1. Enhanced Slotted Aloha Protocols for Underwater Sensor Networks with Large Propagation Delay Kai Chen † Jianhua He § Yi Zhou ‡ Haibing Guan ‡ †School of Information Security and Engineering, Shanghai Jiaotong University, China. ‡School of Electronic, Information and Electrical Engineering, Shanghai Jiaotong University, China. §School of Engineering, Swansea University, UK. IEEE VTC 2011

2. Outline Introduction System model SA-ALOHA ISA-ALOHA Simulation Conclusion

3. Introduction Underwater sensor networks(UWSNs) have attracted large research interests from both academy and industry Due to the importance of MAC protocols for UWSNs – Design and analysis of MAC protocols

4. Introduction Among the existing MAC protocols in shared wireless medium – ALOHA protocols Pure-ALOHA Time A B C DATA Slotted-ALOHA Time A B C DATA

5. Introduction This frame can be received successfully – There are no other frames arrival at node in conflict free period (P cf ) t i,k : node i send the kth frame to node A T i,A : actual propagation delay T f : frame transmission time

6. Introduction Conflict free for two different frame transmission ∆t ij : the difference of start for two frame transmission ∆T ij : the difference between propagation delay N i to N A and that N j to N A T f : frame transmission time

7. Introduction RF network scenarios Pure-ALOHASlotted-ALOHA protocol ∆t ij Any valueMultiple of T f throughput0.180.36 Time A B C A B C DATA TIME Sender Receiver Radio wave Propagation speed : 3*10 8 m/s

8. Pure-ALOHASlotted-ALOHA protocol ∆t ij randomMultiple of T f ∆T ij random throughput0.18 Introduction UWSN scenarios Pure-ALOHASlotted-ALOHA protocol ∆t ij randomMultiple of T f ∆T ij random Time A B C A B C DATA collision DATA collision TIME Propagation delay Underwater Sender Receiver Acoustic wave Propagation speed : 1500 m/s

9. Introduction- motivation The performance of Aloha in UWSNs can drop quickly with increasing propagation delay

10. Goal Reuse the idea of synchronous transmission in S-Aloha protocol – SA-ALOHA – ISA-ALOHA Improvement for the SA-ALOHA

11. System model & Assumption Single hop star topology with a central control node A Fixed N ordinary nodes Position information Time synchronized Each ordinary nodes may occasionally send data frames to the central control node

12. SA-ALOHA Example of frame transmission and reception

13. SA-protocol Calculation of T pre T i,A : propagation delat of node i to node A T slot : slot size

14. SA-protocol Problem – Propagation delay is not accurate T err : Estimation error of T i,j T ~ i,A : estimated value of T i,j

15. T slot,isa : T slot for ISA protocol ISA-protocol Solution T inc : the increment of time from T slot for T slot,isa

16. ISA-protocol Solution Sender, N 1 Sender, N 2 Receiver, N A T slot,isa =T f +k*T emax Frame1 Tx Frame2 Tx Frame1 Rec Frame2 Rec Tolerant of the error of estimation

17. Simulation parametervalue Ordinary node50 Transmission range1000 RFUWSN Propagation speed3*10 8 m/s1500 m/s Frame length512 bytes50 bytes Data rate2 Mbps2 kbps TfTf 2.048 ms200 ms T slot = 1.01*T f 2.06848 ms202 ms 1000 m Center node

18. Simulation result

21. Simulation results

22. Simulation result T emax = 33 ms

23. Conclusion In this paper, the authors investigated the performances of Aloha protocols in (UWSN) – Long propagation delay SA-protocol ISA-protocol Simulation results demonstrate the effectiveness of our proposed protocols

24. 24 Thanks for your a ttention