realistic and efficient multi-channel communications in wireless sensor network
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Realistic and Efficient Multi-Channel Communications in Wireless Sensor Network. Reference. Yafeng W., Stankovic J.A., Tian H, Shan L, “Realistic and Efficient Multi-Channel Communications in Wireless Sensor Networks,” In proceedings of INFOCOM 2008, Phoenix, AZ, USA, April 13-18, 2008. Outline. - PowerPoint PPT PresentationTRANSCRIPT
Realistic and Efficient Multi-Channel Communications in Wireless Sensor
Network
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Reference
• Yafeng W., Stankovic J.A., Tian H, Shan L, “Realistic and Efficient Multi-Channel Communications in Wireless Sensor Networks,” In proceedings of INFOCOM 2008, Phoenix, AZ, USA, April 13-18, 2008.
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Outline
• Introduction• Experiments on Multi-Channel Reality• Tree Based Multi-Channel Protocol (TMCP)• Minimum Interference Channel Assignment
Problem• Performance Evaluation• Conclusion
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Introduction
• Wireless sensor network (WSN)
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(Base Station)
Introduction• Current WSN hardware such as Micaz and Telos
provide multiple channels– Improve network throughput– Provide reliable and timely communication services
• Recently MAC layer multi-channel protocols are proposed– To assign different channels to two-hop neighbors (hidden
terminal problem)and coordinate channel switching
– Also called node-based schemes– E.q., MMSN(INFOCOM2006), TMMAC(ICC2007), MCMAC(CIT2006).
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Introduction
• Practical issues for node-based scheme– A large number of channels are needed in dense
networks.– Require precise time synchronization at nodes.– Channel switching delay and scheduling overhead.– Complex.
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Outline
• Introduction• Experiments on Multi-Channel Reality• Tree Based Multi-Channel Protocol (TMCP)• Minimum Interference Channel Assignment
Problem• Performance Evaluation• Conclusion
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Experiments on Multi-Channel Reality
• Number of available channels– Adjacent Channel Interferences– Interferences with 802.11 network
• Impact of time synchronization errors
• Experiment setup– CC2420 radio chip used in Micaz motes– 16 non-overlapping channels, with 5MHz spacing
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Adjacent Channel Interferences
• Place three Micaz motes in a line– One transmitter, one receiver, and one jammer– The jammer’s transmission is synchronized with
the transmitter.
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Transmitter : channel 11Receiver : channel 11
Jammer : channel 12 (adjacent) channel 13 (2 channel
away)
Adjacent Channel Interferences
• Adjacent channel interference can cause collisions and packet losses.
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Interferences with 802.11 networks• Put 8 pairs of Micaz motes closely in a department
office with 802.11 networks– Each pair uses unique channel and all 8 channels are non-
adjacent.– Multi-channel protocols must have capabilities to work
well with a small number of available channels.
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Impact of Time Synchronization Errors
• Put 5 Micaz motes on a line• Node-based scheme
– Each node with unique channel and all are synchronized.
– A time period is divided into 2 time slots• 1st time slot
– Nodes in odd positions send packets – Nodes in even positions receive packets
• 2nd time slot is vice versa
1 2 3 4 5
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Impact of Time Synchronization Errors
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Outline
• Introduction• Experiments on Multi-Channel Reality• Tree Based Multi-Channel Protocol (TMCP)• Minimum Interference Channel Assignment
Problem• Performance Evaluation• Conclusion
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TMCP
• To overcome two problems in practical networks– The small number of available non-adjacent
channels.– Unavoidable time errors.
• Data collection traffic – Multiple information flows generated at sensor
nodes converge to the base station.
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TMCP• Main idea
– Partition the whole network into multiple vertex-disjoint subtrees all rooted at base station
– Allocate different channels to each subtree.– Forward each flow only along its corresponding
subtree.• 3 components
– Channel detection (CD)– Channel assignment (CA)– Data communication (DC)
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TMCP
• CD finds available non-adjacent channels – Two motes are used to sample the link quality, and
we selected good link qualities with non-adjacent channel.
– Assume we have k channels at this point.
• CA partitions the whole network into k subtrees and assigns one unique channel to each subtree– Intertree interference is eliminated– Intra-tree interference is minimized
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TMCP
• DC manages the data collection through each subtree– Assume the base station is equipped with multiple
radio transceivers.– Without time synchronization
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Outline
• Introduction• Experiments on Multi-Channel Reality• Tree Based Multi-Channel Protocol (TMCP)• Minimum Interference Channel Assignment
Problem• Performance Evaluation• Conclusion
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Model and Problem Definition
• The goal is to minimize intra-tree interferences.
• Assume that a sensor network is a static.– Interference value: int(u) = the number of other
node by which the reception at u can be distrurbed
• The intra-tree interference value of a tree T is defined as– int(T) = max{int(u): u is a non-leaf of T}
2008/9/1 20* M. Burkhart, P. V. Rickenbach, R. Wattenhofer, and A. Zollinger, “Does topology control reduce interference,” in ACM MobiCom, 2004.
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The intra-tree interference value of the tree is 4.
PMIT Algorithm• Apply Breadth-First search algorithm from the base
station to construct a fat tree.– Nodes keep height and have multiple parents on the fat
tree.– The tree is a shortest path tree.
• Execute the channel allocation one-by-one level from top to bottom on the fat tree– For each node, choose an optimal tree and add this node
to bring the least interference to this tree.– Selects a parent which has the least interference value.– Nodes with fewer parents first, because they are less free
to choose channels.
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Greedy PMIT
• K = 3
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Evaluation of the PMIT Algorithm
• Simulations parameters– 200m x 200m field– 250 nodes are uniformly distributed– Communication range is 10~35m – Interference range is 1.5 times as the
communication range
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Evaluation of the PMIT Algorithm
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Prim’s algorithm constructs “Minimum Spanning Tree” (single channel)
Eavesdropping is a node-based protocol (multi-channel)
Lower bound : maximum interference value among all nodes divided by k channels
Outline
• Introduction• Experiments on Multi-Channel Reality• Tree Based Multi-Channel Protocol (TMCP)• Minimum Interference Channel Assignment
Problem• Performance Evaluation• Conclusion
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Performance Evaluation of TMCP
• Simulation parameters– 200m x 200m field– 250 nodes are uniformly distributed– Communication range is 10~40m – Interference range is 1.5 times as the
communication range– 50 Many-to-one CBR streams
• 40 packets / second
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Performance with different node density
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workload
workload workload
Performance with different workload
Performance comparison of TMCP and MMSN• 50 CBR streams• Node density: 38• The radio range: 40m
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Evaluation in a Real Testbed
• Experiment setup– A real testbed with 20 Micaz motes.– Four motes are laid closely together to act as a
base station with four transceivers.
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• TMCP effectively reduces interferences and mitigates congestion at nodes.• TMCP works well in a real sensor network.
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Saturated data rate (reception radio above 80%)
Outline
• Introduction• Experiments on Multi-Channel Reality• Tree Based Multi-Channel Protocol (TMCP)• Minimum Interference Channel Assignment
Problem• Performance Evaluation• Conclusion
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Conclusion• This paper studies how to efficiently use multiple
channels to improve network performance in WSNs.• TMCP
– Work with a small number of channels.
– Work without the need of time synchronization.– Decrease potential radio interferences.
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