WSN.ppt
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Transcript of WSN.ppt
Wireless Sensor Networks
Mote
•A very low cost low power computer•Monitors one or more sensors•A Radio Link to the outside world•Are the building blocks of Wireless Sensor Networks (WSN)
External Memory
Dig
ital I
/O p
ort
s
Radio Transceiver
An
alo
g I
/O P
ort
s
Microcontroller
A/D
D/A
Sensor
Sensor
Wireless Sensor Network
“A wireless sensor network (WSN) is a wireless network consisting of spatially distributed
autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as
temperature, sound, vibration, pressure, motion or pollutants, at different locations.”
- Wikipedia
Wireless Sensor Networks
• Formed by hundreds or thousands of motes that communicate with each other and pass data along from one to another
• Research done in this area focus mostly on energy aware computing and distributed computing
Super Node
Links to Other networks or Similar Super Nodes
Motes
WSN Applications•Environmental/Habitat monitoring •Acoustic detection •Seismic Detection •Military surveillance •Inventory tracking •Medical monitoring •Smart spaces •Process Monitoring
WSN vs Ad-HocWire Sensor Network Ad-Hoc Networks
Large number of nodes Lesser number of nodes in comparison with WSN
Nodes are more prone to failure and energy drain, batteries are not replaceable or rechargeable
Power source can be replaced or recharged
Sensor nodes may not have unique global identifiers
Unique addressing is possible
Data Centric and do not have unique global identifiers
Address Centric and have unique addresses
Data fusion to reduce BW No data fusion
Routing protocols in ad-hoc cannot be directly ported to sensor networks due to limitation in memory, power, and processing capabilities in the sensor nodes and the non scalable nature of the protocols.
Issues and Challenges• Nodes are randomly deployed and no regular topology, so
setup and maintenance should be autonomous.• Network is infrastructure less so all routing and routing
algorithms must be distributed.• Energy constraint is there so power efficient protocols are
needed.• Hardware design of sensor nodes should be energy efficient.• Sensor nodes must be synchronized with each other in
distributed manner so that TDMA schedules can be imposed.• Sensor networks must be adaptive to changing connectivity due
to failure of nodes and powering-up of new nodes.• Routing protocols must be dynamic.• Communication security must be there.
Classification of Sensor Network Protocols
Sensor Network Architecture• Layered Architecture: Single powerful base station(BS) and layers of sensor
nodes around it. Nodes of each layer have the same hop count to BS. Used with in-building wireless backbone and military such
as Multi-hop Infrastructure Network Architecture (MINA). In the in-building scenario BS acts as an access point to a
wired network. Advantage is that each node is involved only in short
distance, low power transmissions to nodes of neighboring nodes.
Layered Architecture
Unified Network Protocol Framework (UNPF)
• UNPF: Set of protocols for complete implementation of layered architecture.
• which includes»Network initialization and Maintenance
Protocol»MAC Protocol»Routing Protocol
Network initialization and Maintenance Protocol
• Uses broadcast capability of BS.• BS broadcasts its identifier (ID) using CDMA code.• Nodes after hearing this record the BS ID and send a beacon
signal with their own IDs and low default power levels.• The nodes BS can hear form Layer-1 as they are a single hop
away.• BS again broadcasts a control packet with all Layer-1 node
IDs.• All nodes send a beacon signal again.• Layer-1 nodes record the IDs which they hear and these form
Layer-2 as they are one hop away from layer-1 nodes.• In the next round Layer-1 nodes inform about the Layer-2
nodes to the BS.• So layers are built with successive round of beacons.
MAC Protocol
• During data transmission phase Distributed TDMA Receiver Oriented Channel assignment (DTROC) MAC protocol is used.
• Two steps of DTROC are:• Channel Allocation (assignment of channels)• Channel Scheduling (sharing of the channel by
neighbors)• BS assigns a reception channel for each node with channel
reuse.• Nodes schedule transmission slots for all the neighbors and
broadcast the schedule.• It enables collision free transmission and saves energy• Nodes can turn off when they are not in send/receive
operation.
Routing Protocol• Downlink from BS is by direct broadcast on the
control channel.
• With the layered architecture nodes forward the data to BS through multiple hops.
• The node to which a packet is to be forwarded is selected as per the remaining energy
Clustered Architecture The Sensor nodes are organized into clusters each
governed by a cluster-head Each node provide information to their cluster-head
and these heads send messages to the BS (BS connected to a wired network)
Cluster architecture is useful for the sensor networks because of its inherent suitability for data fusion.
The data gathering by all the members of the cluster can be fused at cluster-head, and only the resulting information needs to be communicated to the BS
LEACH (Low-Energy Adaptive Clustering Hierarchy) Protocol governs the formation of cluster-head and entire working of cluster architecture.
LEACH (Low-Energy Adaptive Clustering Hierarchy) Protocol
LEACH is a clustering-based protocol that minimizes energy dissipation in sensor networks.
It randomly selects cluster-heads and performs periodic re-election, so that the high energy dissipation experienced by cluster-head in communicating with BS is spread across all the nodes of the network.
Two Phases: (1) Set-Up and (2) Steady In set-up phase, each sensor node chooses a random
number between 0 & 1, if this is lower than threshold for a node, the sensor nodes become the cluster-head.
Each node then chooses their cluster-heads on the basis of signal strength received from them.
In steady state, data fusion takes place at cluster head and then forwarded to the BS.
Data Dissemination• The process by which queries or data are routed in the sensor
network i.e, to the BS or to the other nodes.• Source: A node that generates data.• Event: The information to be reported.• Sink: A node which is interested in an event and seeks
information.• Data dissemination is done by Dissemination Models which
may be periodic or on-demand.• Data Diffusion: Consists of Interest Propagation and Data
Propagation.• Interest Propagation: particular kind of data or event that a
node is interested such as temp, intrusion or presence of Bio agents.
• Data propagation: Shortest path and strongest path is selected.
Flooding• Each node which receives a packet broadcasts it if the
maximum hop count of the packet is not reached or the node itself is not the destination.
• Disadvantages of Flooding:
• Implosion (duplicate messages are sent to same node)
• Overlap (same event sensed by more node due to overlapping of coverage regions)
• Resource blindness (Flooding protocol doesn’t consider the available energy at the nodes and result in many redundant transmission)
•
Gossiping• Modified version of Flooding.
• Nodes don’t broadcast a packet but send it to a randomly selected neighbor.
• It avoids the problem of Implosion.
• Problem is that it takes a longer time for a message to propagate throughout the network
• Doesn’t guarantee all nodes of the network will receive the message.
Rumor Routing
Rumor Routing
Sequential Assignment Routing
DATA GATHERING
Direct Transmission
Power Efficient Gathering for Sensor Information Systems (PEGASIS)
Binary Scheme
Chain Based Three Level Scheme
Thank you..