1 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

2 Outline Introduction The Y-MAC Implementation Evaluation Conclusions

3 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

4 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

5 Frame architecture

6 Control Message The sink node periodically broadcasts control messages to initiate the network

7 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

8 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

9 Time Slot Assignment A B C E D B C C B B D C A A C D E E

10 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

11 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

12 Channel Hopping Mechanism 1/2 DATA ACK Notify message ABCD Channel polling ABCD A -> B D -> C Contention window

13 Channel Hopping Mechanism 2/2 ABCD ABCD C -> BD -> C

14 Implementation Implemented in RETOS operating system on TmoteSky Motes

15 Experimental Setup

16 Single-Hop Environments 1 packet per 10 seconds

17 Single-Hop Environments 1 packet per second

18 Multi-Hop Environments

19 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

20 ~THE END~