Experiencias sobre calidad subjetiva percibida en redes acústicas submarinasUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Poncela-Gonzalez, Javier

Poncela, Javier

Repositorio Institucional de la Universidad de Málaga

Subjective quality in underwater acoustic networks

Poncela-González, Javier

Repositorio Institucional Universidad de Málaga

SUBJECTIVE QUALITYinUNDERWATER ACOUSTIC NETWORKSDr. Javier PoncelaTELECOMMUNICATIONS TECHNOLOGIES RESEARCH GROUPUNIVERSITY OF MALAGA, SPAINContents1. Introduction2 U d t A ti Ch l. n erwa er cous c anne3. Quality Assessment in Underwater Video2INMIC‘14Introduction• Oceans cover about 70 percent of the Earth’s surface, and much of this vast resource remains to be explored– It is possible to chat from the International Space Station and k h ll f th it f M t E t hma e p one ca s rom e summ  o  oun  veres , so w y can't we check our email from the ocean floor? • The volume below the sea surface has been traditionally         ignored– It’s a harsh environment that requires advanced technology – Resources are much easier to collect on the surface– Expansion has been possible without  much effortE l k– ven now, space resources oo  more tempting3INMIC‘14UAC Applications• Scientific– Submarine life monitoring– Natural phenomena forecasting• Industrial– Aquaculturef– Exploitation o  mineral resources • EnvironmentalPollution control–  – Climate parameters recording• Safety– Search and rescue missions,– Communication between divers and vehicles4INMIC‘14Málaga• Phoenicians Greeks, , Romans, Arabs, …– Multicultural city • Metropolitan Area> 700.000 people• Important Airport & Harbour• Coastal CityWireless Underwater Waves• Traditionally, underwater communication is achieved via cables– Cables are expensive and heavy-weighted: several tens or h d d f tun re s o  me ers– Movement constraints for vehicles and divers– Safety issues as cables may pose dangers      Wireless underwater communications is a must6INMIC‘14Wireless Underwater Waves• Radio-Electromagnetic waves– EM waves do not travel well through thick electrical conductors like salt waterSt b ti H tt ti ith di t– rong a sorp on + uge a enua on w  s ance Only for very short range communications• Optical communicationBlue-green region (450-550 nm)Light Depth Attenuation+ High bandwidth (~Mbps)+ Negligible delaySh t di t ( 100 )– or  s ance <  m– Alignment of transmitter/receiver7INMIC‘14Underwater Acoustics• Used by submarine fauna• Frequency range: 1 Hz - 500 kHz    – A 30 kHz frequency (ultrasound) = 6 GHz in air (microwave)(wavelength = 5 cm)• Negative propagation characteristicsLimited bandwidth: 8kH t 48 78 kH–   z o -  z– Time-varying multipath propagation: Reflections from surface, sea floor – Low speed of sound underwater: ~1500 m/s8INMIC‘14Contents1 I t d ti. n ro uc on2. Underwater Acoustic Channel3. Quality Assessment in Underwater Video9INMIC‘14Underwater Acoustic Channel• The underwater acoustic channel is affected by many factors– Salinity – Speed of sound– Temperature– Seabed topologyThi lti th b ti D l ti– Surface wind-speed– …• s causes mu -pa s, rever era on, opp er, me-varying paths, …• The result: the communication channel has poor quality and high latency– Challenges are very different from terrestrial wireless10INMIC‘14Propagation Speed• Typical: 1500 m/s Range: 1450m/s 1540 m/s  –  • As depth increases, speed decreases• After 500-600 meters the increasingpressure causes an increase in speedSummer Winter11INMIC‘14Scattering• When the surface of the water is in movement, it causes a dispersal of the delays of the multiple reflections• Time of coherence decreases• Experimental measurements show that scattering increases with frequency, distance and wind speedmultipathTx RxLOSseabed12INMIC‘14Bubbles are not So Funny• Bubbles that appear on the surface may have a biginfluence on high frequency acoustic signals• Effect: Increased attenuation of reflected signals• Bubble density increases with wind speed– At 10 m/s, attenuation due to bubbles is up to 20 dB• Bubbles underwater also createadditional scatteringINMIC‘14 13Noise• Impacts the choice of carrier frequencies• Natural and human-origin sources of noise: waves, turbulences, animals, ships• Frequency rangesLow (< 10 Hz):              seismic, storm, turbulencesMedium (50 ~ 300 Hz): shipsHigh (> 500 Hz):           wind, cavitation, bubbles• Discontinuous biological noise (in time and space)• Decreasing power spectral density:< 10Hz: 8 ~ 10 dB/octave Above 10 Hz: 5 dB/octaveINMIC‘14 14Submarine EnvironmentGlobal Shipping Noise at 200 Hz – Points of Origin[Ocean Acoustics Library ]  15INMIC‘14Submarine EnvironmentGlobal Shipping Noise at 200 Hz - Aggregate [Ocean Acoustics Library ]  16INMIC‘14Contents1 I t d ti. n ro uc on2. Underwater Acoustic Channel3. Quality Assessment in Underwater Video17INMIC‘14Motivations• Ocean scientists often need not only sensor measures (temperature salinity ) but also they need to watch, …       underwater environments.• Images from oceanic resources are currently difficult and expensive to obtain.  – Exploration expeditions with divers or robots submerging with cameras are needed.• Video services in USNs would allow to reduce these costs   .18INMIC‘14Problems and research targets• Main problem for underwater id i i th hi hlv eo serv ces s e g y limited bitrate available with current technology .– State of the art acoustic modems reach 31,2 kbps peak data rate at physical layer.• It is necessary to study if video services are possible and what            QoS could be achieved in these low bitrate conditions.19INMIC‘14ITU-T G.1070 model – Definition• Mean Opinion Score (MOS) is a subjective parameterP i d lit i ll d i fi k l– erce ve  qua y s usua y score  n a ve ran  sca e.• The only ITU model for parametric MOS estimation in video services .– Oriented to video-conference services but de-facto used for other services too.• Network parameter as variables in the model:– Video coding bitrate.– Frame rate.– End to end loss rate for IP packets, (packet loss).Model also needs a set of coefficients depending on: video•          codec, resolution and screen size.20INMIC‘14Subjective quality assessment• ITU Recommendation for subjective video quality t f lti di li ti It d ibassessmen  or mu me a app ca ons.  escr es:– Source signal.Test methods–  .– Evaluation procedures.– Statistical analysis and reporting of results.• In absolute category rating (ACR) test method, several video sequences are presented to human viewers who score them within a qualitative scale.Bad Poor Fair Good Excellent21INMIC‘14Encoding - Experiment• Configurations for video services need to be adapted to bitrate limitation .Si l f t id t b id d b th till• nce ow rame ra e v eo mus  e cons ere , o  s  image sequence transmission and regular video encodingare under study  .• Work settings:Setting Values UnitResolution 320x180160 90px xEncoding JPEG, JPEG2000H.264-Frame rate 1-25 fpsBitrate 6, 12 kbps22INMIC‘14Conclusion• Underwater channel is very unfriendly• Terrestrial wireless techniques must be adapted     • Quality is not perceived by viewer the same way as in           videoconferencing/TV• Video, even with low resolution and fewer frames per second, is considered better than still images23INMIC‘14

Subjective quality in underwater acoustic networks

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Repositorio Institucional de la Universidad de Málaga

Repositorio Institucional Universidad de Málaga