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Robust Gridbased Deployment Schemes for Underwater Optical Sensor Networks

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Cycles are needed to produce Connected Topology. We have to span all nodes ... A Better Design: 4 Hamiltonian Cycles. Robustness: Better. Not 2-edge-connected yet ... – PowerPoint PPT presentation

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Title: Robust Gridbased Deployment Schemes for Underwater Optical Sensor Networks


1
Robust Grid-based Deployment Schemes for
Underwater Optical Sensor Networks
  • Abdullah Reza
  • Janelle harms
  • Department of Computing Science
  • University of Alberta
  • Edmonton, Alberta, Canada

2
Organization
  • Underwater Sensor Network
  • Problems of Acoustic Communication and Motivation
  • Problem Definition
  • Formulation of Robust Grid-Based Deployment
    Patterns
  • Performance Evaluation
  • Conclusions and Future Work

3
Underwater Sensor Networks (UWSN)
  • Immense Research Potential
  • Unmanned sea/ocean observation
  • 70 of earth surface constitutes water
  • A new and evolving field for research

4
UWSN Architecture-2d Akyildiz et al. 1
5
UWSN Architecture-3d Akyildiz et al. 1
6
Difference from Terrestrial
  • Nodes 1
  • More expensive
  • Sparse Deployment
  • Uncorrelated reading
  • Higher Energy consumption

7
Difference from Terrestrial
  • Physical Layer (Acoustic)
  • Penetrates well in water
  • Long range (several hundred meters)
  • - Very low bandwidth (5 Kbps 2)
  • - Very slow propagation (1500 m/s 3)
  • - High error rate 4, 5
  • - High cost of acoustic modems 2

8
Optical Communication An Alternative of
Acoustic Communication
  • Advantages
  • High bandwidth
  • experimented with 320 Kbps 2 and 4.4 Mbps 10
  • Fast propagation
  • Disadvantages
  • Reduced range of communication
  • 8m to 40m 2, 10

9
Optical UWSN Target Application
  • Stringent requirement for high bandwidth
  • Smaller area of observation
  • Observation area not close to the coast

10
Optical UWSN Design Challenges
  • Intelligent Deployment (expensive nodes)
  • Connectivity is not inherent
  • Cost of Deployment (directional transceivers)

11
Optical UWSN Example 1 Vasilescu et al.2
  • Hybrid network both optical and acoustic
    interface
  • Acoustic communication is used for localization
  • An AUV (Autonomous Underwater Vehicle) goes to
    each node periodically and downloads sensed data
    optically using short-range communication
  • A powerful and intelligent AUV is needed and high
    amount of energy is expended in AUV movement

12
Optical UWSN Example 2 Kedar et al. 16
  • Oceanographic Contamination Detection System
  • Distributed clusters of sensor nodes
  • Each cluster consists of a sink and a number of
    sensor nodes transmitting directly to the sink
    optically
  • Inter-cluster connectivity to support wider area
    of observation

13
Our Approach An Optical UWSN with Static Sink(s)
  • The VENUS Project at University of Victoria 11

14
Problem Definition
  • Place nodes on grid corners
  • Select a set of point-to-point links from the
    available pool
  • Placing nodes on the grid and setting their
    interface directions can be done manually or
    using AUVs

15
Problem Definition Design Goals
  • 1) Robustness
  • Deterministic (2-edge-connected)
  • Probabilistic
  • 2) Path Quality
  • 3) Interface-count
  • Per node constraint (Maximum 1, 2 and 3
    interfaces per node)
  • Minimum total interface in the network

16
Optical Interface Model 2
  • Maximum 1 interface per node
  • 2 or more interfaces per node

17
Robust Deployment Maximum 1 Interface per Node
  • Cycles are needed to produce Connected Topology
  • We have to span all nodes
  • One Hamiltonian Cycle Always possible with even
    number of rows and/or columns 12
  • Robustness poor
  • Path quality poor

18
Robust Deployment Maximum 1 Interface per Node
  • A Better Design 4 Hamiltonian Cycles
  • Robustness Better
  • Not 2-edge-connected yet
  • Path Quality Better
  • The sink has longer links and more than one
    interface

19
Robust Deployment Maximum 2 Interfaces per Node
  • We have undirected edges now
  • 2-degree constraint on each node
  • We aim to build a 2-edge-connected topology
  • Only way to build a 2-ec topology with 2-degree
    constraint is to build a ring/cycle spanning all
    nodes 13

20
Robust Deployment Maximum 2 Interfaces per Node
  • We use 4 undirected Hamiltonian Cycles
  • Robustness
  • 2-edge-connected
  • Better than directed cycles
  • Path Quality
  • Better than directed cycles

21
Robust Deployment Maximum 3 Interfaces per Node
  • Design Approach
  • 1) Generate a 3-degree constrained shortest path
    spanning tree from the sink with minimum number
    of 3-d nodes (optimal pattern)
  • 2) Add additional edges to make it
    2-edge-connected
  • 3) Add additional edges to improve probabilistic
    robustness
  • Introduce minimum number of 3-degree nodes in
    each step

22
Manhattan Distance Property 14
  • Manhattan Distance between points (x1, y1) and
    (x2, y2) in a grid is given by x1-
    x2y1-y2

23
Subproblem Quadrants
24
Lower Bound for Number of 3-d nodes in a Quadrant
  • Theorem Consider a quadrant with sides of size m
    and n where mn. A sink is placed in a corner. A
    3-degree constrained shortest-path tree rooted at
    the sink and spanning all nodes inside and on the
    boundaries of the quadrant require at least (m-2)
    3-degree nodes.

25
Optimal Pattern for a Quadrant
26
Do Optimal Patterns for Quadrants Give Optimal
Pattern for the Grid?
  • Depends on whether or not 3-degree constraint is
    violated on the axes
  • In any case, (l1l2l3l4) remains the lower
    bound
  • We call LB (l1l2l3l4) ? li

27
A Pattern for a Quadrant that Avoids Conflict on
the Axes
  • A pattern that draws edges only from the vertical
    axis
  • Has minimum number of 3-d nodes (li ) of y x
    but has minimum1 number of 3-d nodes (li1) if y
    gt x

28
Pattern Applied on the Entire Grid
  • Shortest path spanning tree from the sink with
    3-degree constraint
  • Number of 3-degree nodes in the worst case is
    LB4 which can be shown to be actually LB3
  • clockwise counterclockwise LB2 in worst case

29
Next Step Add Edges to Make it 2-edge-connected
30
Next Step Add 2 More Edges to Make it More Robust
31
Summary of Proposed Deployments
TOP2
TOP3
TOP1
TOP4
TOP5
TOP6
32
Summary of Proposed Deployments 12x12 Grid
33
Static Evaluation of Deployment Topologies
  • Two failure models
  • Isolated Model 15
  • Patterned Model 15
  • Metrics Robustness Path Quality
  • 12x12 grid with r 20m

34
Results Isolated Failure
Path Quality
Robustness
35
Results Patterned Failure
Path Quality
Robustness
b4m and ?3
36
Dynamic Evaluation of Deployment Topologies
  • Resilient Routing Protocols
  • Memory-constrained Flooding (FLD)
  • Dual Paths Protocol (DPP)
  • Hop-by-Hop Acknowledgment with local update
    protocol (HHA)

37
HHA Protocol Routing Around Error Blobs
38
Simulation Environment
  • Single Packet generating source
  • Ten packets generated per second, each with 1 Kb
    payload
  • Three error blobs (20mx4m) moving at 15 cm/sec
    speed in the grid in a random-walk fashion

39
Simulation Metrics
  • Delivery Ratio
  • Average Delay Per Packet (ADPP)
  • Average number of Payloads Transmitted per
    Successful packet (APTS)

40
Experiments
  • 3 experiments for each protocol
  • Vary hop distance of the source node from the
    sink
  • Vary the size of obstructing error blobs (not
    presented)
  • Vary the speed of obstructing error blobs (not
    presented)

41
Comparison of 3 protocols on TOP6
Hop Distance 10 A 20m b 4m Speed 15cm/sec
42
Comparison of 3 protocols on TOP6
Hop Distance 10 A 30m b 4m Speed 15cm/sec
43
Conclusions
  • Robust deployment topologies for optical UWSN
    with 1, 2 and 3 interfaces per node constraints
  • For 1 and 2 interfaces cases, topologies that
    utilize four directed and undirected Hamiltonian
    cycles in the grid, respectively.
  • For 3 interfaces case, formulation pattern for a
    3-degree constrained shortest path spanning tree
    in the grid with arbitrary root and arbitrary
    dimension that results in (LB2) 3-degree nodes
    in the worst case.
  • A series of deployment patterns built on the
    3-degree constrained shortest path tree

44
Conclusions
  • Static evaluation of the proposed topologies show
    that a very high degree of robustness (95) is
    maintained by TOP6 even at reasonably harsh
    conditions
  • Dynamic evaluation of the proposed topologies
    with three simple routing protocols
  • FLD achieves a very high degree of delivery ratio
    when applied on TOP6 but incurs excessive
    communication
  • DPP fails to utilize the inherent redundancies of
    the proposed topologies
  • HHA achieves delivery ratio as good as FLD with
    very small communication overhead but slightly
    higher average delay

45
Future Work
  • 3-degree constrained shortest path spanning tree
    for a grid with LB number of 3-degree nodes (or
    prove that such a tree cannot be formed)
  • Prove or disprove that our pattern is a pattern
    with minimum number of 3-degree nodes in all
    settings
  • Design similar patterns for 3D deployment
    scenario
  • Consider non-grid deployments such as triangular
    or hexagonal

46
Future Work
  • Experiment with multiple packet generating
    sources in the network
  • Design more intelligent routing protocols that
    perform load balancing
  • Use more intelligent multi-path routing protocols
    in evaluation
  • Optimize HHA to avoid including path and link
    information in the packet

47
References
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    Melodia, Challenges for efficient communication
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    SIGBED Review, Volume 1, Issue 2, July, 2004,
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  • 2 I. Vasilescu, K. Kotay, D. Rus, M.
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