T-Lohi: A New Class of MAC Protocols for Underwater Acoustic Sensor Networks

1. T-Lohi: A New Class of MAC Protocols for Underwater Acoustic Sensor Networks Affan A. Syed, Wei Ye, John Heidemann Information Sciences Institute/USC IEEE INFOCOM 2008

2. Outline • Introduction • Proposed Mechanism: Tone Lohi • Performance Evaluation • Conclusions

3. Introduction • In underwater sensor networks (underwater acoustic sensor networks, UWSN), a shared acoustic medium adds more challenges. • Acoustic communication suffers from latencies five orders-of-magnitude larger than radio communication. A B C D E

4. Introduction • 802.11 DCF in UWSN • Unfairness Receiver Sender Sender A B E B can’t hear from E. RTS RTS 5ms 15ms 25ms CTS RTS data Random Backoff ack Both A and E want to transmit to B, A gets more opportunities than E.

5. Motivation • The large propagation delay is especially harmful to protocols designed for radio networks, and so must be handled explicitly. • Challenge • Unfairnessresults from Space-Time Uncertainty

6. Goals • Propose a MAC protocol called Tone Lohi (T-Lohi). • Besides being energy and throughput efficient, T-Lohi provides flexible, fair, and stable medium access for acoustic networks.

7. =CR Overview of T-Lohi potential sender Receiver Receiver Sender Sender A B A B C Tone Tone Tone Ttone=5ms CR=35ms Propagation delay =TA,B=30ms data … backoff Tone data …

8. T-Lohi • Three reservation mechanism • Synchronized T-Lohi (ST-Lohi) • Aggressive Unsynchronized T-Lohi (aUT-Lohi) • Conservative Unsynchronized T-Lohi (cUT-Lohi)

9. Synchronized T-Lohi (ST-Lohi) Receiver A and C attempt synchronously B C A tone packet CRst=worst_propogation_delay+ Tone_detection_time =τmax+Ttone =30ms+5ms CRst Reservation Period Window=2, A&C backoff. A attempts. A “wins” and transmits data. Data packet … Data Period

10. Aggressive Unsynchronized T-Lohi (aUT-Lohi) Receiver B C A tone packet CRaUT=τmax+Ttone=30+5=35ms C’ data … C assume it won and transmit data. but unfairness for A and C. A’ backoff period C’ data

11. Conservative Unsynchronized T-Lohi (cUT-Lohi) Receiver B C A tone packet CRcUT=2τmax+2Ttone=2*(30+5)=70ms A’s backoff period C hears A and both back off.

12. Discussion • Deafness Receiver C B A ttx,c=0 SIFS=0.1ms TA,B=8ms A’ data C’ data … data-data collision B broadcasts that can’t recognize packets from A&C Ttone=1ms

13. Simulation and Performance Evaluation

14. Performance Evaluation 2 nodes

15. Performance Evaluation 8 nodes

16. Relative energy overhead for T-Lohi for an 8 node network

17. Conclusion • The authors leveraged the opportunities in acoustic medium access along with low power wakeup tone hardware to design T-Lohi.

18. Thank you~