1. An Improved CDMA-Based MAC Protocol for Underwater Acoustic Wireless Sensor Networks Guangyu Fan, Huifang Chen, Lei Xie, Kuang Wang IEEE WICOM 2011

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

3.  Underwater sensor network technology can be applied in many fields  Environment monitoring  Geographic data collection  Offshore exploration  Assisted navigation  Disaster prevention  Tactical surveillance Introduction

4.  Transmission rate  WSN: 3 x 10 8 m/s  UWSN: 1500 m/s  Propagation delay Introduction A B Propagation delay BA

5.  Problem  Long propagation delay Introduction RTS CTS DATA RTS CTS A B C

6.  CDMA-based protocols  Transmitter-oriented code assignment (TOCA)  Receiver-oriented code assignment (ROCA)  Path-oriented code assignment (POCA) Introduction

7.  Slotted FAMA Related works RTS CTS DATA RTS CTSDEFERS TRANSMISSIONS A B C Maximum Propagation Delay+CTS Waste time !

8.  RIPT Related works

9.  Disadvantage Related works Collision

10.  In the paper, POCA-CDMA-MAC is proposed for UWASNs.  It utilizes a round-robin method and CDMA technology to reduce collisions of packets. Goal

11.  Assumption  Sink can receive packets from multiple neighbors at the same time  Routes will be built  All sensor nodes are equipped with a half-duplex, omni-directional transceiver Network environment

12. POCA-CDMA-MAC A P1 B P1 A P2 B P2 C P2 B P3 B P4 A P5 B P5 C P5 A P6 B P6 C P6 C P7 Surface station Sink

13. POCA-CDMA-MAC A P1 B P1 A P2 B P2 C P2 B P3 B P4 A P5 B P5 C P5 A P6 B P6 C P6 C P7 Sink (s1,s2,s3,s4,s5,s6,s7)

14. POCA-CDMA-MAC A P1 B P1 A P2 B P2 C P2 B P3 B P4 A P5 B P5 C P5 A P6 B P6 C P6 C P7 Sink (s2,s3,s4,s5,s6,s7) s1

15. POCA-CDMA-MAC A P1 B P1 A P2 B P2 C P2 B P3 B P4 A P5 B P5 C P5 A P6 B P6 C P6 C P7 Sink (s2,s3,s4,s5,s6,s7) s1

16. POCA-CDMA-MAC A P1 B P1 A P2 B P2 C P2 B P3 B P4 A P5 B P5 C P5 A P6 B P6 C P6 C P7 Sink (s5,s6,s7) s1 s2 s3 s4

17. POCA-CDMA-MAC A P1 B P1 A P2 B P2 C P2 B P3 B P4 A P5 B P5 C P5 A P6 B P6 C P6 C P7 Sink (s5,s6,s7) s1 s2 s3 s4

18. POCA-CDMA-MAC A P1 B P1 A P2 B P2 C P2 B P3 B P4 A P5 B P5 C P5 A P6 B P6 C P6 C P7 Sink s1 s2 s3 s4 s5 s6 s7

19. POCA-CDMA-MAC A P2 B P2 C P2 Sink C P2 B P2 A P2 Sink

20. POCA-CDMA-MAC A P2 B P2 C P2 Sink C P2 B P2 A P2 Sink

21. POCA-CDMA-MAC A P2 B P2 C P2 Sink C P2 B P2 A P2 Sink

22. POCA-CDMA-MAC A P2 B P2 C P2 Sink C P2 B P2 A P2 Sink

23.  Problem POCA-CDMA-MAC A P2 B P2 C P2 Sink C P2 B P2 A P2 Sink

24.  Solution POCA-CDMA-MAC A P2 B P2 C P2 Sink C P2 B P2 A P2 Sink Passing token

25. Simulation ParameterValue Transmission range7.5 km Data packet500 bytes Static Nodes8 Control packet12.5 bytes

26. Simulation

29.  In the proposed MAC protocol prevent collision of packets and the length of the spreading sequence codes is shortened by using  round-robin method  CDMA technology  Each node encodes its packets with a spreading sequence, so the sink can receive packets from multiple neighbors at the same time. Conclusion