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BITS PILANI KK BIRLA GOA CAMPUS

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Introduction

RBS

Adaptive Clock Synchronization Multi-hop Synchronization

summery

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Applications of clock sync: Data Integration

Data fusion

Energy mode saving

Traditional clock sync protocol approach Non-deterministic factors

Send time Access time

Propagation time

Receive time

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Receiver to Receiver sync

Eliminatessend time, Access time

RBS does not contain any analysis on the number ofreference broadcasts necessary, or the frequency ofreference broadcasts

More overhead in terms of exchanging their information

between the receivers Assumes single Broadcast region for sender and all receivers

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Protocol Description1] A sender broadcasts n reference packets to its neighbors2] Receivers record time according to own local clock. It uses

Linear Regression to fit a line on these data. Slope of the lineapproximates relative clock skew between receiver andsender

3] Receivers send back packets containing the slope of the line

and one point on that line4] Sender composes all slopes together and broadcasts a

packet containing its relative clock skew slope to all thereceivers

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5] Receivers now calculate their own slope relative to all theother receivers

Time Period for Resynchronization

max = max + (Tsync + max )

Relationship between the number of messages and achievedsynchronization error with certain probability

P(| |

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max : maximum allowable synchronization

max: maximum delay in the time values of one receiverreaching another receiver

:Maximum drift of the clock rate

max : maximum specified clock skew at synchronization

point

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Introduce levels for senders

Level zero

Level one sensor node within the broadcast level of a level 0 sensor can

be a sender to synchronize sensors which are two hops awayfrom the level 0 sensor

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Fig.1 Multiple hop synchronization

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Limitation:

Protocol essentially floods the entire network with reference packets

Can be fixed by making time synchronization sensor initiated

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Not Energy aware

Not Light weight

Robust Server less

Not secure

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Relationship between the number of

messages, the achieved synchronization error

(with a certain probability).

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1] Santashil PalChaudhuri, Amit Kumar Saha, David B. Johnson,Adaptive

Clock Synchronization in Sensor Networks, Department of Computer

Science Rice University Houston.

2] Jeremy Elson, Lewis Girod and Deborah Estrin, Fine-Grained Network

Time Synchronization using Reference Broadcasts, Department ofComputer Science, University of California, Los Angeles.

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