1. 6/8/2006UWSN Reading Group1 Tutorial on Underwater Acoustic Communications Speaker: Baosheng Li Advisor: Shengli Zhou June 8, 2006 Presentation is based on the book chapter of Underwater Acoustic Communications by Milica Stojanovic

2. 6/8/2006UWSN Reading Group2 Outline Introduction System requirements Channel characteristics System design Active research topics Conclusions

3. 6/8/2006UWSN Reading Group3 Introduction Applications (omissible) Why acoustic? - Radio waves (30Hz-300Hz) - Optical waves - Acoustic waves: Da Vinci; 1945, SSB SC AM*, 8kHz-11kHz, 1 ’ s km;SSB SC AM VLSI & DSP: FSK (80 ’ s), PSK (90 ’ s), Multi-carrier (Active). Achievements - Acoustic controlled robots; high-quality video transmission (6500km depth); telemetry (200km horizontal dist.) Challenges - extremely low bandwidth; slow propagation speed; high time variation etc.

4. 6/8/2006UWSN Reading Group4 System requirements Control signals - data rate: up to 1 kbps; low BER Telemetry data - data rate: 1~10 ’ s kbps; BER: ~ Speech signals Video transmission - data rate: 3 kbps (SSB); BER: - data rate: 10~100 ’ s kbps; BER: ~

5. 6/8/2006UWSN Reading Group5 Channel characteristics Range and bandwidth - Transmission loss: Energy spreading, absorption loss, Spatial dependence - Noise: Ambient noise (deep ocean & near shores, WGN, exception); Man-made noise (near shores, be significantly increased) - Links: * Links: Very long distance (1000km, Bandwidth < 1 kHz); Long-range system (10-100km, 1 ’ s kHz); Medium-range system (1-10km, 10kHz); Very short range ( 100kHz).

6. 6/8/2006UWSN Reading Group6 Channel characteristics (cont ’ d) Multipath - Slow propagation speed -> long multipath channels Ex: in medium-range shallow water, multipath spread 10 ms, data rate 10 ksps. It will cause ISI to extend over 100 symbols. - Formation mechanisms: Shallow water -> reflection at boundaries; Deep water -> ray bending.

7. 6/8/2006UWSN Reading Group7 Channel characteristics (cont ’ d) Time-variation * Time-variation - No single model accepted for UWA channel - A trade-off in the choice of signaling rate (ISI, T-V slower) - For mobile UWA channel, time-coherence properties of channel (Refer to land-mobile radio systems.)

8. 6/8/2006UWSN Reading Group8 System design Systems based on non-coherent modulation - FSK (Frequency Shift Keying) Ex. A telemetry UWA system: Signals band 20~30kHz; Max. data rate 5 kbps; 16 subbands; 4-FSK for each subbands; 32 bits info. transmitted in parallel; BER ~ for a less than 1 km long shallow water path.

9. 6/8/2006UWSN Reading Group9 System design (cont ’ d) Systems based on coherent modulation Channel coding can also greatly increase the system performance. - Purely phase-coherent modulation Ex. A practical QPSK system: Carrier frequency 15kHz; Data rate 5 kbps; BER about

10. 6/8/2006UWSN Reading Group10 Active research topics Reducing the receiver complexity Interference cancelation Multiuser communications Underwater sensor networks System self-optimization Advanced modulation and coding such as MIMO OFDM Mobile underwater communications

11. 6/8/2006UWSN Reading Group11 Conclusions The need for underwater acoustic communications exists in lots of applications. The UWA communications channels, however, have limited bandwidth, and often cause signal dispersion in time and frequency. Despite these limitations, UWA communications are a rapidly growing field of research and engineering.

12. 6/8/2006UWSN Reading Group12 Thank you !

13. 6/8/2006UWSN Reading Group13

14. 6/8/2006UWSN Reading Group14 - Save transmitted power ( No carrier; SSB ) - Save RX bandwidth (http://www.williamson-labs.com/480_ssb.htm)

15. 6/8/2006UWSN Reading Group15 Available range, bandwidth and SNR at RX input.

16. 6/8/2006UWSN Reading Group16 Deep, Pacific ocean, off the coast of California.

17. 6/8/2006UWSN Reading Group17 Shallow, Atlantic ocean shelf, off the coast of New England.

18. 6/8/2006UWSN Reading Group18 Shallow, Buzzards Bay, near the coast of New England.