Scientech Technologies ST2276 User manual

GPSTrainer
ST2276
OperatingManual
Ver1.1
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GPSTrainer
ST2276
TableofContents
1. Introduction4
2. Experimentstobeperformed:
•Experiment15
Understanding theprincipleofGPSTechnology
•Experiment212
a. UnderstandingtheprincipleofGPSSatellite
b. UnderstandingthegenerationofL1carrierfrequency.
c. UnderstandingtheoperationofGPSReceiver.
d. EstablishingthelinkbetweentheGPSSatelliteandGPSTrainer.
•Experiment315
a. UnderstandingtheshapeofEarth.
b. Measurementoflatitude, longitude.
•Experiment417
a. UnderstandingtheprincipleofPRNcodeinGPS.
b. UnderstandingtheprincipalofautocorrelationinGPS.
•Experiment521
a. UnderstandingtheprincipleofGeometryoftheSatellite.
b. Understandingtheimportance ofPDOP, HDOP,andVDOP.
•Experiment624
a. UnderstandingtheprincipleofNMEA0183protocol.
b. AnalysisofNMEA0183protocols
•Experiment728
StudyofotherNMEASentence
•Experiment847
StudyofthecompleteGPSEnvironment.
3. GPSQuiz49
4. GPSGlossary52
5. GPSAcronyms63
6. Warranty64
7. ListofAccessories64
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RoHSCompliance
ScientechProducts areRoHSComplied.
RoHSDirectiveconcerns withtherestrictiveuseof
Hazardoussubstances (Pb,Cd, Cr, Hg,
Brcompounds)inelectricandelectronicequipments.
Scientechproducts are“LeadFree”and “EnvironmentFriendly”.
Itismandatorythatserviceengineersuseleadfree solderwireandusethesolderingirons
upto(2
5W)thatreachatemperatureof450°Catthetipasthemelting temperatureofthe
unleadedsolderis higherthantheleadedsolder.
Introduction
Haveyou everbeenlostandwishedtherewasaneasywayyouneededtogo?
Everfindthatperfectfishingorhunting spotandnotbeenabletorememberhowto
getbacktoiteasily?
Howaboutfinding yourselfouthikingandnotknowing whichdirectionyoushould
gotogetbacktoyourcamporcar?
Everbeenflyingalong andneededtolocatethenearestairspaceyouwerein?
Maybeyou'vebeenfacedwiththefactthatit'stimetopull overandasksomeonefor
directions.
GlobalPositioningSystem technologyisrapidlychanginghowpeoplefindtheirway
aroundtheearth.Whetheritisforfun,saving lives,getting therefaster,orwhatever
usesyoucandreamup,GPSnavigationisbecoming morecommoneveryday.
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Experiment1
Objective:
UnderstandingtheprincipleofGPSTechnology
Theory:
TheGlobalPositioning System(GPS)isandearthorbiting-satellitebasednavigation
system.GPS isanoperationalsystem,providingusersworldwidewithtwenty-four
houradayprecisepositioninthreedimensionsandprecisetimetraceabletoglobal
timestandards. GPS isoperatedbytheUnitedStatesAirForceunderthedirectionof
theDepartmentofDefense(DoD)andwasdesignedfor,andremainsunderthe
controlof,theUnitedStatesmilitary.Whiletherearenowmanythousandsof
commercialandrecreationalciviluser’sworldwide,DoDcontrolstillimpactsmany
aspectsofGPSplanning,operation,anduse.Primarilydesignedasaland,marine,
andaviationnavigationsystem,GPSapplicationshaveexpandedtoinclude
surveying,space navigation,automaticvehiclemonitoring,emergencyservices
dispatching,mapping,andgeographicinformationsystemgeoreferencing.Because
thedissemination ofprecisetimeisanintegralpartofGPS,alargecommunityof
precisetime,timeinterval,andfrequencystandardusershascometodependonGPS
asaprimarysourceofcontroltraceablethroughtheUnitedStatesNavalObservatory
toglobaltimeandfrequencystandards.
HistoryofGPS:
Developedinthe1960s,theNavyTransitsatellitenavigationsystemstillprovides
someserviceasatwo-dimensional(horizontal)positioning system. Good (200meter)
Transitpositioningrequiresknowledgeoftheuseraltitudeaswell asamodelofuser
dynamicsduring thefix,aprocess ofintegratingsatellitesignalDopplershifts(the
changeinreceivedsignalfrequencycausedbythechangingrange)during thefly-over
ofthesatellite.AnotherNavysystem,basedontheTimationsatellitescarriedstable
clocks(quartz,rubidium, andcesium)overthecourseoftheprograminthe1960sand
70sandwastheprecursortotheprecisetimecapabilitiesofGPS(Easton1978).GPS
beganin1973 asatestprogramusingground-basedtransmittersattheU.S.Army
ProvingGroundatYuma,Arizona,lateraugmentedwithearlyversionsofGPS
satellitesfirstlaunchedin1978.During the1980s,GPS,althoughnotyetfully
operationalandrequiringcarefulplanning formissionsduringtimesofsatellite
availability,wasincreasinglyusedbybothmilitaryandcivilianagencies.Land,air,
andseanavigation,precisepositioning,carrierphasesurveytechniques,andprecise
timeandfrequencydisseminationwereallaccomplishedtoalimitedextentduring the
initialphasesofGPSdeployment(Klepczynski1983).By1989 tendevelopment
satellites,termedBlockIsatellites,hadbeensuccessfullylaunched.By1990,43
laboratoriesrequiringprecisetimewereusingGPStosynchronizetheiratomicclocks
(Clements1990).By1994,24BlockIIandIIAoperationalGPSspacevehicles
(SVs)hadbeenlaunched.TheBlockIIASVscanstoreup to14daysofuploaded
dataincasecontactislostwithgroundstationsandcanoperatefor180 dayswith
degradednavigationreceiverperformance.Thenextgenerationofspacevehicles,the
BlockIIRSVswillincorporatechangestoincludethecapabilityofmaintaining
precisetimekeeping withoutControlSegmentuploadsforperiodsofup to210days
byexchangingdatabetweenGPSSVs(Rawicz, Epstein, andRajan1992).
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InDecemberof1993,GPS reachedInitialOperationalCapability,withaminimumof
24 satellitesinorbit.OnJuly17,1995 theAirForceannouncedthatGPShadmetall
requirementsforFull OperationalCapabilitywith24 BlockII SVsinorbit.Withover
50 companiessupplyingaselectionofover275 GPSreceiverstoaglobalmarket,the
wellestablishedusercommunityofnavigators, surveyors,geologists,geodesists,time
andfrequencyusers, andmanythousandsofrecreationaluserhascometoacceptGPS
asaviablemilitaryandciviliansystem.
Civil andMilitaryGPS:
WhilecontrolledandmaintainedbytheDoD,theGPSusercommunityhasalarge
civilcomponent.Inthe1977NationalPlanforNavigation,publishedbytheU.S.
DepartmentofTransportation(DoT),theNAVSTARGPS usercommunitywas
plannedtoinclude27,000militaryreceivers.Whilethepotentialforacivil-sectoruser
basewasrecognized,thedocumentdidnotincludeplansforacivilGPSservice
(U.S.DoT19773-14;3-15).AdecadelatertheFederalRadionavigationPlan(FRP)
(U.S.DoDandDoT1986)statedthatGPSwouldbeavailabletocivilusers,
worldwide,onacontinuousbasisbutwithaccuracylimitedto100 meters(95
percent).
Intheseradionavigationdocumentspositionaccuracyisusuallyspecifiedasatwo
standarddeviation(95 percent)radialerroror2drms(2distancerootmeansquared)
uncertaintyestimate.ForGPSthe95percentprobabilityand2drmsaccuracyare
equivalent(DoDandDoT1995,A-2).The1985 ComprehensiveGlobalPositioning
SystemUserPolicy definedbothamilitary,encrypted,PrecisePositioningService
anda"lowerlevelofaccuracy"StandardPositioningService(U.S.DoDandDoT
1986, B-32).
StandardPositioningService:
TheStandardPositioning Service(SPS)isdefinedinthemostrecentFRPas:the
standardspecifiedlevelofpositioningandtimingaccuracythatisavailable,without
restrictions, toanyuseronacontinuousworldwidebasis. Theaccuracyofthisservice
willbeestablishedbytheDODandDOTbasedonU.S.securityinterests.SPS
providesapredictablepositioningaccuracyof100 meters(95percent)horizontally
and156 meters(95 percent)verticallyandtimetransferaccuracytoUTCwithin340
nanoseconds(95percent).
PrecisePositioningService :
TheFRPdefinesthePrecisePositioning Service(PPS)as:themostaccuratedirect
positioning,velocity,andtiming informationcontinuouslyavailable, worldwide, from
thebasicGPS.ThisserviceislimitedtousersspecificallyauthorizedbytheU.S.
P(Y)-codecapablemilitaryuserequipmentprovidesapredictablepositioning
accuracyofatleast22meters(95percent)horizontallyand27.7meters(95percent)
verticallyandtimetransferaccuracytoUTCwithin200nanoseconds(95 percent)
(DoDandDoT1995,A-36).Bythetimethe1992 FRPwaspublished,theprojected
1995 estimateof53,000civilusersofGPS exceededtheprojectednumberofmilitary
usersestimatedat19,000 (U.S.DoDandDoT 1993,3-41).Civilusersnowconstitute
themajorityofGPS users.The1994FRPestimatesthecurrenttotalnumberofGPS
usersatover500,000intheUnitedStatesalone(U. S. DoDandDoT 1995,3-7).
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GPSSegments:
TheGlobalpositioningSystem(GPS)comprisesthreesegments:
The space segment (all functionsatellites)
The Controlsegment (allgroundstationinvolvedinthemonitoringofthesystem:
mastercontrolstation,monitoringstations&groundcontrol)
The usersegment (all civilandmilitaryGPSusers)
Figure1
SpaceSegment:
TheSpace Segmentisdesignedtoconsistof24 satellitesorbiting theearthat
approximately20200Kmevery12hours.At timeofwritingthereare26operational
satellitesorbiting theearth.Thespacesegmentissodesignedthattherewillbea
minimumof2to3satellitevisibleabovea15degcutoff angleatanypointofthe
earth'ssurface atanyonetime.EachGPS satellitehasseveralveryaccurateatomic
clockson board. Theclocksoperateatafundamentalfrequencyof10.23MHz. Thisis
usedtogeneratethesignalsthatarebroadcastfrom thesatellite.
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Figure2
Positionofthe28GPSsatellitesat12.00hrsUTCon14th April 2001
Figure3
ControlSegment:
TheControlSegmentconsistsofonemastercontrolstation,5monitorstationsand4
groundantennasdistributedamong5locationsroughlyontheearthequator.The
ControlSegmenttrackstheGPSsatellites,updatestheirorbiting positionand
calibratesandsynchronizestheirclocks.
Afurtherimportantfunctionistodeterminetheorbit ofeachsatelliteandpredictits
pathforthefollowing24hours.Thisinformation isuploadedtoeachsatelliteand
subsequentlybroadcastfrom it.ThisenablestheGPS receivertoknowwhereeach
satellitecanbeexpectedtobefound.ThesatellitesignalsarereadatAscension,
Diego,Garcia&Kwajalein.Themeasurementsarethensenttothemastercontrol
stationinColoradoSpringswheretheyareprocessedtodetermineanyerrorsineach
satellite.Theinformationisthensentbacktothefourmonitoring stationsequipped
withgroundantennasanduploadedtothesatellites.
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Figure4
UserSegment:
TheUserSegmentcomprisesofanyoneusingaGPS receivertoreceivetheGPS
signalanddeterminetheirpositionand/ortime.Typicalapplicationswithintheuser
segmentarelandnavigationforhikers,vehiclelocation,surveying,marine,
navigation,aerialnavigation, machinecontroletc.
Figure5
Figure 6a
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Figure 6b
InformationTransmittedbythesatellites?
Thefollowingisthekeyinformationtransmittedbythesatellitesconstellationon
eitheracontinuousorperiodicalbasis.
1. SatelliteHealth
2. Ephemeredes
3. ConstellationAlmanac
4. Time
5. RangingSignals
6. AtmosphericCorrectionalData
TheEphemeredesdescribethedetailedorbitalcharacteristicsofthesatellitefrom
whichitistransmitted.Simplythisisthesatellite'smechanismfordescribing whereit
is.
ThesatellitesAlmanac describethecourseorbitaldataforallsatellitesinthe
constellation.Simplythisdatadescribeswhereall thesatellitesare,roughly, allowing
thereceivertoknowwheretolook,roughly,forasatellite.
ThisdataisbroadcasttotheUserSegmentsothatit canbestoredandemployedfor
initialsatelliteacquisitionandforvisibilityprediction.
Satellitesareidentifiedby:
1. SpaceVehicleNumber(SVN),and
2. PseudoRandomNoisenumber(PRN)
TheSpaceVehic1enumberindicatesthechronologicalorderinwhichthesatellites
werelaunched.MostGPS ReceiversemploythePRNtoidentifywhichsatellitethey
areobserving.
Howdoesit Work?
SomePrinciplestoAcknowledge
Thereare24operationalsatellites
Theyorbittheearthapproximatelyevery12hours
Theyarepositionedinsix(6)orbitalplanes
Thereforetherewill usuallybesomething intheorderof6to8satellitesvisibleabove
thehorizonatanypointintheworldandatanytimeoftheday.
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