Chapter 5. Satellite Networks.ppt

cse475satelliteandspacenetworks,merkorak.trmarmarauniversitydepartmentofcomputerengineeringsatellitenetworksresearchlaboratory(satlab)departmentofcomputerengineering,boaziiuniversityistanbul,turkey,2,outline,satellitesgeo,meo,leohighaltitudeplatformsintegrationscenarioproblemdefinitionawfulbusinessplancannotcompetewithgsmnow,ownedbyiridiumsatellitellc.280.000subscribers(asofaug.2008)multi-yearcontractwithusdod.satellitecollision(february10,2009).,19,cospas-sarsat(searchandrescuesatelliteaidedtracking),aninternationalsatellite-basedsardistressalertdetection&informationdistributionsystem.4geo,5leosatellitesaircraft&maritimeradiobeaconsareautomaticallyactivatedincaseofdistress.newestbeaconsincorporategpsreceivers(positionofdistressistransmitted)supportersareworkingtoaddanewcapabilitycalledmeosar.thesystemwillputsarprocessorsaboardgpsandgalileosatellites,20,since1982,30.713personsrescuedin8.387distresssituation.,satellites-overview,geoshavegoodbroadcastingcapability,butlongpropagationdelay.leosofferlowlatency,lowterminalpowerrequirements.inter-satellitelinksandon-boardprocessingforincreasedperformanceandbetterutilizationofsatellitesfromflyingmirrorstointelligentroutersonsky.majorproblemwithleos:mobilityofsatellitesfrequenthand-overanotherimportantproblemwithsatellites:infeasibletoupgradethetechnology,afterthesatelliteislaunched,21,highaltitudeplatforms(haps),aerialunmannedplatformsquasi-stationaryposition(at17-22km)telecommunications&surveillanceadvantages:coverlargerareasthanterrestrialbasestationsnomobilityproblemslikeleoslowpropagationdelaysmallerandcheaperuserterminalseasyandincrementaldeploymentdisadvantages:immatureairshiptechnologymonitoringoftheplatformsmovement,22,hapcoverage,23,hap-satelliteintegration,hapshavesignificantadvantages.satellitesstillrepresentthemostattractivesolutionforbroadcastandmulticastservicesshouldbeconsideredascomplementarytechnologies.,24,anintegrationscenario,integrationofhapsandmobilesatellitesestablishmentofopticallinks,haps,satellites,25,optimalassignmentofopticallinks,constraints:asatelliteandahapshouldhavelineofsightinordertocommunicatewitheachother.elevationanglebetweenhapandsatelliteshouldbelargerthanacertainminvalue.numberofopticaltransmittersinsatellitesislimited.asatellitecanservemaximumofhmaxhaps.onetomanyrelationbetweenhapsandsatellites.aims:asmuchhapaspossibleshouldbeserved(maximumutilization)averageofelevationanglesbetweenhapsandsatellitesshouldbemaximized.,26,optimalassignmentofopticallinks(cont.),solutionapproachesthisoptimizationproblemcanberepresentedasanintegerlinearprogramming(ilp)problemilpsolutionapproaches:exclusivesearch,branch-and-boundalgorithms,etc.exponentialtimecomplexitynotfeasibleforlargenetworksoptimizationalgorithmshouldbeappliedrepeatedlyinperiodicmanner:everyttimeunitinevent-drivenmanner:whenalinkbecomesobsoletefasteralgorithmisnecessary.thereexistsapolynomialtimesolutionapproach,27,solutionapproach,examplescenariothreesatellites&sevenhapsvisiblepairsareconnectedelevationanglesaregivenonthelinks,28,solutionapproach(cont.),bipartitegraphfirstgroup:nodeforeachsatellitetransmittersecondgroup:nodeforeachhapedgeexistsbetweenahapandeachtransmitterofasatellite,iftheyarevisibletoeachother.weights:elevationangles,29,maximumweightedmaximumcardinalitymatching,maxweightedmaxcardinalitymatching,matching:asubsetofedges,suchthatnotwoedgesshareacommonnode.maximumcardinalitymatching:matchingwithmaximumnumberofedges.maximumweightedmaximumcardinalitymatching:maximumcardinalitymatchingwherethesumoftheweightsoftheedgesismaximum.hungarianalgorithm:o(n3),30,results,31,100haps(height:20km)10meosatellites:ico(height:10350km,inclination:45)totaltime:1day,t=1minute,increasingthelinkdurations,matchingwithmaximum“averageelevationangle”mayresultinfrequentopticallinkswitchingswitchingfromonesatellitetoanotherisanexpensiveoperation.reductionofswitching=increasingthelinkdurationsmethod:favorexistinglinkswithaparticularamountweightsofutilizededgesareincrementedby,32,results-2,33,min=-2,netgainfunction,“efficientintegrationofhapsandmobilesatellitesviafree-spaceopticallinks,”computernetworks,2011,moreonsatellites,hand-oversatellite-fixed/earth-fixedfootprintsnetworkmobilitymanagementrouting,35,handoverinsatellitesystems,severaladditionalsituationsforhandoverinsatellitesystemscomparedtocellularterrestrialmobilephonenetworkscausedbythemovementofthesatellitesintrasatellitehandoverhandoverfromonespotbeamtoanothermobilestationstillinthefootprintofthesatellite,butinanothercellintersatellitehandoverhandoverfromonesatellitetoanothersatellitemobilestationleavesthefootprintofonesatellitegatewayhandoverhandoverfromonegatewaytoanothermobilestationstillinthefootprintofasatellite,butgatewayleavesthefootprintintersystemhandoverhandoverfromthesatellitenetworktoaterrestrialcellularnetworkmobilestationcanreachaterrestrialnetworkagainwhichmightbecheaper,hasalowerlatencyetc.,36,satellite-fixedvsearth-fixedfootprints,satellitefixedfootprints(asynchronoushandoff),earthfixedfootprints(synchronoushandoff),37,physicalnetworktopologyisdynamic,virtualnodetopologyisfixed,asatellitecorrespondstoavninatime.,routingiscarriedoutwithoutconsideringthemovementofsatellites,virtualnode,38,routing,onesolution:intersatellitelinks(isl)reducednumberofgatewaysneededforwardconnectionsordatapacketswithinthesatellitenetworkaslongaspossibleonlyoneuplinkandonedownlinkperdirectionneededfortheconnectionoftwomobilephonesproblems:morecomplexfocusingofantennasbetweensatelliteshighsystemcomplexityduetomovingroutershigherfuelconsumptionthusshorterlifetimeiridiumandteledesicplannedwithislothersystemsusegatewaysandadditionallyterrestrialnetworks,39,featuresofsatellitenetworks,effectsofsatellitemobilitytopologyisdynamic.topologychangesarepredictableandperiodic.trafficisverydynamicandnon-homogeneous.handoversarenecessary.limitationsandcapabilitiesofsatellitespowerandonboardprocessingcapabilityarelimited.implementingthestate-of-the-arttechnologyisdifficult.satelliteshaveabroadcastnature.natureofsatelliteconstellationshigherpropagation