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Application Note: Testing GNSS System Errors

Testing GNSS System Errors Cover

From inaccuracies in satellite control to tropospheric delay, errors are unavoidable in GNSS systems—and must be accounted for in any set of tests hoping to deliver a true picture of GNSS receiver performance.

Download the Application Note to learn how you can use Spirent RF simulators to replicate system errors during receiver testing. Topics include:

  • The main sources of GNSS system error
  • The advantages of using RF simulation to model and mitigate errors
  • How to replicate errors in all parts of a GNSS system

Simply enter a few details opposite to receive the Application Note—and happy reading!

About Spirent

Spirent has been the global leader in GNSS testing for near 30 years. Spirent delivers navigation and positioning test equipment and services to governmental agencies, major manufacturers, integrators, test facilities and space agencies worldwide.

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    Testing GNSS System Errors APPLICATION NOTE Spirent Communications PLC Paignton, Devon, TQ4 7QR, England Web: nulltp:nullnullnullnullpirentnullomnullositioning Tel: null4 nullnull nullnullnull nullanull null4 nullnull nullnullnull Copnullignull nullnullnull Spirentnull nulll Rignulls Reservednull nulll onulltnull compannullnames andnullr brand names andnullr product names renullrred to in tnulls document, in particular, tnull name nullpirentnulland its logo device, are eitnullr registered trademarnull or trademarnull onull Spirent plc and its subsidiaries, pending registration in accordance nulltnullrelevant national lanullnullnulll otnullr registered trademarnull or trademarnull are tnull propertnull onulltnullir respective onullersnull Tnull innullrmation contained in tnulls document is subnullct to cnullnge nulltnullut notice and does not represent a commitment on tnull part onullSpirentnull Tnull innullrmation in tnulls document is believed to be accurate and reliablenull null ever, Spirent assumes no responsibilitnull or liabilitnullnullr annullerrors or inaccuracies tnullt manullappear in tnull documentnull Page 2SPIRENT Application Note Contents nulludience 4 nullntroduction 4 RnullSimulation null Tnullical nullS Simulators null Tnull nullSS Environment null null Tnullical nullSS Snulltem 7 Sources onullError null Space Segment Errors null Control Segment and nullser Segment errors null Conclusions null Renullrenced Documents null nulllossarnullonullTerms null Page 3SPIRENT Application Note Audience Tnulls nullpplication nullote is nullr designers, developers, integrators and testers onull nullSS receivers or snulltems, nullo need to ensure tnullir products nullll pernullrm in tnull automotive environmentnull Spirent recommends nullou nullve a basic understanding onullsatellite navigation principles and anullreness onullRnullsimulation as a test metnulld is desirablenull Introduction Tnullre is a steadnullgronullnullin tnull use onullnullSS navigation snulltems in all areas onulltnull automotive marnulltplacenullnull varietnull onullnullSS receivers, commonlnullrenullrred to as nullat nullavnull snulltems, are nonullnullund in venullcles used nullr private and recreational purposes, as nullell as commercial and public transportnullnulln some cases, tnullse snulltems relnullsolelnullon standalone nullSS operation, in otnullr cases tnullnullare coupled nulltnull an nullnertial nullavigation Snulltem nullnullnull Tnull increasing use onullnullSS brings an increasing reliance on tnull tecnullolognullnull nullndividuals, businesses and organisations are all relnullng on tnull tecnullolognullnullr annullnullng nullom personal pleasure and sanulltnull to commercial advantagenull Witnulltnulls in mind, it is important nullr designers, manunullcturers and consumers onulltnullse products to understand nullat to enullect nullom nullSS snulltems, nullicnull renullires an understanding onulltnull limitations and problems onullnullat can onullen be a nullagile, prone to error, and easilnulldisabled tecnullolognullnull Tnulls application note discusses some onulltnull main sources onullerror botnull specinull to tnull automotive environment, and more generallnullapplicable to nullSS snulltemsnullComplementarnullto tnulls, it demonstrates nullnullSpirentnulls range onullnullSS Test Solutions enable tnull simulation onulltnullse conditions in a controlled and repeatable nullnull, allonullng a nullSS receiver andnullr nullS nullnullS snulltem to be properlnulltested nullr use in automotive applicationsnull Page 4SPIRENT Application Note RF Simulation null RnullConstellation Simulator reproduces tnull environment onulla nullSS receiver on a dnullamic platnullrm bnullmodelling venullcle and satellite motion, signal cnullracteristics, atmospnullric and otnullr enullnullcts, causing tnull receiver to actuallnullnavigate according to tnull parameters onulltnull test scenarionull nullnullits vernullnature, simulation is a representation onulltnull real nullrldnull Simulation cannot reproduce tnull nullll ricnulless onullreal nullrld conditionsnull null common misconception is tnull need to enullctlnullreplicate real nullrld conditions nullr a nullSS test to be validnullnullonullever, application onullrepresentative enullnullcts via simulation is proven nullver some null nullears onulltestingnullto enullercise receivers and adenullatelnullidentinull tnullir limitations allonullng nullr design centering and optimisationnull nullore importantlnull, it gives complete repeatabilitnull, control and enullct nullonulledge nulldonull to bit level nullonulltnull signal stimulating tnull receivernullTnulls is not possible in tnull real nullrldnullWe snulluld loonullupon simulator testing as representing tnull real nullrld, ratnullr tnulln replicating itnullSpirent simulators include statistical models enabling simulation onullricnullr multipatnull environments, but consideration onulltnullse is outside tnull scope onulltnulls documentnull nulligure nullsnullnull tnull concept onullsimulation nullsing a nullSnullnull simulatornull Page nullSPIRENT Application Note Tynullcal GPS Simulators nulll tnull tests discussed in tnulls nullpplication nullote can be pernullrmed using annullonull Spirentnulls multinullnullnnel simulatorsnull nullor nullrtnullr innullrmation on Spirentnulls range onullSimulators, please contact nullour local Spirent representative, or visit nullnullnullpirentnull comnullositioning null Tnull GNSS Ennullronment null nullSS receiver nullrnull nullell nullen it nulls a clear, unnullnterrupted vienullonulltnull orbiting satellites transmitting tnull ranging and navigation signalsnullnulln mannullsituations tnulls is not tnull case and ranging measurements to tnull satellites are anullnullctednull Tnull degree tnullt pernullrmance is anullnullcted depends on tnull application and tnull environment onulltnull receivernull Common to all applications, are additional sources onullerror nullom tnull nullSS snulltem innullastructurenullTnullse errors are produced bnullinaccuracies in tnull satellites and in control enullipment, denulliencies in monitoring and prediction snulltems and data processing anomaliesnullnullinallnull, tnull receiver generates its onull errorsnull Page nullSPIRENT Application Note A Tynullcal GNSS System nullasicallnull, a nullSS comprises tnullee main parts: Tnull Space Segment:nulltnull constellation onullorbiting satellites tnullt transmit ranging and navigation data signalsnullTnull Control Segment:nulltnull nullaster Control Station and associated monitoring and data uplinnullstationsnullacilities tnullt measure and predict space segment pernullrmance and provide tnull corrections broadcast in tnull navigation datanull Tnull nullser Segment:nullnullSS receivers and snulltems tnullt autonomouslnullnavigate using tnull nullSS signalsnull Tnull most important pernullrmance cnullracteristics nullr all nullSS snulltems are: null nullccuracnull nullnullvailabilitnull nullnullntegritnull nullContinuitnull Tnull nullalitnullonulltnullse depends on tnull particular nullSS snulltemnull Eacnullcnullracteristic is denulled nulln renullrence nullas nullllonull: Accuracy nullnullr a given constellation, nullnullclose to tnull tnulloretical true position nullou can get in tnullee dimensionsnull nullor several measurements tanulln in a static position, it is normallnullspecinulld as tnull error magnitude spnullre containing nullnull onullmeasurementsnullnullor nullS SPS, nullnull vertical Position nullccuracnullis nullnullm nullased on a nullnullatellite constellation nulltnull nullnull onullnullnull and snulltem nullRE onull7nullnull nullccuracnullis a complenulltopic, and can be denulled in a number onullnullnullnull Renullrence nulldiscussed accuracnullin detailnull Anullailanulllity nulltnull percentage onulltime tnull services onulltnull snulltem are useablenull Integrity nulltnull abilitnullonulltnull nullSS to provide timelnullnullrnings and alerts to users tnullt advise nullen tnullnullsnulluld not use tnull snulltemnull Continuity nulltnull probabilitnulltnull specinulld snulltem pernullrmance nullll be maintained nullr tnull duration onulla pnullse onulloperationnull nullnless otnullrnullse stated, details renullr to tnull nulllobal Positioning Snulltemnull Page null SPIRENT Application Note Sources onullError Tnulls section describes tnull main sources onullerror, and nullnulla simulator can be used to reproduce eacnullerrornull Tnull contribution onullerrors nullom eacnull segment is summarised in Table null Segment Error Source nullS null Error nullnull SPnullCE Satellite ClocnullStabilitnull nullnull Satellite perturbations nullnull CnullTRnull Epnullmeris prediction error 4null nulltnullr nullnulluster pernullrmance etcnull nullnull nullER nullonospnullric Delanull nullnull Tropospnullric Delanull nullnull Receiver noise resolution nullnull nullultipatnull nullnull nulltnullr nullntercnullnnel bias, etcnull nullnull TnullTnullL vSnulltem nullRE Total nullSSnull nullnull Table null nullSS Error Sources Page nullSPIRENT Application Note Snullce Segment Errors Satellite clocnullerrors nullundamental to nullSS operation is tnull radio ranging tnullt ultimatelnulldepends upon predictabilitnullonullsatellite clocnullstabilitnullnull nulltnullugnullsatellites nullve accurate atomic clocnull, a nullmillisecond error enullates to a nullnullm pseudorange error, so even small clocnullerrors are signinullantnullErrors null nullurs anuller an upload onullnavigation data can be in tnull order onullnullto 4m nullee Renullrence nullnullEpnullmeris error and clocnullerror are progressive, getting steadilnullnullrse over time, until corrected nullr in tnull nenull control segment navigation data uploadnull nullor a simulator test, nullou can denulle a scenario in nullicnulltnull clocnullcorrection terms transmitted in tnull navigation data diverge nullom tnull clocnullbenullviour as represented bnulltnull simulated Rnullsignalnull nulln Spirentnulls Simnullnull sonullnullre, nullr annull satellites, nullou can enter nullero nullnullst null and secondnullrder nullnullnull terms nullr tnull clocnull corrections, nullicnullnullll be transmitted in tnull navigation data nullD modelled in tnull simulated Rnullsignalnullplus nulleltanullnull terms, describing a signal timing error, nullicnullare modelled onlnullbnulltnull simulated Rnullsignal and nullT declared in tnull navigation datanull null receiver applnullng tnullse Deltanullnull corrections nullll see tnull enullnullct onullan incorrect pseudorange due to clocnullerrornull nullntentional Satellite Clocnullnulloise nullSCnull Selective nullvailabilitnullnullnullnullis an intentional satellite clocnullnoise errornullnullt is tnull onlnull intentional error associated nulltnulltnull nullS snulltemnullSnull nulls not been enabled since nullanullnullnull, but is a potential source onullerror to Cnull code receiversnull Snull is tnull deliberate degradation onull tnull SPS signals bnulla time varnullng biasnull Snull is controlled bnulltnull null DoD to limit accuracnullnullr nonnullnullnullmilitarnulland government usersnullTnull accuracnullonulltnull Cnull code is reduced to nullnullmetres nullnull standard deviationsnull Tnull Snull bias on eacnullsatellite signal is dinullnullrent, tnullrenullre tnull resulting position solution is a nullnction onulltnull combined Snull bias nullom eacnullSnullused in tnull navigation solutionnullnullecause Snull is a cnullnging bias nulltnulllonullnullenullencnullterms in enullcess onulla nullnullnullurs, position solutions or individual Snullpseudonullanges cannot be enullnullctivelnullaveraged over periods snullrter tnulln a nullnullnullursnull Wnullle tnull null government nulls stated tnullnull nullll not renullnable Snull and nullture satellites nullll not nullve tnull capabilitnull, denial on a regional basis is tnulloreticallnullpossiblenull Spirent recommends nullou test nullr tnulls potential occurrencenull Spirent simulators controlled bnullSimnullnull allonullnullou to test nullour receiver in tnull presence onullnullCnull nullou can applnulla number onulldinullnullrent models to all satellites or selected satellites tnullt nullll generate Snullnull linull enullnullcts on tnull simulated Rnullsignal tnullt are not declared in tnull navigation datanull Page nullSPIRENT Application Note Receinuller Autonomous Integrity nullonitoring nullAInull Rnullnullis a tecnullolognulldeveloped to assess tnull integritnullonullnullS signals in a nullS receiver snulltemnullnullt is onullspecial importance in sanulltnullcritical nullS applications, sucnullas aviation or marine navigationnull Rnullnulldetects nullults nulltnullredundant nullS pseudorange measurementsnullTnullt is, nullen more satellites are available tnulln needed to produce a position null, tnull enullra pseudoranges snulluld all be consistent nulltnull tnull computed positionnullnull pseudorange dinullnullring signinullantlnullnullom tnull enullected value manullindicate a nullult nulltnulltnull associated satellite nullucnullas a clocnullnullilurenull or anotnullr signal integritnullproblem nullucnullas ionospnullric dispersionnull Traditional Rnullnulluses nullault Detection onlnullnullDnull nullnullever nenuller nullS receivers incorporate nullault Detection and Enullclusion nullDEnullnullicnullenables tnullm to continue to operate in tnull presence onulla nullS nullilurenull Spirent simulators controlled bnullSimnullnull nullve a Pseusorange Ramp nullature tnullt allonull nullou to cnullnge tnull simulated position onulltnull satellite in a controlled, but abnormal nullnulland is not declared in tnull navigation messagenullnull receiver nulltnulla Rnullnull algoritnull snulluld detect tnulls abnormalitnull and eitnullr initiate an alert or enullclude tnull onullnullnding satellite nullom its solutionnull Tnull speed onulltnull pseudrorange cnullnge can be adnullsted nullraduallnullreducednulluntil tnull receivernulls detection tnullesnullld is reacnulldnull Ornulltal Perturnulltions nullrbital perturbations are caused bnullenullernal innullences tnullt alter tnull satellite orbitsnull Sucnullinnullences includenull null nullonnullentral gravitational nullrce due to tnull Eartnullbeing slignulllnullelliptical nullt is nullnull larger in its enullatorial radius tnulln its polar radiusnull Tnulls causes orbital plane rotation and nullrmonic perturbations nulltnull a nullnullur period corresponding to tnull satellitenulls transition over tnull enullator, nullere its velocitnullincreasesnull null nullravitational nulllds onulltnull Sun and nulloonnull Tnull nulloon dominates, as it is mucnullcloser to tnull eartnull nullisual enullmples onulltnulls are tnull tidesnullnulln a similar nullnull, tnull nulloon nullnd negligiblnulltnull Sunnullpull on tnull satellitenulls orbitnullTnull enullnullct is vernullsmall, but cumulative, and must be corrected nullr in tnull control segmentnulls orbital predictionsnullnullnulllenull unnullorrected, a nullm error nulluld result anuller nullst one nullur, nullee renullrence nullnull null Solar radiation pressure: Pnulltons nullom tnull sunnulls radiation enullert a minute nullrce on itnullTnull nullrce depends on tnull mass onulltnull satellite and nullnullmucnullonullit is enullosed to tnull sunnull Page nullSPIRENT Application Note nullor tnull nullS snulltem, tnull navigation data contains sinullparameters relating to cnullclic perturbation: CucnullCus nullnullplitude onulltnull cosine and nullrmonic correction terms to tnull argument onulllatitude CicnullCis nullnullplitude onulltnull cosine and sine nullrmonic correction terms to tnull angle onullinclination CrcnullCrs nullnullplitude onulltnull cosine and sine nullrmonic correction terms to tnull orbit radius nulln Simnullnull , applnullperturbations using tnullse sinullterms to one or more satellitesnull Tnullse are errors, as tnullnullare not declared in tnull navigation messagenull Satellite Geometry Tnull relative positions onullvisible satellites, as observed bnulltnull receiver, determine a nullnullalitnullparameternull called Dilution nullnull Precision nullnullnull nullnulla receiver sees nullur satellites and all are arranged, nullr enullmple, in tnull nortnullnullest, tnulls leads to a nulladnull geometrnullnullnulln tnull tnulloretical nullrst case, no position determination is possible, because all distance determinations point to tnull same directionnullEven inulla position is determined, tnull error onulltnull positions manullbe up to nullnullnullnullnullmnullnullnulltnull nullur satellites are nullell distributed over tnull nullole snull tnull position is mucnullmore accuratenull Depending on tnull nullctors used nullr calculation onullDnull values, dinullnullrent variants onullDnull are used: null nullnull nulleometric Dilution nullnullPrecisionnull nullerall accuracnull nullD coordinates and time null PDnull nullositional Dilution nullnullPrecisionnull Position accuracnull nullD coordinates null nullnull nullorinullontal Dilution nullnullPrecisionnull nullrinullontal accuracnull nullD coordinates null nullnull nullnullertical Dilution nullnullPrecisionnull vertical accuracnull nullignull null TDnull nullTime Dilution nullnullPrecisionnull time accuracnull time nullnull values belonull4 are good, above nullbadnullnullnull values become nullrse inulltnull received satellites are nullgnullin tnull snullnull nullnull values become nullrse tnull closer tnull satellites are to tnull nullrinullon and PDnull values are best inullone satellite is positioned verticallnullabove and tnullee are evenlnulldistributed close to tnull nullrinullonnull To determine accurate positions, tnull nullnull value snulluld not be less tnulln nullenull Tnull satellite geometrnulldoes not cause inaccuracies in tnull determination onullposition, so Dnull is unitlessnullDnull values amplinull otnullr inaccuracies and nullgnullDnull values amplinull otnullr errors more tnulln lonullDnull valuesnull Tnull error in position caused bnulltnull satellite geometrnullalso depends on tnull latitude onulltnull receivernull Page nullSPIRENT Application Note nullor a simulator test nullou can subnullct a receiver to dinullnullrent combinations onullsatellites bnulldeliberatelnullenullcluding certain satellites nullom tnull simulated visible constellationnullSimnullnull nullll identinull tnull nullur satellites in a given constellation tnullt nullll give tnull best Dnull pernullrmance, depending on tnull selection criteria, nullicnull nullll be one onulltnull nulle Dnull tnullesnull nullnull, nullr enullmple tnullse satellites are deliberatelnullenullcluded, tnulls nullll nullrce tnull Dnull to be nullrsenednullTnulls nullature is usenulll nullr identinulling a receivernulls abilitnullto use satellites tnullt are not ideallnullpositionednull nullor enullmple, in an urban cannullon environment a receiver nullll probablnull see onlnullsatellites tnullt are directlnullabovenull Tnulls means tnull nullnull nullll be poor so tnull receiver or snulltem developer must optimise tnull design to nullrnullin tnullse conditionsnull Tnullre are several dinullnullrent metnullds nullr restricting a receivernulls visibilitnullonullcertain satellites, including manualnullenabling and disabling satellites or using scripted commands to enable and disable satellites, using terrain obscuration and bnullusing antenna patterns nullee renullrence 4null Page nullSPIRENT Application Note Control Segment and nullser Segment errors Epnullmeris prediction errors Tnullse are errors in tnull declared position onulla satellite nulls transmitted in tnull navigation data messagenull nulln otnullr nullrdsnull tnull satellite nullsnnull nullere tnull snulltem said it nulls nullen nullou made a measurement on its signalnull Radial and crossnullracnullerrors contribute to epnullmeris errorsnull Epnullmeris corrections are calculated using a curvenullt onulltnull control segmentnulls best prediction onulleacnullsatellitenulls position at tnull time onullan upload and contain innullrent errorsnullnulln addition, tnull errors tend to gronull over time nullom tnull last control segment navigation data uploadnull nullor a simulator test, nullou can denulle a scenario in nullicnulltnull epnullmeris prediction data in tnull navigation message graduallnulldiverges nullom being correct according to a specinulld nullgracenulll degradation onullaccuracnullnull curve as denulled in Renullrence null Wnulln nullou enable tnull Diverge Epnullmeris nullature Simnullnull applies errors to tnull data nullr eacnullsatellite, but does not alter tnull simulated signalnull Tnulls is opposite to tnull real nullrld, nullere tnull pnullsical satellite position nullnd signalnull cnullngesnullnullnullever, tnull enullnullct is identicalnull nullotnullr enullnullct nullou can applnullis a Tracnull Error, nullere nullou specinull tnull orbit tranullctornull onulla given satellite to nullve an error in eitnullr or all onulltnull tnullee anullesnullnullong nullornullrd or bacnullard on tnull tranullctornull, nullcross nullenull or rignull on tnull tranullctornull and Donull nullp or donull nullom tnull tranullctornullnull nulligure nullillustrates tnulls principlenull nulligure null Satellite orbital tracnullerrors Page nullSPIRENT Application Note Nanullgation data errors nullavigation data is a nullnullpart onullannullnullSS snulltemnullnullor nullS, eacnullsatellite broadcasts tnulls as a null bps message nullrmatted into null nullames onullnullnull bitsnullEacnullnullame tanulls null seconds to transmitnullTnull nullames are subnullivided into nulle subnullrames, eacnull containing ten, nullnullit nullrds and tanullng sinull seconds to transmitnullTnull last nullbits onulleacnull nullrd are paritnullbits emplonullng a null,null nullamming code tnullt allonull tnull receiver enullipment to detect bit errors during demodulationnullnullt tanulls nullnull minutes to transmit tnull complete navigation messagenull Tnull data content is updated bnulltnull Control Segment appronullmatelnulltnullce a danullnullr eacnullsatellitenull Tnull content onulltnull message subnullrames is summarinulled as nullllonull: null null satellite clocnullcorrections, nullaltnull indication, age onulldatanull null nulland null satellite epnullmeris parametersnull null 4: ionospnullre model parameters, nullC data, almanac nullnullaltnullstatus data nullr satellites numbered null and nullgnullrnull null null almanac nullnullaltnullstatus data nullr satellites numbered nullto nullnull Renullrence nullgives a detailed description onulleacnullbit onulltnull navigation messagenull nullecause tnull navigation message contains innullrmation vital to tnull operation onulltnull receiver, annullerrors in tnull message not detected bnulltnull paritnullcnullcnullmanullcorrupt tnull receivernulls calculation onullPnullnull nullou can replicate sucnullerrors using a simulatornull Simnullnull lets nullou simulate errors and applnullvarious postnullaritnullcorruptions to selected nullrdsnullubnullrames at certain times and on certain satellitesnullTnulls tests a receivernulls error detection nullcorrection algoritnullsnull nullou can also modinull annullonulltnull navigation message to maintain paritnullnullnullotnullr nullature relevant to tnull navigation message is scnullduling an uploadnullnullt is possible to simulate control segment uploads to eacnull or all satellites and specinull tnull subsenullent upload times, applnullvarious nullaltnullstatus settings, LnullLnulldelanull and nullnull Specinulling an abnormallnulllong time betnulleen uploads nullll manull tnull age onulltnull data increase and nullr enullmple, clocnullcorrections nullll be less and less accuratenullTnulls tests a receivernulls satellite enullclusion algoritnull, nullere it reads tnull nullDC value and determines tnullt a particular satellite is bad due to tnull age onulltnull clocnull correction datanull Page nullSPIRENT Application Note Ionosnulleric nullediction error Subnullrame 4, page nullonulltnull nullS navigation message contains tnull data describing tnull ionospnullric model used bnullsingle nullenullencnull Lnullreceivers nullnullnullLnullreceivers can all but eliminate ionospnullric delanullnull Tnulls model nulls developed bnullnullobucnullr in nullnull nullee Renullrence nullnullTnull nullS nullaster Control Station selects a set onullcoenullcients nullom a database onullnullnullsucnullsets associated nulltnulldinullnullrent seasons and levels onullsolar activitnullnullTnull model is constrained bnulltnull number onullparameters tnullt can be used and tnull nullenullencnull onullupdates nullne per danullmanullmumnull tnullrenullre it is not completelnullaccurate and annullreceiver using it to correct nullr tnull ionospnullric delanullnullll benenull nullom a nullnull reduction in error compared to a completelnull unnullompensated delanullnull nullor a simulator test nullou can simulate tnull inaccuracies innullrent in tnull control segmentnulls ionospnullric predictionsnull Simnullnull allonull nullou to enter a model to be applied to tnull Rnullsignal, and a dinullnullrent model to be broadcast in tnull navigation messagenullnulln addition, it is possible to enter dinullnullrent broadcast models depending on tnull control segment navigation data upload, simulating eitnullr an improvement onulldegradation due to tnull cnullnge in datanull nullt is also possible to null tnull ionospnullric delanulland even disable tnull ionospnullrenull null receiver can navigate nullr more accuratelnull tnulln it nulluld in real linull inullits ionospnullric model is disabled and tnull simulatornulls model is also disablednullDisabling tnull ionospnullre can nulllp to bencnullarnulltnull receivernulls true tnulloretical pernullrmance and nullantinull tnull relative pernullrmance onullits atmospnullric modelling capabilities nullen tnullnullare renullnablednull Tronullsnulleric delay Tnull lonuller part onulltnull atmospnullre is nullonull as tnull TropospnullrenullTnulls contains tnull nullnulleatnullr regionnull in tnull lonullest part and a nulldrnullregionnull in tnull uppermost partnull nullnlinull tnull nullonospnullre, tnull Tropospnullre is a nonnullispersive medium nullere radio signals are renullacted enullallnull, regardless onullnullenullencnullnullnulliven tnulls, it is not possible to use nullS measurements on Lnulland Lnull to estimate tnull delanulland nullou nullve to relnull on a modelnullTnull navigation message does not provide Tropospnullric prediction as tropospnullric enullnullcts are too regionalnull null Simulator applies a Tropospnullric model to tnull Rnullsignal to simulate tnull enullnullcts onull tnull Tropospnullrenullnulln Simnullnull, tnull STnullnullnull nulleannullutton null RTCnullnulland RTCnullnullmodels are available, togetnullr nulltnulla surnullce renullactivitnullindenulldata entrnullnull null nulltnulltnull nullonospnullre model, tnull Tropospnullre model can also be disablednull Page nullSPIRENT Application Note nullultinulltnull nullultipatnull, a pnullnomenon nullere a signal tnullt tanulls one linenullnullsignull patnullnullom tnull satellite to tnull receiver, in practice undergoes a renullctionnullnulland a receiver sees multiple versions onulltnull direct signal, eacnullnulltnulldinullnullrent time onullarrival and signal levelnull Tnull receiver nulls no nullnullonulldetermining nullicnullsignal is tnull nullealnull nonnullelanulled one, as it cannot distinguisnulltnullm as discrete nullanullnull nullsuallnull, a receiver can readilnullresolve a multipatnullsignal inulltnull patnulltravelled is greater tnulln tnullce tnull spreading code snullbol period nullr tnull nullSnullmodulationnull Tnulls is because tnull direct nullantednullsignal arrives mucnullearlier tnulln annullmultipatnull Tnull problem is nullen multipatnullrenullctions nullom nearbnullobnullcts arrive vernullsoon anuller tnull arrival onulltnull nullnted signalnull Sucnullsignals nullitnulldelanull as small as null to nullnullnsnulldistort tnull correlation nullnction betnulleen tnull received signal and tnull locallnullgenerated renullrence in tnull receivernull Tnullnullalso distort tnull composite pnullse onull tnull received signal, introducing errors in pseudorange and carrier pnullse tnullt varnull betnulleen dinullnullrent satellitesnull Tnullse errors contribute to an overall error in tnull receivernulls Pnull solutionnull nulligure nullsnullnull tnull concept onulla simple singlenullenullction multipatnull Tnullre are mannulltnulles onullmultipatnull and a detailed discussion is benullond tnull scope onulltnulls documentnullRenullrence nullgives an innulleptnullloonullat multipatnull and nullnullto test a receiver under multipatnullconditionsnull Receinuller errors nullotnullr source onulluser segment errors are tnullse due to tnull receivernull nullodern receivers nullve multiple digital receiver cnullnnels, and nulltnullsilicon cnullp integration densities continuallnullincreasing, more parallel processing is possible, leading to, nullr enullmple, snullrter time to nullst null pernullrmancenull nullonullever, nulltnullincreased processing comes increased noise, and nenulldesigns are still susceptible to classical error sources sucnullas Lnull noise, PLLnullLL tnullrmal noise, oscillator pnullse noise and nullC aliasingnull null average modern receiver snulluld contribute less tnulln nullnullm rms error in bias and less tnulln nullnullm in noise, according to Renullrence null null tnull receiver under test is obviouslnullpart onulltnull test setnullp, it nullll contribute its onull errors and tnullre is no renullirement nullr tnull simulator to replicate receiver errorsnull nulligure null nullultipatnullConcept nullore innullrmation on nullultipatnullcan be nullund bnulldonullloading tnull Spirent Enulloonull Testing nullultipatnullPernullrmance onullnullSS Receivers Page nullSPIRENT Application Note Conclusions Tnulls nullpplication nullote describes some onulltnull mannullsources onullerror nulltnulln tnull nullSS snulltemnullTnullse errors are common to all applications and are in addition to applicationnullpecinull errors due to tnull local environmentnull Tnulls nullpplication nullote identinulls tnull principal sources onullerror and snullnull tnullt a nullSS simulator allonull nullou to introduce tnullse errors in a test scenario, enabling tnull receiver under test to be nullllnullenullercisednullSimnullnull onullnullrs vernullnullgnull resolution control onullsignals and bitnullevel manipulation onulldata, reproducing tnull most complenullerror enullnullcts nullile its easnulltonull use internullce allonull straignullnullrnullrd tests to be carried out nulltnulltnull same ponullernulll modelling tanullng place in tnull bacnullroundnull Renullrenced nullocuments null nullDnullPSnullnull nullavstar nullS Space Segmentnullavigation nullser nullnternullce Control Document, Revision nullnull nullnullnullnull, nulltnullnullpril nullnull null nullnderstanding nullS nullPrinciples null nullpplications, nullnullnullplan, Cnullnullegartnull, nulld Ed, nullnullnull null Wnullte nullouse Press Release on tnull disabling onullSnull nullnullce onulltnull Press Secretarnull, nullt nullanullnullnullnull 4null DnullnullnullTesting nullSS nullr automotive applications nullpirent nullpplication nullotenull null nulllobal Positioning Snulltem nullSignals, nulleasurements nullPernullrmance nullnullnullisra, PnullEng, nullnullnull null Dnullnull4nullnullSimulating nullultipatnull nullpirent nullpplication nullotenull Page nullSPIRENT Application Note Glossary onullTerms nullC nullalogue to Digital converter nullSnull nullinarnullPnullse snullnull nullenullng modulation DoD nullnited Stated Department onullDenullnce Dnull Dilution onullPrecision nullDnull nullnulleometric Dnull, nullnull nullnullorinullontal Dnull, nullnull nullnullertical Dnull, PDnull nullPosition Dnull, TDnull nullTime Dnullnull Epnullmeris Precise satellite orbital innullrmation nullirmament Tnull nullavens, tnull snull nullL nullrenullencnullLocnulld Loop nullSS nulllobal nullavigation Satellite Snulltem nullPS, nullalileo, nullnullnullS etcnull nullDC nullssue nullnullData Clocnull Tnull issue number nullr tnull clocnullcorrection data set tnullt identinulls its age Lnull Lonullnulloise nullplinullr nullavigation Data nulln tnull contenull onulla nullSS, tnull data transmitted bnulltnull satellite to tnull user convenullng snulltem innullrmation necessarnullnullr navigation Pseudorange PLL Pnullse Locnulld Loop Pnull Position nullelocitnullnullTime, tnull tnullee navigational parameters calculated bnulla nullSS receiver RSS Tnull snullare root or tnull sum onulltnull snullares onulla range onullvalues SPS Standard Positioning Service onullnullS Snull Satellite nullenullcle nullnull nullser Range nullccuracnull nullRE nullser Estimated Range Error Page nullSPIRENT Application Note Page nullSPIRENT Application Note CONTACT null Snullrent Communications null4 nullnull nullnullnull globalsalesnullpirentnullom nullnullnullpirentnullomnullositioning Snullrent Federal Systems null 7null nullnullnullnull innullnullpirentnullderalnullom nullnullnullpirentnullderalnullom nully not snullre tnulls documentnull Got a smartnullonenull If you have a smartphone download a QR Code reader and then point your phone camera at the QR Code to read the graphic. DnullnullnullnullSnull nullnull Revnullnullnullnullul nullnull nullaceboonull Linnulldnulln Tnulltter Tecnullorati nulloogle nullunull Digg Delicious Reddit Stumbleupon nulle are adding nenullcontent to our nullenullite on a regular nullsisnull nullonullarnulltnulls linnull nullnullnullpirentnullomnullositioning nullisit tnull Snullrent GNSS nullognulltnullre are currently onuller null nullsts nulltnull2 to 3 nenullnullsts added eacnullnulleenull Catcnullunullon nullatnulls nenullnull nullnullnullpirentnullomnulllognullositioningnullspnull Need more innullrmationnull gnssnullolutionsnullpirentnullom