u-blox ANTARIS 4 - Considerations for GPS Performance

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1.4 Considerations for GPS Performance
GPSworkswithweaksignals.Thesignalstrengthonearthisapproximately15dBbelowthethermalnoisefloor.
In order to design a reliable GPS system, the following parameters have to be considered carefully during the
designphaseastheymaysignificantlydegradetheGPSperformance.
1. Antennalimitations
• PoorgainoftheGPSantenna
• Poordirectivity(radiationpattern)oftheGPSantenna
• Improperorientationoftheantennatothesky
• Poormatchingbetweenantennaandcableimpedance
• Poornoiseperformanceofthereceiversinputstageortheantennaamplifier
2. ElectricalEnvironment
• Jammingfromexternalsignals
• Jammingfromsignalsgeneratedbythereceiveritself
3. GPSrelatedeffects
• Signalpathobstructionbybuildings,foliage,covers,snow,etc.
Multi-patheffects•
Satelliteconstellation•
an nnarelatedissuesfromtheabovelist
andgeometry
The te willbefurtherdiscussedinSection 1.5.Jammingandinterference
TheDilutionofPrecision(DOP)isa unitlessvaluethatindicateswhenthesatellitegeometryprovidesthemost
bination of horizontal
 Note ApointcalculatedwithaPDOPof30.0candeviatebymorethan150mfromitstruelocation.
issueswillbeextensivelydiscussedinSection 1.6.
1.4.1 Dilution of Precision (DOP)
accurate results. It is the mathematical representation of the quality of the navigation solution, based on the
geometryof thesatellites used inthe calculation.The numberof visiblesatellitesandtheir
relative positionsin
theskymainlycontrolDOP.Satellitesspreadovertheskygivebetterresults(lowerDOP).
The most commonlyusedDOP is position dilution of precision (PDOP), which is the com
dilutionofprecision (HDOP)andverticaldilution ofprecision (VDOP).APDOPvalue of1
indicatesanoptimum
satelliteconstellationandhigh-qualitydata.ThequalityofthedatadecreasesasthePDOPvalueincreases.PDOP
valuesinexcessof8areconsideredpoor.
GPSModules-SystemIntegrationManual(SIM)(incl.ReferenceDesign) GPSFundamentals
GPS.G4-MS4-05007-A1
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