive the transmission of S2 without interference because it is out of range of S1
Department of Electronics and Communication Engineering, KUET

30. IEEE 802.11 MAC Protocol: CSMA/CA
CSMA: Sender
If sense channel idle for DIFS (Distributed Inter Frame Space) then transmit entire frame (no collision detection)
If sense channel busy then binary back off
CSMA: Receiver
If received OK return ACK after SIFS --Short IFS (ACK is needed due to hidden terminal problem)
NAV: network allocation vector
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31. Collision Avoidance Mechanisms
Problem:
Two nodes, hidden from each other, transmit complete frames to base station
Wasted bandwidth for long duration!
Solution:
Small reservation packets: RTS+CTS
Nodes track reservation interval with internal (NAV)
Department of Electronics and Communication Engineering, KUET

32. Department of Electronics and Communication Engineering, KUET
Thanks for Your Kind
Attention
Department of Electronics and Communication Engineering, KUET