SR: A Cross-Layer Routing in Wireless Ad Hoc Sensor Networks

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SR A Cross-Layer Routing in Wireless Ad Hoc
Sensor Networks

• Zhen Jiang
• Department of Computer Science
• West Chester University
• West Chester, PA 19335, USA

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Outline

• Introduction
• Problem
• Our Approach
• Conclusion

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Introduction

• Routing problems in WASN applications
• Improvement on the entire routing path
• Length, delay, and performance
• Security, etc
• Topology information model
• Where link connections change dynamically
• For each relay at intermediate nodes
• Main factors
• Reliability, scalability, and cost effectiveness

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Existing routing schemes
Not suitable in a highly dense and dynamic
environment
Centralized connection
(1) Singe point of failure
(2) Hot spots (energy depletion, interference,
performance bottle neck, etc) (3) Low reliability
(impossible for multi-hop relay in real
applications) (4) Low scalability
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Problems
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Idea Solution
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Challenges

• Unpredictable configuration ahead due to
• Interferences
• Node failure
• Node mobility
• Privacy and selfishness
• Signal strength and energy consumption
• Traffic jamming
• Huge cost in probing to catch the configuration
  change
• Delay
• Information storage
• Computational cost

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Observations

• Reactive information model
• Not suitable for routing in dynamics
• Passive information model
• Hard to find an effective description for various
  pair of the source and destination
• Information Scale
• The farther the relay node to the destination,
  the less accurate information is needed.
• 1-hop direct connection k-hop reachability
  information

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Problem

• A new information model
• Indicate the neighbor preference for a 1-hop
  decision with the global path optimization
• Existence of such a preference?
• Constructed in a passive information model,
• How to keep relatively stable after dynamic
  changes (reliability when link changes and
  positions of source and destination change)?
• Minimize the construction process within a
  limited area to reduce the cost and to achieve
  scalability
• How to ensure a quick converging construction of
  such a preference information?
• How to achieve the global optimization with the
  information in those limited areas

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Our approach

• Descriptor S?0,1
• Representative of preference, not ETX metric
• The higher its value, a better routing path there
  likely will be to reach the boundary of the
  network
• Used for routing decision to select the successor
  with a relatively high index value among all
  available neighbors
• Use a single reference (path to network boundary)
  to reach the destination
• Interchangeable use multiple references to
  approach to the destination
• A tradeoff between cost and accuracy of
  information!!!
• S(u) max S(n(u))
• Relatively stable and quickly converging

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Detailed Process

• Network Model
• Information Construction
• Collection and distribution
• Information Utilization

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Network Model
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Asynchronous MAC Layer Support

• Faster
• Less synchronization overhead
• More accurate to describe the link status

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Neighbor Node Appearance
The appearance of neighbor node v is determined
by the Berkeley Mica mote platform as follows,
with respect to the distance of link (i.e., D(u,
v) L(u) - L(v) ).
? (0.9, 1, D(u, v) 10 feet ? 0,
D(u, v) gt 40 feet ? (0, 1),
otherwise (1
? u?v
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Reachability

• Description of 1-hop link quality
• Determined by the Monte Carlo method
• Ratio of the time that a node v appears to the
  total elapsed time
• Estimated by success REQ/ACK processes, supported
  by our asynchronous MAC scheme
• Calculated as
• ?v,u ?u?v ?v?u,

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Forwarding Zone and Request Zone
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Information Construction

• Initialization Phase
• Each node u outside the interest area sets S(u)
  to a fixed (1, 1, , 1) otherwise, sets
  S(u) to a changeable (0, 0, , 0).
• Then, each node will have stable status by
  applying
• Si(u) max?u,v Si(v), 1 i 4
  (2
• and
• Si(u) maxSi(u) , ?u,v Si(v), 1 i 4
  (3
• Such a link u, v is called a key link for Si(u).

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• Identification Phase
• Any node u is called a type-i stuck node if it
  does not have any neighbor appearing inside
  forwarding zone Qi. Set Si(u) 0.
• Uppon detecting a change of the other end of the
  key link, a node u with Si(u) gt 0
• Calculate its type-i status by using Eq. (2)
• Inform all neighbors its new Si(u) in the next
  round
• If Si(u) 0, u is called a type-i unsafe node
  and no longer change its status otherwise, u is
  still type-i safe and Si(u) will eventually
  stabilize by using Eq. (3).

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• Self-healing phase
• Any node u (stuck, unsafe, or safe) will
  recalculate its Si(u) by using Eq. (3), until the
  value becomes stable.

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Information Utilization

• If d ? n(u), v d.
• Determine the request zone Zk(u, d) (1?k ?4),
  according to L(u) and L(d).
• Select v ? n(u)?Zk(u, d), where the forwarding
  from v to d is safe with respect to request zone
  Zk(v, d).

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Routing Properties

• A straightforward path can be derived when the
  destination d is in one type of safe area. Such a
  forwarding, say type-i, can be initiated at a
  source that has a safe successor, i.e., a type-j
  safe neighbor.
• The initiated routing may interrupt when the
  destination is in an unsafe area and disconnected
  with the source. Before the retransmission
  starts, the length of the path approximates to
  D(s, d) ?, where ? is the maximum length of the
  boundary circling an unsafe area.

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• When s is inside an unsafe area, a successful
  routing will achieve a path shorter than D(s, d)
  ?/2.
• If our forwarding advances can reach the
  destination d with updated safety information, a
  path can also be constructed with outdated (or
  lagged) information.
• The self-healing phase converges in a limited
  number of rounds and will not affect any existing
  safety-information-based routing.

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Conclusions

• Traditional source routing is not applicable in
  highly dense and dynamic WASNs.
• A preference information is more suitable for
  forwarding routing, compared with a costly ETX
  like metric.
• Localized method to achieve global optimization
  in WASN is possible, but is very difficult by the
  consideration of overhead.
• With the support of MAC, a routing without
  synchronizing neighbors is faster and can allow
  more concurrent communications, enhancing the
  network performance.

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Thank you!

• Questions and Commons