Combating Routing Microholes in Hybrid WSNs

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Combating Routing Microholes in Hybrid WSNs

• Michael G. Portnoy
• Natalija Vlajic
• Dept. of Computer Science and Engineering
• York University

May 31, 2007
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Presentation Outline

• Intro to wireless sensor networks
• Problem definition - routing holes
• Microholes and our approach for solving them
• Approach feasibility, justifiability
  effectiveness
• Distributed Algorithm for Routing Microholes
  Abolishment (DARMA)
• Discussion, and future work

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Presentation Outline

• Intro to wireless sensor networks
• Problem definition - routing holes
• Microholes and our approach for solving them
• Approach feasibility, justifiability
  effectiveness
• Distributed Algorithm for Routing Microholes
  Abolishment (DARMA)
• Discussion, and future work

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Wireless Sensor Network (WSN)

• Small, cheap, resource constrained devices
• Capabilities
• Sensing
• Computing
• Communicating
• Self organizing
• Each node acts as router
• Geographic routing
• Forward packets to nodes closer to destination

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Can use mobile nodes in WSN to improve network
performance

• Hybrid WSN
• Static and mobile nodes
• Mobile nodes may be used to improve
• Coverage
• Fault tolerance
• Energy efficiency
• New area no field deployments (yet)

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WiDAR Wireless Detection and Ranging
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WiDAR (cont.)

• 4th year computer engineering final project

• www.widar.ca

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Presentation Outline

• Intro to wireless sensor networks
• Problem definition - routing holes
• Microholes and our approach for solving them
• Approach feasibility, justifiability
  effectiveness
• Distributed Algorithm for Routing Microholes
  Abolishment (DARMA)
• Discussion, and future work

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Holes can prevent or diminish proper network
functionality

• Node deployment issues
• Limited precision
• Accidental or environmental damage
• Malicious damage
• Above may cause a number of anomalies (a.k.a.
  holes)
• Various types of network holes
• Coverage
• Jamming, sink/black/worm
• Routing (our research focus)

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Geographic (greedy) routing

• Nodes forward packets to nodes which are closer
  to destination than themselves 4.

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Greedy forwarding strategy can get stuck at node
x (i.e. local minimum)

• The above is a routing hole 5

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Routing holes can cause a number of problems in
WSNs

• Routing holes can create inefficient routing
  paths
• Delays
• Bottlenecks
• Long routes
• Poor load distribution
• Premature energy depletion of edge nodes
• Exacerbate the problem
• Can lead to network partitioning

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Presentation Outline

• Intro to wireless sensor networks
• Problem definition - routing holes
• Microholes and our approach for solving them
• Approach feasibility, justifiability
  effectiveness
• Distributed Algorithm for Routing Microholes
  Abolishment (DARMA)
• Discussion, and future work

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Our contribution - we suggest using mobile nodes
to eliminate routing holes

• To our knowledge, no one has suggested this
  before
• Main idea Place mobile node/s inside the routing
  hole/s

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Advantages of using mobile nodes

• Advantages
• Better traffic load distribution
• Fewer bottlenecks
• Shorter routes
• Fault tolerance
• Hence, fewer delays, efficient operation
• Shorter hop distance reduces energy consumption!
• Average received signal power decreases
  exponentially with distance

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What are microholes

• Our research is still in the preliminary stages,
  therefore we suggest a base hole case the
  microhole.
• Not routing holes in the traditional sense.
  I.e. Do not contain local minima.
• Microholes - Small imperfections in the routing
  path that do not prevent correct geographic
  routing, but can be optimized using mobile nodes.

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Microhole example

• Can reduce average hop length by 0 to 50
• Reduction in average hop length provides for
  significant energy saving due to properties of
  signal propagation.

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Is combating microholes important? We did a
simulation with the following parameters

• Based on Crossbow MPR500CA sensor 1 and the
  Great Duck Island experiment 17
• Tx frequency 900MHz (868/916 Mhz)
• RF Tx power -20 to 5 dBm
• Receiver sensitivity -98 dBm
• Data rate 38.4 kbaud
• Message size 30 Kbytes
• Deployment period ½ year
• 31.7 hop distance reduction
• Tx period variable

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How much energy will be gained if a mobile relay
node is used?
Path loss exponents

• Observation reducing the hop length by the same
  relative amount in environments with greater path
  loss leads to greater energy gains.

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Presentation Outline

• Intro to wireless sensor networks
• Problem definition - routing holes
• Microholes and our approach for solving them
• Approach feasibility, justifiability
  effectiveness
• Distributed Algorithm for Routing Microholes
  Abolishment (DARMA)
• Discussion, and future work

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Approach Feasibility, Justifiability, and
Effectiveness

• We say that for our approach to be employed in a
  real world scenario it has to be
• Feasible - mobile node has the physical
  capacity needed to deploy to a microhole
• Justifiable - benefits outweigh the costs
• Effective - acceptable probability with which the
  mobile node will be successful in completing
  its mission goal

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Feasibility

• The mobile node must have enough energy to move
  to a deployment location and operate there for a
  desired period of time P.

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Justifiability

• The cost of deploying to a microhole should be
  lower than the gain.

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Effectiveness

• Feasibility and justifiability can only be
  calculated based on precise node coordinates.
• Precise node deployment locations cannot usually
  be known prior to the deployment.
• It could be very costly to use our approach if it
  is ineffective.
• Need to have a way to evaluate our approach prior
  to the WSN deployment.

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Effectiveness evaluation

• We try to find the probability with which only a
  single node fails and it is within the mobile
  nodes feasible or justifiable locomotion
  distance.

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Presentation Outline

• Intro to wireless sensor networks
• Problem definition - routing holes
• Microholes and our approach for solving them
• Approach feasibility, justifiability
  effectiveness
• Distributed Algorithm for Routing Microholes
  Abolishment (DARMA)
• Discussion, and future work

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DARMA in a nutshell

• Distributedly determine the existence of
  microhole/s and maps them
• Communicate this information to mobile nodes
  through flooding
• Mobile nodes rank holes
• Mobile nodes exchange hole ranking information
• Mobile nodes deploy based on their own and
  received hole ranking information

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Main issues to consider

• How can we distributedly determine the existence
  and mapping of a hole?
• How do we communicate the hole information to the
  mobile nodes?
• How can the mobile nodes decide who should move
  and where?

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Distributedly determining routing hole existence
and routing hole mapping

• Assumption every node knows its own and its
  neighbors global coordinates
• Use TENT rule and BOUNDHOLE algorithms for large
  holes 10 (future work)
• Microholes are simple to detect and map

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How do can we determine if there is a microhole?

• If s?b, and b?d and
• If ? gt 0 and is a user defined threshold ?
  microhole exists

?
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Ranking holes

• For each microholeMobile would consider
  deploying iff
• Feasible
• Justifiable
• If above is satisfied for hole i,
• Ranki Ge(P) Cmv

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Deciding where to deploy

• Mobiles will want to deploy to the highest
  ranking hole
• Before deploying, mobile nodes exchange their
  hole rankings
• Hence, if (M1, Ranki, R1) gt (M2, Ranki,R2), M1
  will deploy to hole i, while M2 will deploy to a
  its lower ranked hole
• Large random number R will be used for breaking
  ties

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Presentation Outline

• Intro to wireless sensor networks
• Problem definition - routing holes
• Microholes and our approach for solving them
• Approach feasibility, justifiability
  effectiveness
• Distributed Algorithm for Routing Microholes
  Abolishment (DARMA)
• Discussion, and future work

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Discussion

• Energy savings alone might not be sufficient to
  justify our approach. Might have to consider
• Data load distribution
• Fault tolerance
• Mission criticality
• Must consider other approaches during WSN design
  depending on goals. E.g.
• Deploy more static nodes
• Use improved routing algorithms

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Future work

• Current research is a stepping stone
• Extend our approach and DARMA to traditional
  routing holes
• Study effects of our approach on energy
  consumption, load distribution, fault tolerance
  and delays (simulation and real-life deployments)
• Develop better gain models that factor in various
  WSN parameters besides energy consumption

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That is it Thank you!

• Any Questions?
• For more info please visitwww.cse.yorku.ca/mpor
  tnoy

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