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ARTICLE UNDERWATERCOMMUNICATION SOLUTIONFORJAMESCAMERON€™S DEEPSEACHALLENGE Communicationstothe DeepestPointonEarth InMarch2012,filmmakerand explorerJamesCameronsuccessfully completedhisone-mandivetothe bottomoftheMarianaTrench.The divewasthecentrepieceofthe DeepseaChallengeexpedition,ajoint scientificprojectbyCameron,the NationalGeographicSocietyandRolex toconductdeepoceanresearchand exploration.Arangeoftechnological innovationswererequiredforthe venture,oneofwhichwasareliable methodforsendingvoiceanddata betweenthe'DeepseaChallenger' submarineanditssupportvesselson thesurface.Atadepthofalmost 11km,theMarianaTrenchisthemost remoteandisolatedplaceonEarth. In2011,onlysixmonthsbeforethe expedition,theAustraliancompanyL3Oceania(formerlyL-3Nautronix)wastaskedwithprovidingatechnicalsolution thatwouldenableJamesCamerontoremainincontactwiththesurfaceatall times.Inadditiontounderwatercommunicationsconveyingvoiceandtextfor statusupdates,missionsupportandco-ordination,itwasalsoveryimportantto monitorvitalsignslikethesubmarine’soxygenandbatterylevels,depth,speed andrangepositionfromthesurface. FacingtheChallenge Twosignificantchallengeswerequicklyidentified.Firstly,atechnicalsolutionhadto befoundtoensurereliableunderwatercommunicationoversuchanimmensedistance.Secondly,theexpeditionschedule wasextremelytightandofferedaverylimitedperiodforbuilding,installingandintegratingthesystemintothesubmarineand thesupportvesselsMermaidSapphireandPrimeRHIB(RigidHulledInflatableBoat). Long-rangehydroacousticcommunicationisaverychallengingtaskduetolimitedbandwidth,slowpropagationtime,multipathandinter-symbolinterference,raybendingandfrequencydependentattenuation.Thelowcarrierfrequenciesrequired byunderwateracousticsignalsareinfluencedbyDopplershiftarisingfrommovementsofthesenderorreceiver.Noiselevels inparticular,influencedbyseaconditions,weatherandnoisefromthesupportingsurfacevesselswiththeirequipment generatingacousticandstructure-bornenoise,haveasignificantimpactonthequalityofcommunications.Veryfaintsignals receivedfromalongdistancewillbemaskedbythisnoise.Acousticsystemdesignersmusttakeallthesefactorsinto accountaswellasassurethequalityoftheinstallationandeliminateinterferencefromnearbyequipmenttoprovidegood communicationperformance. EngineeringtheSolution Theunderwatercommunicationsolutionthatwasengineeredfortheexpeditionwasbasedonwell-provencomponents:L-3 Oceania’sGPM300modemwithelectronics,transducerassemblyandafulloceandepthhousingalongwiththeGerman sistercompanyL-3ELACNautik’sUT3000underwatercommunicationsystem.Analoguecommunicationsforvoiceand digitalcommunicationsfordataweresupported.Analoguecommunicationsusednormalunderwatertelephone(STANAG 1074)modulation,anddigitalcommunicationsusedthelatestL-3underwaterspreadspectrumsignallingknownasMASQ. EachMASQdigitaldatapacketistime-referencedsothattimeofflightandthusrangecanbecomputed–acapabilitythat wasusedtoassistinlocatingthesubmarine. TheGPM300modemwithitsfulloceandepthhousingwasinstalledontheexteriorofthesubmarine,outsideofthesmall (43-inchdiameter)pressurespherehousingthepilot,savingpreciousspaceinsidethehighlyrestrictedlivingspace.For analoguevoicecommunication,themodemwasattachedtoanaudiointerfaceandspeakerboxallowingittobeoperatedby thepilotusingonlyasmall,lightweightear-mountedmicrophone.DigitaltextmessageswerereceivedandsentbyatabletPC withatouchscreen,whereasvitalstatusinformation(suchasCO2level,temperatureandbatterylevels)wasautomatically retrievedandsentoutfromthespherecontrolsystem.Asecondmodemwasinstalledasanautonomousbackupwithits ownpowersupplyandtheabilitytoindependentlymonitordepth.Thesecondmodemcouldalsobecontrolledfromthe surfacetotriggerdevicessuchaslightsandanemergencyweightrelease. CommunicationwiththeUnderwaterTelephoneUT3000 TheunderwatertelephoneUT3000thatwasinstalledonthetwosurfacevesselscombinesanaloguecommunicationmodes suchastelephony,telegraphyorpingermodewithdigitalcommunicationcapabilitiesbasedonMultipleFrequencyShiftKeying (MFSK)techniques.Similartoamobilephone,theUT3000allowsSMSmessagestobesentusingasmallbuilt-inkeyboardor, forconvenience,usinganexternalUSBkeyboard.Onthereceiverside,SMSreceptionautomaticallyopensanSMSviewer.A binaryfiletransfermodeallowstheselectionofafilefromaUSBmemorystickoranEthernetNetworkFileSystem(NFS) serverconnectedtotheUT3000.Onthereceivingside,filesareautomaticallystoredonanattachedUSBmemorystickoran NFSserver. ThebaudratefordigitalunderwatercommunicationisnotcomparabletoEthernet-basedLANorWLANnetworking.The underlyingmechanismissimilartoold-fashionedacousticcouplerswheredigitaldataisconvertedtoacousticsignals. Travellingthroughwater,soundwavesarecompromisedbytheaforementionedfactors,callingfordatarecoveryand forwarderrorcorrectioninformationtobeincludedinthedatastream.Thisguardinginformationisusedbythereceiverfor datareconstruction.Besidestheslowsignalpropagationspeedinwater,theamountofforwarderrorcorrectioninformation includedreduceseffectivebaudratestolessthan4,000bps.Atypicaltrade-offbetweendatareliabilityandtransmissiontime resultsinabaudrateofapproximately1,000bps.MostdatatransfersincludereadableASCII-basedmessagesandcanbe interpretedevenwhentheyincludecorruptedcharacters.Inanycase,lowtransmissionspeedpracticallyrestricts underwaterfiletransferstofilesofacoupleofkilobytes,whichdespitetheirsmallsizearestillsuitableforunderwatertasks. TheUT3000systemwasdesignedinamodularmanner,allowingtheunittobetailoredtocustomer-specificneeds.Benefits includethecapabilitytoexpandprocessingpowerforsignalprocessingalgorithms,andalsothesupportofdifferent transducerconfigurations.L-3ELACNautiksuppliesarangeoftransducersforvariousunderwatertasks,including transducersespeciallydesignedforunderwatercommunication.Thesetransducerscoverdifferentfrequencybandsand installationaspectsforinstallationonsurfacevesselsorsubmarines. ThestandardUT3000systemincludestwoDigitalSignalProcessor(DSP)boardseachequippedwithfivemulti-coreDSPs. Theseboardsarededicatedtoanalogueanddigitalcommunicationmodes. DigitalCommunicationviaMASQ TheUT3000allowstheadditionofextraDSPboardsforsignalprocessingenhancements.Thiscapabilitywasexploitedwith thedevelopmentofthesophisticatedMASQspreadspectrumdigitalsignalprocessinginaninter-companydevelopment betweenL-3ELACandL-3Oceania.MASQissupportedontheUT3000byaddinganextraDSPboardtorunthespread spectrumcommunicationalgorithms. UnderwaterspreadspectrumtechnologywasfirstintroducedtotheworldbyL-3Oceaniainthe1990stoprovidereliableand discreetcommunicationswhereothersystemsfailed.ThespreadspectrumtechniquesusedinMASQincludemulti-channel directsequencespreadspectrumandforwarderrorcorrectionwhichmakeithighlyresistanttotheproblemsposedbythe underwaterchannel.Signalscanstillbedecodedinhighlyreverberantenvironmentswithlowsignal-to-noiseratiosand receptionlevelswellbelowthebackgroundnoise. FortheDeepseaChallengeproject,thetransferofdatatoandfromexternalsystemssuchasthesubmarinecontrolsystem wasvitalandsotheMASQGraphicalUserInterface(GUI),resemblingakindofemailclient,wasrunonaPCateachend.In addition,bothvesselswereconnectedviaaTCP/IPnetworkthatranoverwirelessEthernet,whichmeantthatalldatacould becollatedinthecommunicationscentreontheprimarydivesupportvessel,theMermaidSapphire. DealingwiththeEnvironment ThetransducerinitiallyselectedfortheDeepseaChallengewastheWB54,asmallomni-directionaltransducer.TheWB54is acircular,barrel-shapedarray,primarilydesignedforinstallationunderthehullofsurfacevessels(typicallycoveredbya sonardomeforacousticalimprovementandmechanicalprotection)orontoahoistinggearforretractionintotheship’s envelopeincaseoftransit. TheWB54waschosenfortheexpeditionasatrade-offbetweensize,performanceandleadtime.Thesmallsizealloweditto beloweredbelowthehulloftheMermaidSapphireusingamoonpool.AsecondWB54wasinstalledonthePrimeRHIB. ThetestdivesperformedduringtheDeepseaChallengeexpeditionshowedthatintelligibleandreliableunderwater communicationcouldbeestablishedbetweenboththeDeepseaChallengerandPrimeRHIBequippedwiththeWB54downto adepthofapproximately8,200metres.UnfortunatelythenoisefromtheMermaidSapphire’sowndynamicpositioning systeminhibitedtheuseoftheWB54fromthatplatform,withthePrimeRHIBprovingamoresuitableplatformforreceiving thequietunderwatersoundsignals. Tocountertheimpactofshipnoise,anexternal,mobiletransducerwasused,equippedwithalongcablewhichalloweditto bedroppedoverboard.Theconfigurationmechanicallydecoupledthetransducerfromtheship,reducingdirectacoustic interferenceandincreasingpenetrationoftheacousticlayersbelowthesurface.Anexternaldunkingtransducerwith125m ofcableandamatchingtransformerwasconnected,andloweredapproximately100mbelowthesurface.Thisallowed communicationsfromtheMermaidSapphiretobecarriedoutbythedunkingtransducer,whereasthePrimeRHIBsystem usedboththeWB54andadunkingtransducer. Atmaximumdepth,thenoiseoftheMermaidSapphirestillpreventedthereliableuseofthedunkingtransducerforreception, maskingthelowlevelreceivesignals.PrimaryreceptionwasthereforecarriedoutbythePrimeRHIB,driftingwithdisengaged engines.ThevoicesignalsreceivedbythePrimeRHIBsystemwererelayedtotheMermaidSapphirebyRFtransmissionand thedatarelayedbywirelessEthernet.Ineffect,mostcommunicationsatfulloceandepthwerecarriedoutdownwardsfrom theMermaidSapphiretotheDeepseaChallengerandthenupwardsfromDeepseaChallengertothePrimeRHIBandontothe MermaidSapphireviaRFlink. HistoricDive At7:52a.m.on26March2012,JamesCamerontoucheddownatadepthof10,911metresandwasabletoanswertoa voicemessagesentdownbyhiswifewhowasontheMermaidSapphireaswellasrelaytheworld’sfirsttweetfromthe deepestpartoftheocean.TheuseofstandardvoicecommunicationsalsomadeitpossibleforPaulAllen,whowaspresent atthedivelocationonboardtheOctopus yacht,tofollowthewholecommunicationwithanotherunderwatertelephone,the L-3ELACNautikUT2000,andtoshareupdatesaboutthediveonTwitter. Throughouthisthree-hourstayonthebottomoftheMarianaTrenchandwhiletaking3Dfilmfootageandscientificsamples, JamesCameronremainedinconstantcontactwiththesurface.CameronlatercommendedtheL-3communicationssolution, saying"Wewerepleasedtohavesolidvoicecommstofull-ocean-depthusingtheL-3system.Itwasamazingtotalktomy wifeSuzyfromthedeepestpointintheworld’soceans." Conclusion Thankstothecloseco-operationoftheengineersworkingonthesubmarineandtheflexibilityoftheUT3000,asophisticated communicationssolutionwasdevelopedinacomparativelyshortamountoftime.Thissolutionhassuccessfullyprovedthat reliabletwo-wayvoiceanddatacommunicationtothedeepestpartoftheoceanispossible. Acknowledgements TheL-3teamwishestothankJamesCameron,RonAllum,TimBulmanandtheothermembersoftheDeepseaChallengeteam aswelltheexpeditionsponsors,NationalGeographicandRolex,fortheopportunitytohaveparticipatedinthishistoricevent. https://www.hydro-international.com/content/article/communications-to-the-deepest-point-on-earth