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Monday, 1 April 2019

Sensor Networks -1 (WSNs)


Wireless Sensor Networks (WSNs)

Consists of a large number of sensor nodes, densely deployed over an area.

Sensor nodes are capable of collaborating with one another and measuring the condition of their surrounding environments (i.e. Light, temperature, sound, vibration).

The sensed measurements are then transformed into digital signals and processed to reveal some properties of the phenomena around sensors.

Due to the fact the sensor nodes in WSNs have short radio transmission range, intermediate nodes act as relay nodes to transmit data towards the sink node using a multi-hop path.


Multi-hop Path in WSNs



Basic Components of a Sensor Node



Sensor Nodes

Multifunctional
  •  The number of sensor nodes used depends on the application type.
Short transmission ranges
Have OS (e.g., TinyOS)
Battery Powered - Have limited life.



Constraints on Sensor Nodes
  • Small size, typically less than a cubic cm.
  • Must consume extremely low power
  • Operate in an unattended manner in a highly dense area.
  • Should have low production cost and be dispensable
  • Be autonomous
  • Be adaptive to the environment
Applications
  • Temperature measurement
  • Humidity level
  • Lighting condition
  • Air pressure
  • Soil makeup
  • Noise level
  • Vibration


Single Source Single Object Detection



Single Source Multiple Object Detection



Multiple Source Single Object Detection



Multiple Source Multiple Object Detection 




Challenges

Scalability 
  • Providing acceptable levels of services in the presence of large number of nodes.
  • Typically, throughput decreases at a rate of 1/✓N, N=number of nodes.
Quality of services
  • Offering guarantees in terms of bandwidth, delay, jitter, packet loss probability.
  • Limited bandwidth, unpredictable changes in RF channel characteristics.
Energy efficiency
  • Nodes have limited battery power
  • Nodes need to cooperate with other nodes for relaying their information.
Security
  • Open medium .
  • Nodes prone to malicious attacks, infiltration, eavesdropping, interference.
Sensor Web



Sensor Web Entanglement
  • Observations & measurements (O&M)
  • Sensor model language (sensorml)
  • Transducer model language (transducerml or TML)
  •   Sensor observations service (SOS)
  • Sensor planning service (SPS)
  • Sensor alert service (SAS)
  • Web notification services (WNS)
Cooperation in Wireless Ad Hoc and Sensor Networks
  • Nodes communicate with other nodes with the help of intermediate nodes.
  • The intermediate nodes act as relays.
  • Wireless nodes are energy-constrained.
  • Nodes may or may not cooperate.

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