简介:Nyquistfoldingreceiver(NYFR)isatypicalwidebandanalog-to-informationarchitecture.Focusingonthenoncooperativereceiving,thepulseradarsignalinterceptedbytheNYFRintimedomainisanalyzed.TheNYFRoutputsunderdifferentinputconditionsareinvestigatedbasedontheextendedFouriertransform(EFT)andthesamplingtheorem.CombiningwiththecharacteristicoftheNYFRoutputintimedomain,anewtimeofarrival(TOA)estimationmethodbasedontheenergyenvelopeandthewavelettransformisproposed.Theproposedestimationmethodcanbeadaptedforthenon-cooperativesituation.Ithasnorequirementforpriorinformationtodeterminethethresholdandisnotnecessarytotransformthesignalintobaseband.SimulationresultsprovethecorrectnessoftheNYFRoutputexpressionsandshowtheefficacyoftheproposedestimationmethod.
简介:CausedbyNon-Line-Of-Sight(NLOS)propagationeffect,thenon-symmetriccontaminationofmeasuredTimeOfArrival(TOA)dataleadstohighinaccuraciesoftheconventionalTOAbasedmobilelocationtechniques.RobustpositionestimationmethodbasedonbootstrappingM-estimationandHuberestimatorareproposedtomitigatetheeffectsofNLOSpropagationonthelocationerror.SimulationresultsshowtheimprovementovertraditionalLeast-Square(LS)algorithmonlocationaccuracyunderdifferentchannelenvironments.
简介:Thispaperdiscussesthetime-of-arrival(TOA)basedindoorvisiblelightcommunication(VLC)positioningsysteminanon-line-of-sightenvironment.Thepropagationdelayisassumedtobegammadistributed.ThegeneralizedCramer–Raolowerboundformultipathpropagationisderivedasthetheoreticalaccuracylimitation.Theperformanceofthepositioningsystemisaffectedbytheshapeparameterandthescaleparameterofgammadistribution.Theinfluencesonpositioningaccuracyofmultipatheffectsareanalyzedthroughdiscussingthephysicalmeaningofthegammadistributionparameters.Itisconcludedthatthelowerboundofpositioningaccuracyisattainedwhenvarianceofthenon-line-of-sightpropagation-inducedpathlengthsiszero.Thesimulationresultprovesthatthetheoreticalpositioningaccuracyisintheorderofcentimeterswiththegivenscenario.
简介:High-resolutionspectralradiancemeasurementsweretakenbyaspectralradiometeronboardahelicopterovertheUSOklahomaSouthernGreatPlainneartheAtmosphericRadiationMeasurements(ARM)siteduringAugust1998.Theradiometerhasaspectralrangefrom350nmto2500nmat1nmresolution.Themeasurementscoveredseveralgrassandcroplandscenetypesatmultiplesolarzenithangles.DetailedatmosphericcorrectionsusingtheModerateResolutionTransmittance(MODTRAN)radiationmodelandin-situsoundingandaerosolmeasurementshavebeenappliedtothehelicoptermeasurementsinordertoretrievethesurfaceandtopofatmosphere(TOA)BidirectionalReflectanceDistributionFunction(BRDF)characteristics.Theatmosphericcorrectionsaremostsignificantinthevisiblewavelengthsandinthestrongwatervaporabsorptionwavelengthsinthenearinfraredregion.AdjustingtheBRDFtoTOArequiresalargercorrectioninthevisiblechannelssinceRayleighscatteringcontributessignificantlytotheTOAreflectance.Theoppositecorrectionstothevisibleandnearinfrarredwavelengthscanaltertheradiancedifferenceandratiothatmanyremotesensingtechniquesarebasedon,suchasthenormalizeddifferencevegetationindex(NDVI).ThedatashowthatsurfaceBRDFsandspectralalbedosarehighlysensitivetothevegetationtypeandsolarzenithanglewhileBRDFatTOAdependsmoreonatmosphericconditionsandtheviewinggeometry.ComparisonwiththeCloudsandtheEarth'sRadiantEnergySystem(CERES)derivedclearskyAngularDistributionModel(ADM)forcropandgrassscenetypeshowsastandarddeviationof0.08inbroadbandanisotropicfunctionat25°solarzenithangleand0.15at50°solarzenithangle,respectively.