1. Chih-Min Chao and Yao-Zong Wang Department of Computer Science and Engineering National Taiwan Ocean University, Taiwan IEEE WCNC 2010 A Multiple Rendezvous Multichannel MAC Protocol for Underwater Sensor Networks

2. Outline Introduction Relate Work Goal MM-MAC Simulation Conclusion

3. Introduction The world's oceans cover over 70 % of its surface Underwater Wireless Sensor Networks (UWSNs)

4. Introduction Underwater Environment Long propagation delay The propagation speed for an acoustic link is 1500 meters/sec 2 × 10 5 times lower than the speed of a radio link Expensive transmitting power consumption The transmit power is 10 W Lower available bandwidth

5. Introduction Underwater Environment + Multichannel Enhance network throughput Achieves low average delay

6. Goal This paper proposes a multichannel MAC protocol for UWSNs Receiver-based protocol Only one transceiver is needed To solve the missing receiver problem in multichannel protocols Data packets will not be collided by control packets Enhances the network performance in a multi-hop UWSN Fairness

7. Assumptions Totally m equal-bandwidth channels are available. Each node is equipped with one half-duplex modem which is able to switch to any channel dynamically. Nodes are time synchronized. Each node knows the identifications (IDs) of its one hop neighbors.

8. System Model …… … Superframe Channel 1 …… Superframe Channel 2 …… Superframe Channel 3 0ACK … 1 2 Data Superframe Control periodData period

9. System Model 0ACK1 2 Data Control periodData period 34 5 0ACK1 2 Data 34 5 0ACK1 2 Data 34 5 0ACK1 2 Data 34 5 A B C D Home-channel=1 Home-channel=2 Home-channel=3 Home-channel=4 A D C B

10. Challenges how to decide the slots which the node should stay in its home-channel. how does the sender know the slots which the receiver stay in its home-channel. How to overcome the long propagation delay in the UWSNs.

11. MM-MAC Default slots A node will stay on its default channel, waiting for transmission requests. Switching slots A node may switch to its intended receiver’s default channel to initiate a transmission 0ACK … 1 2 Data Superframe Control periodData period

12. MM-MAC Cyclic Quorum Systems Z n : n = 4 ~ 111 Z 6 G 0 = {0,1,3} G 1 = {1,2,4} G 2 = {2,3,5} G 3 = {3,4,0} G 4 = {4,5,1} G 5 = {5,0,2} Z 8 G 0 = {0,1,2,4} G 1 = {1,2,3,5} G 2 = {2,3,4,6} G 3 = {3,4,5,7} G 4 = {4,5,6,0} G 5 = {5,6,7,1} G 6 = {6,7,0,2} G 7 = {7,0,1,3} The number of slots any difference set under Z n Plus one each time

13. Superframe # 1 MM-MAC Z 6 G 0 = {0,1,3} G 1 = {1,2,4} G 2 = {2,3,5} G 3 = {3,4,0} G 4 = {4,5,1} G 5 = {5,0,2} A B Slot 023451 DC A =1 DC B =2 DS A ={2,3,5} DS B ={3,4,0} 2+1=3  G 3 ={3,4,0} 111 222 default slot switching slot 0ACK … 1 2 Data Superframe Control periodData period

14. MM-MAC 0ACK … 1 2 Data Superframe Control periodData period Maximum Propagation Delay+CTS

15. MM-MAC Example Superframe # 5 2222 0000 DATA RTS CTS DATA NTF 2 2 2 2 2 2 2 2 2 2 2 0 0 2 0 RTS CTS RTS NTF 012345 control perioddata period default slot switching slot ACK i packet X sent through channel i x A BC D DC A = 3 DS A = {2,3,5} DC B = 2 DS B = {1,2,4} DC C = 1 DS C = {0,1,3} DC D = 0 DS D = {0,2,5} Z 6 G 0 = {0,1,3} G 1 = {1,2,4} G 2 = {2,3,5} G 3 = {3,4,0} G 4 = {4,5,1} G 5 = {5,0,2}

16. Simulation LanguageC++ EnvironmentMulti-hop Transmission range1km Control/Data packets size20/200bytes Number of nodes49 Side length4km Cyclic quorum systemZ6Z6 Number of channels3 Times60 runs

17. Simulation Slotted FAMA RTS CTS DATA RTS CTSDEFERS TRANSMISSIONS A B C Maximum Propagation Delay+CTS In a multihop environment, the RTS/CTS packets may collide with data packets.

18. Simulation Multiple Sinks Model

19. Simulation Single Sink Model

20. Conclusion The proposed MM-MAC protocol Is a multiple rendezvous Only one modem is required for each node Solves the missing receiver problem. Reduce the collision probability of data packets Achieves higher throughput and keeps the retransmission overhead low

21. Thank You