Download Deepest Point on Earth Communications to the

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