ANDSolutionGmbHKarl-Schmid-Strasse1481829Munich,Germany
Munich,28July2017Author:DiarmuidKelly,DirectorSalesInternational©byANDSolutionGmbH
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IntegratedRFcalculationsinAND24May2017
TheemergenceofDOCSIS3.1hasgivencablenetworksanewleaseoflife.
Usingexistingnetworkinfrastructurerelevantcomponentscanbeswappedoutextendingthedownstreamuptoapossible1.8GHzandtheupstreamto200MHz.ImprovedspectralefficiencyincomparisontothecurrentDOCSIS3.0standardalongwithincreasedavailablebandwidthwillenableoperatorstoofferasmuchas1Gigabit/s.Indeed,itisexpectedthateventuallyupto10Gigabit/swillbepossibleonthesameinfrastructurewithoutmakingfurtherphysicalchanges.
Theupgradeprojectswillneverthelesspresentconsiderableengineeringchallenges,which,ifnotproperlyexecuted,couldhaveseriousrepercussionsonnetworkperformanceaswellashavinganegativeimpacton“bitsperdollar”.Inaddition,theupgradetaskswillhavetobecarriedoutwithmilitaryprecisioncausingaslittledisruptiontoservicesaspossible.
ThisdocumentpresentsanoverviewoftheintegratedANDcalculationsforRF/DOCSIScablenetworks.Thesecalculationsallowyoutoeffectivelysimulateyournetworkprovidingyouameansofensuringoptimalperformanceofyourexistinginfrastructureaswellasprovidingyouwiththenecessaryengineeringsupportforfuturenetworkupgradeprojects,e.g.toDOCSIS3.1.
NotonlydoesANDconsiderthecompletenetworkspectrumforbothupstreamanddownstream,italsoconsiderstheend-to-endnetwork,i.e.fromtheheadendrighttoeachandeveryhome,regardlessofwhetherthisisasingle-familybuildingorpartofalargeapartmentcomplex.
Note:ANDprovidesveryprecisecalculationsofintermodulationproducts(2ndand3rdorder)causedbychannelsofnarrowbandwidth.Theseconsidernonlinearitiesofactivecompon-entssuchasamplifiers.Consequently,ANDcomprehendstherateofintermodulationswithineachchannelregardlessofitsbandwidth.
RecentlyimplementedadditionalRFcalculationimprovementshavebeenincludedinthispaper;thesewillbeavailablewiththeANDSystemSolutionreleasescheduledforAugust2017.
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UnitsTocaterforthevarioussignallevelunitformatscommonlydeployedANDallowstheusertoselecteitherdBµV,dBmV,ordBm.Thiscanbedoneduringnormaloperations.
Figure1:SupportedunitlevelsinAND
Levelsareconvertedautomatically.
FrequencyroutingEachfrequencyisroutedseparatelymeaningthatthechannelrasterisknownateachpointinthenetwork.
Inthesinglesource/sourcesofeachchannelinputparameterscanbeenteredfor:
• Noise• RFlevel• Frequency• Modulationtype• Levelreduction
Inthenextrelease(E6/2017)ANDwillsupportindividualCNRlimitvaluesforeachchannelmodulationtypeasdifferentsignalusagerequiresdifferentcarriertonoiseratiolimits.Forexample,QAM64mightneeda27dbratiowhereasQAM256mightrequirea32.5dBratio.
UptonowtheANDuserhasonlybeenabletosetasinglelimitinthewarningsettings.Asaworkaround,theinputlevelsandnoiseratioshadtobeadaptedatthesignalsource.Withthenextrelease(E6/2017)thewarningsettingswillbeextendedallowingtheusertoenteranindividualCNRlimitforeachmodulationtype.Thiscanbeselectedonaperchannel-basisatthesignalsource.
Thenet-checkfunctionwillconsidertheselimitsforeachchannelindividually.
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Attenuation
CableCableattenuationisenteredforselectedfrequencies.ANDusesthesevaluestocalculatetheattenuationforthefrequencyspectrumusingsquarerootinterpolation.Thisreturnsanattenuationcurveasshowninthediagrambelow.
Figure2:Attenuationcurveforcoaxialcable
ANDalsocalculatescableattenuationfordifferenttemperatureswhenconsideringAGCalterations.
PassiveComponentsAttenuationisenteredforselectedfrequencies.Usingthesevaluestheattenuationforindividualfrequenciesiscalculatedbylinearinterpolation.Thisreturnsanattenuationcurveasshowninthediagrambelow.
Figure3:Attenuationcurveforpassivecomponents
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EqualizerTheequalizerisasocalledidealcomponent,neverthelessreal-worlddeviceshavebasicattenuationandthisisconsideredbyAND.
Figure4:Equalisersettings
TheUserentersthefollowingvalues:
• Basicattenuation• Nominalslope• Lowerfrequency• Turningpoint
e.g.10dBslopebetween85and1000MHz.
ANDassumesacombinationoflinearresponse(att(f)=af+b)andsquareroot-likeresponse(att(f)= bfa + ).Themixingratiocanbeenteredasaprojectsettingthatisappliedtoallequalisersofthecurrentproject.Bydefault,amixtureof25%linearand75%squareroot-likeisused.
Figure5:Comparisonofthefrequencyresponseofa10dbequaliserforratios0%,75%,100%
Itisalsopossibletoenterattenuationsforalistoffrequencieswhendeployingequalisersdesignedasstandalonecomponentswithfixedequalisation.Attenuationisthencalculatedbylinearinterpolationaswithotherpassives.
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DownstreamLevelThedownstreamleveliscalculatedasfollowing:
“signalsourcelevelminusattenuationplusamplification”.
Figure6:Signalpathwithamplificationandattenuation
Attenuationiscalculatedforallfrequenciesofallsignalsources.Thisallowscalculationofeachfrequencyatanygivenpoint.Attenuationcanberegulatedusingadjustablecomponents.
AmplifiersareautomaticallyadjustedbyANDtoavaluespecifiedbytheplannerconsideringthereductionsetatsignalsourceforeachchannelsothattheinputattenuatorsandequaliserssetthesignalasflataspossibleandtherequiredslopeisgeneratedintheinterstage.Noise-reducingattenuationisalsotakenintoaccountintheinterstage.
Slopes(tilts)withinchannelsarealsocalculated;thisisparticularlyimportantforbroadbandOFDMchannels:
Figure7:ChannellistwithOFDMchannelsandtiltwithinthechannelbandwidth
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UpstreamLevelThefollowingvaluesmustbedefinedforthecalculationoftheupstream:
• Receptionlevelsatthereceiverorthesignalsource,e.g.70dBµV• Levelrangeinwhichthecablemodemscansend,e.g.100-112dBµV.
Theupstreamlevelforanygivenpointafterthecablemodemiscalculatedasfollows:
“receivinglevel+attenuationofthecableandpassives”.
Attenuationiscalculatedforallreturnpathfrequenciesin1MHzsteps.Slopeofcablesandreturnpathequaliserareconsidered.Thereturnpathamplifiersettingsalsoconsidertheupstreamequaliser.
AsthefrequencybandinDOCSIS3.1ismorethanthreetimeslargerthanthatinDOCSIS3.0theinclusionofcableattenuationcalculationisofutmostsignificance.(Basically,thelongerthecablethegreatertheslope.)ThephysicalpropertiesofthecablearestoredinAND,makingitpossibletocalculateattenuationwithrespecttofrequency.
Figure8:Reversepathamplifiersettings
Theamplifiercanbeadjustedinordertocompensateforattenuationandslope.
Slopecausedbycableandpassives
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AmplifierinputlevelsANDchecksthetargetlevelsattheamplifieroutput.InconjunctionwithCNRcalculationforeachstageamplifierscanbecheckedthattheyareoperatinginaccordancewithspecifiedthresholds.
Newadditionallimitsandchecksforamplifierinputarebeingintroducedinthenextrelease(E06/2017);thesearedescribedbelow.
NEW:DefaultlevelwindowinlibraryAdefaultlevelwindowwithminimalandmaximalvaluesfortheinputofeachamplifierstageisnowavailableinthelibraryeditor.Normallytheuserwillonlyenterthesevaluesfortheinputofthefirstamplifierstage.
NEW:AmplifierInputLevelCheckWheninputlimitvaluesaresetintheANDlibrarytheywillbeaddedtoanewlydrawnamplifier.Theamplifier-packagedialogueinANDwillbeextendedbythenewinputlevelmin/maxvalues.Theusercanedit/overwritethelibraryvalues.
Thewarningssettingsprovideacheckboxandatoleranceparameterallowingtheusertomakeaverificationconfigurationforthenet-checkfunction.
Assumingthefunctionhasbeenactivatedandanamplifierhasvalidmin/maxvaluessetthenawarningwillbeshownduringtheexecutionofthenet-checkfunctionifthecalculatedinputlevelfallsoutsidethepermittedlevelrange.
NEW:WarningifamplifiertargetvaluesarehigherthaninlibraryCheckboxesandtolerancesareincludedinthewarningsettingsallowingtheusertoactivatethelibrarylimitcheckwithinthenet-checkfunction.
Thiswillbecarriedoutfor:
• Inputlevel–iftheamplifierInputLevelwindowhasbeenincreasedbytheuser• Targetlevel–iftheamplifiertargetlevelhasbeenincreasedbytheuser
Awarningwillbeshowninacasewheretherearevalidvaluesinthelibraryandwheretheuserhasoverwrittentheseresultinginpossibleperformanceissues.
NEW:Checkonmax.amplifiersincascadeUsersmaywanttoverifyifthenumberofamplifiersincascadeexceedsapre-definedlimit.
Thewarningsettingswillgetacheckbox“checkonnumberofamplifiersincascade”andaneditablelimitforthenumberofpermittedamplifiers.Ifthefunctionisactivatedthenet-checkfunctionwillissueawarningfortheamplifiersinacascadewherethelimithasbeenexceeded.
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NoiseTheCNRvalueisenteredforeachchannelofthesignalsource.
Degradationateachamplifierstageiscalculatedusingthefollowingformula:
10
−𝐶𝑁𝑅𝑜𝑢𝑡10
=10
−𝐶𝑁𝑅𝑖𝑛10
+10
−𝑍10
CNRout=CNRatoutput
CNRin=CNRatinput
Z=Pin[dBµV]-R[dB]-kTDf[dBµV] R=Noisenumberoftheamplifierstage
Pin=Levelatinputoftheamplifierstage k=Boltzmann-constant
T=Temperature,e.g.293K D=BandwidthofachannelinHz
Thedefaultvalueforthelogarithmicnoisefactoris10.Asthisisnoweditabletheusercanchangethisvalue,e.g.to11.Thisvaluewillthenbeconsideredinthenoisecalculation.
CNRiscalculatedforeachindividualchannelwhichcanbecomparedagainstthresholdvaluesinthewarningsettings.Thesevaluescanbespecifiedforbothdigitalandanaloguechannels;digitalchannel-onlynetworksarealsopossible.
Asstatedearlier,differentsignalusagerequiresdifferentcarriertonoiseratiolimits.
ANDwillallowtheusertoenteranindividualCNRlimitforeachmodulationtypeinthenextrelease(E6/2017).Thiscanbeselectedonaperchannel-basisatthesignalsource.
RemotePoweringElectricalpropertiesforremotesupplyarecateredforinthelibraryobject.Theohmicresistanceofthepowersupplycablesandthecurrentcausedbyactiveremotepoweredcomponentsarecalculatedasavoltagedrop.ANDcheckswhetherthenecessarysupplyisensuredforeachcomponentandalsoifthepowerunitisabletoprovidethenetworkwithenoughcurrent/power.Inaddition,ANDchecksthemaximumpermittedcurrentofcomponent(-ports)andifthereareshortcutsorcomponentsthatshouldn’tbesupplied.
Figure10:Powerunitdata
Figure9:Warningsettings(excerpt)
