Department of Computer Science Southern Illinois University Carbondale Mobile

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Department of Computer ScienceSouthern Illinois
University Carbondale Mobile Wireless
ComputingRouting Protocols for Sensor
NetworksHierarchical Location-based and QoS
Protocols
Dr. Kemal Akkaya E-mail kemal_at_cs.siu.edu
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Hierarchical Protocols

• When sensor density increases single tier
  networks cause
• Sink overloading
• Increased latency
• Large energy consumption
• Clustered Network allow coverage of large area of
  interest and additional load without degrading
  the performance
• Hierarchical clustering schemes are the most
  suitable for wireless sensor networks
• Uses Multi - hop communication within a cluster
• Performs data aggregation and fusion on data to
  reduce number of transmitted messages to the sink
• Maintain the energy reserves of nodes efficiently

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Hierarchical Routing
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LEACH

• LEACH (Low Energy Adaptive Clustering Hierarchy)
  is the first hierarchical routing protocol for
  sensor networks
• W. Heinzelman, A. Chandrakasan, and H.
  Balakrishnan, "Energy-efficient communication
  protocol for wireless sensor networks," in the
  Proceeding of the Hawaii International Conference
  System Sciences, Hawaii, January 2000.
• Self-Organizing, adaptive clustering protocol
• Even distribution of energy load among the
  sensors
• Nodes organize themselves into clusters
• Cluster-heads communicate data with the base
  station (sink)

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LEACH

• Dynamic cluster formation - Cluster-heads are not
  fixed
• They rotate at each round randomly
• Data-fusion at each cluster reduces energy
  dissipation and enhances lifetime

Dynamic Clustering
Cluster-heads at time t
Cluster-heads at time t d
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LEACH uses First Order Radio Model

• Transmit k-bit message a distance d using the
  radio model

ETx-elec Energy dissipated/bit at
Transmitter ERx-elec Energy dissipated/bit at
Receiver ?amp Amplification factor
Energy equation at the Transmitter
Energy equation at the Receiver
Fig 1 First Order Radio Model
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LEACH Algorithm

• Algorithm is broken into rounds, and each rounds
  consists of following 4 phases
• Advertisement phase
• Each node decides whether or not to become
  cluster-head
• Advertises itself as cluster-head
• Cluster Set-up phase
• Each node decides to which cluster it belongs
• Notification to the cluster-head
• Schedule Creation
• Cluster-head creates a TDMA schedule notifying
  each node when it can transmit
• Data transmission
• Each node send data during their allotted time

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Simulation Results
Direct Direct Transmission to the Sink
MTE Minimum Transmission Energy
Energy dissipation
System Lifetime
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Sensor Lifetimes

• System life time after 1200 rounds

Live nodes (circled) Dead nodes (dotted)
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What about MTE Direct Communication?

• No of rounds 180
• Alive (circles) Dead (dots)

Direct Communication
MTE
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LEACH Summary

• Factor of 7 reduction in energy dissipation as
  compared to Direct Communication
• Uniform distribution of energy-usage in the
  network
• Doubles the system lifetime compared to other
  methods
• Nodes die essentially in random fashion, thus
  maintain the network coverage
• Completely distributed, no network knowledge
  required
• Problems
• Nodes use single-hop communication
• Not good for large domains
• Cluster-head change overhead

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PEGASIS

• Power Efficient GAthering in Sensor Information
  Systems
• Improvement to LEACH
• Form chains rather than clusters
• S. Lindsey and C. S. Raghavendra, "PEGASIS Power
  Efficient GAthering in Sensor Information
  Systems," in the Proceedings of the IEEE
  Aerospace Conference, Big Sky, Montana, March
  2002.
• Token-Passing Chain-Based
• Considered Near-Optimal
• Nodes die in random
• Stationary Nodes and Sink
• Every node have a global network map
• Data Fusion
• Greedy chain construction

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Main Procedures

• Greedy Algorithm Construct Chain Start at a
  node far from sink and gather everyone neighbor
  by neighbor
• Node i (mod N) is the leader in round i
• Nodes passes token through the chain to leader
  from both sides
• Each node fuse its data with the rest
• Leader transmit to sink

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PEGASIS - Illustration
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Comparison
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Summary

• Outperforms LEACH by eliminating clustering
  overhead
• Global Information assumed
• Limited Scale
• Information travels many nodes
• Excessive delay for far nodes
• Assumes any node can communicate with sink
• Hierarchical PEGASIS
• Extension of PEGASIS
• Decrease the delay for the packets during
  transmission to the base station
• Simultaneous transmissions of data messages
• Avoid collisions and possible signal interference
• Signal Coding (e.g. CDMA)
• Spatially separated nodes can transmit at the
  same time

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Hierarchical PEGASIS
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Location-based Protocols

• If the locations of the sensor nodes are known,
  the routing protocols can use this information to
  reduce the latency and energy consumption of the
  sensor network.
• Distance between two nodes is calculated using
  location information
• Energy consumption can be estimated
• Efficient energy utilization
• Location of a node can be determined using
• Global Positioning System (GPS)
• Ultrasonic Systems using trilateration
• Beacons
• Although GPS is not envisioned for all types of
  sensor networks, it can still be used if
  stationary nodes with large amount of energy are
  allowed.
• Location based protocols assume that each node
  knows its location in the network

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GAF (Geographic Adaptive Fidelity)

• GAF designed for both ad hoc and sensor networks
• Y. Xu, J. Heidemann, and D. Estrin,
  "Geography-informed energy conservation for ad
  hoc routing," in the Proceedings of the 7 th
  Annual ACM/IEEE International Conference on
  Mobile Computing and Networking (MobiCom01),
  Rome, Italy, July 2001.
• Forms a virtual grid of the covered area
• Each node associates itself with a point in the
  grid based on its location
• Nodes associated with same point in grid are
  considered equivalent
• Some nodes in an area are kept sleeping to
  conserve energy
• Nodes change state from sleeping to active for
  load balancing

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Routing in GAF
Virtual Grid
Sink
Representative Node for the subregion
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States in GAF

• Nodes use GPS to associate itself to the grid
• A node remains active for time Ta
• Ta of a node in the grid is broadcasted to other
  equivalent nodes
• The sleeping time of a node is adjusted depending
  on Ta
• In the discovery state each node broadcasts
  discovery messages periodically (Td)
• Handles mobility

• Three States
• Discovery Determining neighbors
• Active Does routing
• Sleep Turn off radio

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GAF Summary

• Increase the lifetime of the network
  significantly
• Works for MANETs as well
• Handles mobility
• Also considered to be hierarchical protocol
• Each sub-region is a cluster
• Representative node is the cluster-head
• But does not perform any data aggregation
• Not very scalable. As the network size increases
  distance to the sink increases
• Overhead of forming the grid
• Only the active nodes sense and report data.
• Hence data accuracy is not very high.

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Minimum Energy Communication Network (MECN)

• L. Li and J.Y. Halpern, Minimum-Energy Mobile
  Wireless Networks Revisited. Proc. of IEEE Int.
  Conf. on Communications (ICC01), Helsinki,
  Finland, June 2001.
• Uses graph theory
• Each node knows its exact location
• Network is represented by a graph G, and it is
  assumed that the resulting graph is connected
• A sub-graph G of G is computed.
• G connects all nodes with minimum energy cost.

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QoS Routing In WSN

• QoS-aware protocols consider end-to-end delay
  requirements while setting up paths
• End-to-end delay is the most common
• Bandwidth
• Video or image sensors
• Real-time routing in
• Disaster management
• Fire detection
• Tsunami alerts etc.
• QoS in WSN is very challenging
• Already have constraints such as bandwidth and
  energy
• QoS routing will bring a lot of overhead
• QoS in WSN is still in very early stages
• May require redefinition of QoS for WSN

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SPEED

• A real-time routing protocol for WSN
• T. He et al., SPEED A stateless protocol for
  real-time communication in sensor networks, in
  the Proceedings of International Conference on
  Distributed Computing Systems, Providence, RI,
  2003.
• Each node maintains info about its neighbors and
  uses geographic forwarding to find the paths
• Tries to ensure a certain speed for each packet
  in the network
• Congestion avoidance

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Energy-aware QoS Routing Protocol

• K. Akkaya and M. Younis, "Energy-aware routing of
  time-constrained traffic in wireless sensor
  networks," in the International Journal of
  Communication Systems, Vol. 17(6), pp. 663-687,
  2004.
• Finds least cost and energy efficient paths that
  meet the end-to-end delay during connection
• Energy reserve, transmission energy
• WFQ (Weighted Fair Queuing) packet scheduling
  model used to support best-effort and real-time
  traffic
• WFQ can provide upper delay bound
• Used with constant data rate

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Summary of Protocols for WSN