23-07-2014, 11:40 AM
Wireless Sensor Network
Wireless Sensor Network.pptx (Size: 1.23 MB / Downloads: 12)
Introduction
A wireless sensor network (WSN) consists of spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the network to a main location
Sensor nodes are low power multi-functioning devices operating in an unattended environment with limited computations and sensing capabilities.
Sensor nodes are equipped with small, often irreplaceable batteries with limited power capacities.
Lifetime of the WSNs depend on the lifetime of the sensor nodes.
WSN vs MANET
The number of sensor nodes in a sensor network is much more than the nodes in an ad hoc network
Sensor nodes are densely deployed
Sensor nodes are prone to failures
The topology of a sensor network may change very frequently
Sensor nodes mainly use broadcast communication paradigm whereas most ad hoc networks are based on point-to-point communications
Sensor nodes are limited in power, computational capacities, and memory
Sensor nodes may not have global ID because of the large amount of overhead and large number of sensors
The Management Planes
Power management plane manages how a sensor node manages its power. Ex. Turn off the transceiver or when a node is low in power it broadcasts a message to its neighbor saying it can not participate in routing
Mobility Management plane detects mobility and triggers actions needed to handle mobility
Task Management plane balances and schedules sensing tasks
The Physical Layer
The choice of a good modulation scheme is critical for reliable communication in a sensor network.
Binary and M-ary modulation
A low-power direct sequence spread-spectrum modem architecture
Ultra wideband (UWB) or impulse radio (IR)
Low transmission power and simple transceiver circuitry make UWB an attractive candidate for sensor networks.
Data Link Layer
The data link layer is responsible for the multiplexing of data streams, data frame detection, medium access and error control
Error Control - Two important modes of error control
Forward Error Correction (FEC)
Automatic repeat request (ARQ)
ARQ in multihop sensor network environments is limited by the additional retransmission energy cost and overhead
Network Layer
Most important function of the network layer is to forward the messages generated from sensor nodes to sink nodes in an energy efficient manner
Other network layer like the one in Internet uses global addressing for packet forwarding
In WSN, global addressing may be inefficient because of small message size compared to address length
WSN uses content-based addressing or geographical addressing
Data-centric Routing
Requires attribute-based naming
Querying an attribute of the phenomenon, rather than querying an individual node
Ex: “the areas where the temperature is over 70°F” is a more common query than “the temperature read by a certain node”
Sensor management protocol (SMP)
SMP is a management protocol that provides the software operations needed to perform the following administrative tasks:
introducing the rules related to data aggregation, attribute-based naming and clustering to the sensor nodes,
exchanging data related to the location finding algorithms,
time synchronization of the sensor nodes
Task assignment and data advertisement protocol (TADAP)
Users send their interest to a sensor node, a subset of the nodes or whole network.
This interest may be about a certain attribute of the phenomenon or a triggering event.
Another approach is the advertisement of available data in which the sensor nodes advertise the available data to the users
Wireless Multimedia Sensor Network
Increasing demand of imaging and video sensors in many applications of wireless sensor networks has led to the evolution of Wireless Multimedia Sensor Networks (WMSN)
It is network of wirelessly interconnected devices that are able to ubiquitously retrieve multimedia content such as video and audio streams, still images, and scalar sensor data from the environment
It is also be able to store, process, correlate, and transmit multimedia data originated from heterogeneous sources.
It can be considered as the convergence between the concepts of wireless sensor networks and distributed smart cameras.