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Next Century Challenges: Scalable Coordination in Sensor Networks

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Next Century Challenges: Scalable Coordination in Sensor Networks Deborah Estrin, Ramesh Govindan, John Heidemann, Satish Kumar (Some images and s adopted from ... – PowerPoint PPT presentation

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Title: Next Century Challenges: Scalable Coordination in Sensor Networks


1
Next Century Challenges Scalable Coordination in
Sensor Networks
  • Deborah Estrin, Ramesh Govindan, John Heidemann,
    Satish Kumar
  • (Some images and slides adopted from Santhosh R
    Thampuran - CMU)

2
Outline
  • Characteristics of sensor devices.
  • Motivating applications.
  • Key requirements of a sensor network and
    differences with current networks.
  • Localized algorithms for coordination.
  • Directed Diffusion a model for describing
    localized algorithms.

3
Characteristics of Sensor Devices
  • Ability to monitor a wide variety of ambient
    conditions
  • temperature,
  • pressure,
  • mechanical stress level on attached objects
  • Will be equipped with significant processing,
    memory, and wireless communication capabilities.

4
Applications Environmental Analysis
5
Applications Contaminant Flow Monitoring
6
Applications Traffic Control
  • Sensor attached to every vehicle.
  • Capable of detecting their location, vehicle
    sizes, speeds and densities road conditions
  • Alternate routes, estimate trip times

7
Applications Biological Systems
8
Key Requirements
  • These futuristic scenarios bring out two key
    requirements of sensor networks
  • support for very large numbers of unattended
    autonomous nodes.
  • adaptivity to environment and task dynamics.

9
Differences with Current Networks
  • Sensor Networks ratio of communicating nodes to
    users is much greater.
  • extremely difficult to pay special attention to
    any individual node.
  • Sensors may be inaccessible
  • embedded in physical structures.
  • thrown into inhospitable terrain.

10
Differences with Current Networks
  • There are large scale unattended systems, today.
  • Automated factories are deployed with very
    careful planning and react to very few external
    events.

11
Differences with Current Networks
  • Sensor networks deployed in very ad hoc manner.
  • They will suffer substantial changes as nodes
    fail battery exhaustion, accidents new nodes
    are added nodes move.
  • User and environmental demands also contribute to
    dynamics.

12
Overall Design of Sensor Networks
  • Is it sufficient to design sensor network
    applications using Internet technologies coupled
    with ad-hoc routing mechanisms?
  • Data-Centric Application-Specific.
  • Sensor network coordination applications are
    better realized using localized algorithms
    distributed as opposed to centralized.
  • scales with increase in network size, robust to
    network partitions and node failures.

13
Localized Algorithms for Coordination
  • Clustering efficient coordination.

14
Localized Clustering Algorithm
  • For every sensor, level ? radius
  • Advertisement hierarchical level, parent ID,
    remaining energy

C
D
B
E
A
wait time
15
Localized Clustering Algorithm
  • Start promotion timer if no parent.
  • Promotion timer inv prop (remaining energy,
    number of other sensors from whom level 0 adv was
    received)

C
D
B
E
A
promotion timer
16
Localized Clustering Algorithm
  • Periodic advertisements at the level 1 radius.
  • Advertisement B,C,E

C
D
B
E
A
level 1 sensor
17
Localized Clustering Algorithm
  • Two key design constraints
  • asymmetric communication in the network.
  • limited energy of sensors.

18
Application of Clustering Algorithm
  • Aim To pinpoint in an energy-efficient manner,
    the exact location of objects.
  • Accuracy widest possible measurement baseline.
  • Energy efficiency fewest number of sensors
    participating in the triangulation.

19
Triangulation
Z
A
  • Determine position in space.
  • Can specify approx direction of object relative
    to its own location.

20
Base-line Estimation
21
Advantages of Cluster-based Approach
  • Sensor algorithms only use local information.
  • generally lower energy consumption in comparison
    to global communication.
  • Robust to link or node failures and network
    partitions
  • mechanisms for self-configuration can be simpler.

22
Advantages of Cluster-based Approach
  • Local communication and per-hop data filtering
  • avoid transmitting large amounts of data over
    long distances.
  • preserving node energy resources.
  • Node energy resources are better utilized
  • cluster-heads adapt to changing energy levels.

23
Disadvantage of Cluster-based Approach
  • Non-optimal under certain terrain conditions.

24
Several Sensors Electing Themselves
Obstacle
Allow a cluster-head to switch on some number of
child sensors in its cluster to do object
location.
25
Adaptive Fidelity Algorithms
Z
Y
A
quality of the answer can be traded against
battery lifetime, network bandwidth, or number of
active sensors.
26
Tradeoffs
  • Localized algorithms exhibit good robustness and
    scaling properties.
  • May sacrifice resource utilization or sensing
    fidelity, responsiveness, or immunity to
    cascading failures.

27
Directed Diffusion
  • A novel data-centric, data disemmination paradigm
    for sensor networks.
  • Data generated by sensor node is named using
    attribute-value pairs.
  • A sensing task is disseminated throughout the
    sensor network as an interest for named data.

28
Directed Diffusion
  • This dissemination sets up gradients within the
    network designed to "draw" data matching the
    interest.
  • Events start flowing towards the originators of
    interests along multiple paths. The sensor
    network reinforces one, or a small number of
    these paths.

29
Directed Diffusion
30
Directed Diffusion
  • Allows intermediate nodes to cache or locally
    transform data.
  • leverages the application-specificity that is
    possible in sensor networks.
  • The diffusion models data naming and local data
    transformation features capture the
    data-centricity and application-specificity
    inherent in sensor networks.

31
Related Work
  • Ad-hoc Networks
  • Proactive vs. reactive routing protocols
  • Energy-efficiency issues
  • Distributed Robotics
  • Robots cooperate to discover entire map
  • Internet Multicast and web caching
  • Lightweight session

32
Current Developments
  • Smartdust project
  • cubic millimeter sensors
  • Sensors float in air like dust
  • WINS (wireless integrated wireless Sensors)
  • WSN (Wireless Sensing Network)
  • Odyssey
  • Habitat monitoring
  • The Cricket Indoor Location System
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