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Y-MAC: An Energy-efficient Multi-channel MAC Protocol for Dense Wireless Sensor Networks

Youngmin Kim, Hyojeong Shin, and Hojung Cha

International Conference on Information Processing in Sensor Networks 2008

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Outline

Introduction The Y-MAC Implementation Evaluation Conclusions

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Introduction

Propose a light-weight channel hopping mechanism

When a traffic burst occurs, a receiver and potential senders hop to other channels

Each node is guaranteed to receive at least one message on the base channel

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The Y-MAC protocol

Y-MAC is a TDMA-based multi-channel MAC protocol

If each node has an exclusive send time slot, it results in idle listening and overhearing

Scheduling receivers is more energy efficient and contention among senders is eliminated

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Frame architecture

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Control Message

The sink node periodically broadcasts control messages to initiate the network

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Initial Time synchronization Nodes periodically broadcast the information

required for time synchronization It consists

time remaining to the start of the next frame and the sequence number originated from the

sink node Once a node receives that, it sets its time

remaining to the next frame equal to sender

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Network partition detection If a node considered to be detached from the

network not received control messages with fresh

sequence numbers for a certain time If a node detects a network partition

it goes into the sleep mode to save energy and wakeup periodically to received control

messages When it fail to rejoin network, sleep interval

will double

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Time Slot Assignment

A

B

C

E

DB

C

C

B

B

DC

A

A

C

D

E

E

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Time Slot Retrieval

A node is removed from networks, or run out of battery its control message has not arrived during a

predefined time the time slot that has been used by that node

must be released for the future use neighboring nodes update their slot allocation

vectors

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Medium Access Design

A node wishing to send a packet sets a random backoff value on contention window

Receiver wakes up at the end of the contention window to receive the data

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Channel Hopping Mechanism 1/2

DATA

ACK

Notify message

A B C D Channel polling

A B C D

A -> B

A -> B

D -> C

Contention window

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Channel Hopping Mechanism 2/2

A B C D

A B C D

C -> B D -> C

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Implementation

Implemented in RETOS operating system on TmoteSky Motes

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Experimental Setup

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Single-Hop Environments

1 packet per 10 seconds

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Single-Hop Environments

1 packet per second

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Multi-Hop Environments

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Conclusion

Proposed a multi-channel MAC protocol for wireless sensor networks

Implemented it in the RETOS operating system running on TMoteSky motes

Also proposed a light-weight channel hopping mechanism

Enables multiple node pairs to communicate simultaneously on multiple channels

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~THE END~