1. Lifetime Elongation in Wireless Sensor Networks Using Heterogeneity
Muharrem Gün

2. Outline
Wireless Sensor Network Lifetime
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3. Critical Issues in WSN
Wireless sensor nodes are battery powered devices.
Battery replacement is generally not possible.
Nodes do sensing and communication tasks,
Communication is primary source of energy consumption
Wireless sensor devices are battery powered devices therefore they have limited operation time
Wireless sensor devices do sensing and communication, the energy consumed during sensing is small compared to the energy spent during communication, therefore the primary concern in energy consumption is communication
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4. Communication Characteristics
Communication is many to one (towards the sink)
Single-hop transmission is not viable for all nodes
Multi-hopping is realized by intermediate relays
Relaying load is unbalanced therefore lifetime of nodes vary.
Wireless sensor networks has many to one communication characteristics.
Single hop transmission to the sink is not possible (since power consumption is limited hence the communication range) for all nodes therefore multi-hop transmission over intermediate nodes is necessary.
This extra task of relaying of the outer nodes' traffic in addition to a node's self traffic has an important shortening effect on the operation time of the node.
The relaying load of nodes is unbalanced. As the distance to the sink location decreases the relaying load increases.
This unbalanced load results in varying operational lifetimes among the nodes in the network
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5. Network Lifetime Network lifetime: Time until
First node dies
Number of living nodes drop below a threshold
First loss of coverage ...
First critical node death makes network highly unconnected
- Network lifetime of the wireless sensor networks is expressed as
- the time passed until the first node dies
- the time passed until the number of living nodes drops below some percentage
- the time until first loss of coverage etc.
- Since the failure of critical nodes in the vicinity of the sink causes the network to become highly unconnected,( The high number of nodes outside these nodes can not reach sink anymore) the lifetime of the network can be taken as the time until one of these critical nodes die
- Since the relaying load is at maximum for the critical nodes, we expect that the first node to die is also among them.
- This bottleneck reduces the network lifetime considerably.
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6. Exploiting Heterogenity
- We apt to utilize heterogenity in order to improve the network lifetime
- The first approach is using heterogeneous battery capacity nodes
- We aim to reinforce the highly loaded nodes with extra energy in order to promote their lifetime such that the maximum attainable lifetime could be achieved
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7. Concentric Ring Deployment
Nodes are deployed in concentric ring areas
Nodes in a ring have similar loads hence they can use the same battery power
Nodes in different rings have different batteries to match their load
Leads to maximum attainable lifetime
- We deploy the nodes in concentric ring areas and provide the same type of battery to all nodes throughout each ring
- The maximum attainable lifetime of the particular network can be attained if all the nodes exhaust their batteries at about the same time.
- If this condition is satisfied no residual energy is left behind as opposed to the situation in the homogeneous case.
- We should decide the battery capacities and the number of nodes in each ring such that the monitored area is covered for the maximum time and cost of nodes are in the available budget.
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8. Cost and Radio Models Tx: Sender Rx: Receiver Cost of a Node = α + βE
α : Fixed Hardware Cost
Transmit electronics
Power amplifier
Receive electronics +
E : Battery Capacity
β : Unit Battery Cost
μxk ν
Transmit Energy: ν + μxk
Relay Energy : 2ν + μxk
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