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Wireless Sensor Networks
Consists of battery operated sensor nodesDeployed randomly on the field in large numbers Resource constrained sensor nodes
– power, computation, communicationNo networking infrastructure
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MOTETwo Board Sandwich– CPU/Radio board– Sensor Board: temperature, light
Size– Mote: 11 in– Pocket PC: 5.23.1 in
CPU– Mote: 4 MHz, 8 bit– Pocket PC: 133 MHz, 32 bit
Memory– Mote: 512 B RAM; 8K ROM– Pocket PC: 32 MB RAM; 16 MB ROM
Radio– 900 Hz, 19.2 kbps– Bluetooth: 433.8 kbps (symmetric)
Lifetime (Power) Mote: 3-65 days Pocket PC: 8 hrs
Cost Mote: $100 Pocket PC: $400
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Motivation: CSIP in sensor networks
Collaborative Signal and Information Processing (CSIP)Each node senses the event individually, need to collaborate with other nodes to exchange information and get final and accurate resultsChallenges– Energy Efficiency– Scalability– Reliability– Real-time Performance
How?
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Architectural overview of the CSIP system
Wireless Communication
Routing Layer
Clustering & Distributed Computing Paradigm
Collaborative Information processing
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Computing paradigms in WSN - Client/Server based paradigm
Client/Server paradigmCentralized processingPowerful central serverNot energy efficientNetwork traffic – highDifficult to reconfigure
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Computing paradigms in WSN - Mobile agent based paradigm
Agent travels to each nodeNo centralized nodeReduced network trafficScalable networkAdaptive to dynamic WSN environment like node failures, etc.
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Using Network Simulator 2 (ns-2)Randomly deployed in a 10m by 10m areaMAC layer protocol: 802.11Routing protocol: DSDVMetrics:
- Execution Time - Energy Consumption
8 experiments are designedResults: When the number of nodes is large, the mobile agent paradigm performs better; But when the number is small, the client/server paradigm is better
Performance Evaluation
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Hybrid Computing Paradigms
Scheme A: mobile agent paradigm within clusters
and client/server paradigm between
cluster heads
Scheme B: client/server paradigm within clusters
and mobile agent paradigm between cluster
heads
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Clustering
Partition the network into clusters– Achieving scalability– Easer to management– Increase lifetime and energy efficiency
Nodes communicate with clusterheads, clusterheads communicate with processing center
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State of Arts and Problems in Sensor Networks
SPAN, GAF– Need to know position of the node in advance
LEACH– Random rotation of cluster head– Need time synchronized in advance
Two level Clustering Algorithm– Estrin’s method– Not event driven, Proactive
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Problems of Existing Clustering Protocols
Proactive clustering results in– unnecessary radio transmission– large transmission power to reach cluster head, lack of
intermediate nodes acting as routing nodes,– energy inefficiency event
w ake up nodes
sleeping nodes
cluster head
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Benefits of DRC
Reactive clustering - driven by eventsLocalized protocolEnergy-efficientLess transmission power to reach cluster head
event
w ake up nodes
sleeping nodes
cluster head
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Message Format
TYPE: the type of message which can be REQUEST, REPLY, JOIN, JOIN-FORWARD and END.Power Level: the transmission power the node currently uses.Destination ID: the destination node identification and we use all 1's as the broadcast address.Source ID: the address of current node. Cluster ID: the cluster head address of the cluster the current node belongs to and we use 0 if the node is unclustered.Energy: the remaining energy of the node.Signal Energy: the signal energy sensed by the current node emitted by the potential target.
TYP E(4 b its)
P owerLeve l
(4 b its)
D estina tionID
(2 bytes)
S ource ID(2 bytes)
C luster ID(2 bytes)
E nergy(4 bytes)
S igna lE nergy
(4 bytes)
Messages are exchanged only locally
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Desirable Features of DRC
Reactive clustering driven by the eventsUses power control technique to minimize the transmission powerA localized clustering protocol that simple local node behavior achieves a desired global objective
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Outline of DRC
Post-deployment PhaseCluster Forming Phase– Wait for a time– Broadcast REQUEST– Increase transmission power and rebroadcast if
receive no message in a certain time– 4 scenarios in determine the clusterhead– A timer in cluster head determines the end of this
phase
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Different Scenarios
Node A, B unclusteredChoose one with higher energy as cluster head
Node A clustered, node B unclustered
B join the cluster A belongs to
Node A unclustered, node B clustered
A join the cluster B belongs to
Node A, B clusteredB discard the message
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Simulation of DRC
In Java3 Classes– Simu.java (main class)– Node.java (node object)– Message.java (message object)
Simple communication model– No routing, transmission error
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Flow chart
Parameters initialize
Generate nodes
Nodes deployment
Calculate distance
Run protocol (DRC, LEACH or Fix)
Change target position
Display results
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Parameters in Simulation
30 by 30 areaTransmit power level: 8Initial energy: 36 joulesData size: 8000 bitsMobile agent size: 800 bitsMessage size: 152 bits
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LEACH
Generate random number
Calculate threshold
Determine clusterhead
Use client/server to transfer data
Divide the network into random number of clustersUse client/server paradigm in each clusterNodes are driven by events and go back to sleep after sending data
Change target position
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Fix clustering
Determine cluster head
Member sends data to cluster head
Change target position
Divide the network into 4 fixed clustersUse client/server paradigm in each clusterUse highest level of transmission powerNodes are driven by events and go back to sleep after sending data
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Output results
Each node’s ID, status, energy and clusterIDTotal energy consumptionLifetime of the network
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Number of Nodes
DRC consumes less energy and has longer lifetime than LEACH and predefined
clustering
(A) Energy Consumption (B) Network Lifetime
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Target Speed
DRC performs better than LEACH and predefined clustering
(A) Energy Consumption (B) Network Lifetime
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Signal Range
More nodes will wake up as signal range increases, thus consume more energy
(A) Energy Consumption (B) Network Lifetime
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Number of Events
More events will cause more nodes to wake up and thus consume more energy
(A) Energy Consumption (B) Network Lifetime