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Efficient Scheduling for Sensor Networks. Andreea Berfield & Daniel Mosse Computer Science Department University of Pittsburgh. Overview. Introduction and motivation Proposed protocols: ETDMA and OTAG Example Experimental results Discussion Conclusions. Introduction and Motivation.

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efficient scheduling for sensor networks

Efficient Scheduling for Sensor Networks

Andreea Berfield & Daniel Mosse

Computer Science Department

University of Pittsburgh

overview
Overview
  • Introduction and motivation
  • Proposed protocols: ETDMA and OTAG
  • Example
  • Experimental results
  • Discussion
  • Conclusions
introduction and motivation
Introduction and Motivation
  • Sensors suffer from different crippling limitations
    • Power consumption
    • Communication range
    • Processing capabilities
introduction and motivation1
Introduction and Motivation
  • Self-organizing sensors
  • Collisions-detection protocols(TAG, Cougar)
    • Creation of routing trees using broadcast messages
    • Transmission: all sensors on a level have an interval of time/epoch to send their results parents

BS

Level 0

Level 1

Level 2

introduction and motivation2
Introduction and Motivation
  • Fixed timeslots protocols (TDMA)
    • No collisions, no retransmissions
    • Less time awake
    • Problems?
      • Efficient creation and distribution of the transmission schedule: many messages exchanged or global knowledge required, time and energy consumption
proposed solutions etdma and otag overview
Proposed Solutions: ETDMA and OTAG Overview
  • Sensors organize in tree hierarchy
  • Passes needed to create the routing tree (RT) & disseminate the schedule:
    • Message from base station (BS) to join the RT
    • Communicate to parent the time in your sub-tree
    • Message from BS to help pick a time slot
etdma and otag overview
ETDMA and OTAG Overview
  • The third phase:
    • Each sensor receives and interval

Ti = [starti, endi]

    • Selects time to sense, receive, compute and send
    • Sends smaller sub-intervals to its children

Ti, child j = [starti,j, endi,j]  Ti

etdma e fficient tdma
ETDMA (Efficient TDMA)
  • Actions of leaf nodes are serialized
    • Each node stays awake minimum time
    • No collisions
  • All non-leaf nodes wake up when their first child sends its result, at time

endi,0 - TRANSMIT and go to sleep after last child transmits at time

endi,totalChildren -1

etdma variants
ETDMA Variants
  • ETDMA-Opt1
    • Schedules Sense and Compute in parallel for all leaf nodes
  • ETDMA-Opt2
    • Improves ETDMA-Opt1 by allowing BSs to go to sleep between consecutive transmissions from children
otag o ptimal tag
OTAG (Optimal TAG)
  • Perfect TAG or Optimal TDMA
  • TAG with no collisions
  • All nodes stay awake minimum, only to sense, receive, compute and send
  • Ideal protocol, lower bound for comparison
example
Example

Possible RT configuration for 5*5 grid topology:

etdma for sub tree in fig a
ETDMA for Sub-tree in Fig. a)

S10

R10

C10

T10

S,C5

T5

S,C11

T11

S,C15

T15

Time

otag for sub tree in fig a
OTAG for Sub-tree in Fig. a)

S10

R10

C10

T10

S,C5

S,C11

S,C15

T5

T11

T15

Time

experimental setup
Experimental Setup
  • CSIM simulator
  • Grid topology with different sizes (25*25 to 45*45) and different # of BSs
  • Sense and Compute are 1ms, Receive and Transmit 9ms and collision backoff 44ms
experimental setup1
Experimental Setup
  • The results presented are the averages obtained after 10 different runs
  • Different network configurations lead to different # levels and # nodes/level
  • Metrics used:
    • Average Time Awake (ATA)
    • ATA per Level (ATAL)
discussion potential issues
Discussion: Potential Issues
  • Failures and mobility
    • Global reconstruction
    • Dynamic local reconstruction
  • Parallelism
    • TAG has inherit parallelism in transmission
    • A*, schedule RT and parts of RT in parallel
  • Clock synchronization
    • Assume loose clock synchronization
conclusions
Conclusions
  • We proposed two energy-minimization protocols for both schedule creation and distribution
  • They require small amount of global information
  • Experimental results suggest a 2-3 fold reduction in average time awake per node compared to TAG
slide20
Thank you!

Questions?