Define node clustering in IoT networks
- It aggregates nodes into groups (clusters) to facilitate deployment and operation when base stations are far away
Considerations of node clustering in WSNs
- sensor nodes are densely deployed
- sensor nodes are prone to failure
- Topology of WSN can change frequently
- Sensor nodes mainly use broadcast
- Sensor nodes are limited in power, computation capacity, and memory
- Sensor nodes may not have global ID due to large number of sensors
What is the need of structuring node clusters and two deployment techniques?
- Necessary for maintaining power efficiency among nodes
- Types: regular and random
Explain regular and random deployment techniques
- Regular: follows standard geometric shapes (i.e. triangle). Offers best possible coverage.
- Random: randomly distributed. Nodes need to discover neighbours by themselves.
Draw an schematic of rectangular cluster topology (L7 7)
write on paper
How are nodes distributed in a randomly-distributed scenario?
- Nodes are randomly distributed over an area (A) with a Poisson distribution
Draw schematic of flat homogeneous network topology (L7 10)
write on paper
Draw schematic of hierarchical network topology (L7 11)
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Draw schematic of heterogeneous network topology (L7 12)
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Draw schematic of cellular structured cluster (L7 13)
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Explain how the cluster-head is selected using highest connectivity algorithm and draw schematic (L7 14)
- Node with highest connectivity degree is chosen
Explain idea of mobility-based clustering algorithm
- Adaptative algorithm which keeps track of any mobility events within the network
- Node with higher mobility is not elected as cluster-head
Why is localization crucial for IoT?
- Nodes are mostly mobile, accurate data requires accurate positioning
- nodes need to collaborate and exchange data from time to time
- If a node fails, a backup node is needed
4 Common localization metrics
- Time of arrival (TOA): propagation delay is used to estimate travelled distance
- Time difference of arrival (TDOA): requires two or more receivers to calculate time delay difference and find position
- Angle of arrival (AOA): signal phase used to calculate distance
- Received signal strenght (RSS):
Draw an schematic of 2D localization using three anchors (L7 23)
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Draw an schematic of TOA-based ranging (L7 24, 27)
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How can we use TOA when there is no direct path to localize a node?
- use amplitude and propagation delay of non-direct path (NDP)
- requires highly-sensitive receiver
How can we eliminate the effect of multipath fading in the RSS localization metric?
- By averaging the signal over a longer period
- Effect of signal bandwidth is negligible
Draw an schematic of RSS based ranging (L7 32)
write
Compare TOA and RSS techniques (L7 33)
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Examples of 2D geometric triangularization techniques
- 2D localizations require at least 3 anchors
- Least-square algorithms
2 types of cooperative localization in WSNs
- centralized: processing performed in the cloud
- distributed: processing performed in the same network nodes
