Outline Paper presentation Ultra-Portable Devices Introduction - - PowerPoint PPT Presentation

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Paper presentation Ultra-Portable Devices

Paper: Presented by:

Ultra-Low Duty Cycle MAC with Scheduled Channel Polling

Wei Ye, Fabio Silva and John Heidemann USC Information Science Institute Proceedings of the 4th international conference on embedded networked sensor systems, 2006, pages 321-324, ACM

Nafiseh Mazloum

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Outline

Introduction MAC protocol design Lower bound of energy performance Protocol implementation Experimental evaluation Summary and discussion

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Introduction(I)

Major sources of energy waste

Idle listening => duty cycle Collision Overhearing Control overhead

Approaches to keep connectivity of network

Scheduled channel access like TDMA Random channel access

Scheduled contention Low-power listening

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Introduction(II)

Scheduled contention

Overhead due to schedule maintenance Listening during contention interval when nothing to send

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Introduction(III)

Low-power listening

Efficiency is at cost of transmitter Sensitive to traffic and network size Challenging to adapt LPL to new radios

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MAC protocol design(I)

Main goals

To reduce the duty cycle To adapt to variable traffic loads

Scheduled channel polling MAC (SCP-MAC) design

Synchronized channel polling Adaptive channel polling

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MAC protocol design(II)

Synchronized channel polling

short wake-up tone Scheduled neighbor polling time Robust to varying traffic load Penalty => maintaining schedule synchronization

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MAC protocol design(III)

Adaptive channel polling

Channel characteristics

mix periodic and bursty traffic unpredictable traffic mixes

To detect bursty traffic To add dynamically high-freq. channel polling

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MAC protocol design(IV)

Design optimization

Two phase contention to reduce collision probability Overhearing avoidance

based on address destination in MAC header

• ptional RTS/CTS

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Lower bound of energy performance(I)

Assumption

Periodic traffic Single hop with n+1 nodes Broadcast traffic with interval Tdata

Expected energy consumption by radio

tpoll= radio transision from sleep to listen + sampling time to detect channel ignor radio transition costs of other states

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cost of maintaining synchronization

+

Lower bound of energy performance(II)

Wake up tone duration

Tsync is synchronization period Tsync is clk drift rate trade off in determining Tsync

Synchronization frequency and polling period

Best case: perfect piggybacking Worst case: explicit synchronization

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Lower bound of energy performance(III)

Analytical results

Synchronization can be quite rare (7xTdata-16xTdata). Piggybacking reduces energy by half when send data is very rare. Energy usage in LPL increases with higher speed radio.

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Protocol implementation(I)

Software architecture

Tiny OS (and Mica2 motes and CC1000 radio) MAC functionality is broken to

physical layer (PHY) basic CSMA layer LPL layer SCP layer

Interaction with Tiny OS

CPU sleeps when radio is off Implementation of timer with very low-jitter

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Protocol implementation(II)

Efficient piggybacking of information

Using dest. address for piggyback synchronization info. in broadcast packets

Port to IEEE.15.4 radio

To adapt SCP-MAC to run on IEEE.15.4 radio

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Experimental evaluation(I)

Optimal set up with periodic traffic

10 nodes in a single-hop network Each node generates 40B msg. periodically

• Msg. time interval is 50-300s

Optimal polling period from analytical model

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Experimental evaluation(II)

Performance with unanticipated traffic

Duty cycle of 3% and polling of every second Twenty 100B long broadcast message by each node

• Msg. time interval is 50-300s
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Experimental evaluation(III)

Performance in a multi-hop network

Varying traffic load Duty cycle of 0.3% and channel polling of 1 second 9-hop linear network with 10 nodes Inter-packet interval is 0-10s (20 packet send, each 50B long)

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Summary

A new MAC protocol based on scheduled channel polling is proposed. By optimally combining channel polling and scheduling, duty cycle reduces to 0.1% and lower. A lower bound on energy consumption is derived by analytical model. SCP-MAC can handle bursty and varying traffic load.

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