1. Slide 1 NATO UNCLASSIFIED Environment monitoring Review how human activities affect the marine echosystem Undersea explorations Detect underwater oilfields Disaster prevention Monitoring ocean currents and winds (Tsunamis) Assisted navigation Locate dangerous risks in shallow waters Distributed tactical surveillance Intrusion detection (Navy), harbour protection …… Use cases for Underwater networking

2. Slide 2 NATO UNCLASSIFIED We don’t like our autonomous vehicles to be too autonomous Safety of operations Real-time data is usually a requirement Cooperation, in general, requires some kind of explicit information exchange Increased number of assets being deployed (currently from few up to 15 underwater and surface nodes) The Requirement for Underwater Communications

3. Slide 3 NATO UNCLASSIFIED UW Communications Channels: Qualitative overview ACOUSTIC ELECTROMAGNETIC Low power Small hardware High Bandwidth Requires line of sight Requires tight alignment of end points Susceptible to marine fouling Sensitive to suspended particles and turbidity Unaffected by turbidity,marine fouling or acoustic noise Crosses the air- water boundary High bandwidth Very limited networking support for underwater communication Loop antennas far from ideal for small AUV integration Established technology Full networking support Supports ranges of 10s of Km Sensitive to pressure and temperature gradients Performance degrades in shallow water Limited bandwidth Range Bandwidth 10s b/s 10s Kb/s G b/s OPTICAL 10s m100s m10s Km

4. Slide 4 NATO UNCLASSIFIED Acoustic communications: The Channel “Advances in Integrating Autonomy with Acoustic Communications for Intelligent Networks of Marine Robots”,Toby Schneider, PhD thesis, 2013

5. Slide 5 NATO UNCLASSIFIED Slow speed of propagation: five orders of magnitude lower than in Radio Frequency) – High Doppler shifts (example: v=2m/s, f=25 kHz, shift = 33 Hz) Spreading Loss – Energy covering a big volume Absorption Loss (Frequency Dependent) – Losses from energy propagation/ transfer Scattering Loss – Surface scattering – rough sea surface introduces rapidly fluctuating arrivals – Bubble layer scattering Acoustic communications: The Channel

6. Slide 6 NATO UNCLASSIFIED Low Bandwidth Ambient noise and high interference level High bit errors and temporary loss of connectivity with possible asymmetric links Waveguide, multipath, shadow zones – Reflections from bottom and surface – Refraction form spatially varying sound speed – Masses of water with different characteristics – Imposes multipath and time spread –ISI Acoustic communications: The Channel

7. Slide 7 NATO UNCLASSIFIED Channel Impulse Responses : Examples “Channel Sounding For Acoustic Communications: Techniques and Shallow Water Examples”, Paul Van Walree, Technical Report 2011 Wind burst at around t=25 seconds Cyclic arrival agreeing with the period of the dominant waves

8. Slide 8 NATO UNCLASSIFIED What a very benign acoustic channel will do to your signals “Underwater Acoustic Communications Performance Modeling in Support of Ad Hoc Network Design”, Fox, W. L J; Arabshahi, P.; Roy, S.; Parrish, N., OCEANS 2007, vol., no., pp.1,5, Sept. 29 2007-Oct. 4 2007

9. Slide 9 NATO UNCLASSIFIED UW Acoustics Physical Layer Performance “The state of the art in underwater acoustic telemetry” Kilfoyle, D.B.; Baggeroer, A.B.; MIT & Woods Hole Oceanogr. Instn. Joint Program in Oceanogr. Eng., Woods Hole Oceanogr. Instn., MA IEEE Journal of Oceanic Engineering, Jan 2000

10. Slide 10 NATO UNCLASSIFIED Interoperability is nonexistent ! Software architectures based on the OSI stack fall short of providing cross-layer information essential for achieving optimized solutions There is no single adopted way to simulate the acoustic channel Usually simulations fail to fully capture underwater channel dynamics resulting in oversimplified scenarios Going at sea is expensive. Doing it in a controlled way even more so. Reliable and robust multi-hop communication coping with channel dynamics Challenges

11. Slide 11 NATO UNCLASSIFIED Interoperability will hopefully come ! JANUS is here, hopefully promulgated as a standard soon. Improved data throughput to be pursued by: More sophisticated modulation and coding schemes, signal processing techniques. Multi-carrier systems, Multi-modality, hybrid systems Software-defined architectures will improve sharing of solutions and promote a true “survival of the fittest” in terms of protocol solutions Network security for underwater communications Combination of sensing, networking, communication and navigation capabilities to improve underwater node operations Network coding, data compression and DTN solutions Trends