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AND RF calculations V05.06 document presents an overview of the integrated AND calculations for...
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AND Solution GmbH Karl-Schmid-Strasse 14 81829 Munich, Germany Munich, 28 July 2017 Author: Diarmuid Kelly, Director Sales International © by AND Solution GmbH For further information contact [email protected] Join us at LinkedIn and follow Visit us at www.and-solution.com Integrated RF calculations in AND 24 May 2017 The emergence of DOCSIS 3.1 has given cable networks a new lease of life. Using existing network infrastructure relevant components can be swapped out extending the downstream up to a possible 1.8 GHz and the upstream to 200MHz. Improved spectral efficiency in comparison to the current DOCSIS 3.0 standard along with increased available bandwidth will enable operators to offer as much as 1 Gigabit/s. Indeed, it is expected that eventually up to 10 Gigabit/s will be possible on the same infrastructure without making further physical changes. The upgrade projects will nevertheless present considerable engineering challenges, which, if not properly executed, could have serious repercussions on network performance as well as having a negative impact on “bits per dollar”. In addition, the upgrade tasks will have to be carried out with military precision causing as little disruption to services as possible. This document presents an overview of the integrated AND calculations for RF/DOCSIS cable networks. These calculations allow you to effectively simulate your network providing you a means of ensuring optimal performance of your existing infrastructure as well as providing you with the necessary engineering support for future network upgrade projects, e.g. to DOCSIS 3.1. Not only does AND consider the complete network spectrum for both upstream and downstream, it also considers the end-to-end network, i.e. from the headend right to each and every home, regardless of whether this is a single-family building or part of a large apartment complex. Note: AND provides very precise calculations of intermodulation products (2 nd and 3 rd order) caused by channels of narrow bandwidth. These consider nonlinearities of active compon- ents such as amplifiers. Consequently, AND comprehends the rate of intermodulations within each channel regardless of its bandwidth. Recently implemented additional RF calculation improvements have been included in this paper; these will be available with the AND SystemSolution release scheduled for August 2017.
Transcript of AND RF calculations V05.06 document presents an overview of the integrated AND calculations for...
ANDSolutionGmbHKarl-Schmid-Strasse1481829Munich,Germany
Munich,28July2017Author:DiarmuidKelly,DirectorSalesInternational©byANDSolutionGmbH
Forfurtherinformationcontactinfo@and-solution.comJoinusatLinkedInandfollowVisitusatwww.and-solution.com
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)
