1. Introduction to Wireless Sensor Networks (WSNs)
GholamHossein Ekbatanifard
Assistant Professor

2. What is WSN? Wireless Sensor Network WSN Wireless Network
Computational
Power
Sensor
Technology
Wireless Network
WSN

3. Network
In general, the term network can refer to any interconnected group or system.
A network is any method of sharing information between two systems.

4. Deployment Challenges - Network
How scalable is the network?
How fault tolerant is the network?
How is the network affected by node failure?
What is the network latency?
What is the packet loss behavior?

5. Wireless
The term wireless is normally used to refer to any type of electrical operation which is accomplished without the use of a "hard wired" connection.
Wireless communication is the transfer of information over a distance without the use of electrical conductors

6. Deployment Challenges - Wireless
Transmission Medium
Vegetation vs desert
High vs low humidity etc
Coverage
What is the range of the mote?
Connectivity
How stable is the connection?
How is it affected by the change in battery voltage?
Power consumption
How much power does the radio use?
What happens when the voltage drops?

7. Size reduction of cellular telephones
Wireless Revolution
Size reduction of cellular telephones

8. Wireless Networking

9. Threats Disclosure of sensitive/confidential data
Denial of Service (DoS)
Unauthorized access to wireless-enabled resources
Potential weakening of existing security measures on connected wired networks and systems

10. Infrastructure-based Wireless Networks
Typical wireless network: Based on infrastructure
E.g., GSM, UMTS, …
Base stations connected to a wired backbone network
Mobile entities communicate wirelessly to these base stations
Traffic between different mobile entities is relayed by base stations and wired backbone
Mobility is supported by switching from one base station to another
Backbone infrastructure required for administrative tasks
IP backbone
Further networks
Gateways
Server
Router

11. Infrastructure-based Wireless Networks – Limits?
What if …
No infrastructure is available?
E.g., in disaster areas, under-developed countries
It is too expensive/inconvenient to set up?
E.g., in remote, large construction sites
There is no time to set it up?
E.g. in military operations

12. Solution: (Wireless) Ad hoc Networks
Try to construct a network without infrastructure, using networking abilities of the participants
This is an ad hoc network – a network constructed “for a special purpose”
Simplest example: Laptops in a conference room – a single-hop ad hoc network

13. Possible Applications for Infrastructure-free Networks
Factory floor automation
Disaster recovery
Car-to-car communication
Military networking
Search-and-rescue
Personal area networking (watch, glasses, PDA, medical appliance, …) …

14. Problems & Challenges for Ad hoc Networks
Without a central infrastructure, things become much more difficult
Problems are due to
Lack of central entity for organization available
Limited range of wireless communication
Mobility of participants
Battery-operated entities

15. No Central Entity ! Self-Organization
Without a central entity (like a base station), participants must organize themselves into a network.
Pertains to (among others):
Medium access control (MAC)
no base station can assign transmission resources, must be decided in a distributed fashion
Finding a route from one participant to another (Routing)

16. Limited Range ! Multi-Hopping
For many scenarios, communication with peers outside immediate communication range is required
Direct communication limited because of distance, obstacles, …
Solution: multi-hop network ?

17. Mobility  Suitable, Adaptive Protocols
In many ad hoc network applications, participants move around
In cellular network: simply hand over to another base station
In mobile ad hoc networks (MANET):
Mobility changes neighborhood relationship
Must be compensated
Routes in the network have to be changed
Complicated by scale
Large number of such nodes difficult to support

18. Battery-Operated Devices  Energy-Efficient Operation
Often participants in an ad hoc network draw energy from batteries
Desirable: long run time for
Individual devices
Network as a whole
 Energy-efficient networking protocols
E.g., use multi-hop routes with low energy consumption (energy/bit)
E.g., take available battery capacity of devices into account
How to resolve conflicts between different optimizations?

19. Advantages of wireless networks
Easy to Install:
hard-to-networking environment: river, highway, historic cites
fast installation: festival, assembly, Q-&-A in congress
reliability: (wired cables might be cut, get rusty, …)
in a company: re-organization, change office, etc.

20. Features of Wireless Communication
One global bandwidth shared by all users
Fortunately channels, such as (frequency, time-slot) pairs, can be reused
Radio-based
Low bandwidth
High latency radio communication links
Higher bit error rate (BER)
Fading
Short-term multipath fading (Rayleigh effect)
Due to same signal taking different paths and arriving at the receiver shifted in phase
Long-term fading (radio shadow)
Topology of the terrain (like mountains) can cause signal dropouts
Solution: deploying multiple antenna sites

21. Sensor
A SENSOR is a device which measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument.
Technological progress allows more and more sensors to be manufactured on a microscopic scale as microsensors using MEMS (Micro-Electro-Mechanical Systems) technology.

22. Types of Sensor Thermal Electromagnetic Mechanical Chemical
Optical radiation
Ionizing radiation
Acoustic

23. Types of Sensor-Actuator Hardware Platforms
RFID equipped sensors
Smart-dust tags
typically act as data-collectors or “trip-wires”
limited processing and communications
Mote/Stargate-scale nodes
more flexible processing and communications
More powerful gateway nodes, potentially using wall power

24. Deployment Challenges - Sensor
What kind of sensor modality should be used? – acoustic, magnetic, seismic…
What is the range of the sensor?
How reliable is the sensor?
What is the resolution of the sensor?
How much power does the sensor use?
What is the cost of the sensor?

25. WSN Node Components Low-power processor. Limited processing. Memory.
Limited storage.
Radio.
Low-power.
Low data rate.
Limited range.
Sensors.
Scalar sensors: temperature, light, etc.
Cameras, microphones.
Power.
Sensors P O W E R
Storage
Processor
Radio
WSN device schematics

26. Block Diagram – Mote

27. Picture- Mote

28. WSN: “Motes”

29. Mote Evolution

30. Challenges Challenges Limited battery power
Limited storage and computation
Lower bandwidth and high error rates
Scalability to 1000s of nodes
Network Protocol Design Goals
Operate in self-configured mode (no infrastructure network support)
Limit memory footprint of protocols
Limit computation needs of protocols -> simple, yet efficient protocols
Conserve battery power in all ways possible

31. Typical Features of WSN
A very large number of nodes, often in the order of thousands
Asymmetric flow of information, from the observers or sensor nodes to a command node
Communications are triggered by queries or events
At each node there is a limited amount of energy which in many applications is impossible to replace or recharge
Almost static topology

32. Typical Features of WSN (cont.)
Low cost, size, and weight per node
Prone to failures
More use of broadcast communications instead of point-to-point
Nodes do not have a global ID such as an IP number!
The security, both physical and at the communication level, is more limited than conventional wireless networks

33. Design Considerations
Fault tolerance – The failure of nodes should not severely degrade the overall performance of the network
Scalability – The mechanism employed should be able to adapt to a wide range of network sizes (number of nodes)
Cost – The cost of a single node should be kept very low
Power consumption – Should be kept to a minimum to extend the useful life of network

34. Design Considerations (cont.)
Hardware and software constraints – Sensors, location finding system, antenna, power amplifier, modulation, coding, CPU, RAM, operating system
Topology maintenance – In particular to cope with the expected high rate of node failure
Deployment – Pre-deployment mechanisms and plans for node replacement and/or maintenance
Transmission media – ISM bands, infrared, etc.

35. Design Considerations (cont.)
Environment
Busy intersections
Interior of a large machinery
Bottom of an ocean
Inside a twister
Surface of an ocean during a tornado
Biologically or chemically contaminated field
Battlefield beyond the enemy lines
Home or a large building
Large warehouse
Animals
Fast moving vehicles
Drain or river moving with current.

36. Application Spectrum

37. Some Problems
Calibration = correcting systematic errors in sensor data
Causes: manufacturing, environment, age, crud
Localization = establish spatial coordinates for sensors and target objects
Power-aware Networking
low-power media access; power-aware routing of data packets
Macro-programming= high-level program for a sensor network; not low-level programs for individual sensors

38. WSN Communications Architecture
Sensing node
Sensor nodes can be
data originators and
data routers
Internet
Sink
Manager Node
Sensor nodes
Sensor field

39. Objective

40. Network Architectures
Clustered Architecture
Layered Architecture
Base
Station
Larger Nodes denote Cluster Heads
Base
Station
Layer 1
Layer 2
Layer 3

41. Clustered Network Architecture
Sensor nodes autonomously form a group called clusters.
The clustering process is applied recursively to form a hierarchy of clusters.

42. LEACH (Low Energy Adaptive Clustering Hierarchy)
It uses two-tier hierarchy clustering architecture.
It uses distributed algorithm to organize the sensor nodes into clusters.
The cluster-head nodes create TDMA schedules.
Nodes transmit data during their assigned slots.
The energy efficiency of the LEACH is mainly due to data fusion.

43. Sensor Network Protocol Stack
Power Management – How the sensor uses its power, e.g. turns off its circuitry after receiving a message.
Application
Task Management
Transport
Mobility Management
Mobility Management – Detects and registers the movements of the sensor nodes
Network
Power Management
Data Link
Task Management – Balances and schedules the sensing tasks given to a specific region
Physical

44. Application Layer
Makes the hardware and software of the lower layers transparent to the sensor network management applications.
Different management protocols:
Sensor Management Protocol (SMP)
Task assignment and data advertisement protocol (TADAP)
Sensor Query and Data Dissemination Protocol (SQDDP)

45. Transport Layer
This layer is especially needed when the system is planned to be accessed through Internet or other external networks.
End to end delivery
Reliability
Congestion control

46. Network 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.

47. Routing Problem – How to efficiently route:
Data from the sensors to the sink and,
Queries and control packets from the sink to the sensor nodes

48. Routing Multihop routing is common due to limited transmission range
Phenomenon being sensed
Data aggregation
takes place here
Sink
Multihop routing is common due to limited transmission range
Low node mobility
Power aware
Irregular topology
MAC aware
Limited buffer space
Some routing issues in WSNs

49. Communication architecture of sensor networks
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
Minimum longest edge route: Route 1

50. Data Aggregation
Data coming from multiple sensor nodes are aggregated, if they have about the same attributes of the phenomenon being sensed
Phenomenon being sensed

51. Data Link Layer (MAC Layer)
The data link layer is responsible for :
Medium access
Creation of the network infrastructure
Fairly and efficiently share communication resources between sensor nodes
Power saving modes of operation
Error control.
Forward Error Correction (FEC)
Automatic Repeat Request (ARQ).
Reliable point-to-point
Point-to-multipoint connections

52. Physical Layer The physical layer is responsible for:
Frequency selection
Frequency generation
Signal detection
Modulation
Data encryption
Open research issues
Modulation schemes
Strategies to overcome signal propagation effects
Hardware design

53. WSN: Open Source Tools Simulators Programming Languages
TOSSIM
Avrora
NCTUns
OMNET++
J-Sim
Ptolemy
Programming Languages
Assembly C
Giotto
Esterel
Lustre
Signal
E-FRP
nesC
Operating Systems
TinyOS
YATOS
Contiki
MANTIS
SOS
Application Tools
Localization Tools
TinyDB
Surge
TOSBase