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1、CSE475Satellite and Space Networks MER KORAKMER KORAKomer.korcakmarmara.edu.tromer.korcakmarmara.edu.trMarmara UniversityMarmara UniversityDepartment of Computer EngineeringDepartment of Computer EngineeringSatellite Networks Research Laboratory (SATLAB)Satellite Networks Research Laboratory (SATLAB
2、)Department of Computer Engineering, Department of Computer Engineering, BoaziBoazi i Universityi UniversityIstanbul, TurkeyIstanbul, Turkey2OUTLINESatellitesGEO, MEO, LEOGEO, MEO, LEOHigh Altitude PlatformsIntegration ScenarioProblem Definition & Solution ApproachSATELLITES3Distance: 378.000 kmPeri
3、od: 27.3 daysBasics Satellites in circular orbitsSatellites in circular orbits attractive force Fattractive force Fg g = m g (R/r) = m g (R/r) centrifugal force Fcentrifugal force Fc c = m r = m r m: mass of the satellitem: mass of the satellite R: radius of the earth (R = 6370 km)R: radius of the e
4、arth (R = 6370 km) r: distance to the center of the earthr: distance to the center of the earth g: acceleration of gravity (g = 9.81 m/s)g: acceleration of gravity (g = 9.81 m/s) : angular velocity (: angular velocity ( = 2 = 2 f, f: rotation frequency) f, f: rotation frequency) Stable orbitStable o
5、rbit F Fg g = F = Fc c4Satellite period and orbits10203040 x106 m2420161284radiussatellite period hvelocity x1000 km/hsynchronous distance35,786 km5Basicsqqelliptical or circular orbitselliptical or circular orbitsqqcomplete rotation time depends on distance satellite-earthcomplete rotation time dep
6、ends on distance satellite-earthqqinclination: angle between orbit and equatorinclination: angle between orbit and equatorqqelevation: angle between satellite and horizonelevation: angle between satellite and horizonqqLOS (Line of Sight) to the satellite necessary for connectionLOS (Line of Sight) t
7、o the satellite necessary for connection high elevation needed, less absorption due to e.g. buildings high elevation needed, less absorption due to e.g. buildingsqqUplink: connection base station - satelliteUplink: connection base station - satelliteqqDownlink: connection satellite - base stationDow
8、nlink: connection satellite - base stationqqtypically separated frequencies for uplink and downlinktypically separated frequencies for uplink and downlink transponder used for sending/receiving and shifting of transponder used for sending/receiving and shifting of frequenciesfrequencies transparent
9、transponder: only shift of frequenciestransparent transponder: only shift of frequencies regenerative transponder: additionally signal regenerationregenerative transponder: additionally signal regeneration6Inclinationinclination d dd dsatellite orbitperigeeplane of satellite orbitequatorial plane7El
10、evationElevation:angle e between center of satellite beam and surfaceeminimal elevation:elevation needed at leastto communicate with the satellitefootprint8Link budget of satellites Parameters like attenuation or received power determined by four Parameters like attenuation or received power determi
11、ned by four parameters:parameters:qqsending powersending powerqqgain of sending antennagain of sending antennaqqdistance between sender distance between sender and receiverand receiverqqgain of receiving antennagain of receiving antenna ProblemsProblemsqqvarying strength of received signal due to mu
12、ltipath propagation varying strength of received signal due to multipath propagation qqinterruptions due to shadowing of signal (no LOS)interruptions due to shadowing of signal (no LOS) Possible solutionsPossible solutionsqqLink Margin to eliminate variations in signal strength Link Margin to elimin
13、ate variations in signal strength qqsatellite diversity (usage of several visible satellites at the same time) satellite diversity (usage of several visible satellites at the same time) helps to use less sending powerhelps to use less sending powerL: Lossf: carrier frequencyr: distancec: speed of li
14、ght9Atmospheric attenuationExample: satellite systems at 4-6 GHzelevation of the satellite5 1020304050Attenuation of the signal in %1020304050rain absorptionfog absorptionatmospheric absorptione10Satellite OrbitsDistance (km)PeriodLow Earth Orbit (LEO)700 - 20002 hrMedium Earth Orbit (MEO)10.000 15.
15、0006 hrGeosynchronous Earth Orbit (GEO)36.00024 hr11Satellite Orbits 2earthkm35768100001000LEO (Globalstar,Irdium)HEOinner and outer VanAllen beltsMEO (ICO)GEO (Inmarsat)Van-Allen-Belts:ionized particles2000 - 6000 km and15000 - 30000 kmabove earth surface12GEO Satellites No handoverNo handover Alti
16、tude: 35.786 km.Altitude: 35.786 km. One-way propagation delay: 250-280 msOne-way propagation delay: 250-280 ms 3 to 4 satellites for global coverage3 to 4 satellites for global coverage Mostly used in video broadcastingMostly used in video broadcasting Example: TURKSAT satellitesExample: TURKSAT sa
17、tellites Another applications: Weather forecast, global Another applications: Weather forecast, global communications, military applicationscommunications, military applications Advantage: well-suited for broadcast servicesAdvantage: well-suited for broadcast services Disadvantages: Long delay, high
18、 free-space attenuationDisadvantages: Long delay, high free-space attenuation13MEO SatellitesAltitude: 10.000 15.000 kmOne-way propagation delay: 100 130 ms10 to 15 satellites for global coverageInfrequent handoverOrbit period: 6 hrMostly used in navigationGPS, Galileo, GlonassGPS, Galileo, GlonassC
19、ommunications: Inmarsat, ICO14MEO Example: GPS Global Positioning SystemGlobal Positioning System Developed by US Dept. Of DefenceDeveloped by US Dept. Of Defence Became fully operational in 1993Became fully operational in 1993 Currently 31 satellites at 20.200 km. Currently 31 satellites at 20.200
20、km. Last lunch: March 2008Last lunch: March 2008 It works based on a geometric principleIt works based on a geometric principle “Position of a point can be calculated if the distances between this point “Position of a point can be calculated if the distances between this point and thand threeree obj
21、ects with known positions can be measured” objects with known positions can be measured” Four satellites are needed to calculate the positionFour satellites are needed to calculate the position Fourth satellite is needed to correct the receivers clock. Fourth satellite is needed to correct the recei
22、vers clock. Selective AvailabilitySelective Availability Glonass (Russian):Glonass (Russian): 24 satellites, 19.100 km24 satellites, 19.100 km Galileo (EU): 30 satellites, 23.222 km, under development Galileo (EU): 30 satellites, 23.222 km, under development (expected date: 2013)(expected date: 2013
23、) Beidou (China): Currently experimental & limited. Beidou (China): Currently experimental & limited. 15LEO Satellites Altitude: 700 2.000 kmAltitude: 700 2.000 km One-way propagation delay: 5 20 msOne-way propagation delay: 5 20 ms More than 32 satellites for global coverageMore than 32 satellites
24、for global coverage Frequent handoverFrequent handover Orbit period: 2 hrOrbit period: 2 hr Applications:Applications: Earth Observation Earth Observation GoogleEarth image providers (DigitalGlobe, etc.)GoogleEarth image providers (DigitalGlobe, etc.) RASAT (First satellite to be produced solely in
25、Turkey)RASAT (First satellite to be produced solely in Turkey) CommunicationsCommunications Globalstar, IridiumGlobalstar, Iridium Search and Rescue (SAR)Search and Rescue (SAR) COSPAS-SARSATCOSPAS-SARSAT16Globalstar Satellite phone & low speed data comm.Satellite phone & low speed data comm. 48 sat
26、ellites (8 planes, 6 sat per plane) 48 satellites (8 planes, 6 sat per plane) and 4 spares.and 4 spares. 52 inclination: not covers the polar 52 inclination: not covers the polar regions regions Altitude: 1.410 kmAltitude: 1.410 km No intersatellite link: Ground gateways No intersatellite link: Grou
27、nd gateways provide connectivity from satellites to provide connectivity from satellites to PSTN and Internet.PSTN and Internet. Satellite visibility time: 16.4 minSatellite visibility time: 16.4 min Operational since February 2000.Operational since February 2000. 315.000 subscribers (as of June 200
28、8)315.000 subscribers (as of June 2008) Currently second-generation satellites Currently second-generation satellites are being produced (by Thales Alenia are being produced (by Thales Alenia Space) and 18 satellites launched in Space) and 18 satellites launched in 2010 and 2011. 2010 and 2011. 17Gl
29、obalstar Coverage Map18Iridium 66 satellites (6 planes, 11 sat per plane) 66 satellites (6 planes, 11 sat per plane) and 10 spares.and 10 spares. 86.4 inclination: full coverage 86.4 inclination: full coverage Altitude: 780 kmAltitude: 780 km Intersatellite links, onboard processingIntersatellite li
30、nks, onboard processing Satellite visibility time: 11.1 minSatellite visibility time: 11.1 min Satellites launched in 1997-98.Satellites launched in 1997-98. Initial company went into bankrupcyInitial company went into bankrupcy Technologically flawless, however:Technologically flawless, however: Ve
31、ry expensive; Awful business plan Very expensive; Awful business plan Cannot compete with GSMCannot compete with GSM Now, owned by Iridium satellite LLC.Now, owned by Iridium satellite LLC. 280.000 subscribers (as of Aug. 2008)280.000 subscribers (as of Aug. 2008) Multi-year contract with US DoD.Mul
32、ti-year contract with US DoD. Satellite collision (February 10, 2009).Satellite collision (February 10, 2009).19COSPAS-SARSAT(Search And Rescue Satellite Aided Tracking)(Search And Rescue Satellite Aided Tracking) An international satellite-based An international satellite-based SAR distress alert d
33、etection & SAR distress alert detection & information distribution system.information distribution system. 4 GEO, 5 LEO satellites4 GEO, 5 LEO satellites Aircraft & maritime radiobeacons Aircraft & maritime radiobeacons are automatically activated in case are automatically activated in case of distr
34、ess.of distress. Newest beacons incorporate GPS Newest beacons incorporate GPS receivers (position of distress is receivers (position of distress is transmitted)transmitted) Supporters are working to add a Supporters are working to add a new capability called MEOSAR.new capability called MEOSAR. The
35、 system will put SAR processors The system will put SAR processors aboard GPS and Galileo satellites aboard GPS and Galileo satellites 20Since 1982, 30.713 persons rescued Since 1982, 30.713 persons rescued in 8.387 distress situation. in 8.387 distress situation. Satellites - Overview GEOs have goo
36、d broadcasting capability, but long GEOs have good broadcasting capability, but long propagation delay.propagation delay. LEOs offer low latency, low terminal power LEOs offer low latency, low terminal power requirements.requirements. Inter-satellite links and on-board processing for Inter-satellite
37、 links and on-board processing for increased performance and better utilization of satellitesincreased performance and better utilization of satellites From flying mirrors to intelligent routers on sky. From flying mirrors to intelligent routers on sky. Major problem with LEOs: Mobility of satellite
38、s Major problem with LEOs: Mobility of satellites Frequent hand-overFrequent hand-over Another important problem with satellites:Another important problem with satellites: Infeasible to upgrade the technology, after the satellite is Infeasible to upgrade the technology, after the satellite is launch
39、ed launched 21High Altitude Platforms (HAPs) Aerial unmanned platformsAerial unmanned platforms Quasi-stationary position (at 17-22 km)Quasi-stationary position (at 17-22 km) Telecommunications & surveillance Telecommunications & surveillance Advantages:Advantages: Cover larger areas than terrestria
40、l base Cover larger areas than terrestrial base stationsstations No mobility problems like LEOsNo mobility problems like LEOs Low propagation delayLow propagation delay Smaller and cheaper user terminalsSmaller and cheaper user terminals Easy and incremental deploymentEasy and incremental deployment
41、 Disadvantages:Disadvantages: Immature airship technologyImmature airship technology Monitoring of the platforms movementMonitoring of the platforms movement22HAP Coverage23HAP-Satellite Integration HAPs have significant advantages.HAPs have significant advantages. Satellites still represent the mos
42、t attractive solution for broadcast and Satellites still represent the most attractive solution for broadcast and multicast servicesmulticast services Should be considered as complementary technologies.Should be considered as complementary technologies.24An Integration Scenario Integration of HAPs a
43、nd mobile satellitesIntegration of HAPs and mobile satellites Establishment of optical linksEstablishment of optical linksHAPsSatellites25Optimal Assignment of Optical LinksCONSTRAINTS:CONSTRAINTS: A satellite and a HAP should have line of sight in order to A satellite and a HAP should have line of
44、sight in order to communicate with each other. communicate with each other. Elevation angle between HAP and satellite should be larger than a Elevation angle between HAP and satellite should be larger than a certain certain minmin value. value. Number of optical transmitters in satellites is limited
45、. Number of optical transmitters in satellites is limited. A satellite can serve maximum of A satellite can serve maximum of HHmaxmax HAPs. HAPs. One to many relation between HAPs and satellites.One to many relation between HAPs and satellites.AIMS:AIMS: As much HAP as possible should be served (Max
46、imum utilization)As much HAP as possible should be served (Maximum utilization) Average of elevation angles between HAPs and satellites should be Average of elevation angles between HAPs and satellites should be maximized.maximized.26Optimal Assignment of Optical Links (cont.)SOLUTION APPROACHESSOLU
47、TION APPROACHES This optimization problem can be represented as an Integer Linear This optimization problem can be represented as an Integer Linear Programming (ILP) problemProgramming (ILP) problem ILP solution approaches: Exclusive search, Branch-and-bound ILP solution approaches: Exclusive search
48、, Branch-and-bound algorithms, etc.algorithms, etc. Exponential time complexityExponential time complexity Not feasible for large networksNot feasible for large networks Optimization algorithm should be applied repeatedlyOptimization algorithm should be applied repeatedly In periodic manner: every t
49、 time unitIn periodic manner: every t time unit In event-driven manner: When a link becomes obsoleteIn event-driven manner: When a link becomes obsolete Faster algorithm is necessary. Faster algorithm is necessary. There exists a polynomial time solution approachThere exists a polynomial time soluti
50、on approach27Solution Approach Example scenarioExample scenario Three satellites & seven Three satellites & seven HAPsHAPs Visible pairs are Visible pairs are connectedconnected Elevation angles are Elevation angles are given on the links given on the links 28Solution Approach (cont.) Bipartite grap
51、hBipartite graph First group: Node for each First group: Node for each satellite transmittersatellite transmitter Second group: Node for each Second group: Node for each HAPHAP Edge exists between a HAP Edge exists between a HAP and each transmitter of a and each transmitter of a satellite, if they
52、are visible to satellite, if they are visible to each other.each other. Weights: Elevation anglesWeights: Elevation angles29Maximum weighted maximum cardinality matchingMax Weighted Max Cardinality MatchingMax Weighted Max Cardinality Matching Matching: Matching: A subset of edges, such that no two
53、edges A subset of edges, such that no two edges share a common node.share a common node. Maximum cardinality matching:Maximum cardinality matching: Matching with Matching with maximum number of edges.maximum number of edges. Maximum weighted maximum cardinality matching:Maximum weighted maximum card
54、inality matching: Maximum cardinality matching where the sum of the Maximum cardinality matching where the sum of the weights of the edges is maximum.weights of the edges is maximum. Hungarian Algorithm: O(nHungarian Algorithm: O(n3 3) )30Results31100 HAPs (height: 20 km)10 MEO Satellites: ICO (heig
55、ht: 10350 km, inclination: 45)Total time: 1 day, t=1 minuteIncreasing the Link Durations Increasing the Link Durations Matching with maximum “average elevation angle” may Matching with maximum “average elevation angle” may result in frequent optical link switchingresult in frequent optical link swit
56、ching Switching from one satellite to another is an expensive Switching from one satellite to another is an expensive operation.operation. Reduction of switching = Increasing the link durationsReduction of switching = Increasing the link durations Method: Favor existing links with a particular amoun
57、t Method: Favor existing links with a particular amount Weights of utilized edges are incremented by Weights of utilized edges are incremented by 32Results - 233min=-2Net gain function“Efficient Integration of HAPs and Mobile Satellites via Free-space Optical Links,” Computer Networks, 2011More on S
58、atellites Hand-overHand-over Satellite-fixed / Earth-fixed footprintsSatellite-fixed / Earth-fixed footprints Network Mobility ManagementNetwork Mobility Management RoutingRouting35Handover in satellite systems Several additional situations for handover in satellite systems compared to Several addit
59、ional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks caused by the movement of the cellular terrestrial mobile phone networks caused by the movement of the satellitessatellites Intra satellite handoverIntra satellite handover handover from one spo
60、t beam to anotherhandover from one spot beam to another mobile station still in the footprint of the satellite, but in another cellmobile station still in the footprint of the satellite, but in another cell Inter satellite handoverInter satellite handover handover from one satellite to another satel
61、litehandover from one satellite to another satellite mobile station leaves the footprint of one satellitemobile station leaves the footprint of one satellite Gateway handoverGateway handover Handover from one gateway to anotherHandover from one gateway to another mobile station still in the footprin
62、t of a satellite, but gateway leaves the mobile station still in the footprint of a satellite, but gateway leaves the footprintfootprint Inter system handoverInter system handover Handover from the satellite network to a terrestrial cellular networkHandover from the satellite network to a terrestria
63、l cellular network mobile station can reach a terrestrial network again which might be mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.cheaper, has a lower latency etc.36Satellite-fixed vs Earth-fixed FootprintsSatellite Fixed Footprints(asynchron
64、ous handoff)Earth Fixed Footprints(synchronous handoff)37lPhysical network topology is dynamiclVirtual Node topology is fixedA satellite corresponds to a VN in a time.Routing is carried out without considering the movement of satellitesVirtual Node38Routing One solution: inter satellite links (ISL)O
65、ne solution: inter satellite links (ISL)qqreduced number of gateways needed reduced number of gateways needed qqforward connections or data packets within the satellite network as forward connections or data packets within the satellite network as long as possiblelong as possibleqqonly one uplink an
66、d one downlink per direction needed for the only one uplink and one downlink per direction needed for the connection of two mobile phones connection of two mobile phones Problems:Problems:qqmore complex focusing of antennas between satellites more complex focusing of antennas between satellites qqhi
67、gh system complexity due to moving routershigh system complexity due to moving routersqqhigher fuel consumptionhigher fuel consumptionqqthus shorter lifetimethus shorter lifetime Iridium and Teledesic planned with ISLIridium and Teledesic planned with ISL Other systems use gateways and additionally
68、terrestrial networksOther systems use gateways and additionally terrestrial networks39Features of Satellite NetworksEffects of satellite mobilityTopology is dynamic.Topology changes are predictable and periodic.Traffic is very dynamic and non-homogeneous.Handovers are necessary.Limitations and capab
69、ilities of satellitesPower and onboard processing capability are limited.Implementing the state-of-the-art technology is difficult.Satellites have a broadcast nature.Nature of satellite constellations Higher propagation delays.Fixed number of nodes.Highly symmetric and uniform structure.40Routing &
70、Network MMConsidering these issues various routing & MM techniques are proposed. Main ideas are:To handle dynamic topology changes with minimum overhead.To prevent an outgoing call from dropping due to link handoversTo minimize length of the paths in terms of propagation delay and/or number of satel
71、lite hops.To prevent congestion of some ISLs, while others are idle (Load balancing).To perform traffic-based routing.To provide better integration of satellite networks and terrestrial networks.To perform efficient multicasting over satellites.“Exploring the Routing Strategies in Next-Generation Satellite Networks” IEEE Wireless Communications, 200741Thank YouAny questions?
