u-blox ANTARIS 4 - Multipath

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Examples of DOP values:
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 
PDOP:1.7 PDOP:4.3 PDOP:12.6
DOPvalueisokforgoodGPS
performance
DOPvalueisacceptablefora
goodGPSperformance
DOPtoohigh(allthesatellitesarein
astraightline),thiswilldegradethe
GPSperformance
Figure 4: Examples of DOP values
1.4.2 Multipath
Direct
Direct
Shadowing
Multipath
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Figure 5: A multi-path environment
Amulti-pathenvironmentexistsifGPSsignalsarriveattheantennadirectlyfromthesatellite,(lineofsight,LOS)
andalsofromreflectivesurfaces,e.g.waterorbuildingwalls.Ifthereisadirectpathinadditiontothereflected
pathavailable,thereceivercanusuallydetectthesituationandcompensate
tosomeextent.Ifthereisnodirect
line of sight, but only reflections, the receiver is not able to detect the situation. Under these multipath
conditionstherangemeasurementtothe satellitewill provideincorrectinformationto thenavigationsolution,
resulting ina less accurateposition. If there are
onlyafew satellites in sight,the navigationsolution might be
wrongbyseveralhundredmeters.
IfthereisaLOSavailable,theeffectofmulti-pathisactuallytwofold.First,thecorrelationpeakwillbedistorted
whichresultsinalesspreciseposition.Thiseffectcanbecompensatedforbyadvanced
receivertechnologysuch
astheANTARIS
®
4tpatentedmultipathmitigationscheme.Thesecondeffectrelatestothecarrierphaserelation
ofthedirectandreflectedsignal,thereceivedsignalstrengthissubjecttoaninterferenceeffect.Thetwosignals
maycanceleachother(outofphase)oraddtoeachother(inphase).Evenifthe
receiverremainsstationary,the
motionofthesatellitewillchangethephaserelationbetweendirectandreflectedsignal,resultinginaperiodic
modulationoftheC/N
0
measuredbythereceiver.
GPSModules-SystemIntegrationManual(SIM)(incl.ReferenceDesign) GPSFundamentals
GPS.G4-MS4-05007-A1
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