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1、GPS全球定位系统及其应用系统技术介绍目录1.前言12 .太空段23 .控制段94 .控制段现代化101. 1.持续升级114. 2.过去的升级115 .下一代操作控制系统146 .民用信号286.1.第二个民用信号：L2C296.2.第三民用信号：L5296.3.第四个民用信号：LlC306.4.无代码/半无代码过渡计划307.民用导航(CNAV)消息431 .前言全球定位系统(GPS)是一家美国拥有的公用事业公司，为用户提供定位、导航和计时(PNT)服务。该系统由三个段组成：空间段、控制段和用户段。美国太空部队开发、维护和运营太空和控制部门。GPS空间部分由向用户发送无线电信号的卫星星座组
2、成。美国致力于在24%的时间内保持至少95颗可运行的GPS卫星的可用性。为了确保这一承诺，美国太空部队十多年来一直在飞行31颗可操作的GPS卫星。surplussatellitesthatexistonorbitwilloupyotherlocationsintheorbitalplanes.Therearenoapriorispecifiedslotsforsurplussatellites.Thenominalsemi-majoraxisis26,559.7kilometers.TheSPSSISgenerationandtransmissionprocessforaBlockIIAsat
3、elliteisillustratedinFigure1.6-1.TheAtomicFrequencyStandard(AFS)generatesanominal10.23MHzclocksignal.ThesignalisdistributedbytheFrequencySynthesizerandDistributionUnit(FSDU)tootherpayloadsubsystems.TheNavigationDataUnit(NDU)receivestheuploadednavigation(NAV)datafromtheControlSegment(CS)throughtheTel
4、emetry,Track,andCommand(TT&C)subsystem.TheNavigationBasebandgeneratesthepseudorandomnoise(PRN)rangingcodesandaddstheNAVFigure1.6-1.GPSSISGenerationandTransmission2 .太空段GPS卫星在大约20,200公里（12,550英里）的高度的中地球轨道（MEO）飞行。每颗卫星每天绕地球两圈。GPS星座中的卫星排列成围绕地球的六个等间距轨道平面。每个平面包含四个由基线卫星占用的“插槽”。这种24插槽布置确保用户可以从地球上的几乎任何一点查看至少
5、四颗卫星。太空部队通常飞行超过24颗GPS卫星，以便在基线卫星维修或退役时保持覆盖。额外的卫星可能会提高GPS性能，但不被视为核心星座的一部分。1.6.2GPSControlSegmentTheOperationalControlSystem(OCS)iscomprisedoffourmajorsubsystems:aMasterControStation(MCS1soontobereplacedbyaNewMasterControlStationNMCS),aBackupMasterControlStation(BMCS,sntobereplacedbyanAlternateMasterCo
6、ntrolStationAMCS),anetworkoffourgroundantennas(GAs)1andanetworkofglobally-distributedmonitorstations(MSs).AnoverviewoftheOCSisprovidedinFigure1.6-2.Figure 1.6-2. The GPS Operational Control System (OCS)Performance Assess FunctionSatellite Control Function Command Generation Telemetry Processing Uplo
7、ad Generation & Control Check performance against specificationsif failure detectedPositioning&TimingFunction RangingMeasurementProcessing SatelliteStateEstimatiofVPredictjonDataGeneration2011年4月，美国空军成功完成了被称为“可扩展24”配置的GPS星座扩展。27个插槽中的三个被扩展，六颗卫星被重新定位，因此其中三颗额外的卫星成为星座基线的一部分。因此，GPS现在有效地作为星座运行，在世界大部分地区的覆盖
8、范围有所改善。RAIMrequiresafifthsatellite,orbarometricaiding,toperformansistencychecktodetectafaultonasinglesatellite.TheGPSWAASreceivercompliantwithTSO-C145/146alsousesRAIMforinstanceswhentheaugmentationsignalbecomesunavailable.TheWAASreceiveraddsafaultdetection&exclusion(FDE)featurerequiringaminimumof6sa
9、tellitestodetectandexcludeafaultedsatellite.InsteadofdeclaringGPSSPSserviceunusablewithaRAIMalert,RAIM/FDEexcludesthebadsatelliteandcontinuestoprovideanintegrity-assuredsolutionprovidedthegeometryoftheremainingsatellitesinviewissufficient.TheWAASGEObroadcastalsoprovidesanadditionalrangingsourceforim
10、provedavailabilityofnavigationservices.WhenaWAASreceiverisusingtherrectionsandintegritymessagesbroadcastbytheGEO,onlyfourGPSorGEOsatellitesareneeded,whichincreasestheavailabilityofserviceversusRAIMorRAIM/FDE.WAAScalculatesintegritydataassociatedwithitsgeneratedcorrectionsattherequiredlevelofintegrit
11、yfortheintendedflightoperation.Integritydataisprovidedintheformoferrorboundswhichareusedtocomputetheprotectionlevelstakingallrelevanterrorsourcesintoaccount.TheintegritydataconsistsoftheUserDifferentialRangeError(UDRE)andtheGridIonosphericVerticalError(GIVE).UDREcharacterizestheresidualerrorintheFCa
12、ndLTC.TheUDREistransmittedwiththeFCmessage.GIVEcharacterizestheresidualerrorintheICfortheestimatedionospheresignaldelayscalculatedforIGPs,definedintheIGPmaskandbroadcastevery5minutes.TheGIVEistransmittedwiththeICmessage.IfusingWAASverticalguidance,theuserreceiverutilizesthisintegritydatatocalculatea
13、protectioncylinderasdefinedintheRTCAInc.(formerlyRadioTechnicalCommissionforAeronautics)MinimumOperationalPerformanceStandard(MOPS)(RTCA/DO-229),incorporatedbyreference,inTSO-C145146.AsimplifieddepictionisshowninFigure1.7-2.TheuserreceiverappliesthevariousWAASrectionsdescribedaboveandcalculatesauser
14、positionusingtheWAAScorrectedrangeandephemerisdata.Then,theuserreceiverappliestheUDRE,GIVE(andothererrorcharacteristicsforresidualtropospheredelayandreceivererrors)valuestocalculateVPLandHPL.Theseprotectionlimitscanbeenvisionedasdefiningaprotectioncylinder,depictedasthedarkcylinderinFigure1.7-2.Vert
15、icalandHorizontalAlertLimitCylindCrarcdefinedbythephaseofflightProtection level cylinder: VPL and HPL are computed by the users receiver from error bounds calculated by WAAS (UDRE and GIVE).TheaircraftscalculatedpositionbasedontheWAAScorrectionsisthecenterofthecylinder.TheaircraftstruepositionFigure
16、1.7-2WAASIntegrityProtectionCylinderThisprotectioncylinder,centeredontheuserscalculatedpositionoftheaircraft,representstheuncertaintyofthatcalculatedposition.TheusersreceivercalculatesandcomparestheVPLandHPLagainsttheVerticalAlertLimit(VAL)andHorizontalalertLimit(HAL)values,respectively.Thesealertlimitshavevaluesthatarefixedforeachflightoperationa
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