SoftwareDefinedRadio:Past,Present,andFuture
Publishdate:Mar31,2017
ThePast—30YearsofSoftwareDefinedRadios
It'shardtobelievethattheterm“softwaredefinedradio”(SDR)hasbeenaroundforabout30years.
That’salongtimeinthetechnologyworld.SDR,stillacommontopicofdiscussion,carriesmorethanits
shareofmisconceptions.SDRis“aradioinwhichsomeorallofthephysical-layerfunctionsaresoftware
defined,”pertheWirelessInnovationForum(formerlytheSDRForum).Thetermfocusesonthe
physical(PHY)layerprocessingofthewaveformandisnotrelatedtotheradiofrequency(RF)frontend,
whichisacommonmisconception.
Thirtyyearslater,SDRisnowadominantindustrystandard—frommilitarytacticalradiostocellular
handsets—it’salmostagiventhataradioisanSDR.Therewillcontinuetobeinnovationsin
semiconductorandsoftwaretechnologythatwilldrivehigherdevelopmentproductivityandmorecosteffectiveproducts,sothereisnoendinsightforSDRs.ThesefactorsmeanthatSDRisreallyasolved
problem-andradiosarenowevolvingtobecomefrequency-agileintelligentcommunicationsystems.
ThePresent—SoftwareDefinedRadioBecomestheDeFactoIndustryStandard
Inmarketssuchassignalsintelligence(SIGINT),electronicwarfare,testandmeasurement,public-safety
communications,spectrummonitoring,andmilitarycommunications(MILCOM),SoftwareDefined
Radioshavebecomethedefactoindustrystandard.Someofthesemarketswereusinghardwired
application-specificintegratedcircuits(ASICs),whileotherswerealreadyusingprogrammabledigital
signalprocessors(DSPs).Figure1showstheprogressofSDRadoptionthroughthelast30years.Closest
tothecenter,thedarkbluesectionisrepresentativeofthefirstsetofmarketstomovefromhardware
radioarchitecturestoSDRarchitectures,regardlessofwhethertheyusedthetermSDR.
ThetechnologythatdrovethemovetoSDRinthesemarketswastheadventofRFintegratedcircuits
(RFICs)fromcompanieslikeAnalogDevicesandcost-effectiveDSP-intensiveFPGAsfromcompanieslike
Xilinx.Thesetwotechnologiescametogethertomeetamultibilliondollarneedinthemilitarytactical
radiomarket,creatingsomethingofa“marketripple,”wherethemarkethadahugeimpactonthe
evolutionofSDRtechnologyfarbeyondjusttheMILCOMmarket.TheJointTacticalRadioSystem(JTRS)
programfundedthedevelopmentandproductizationofSDRformilitaryradios,whichcreatedastrong
ecosystemofvendorsincludingsemiconductors,tools,andsoftwarecompanies.Onthetoolsfront,SDR
requiredwaveformstobeasportableaspossiblebetweendifferenthardwareplatforms,whichresulted
intoolsliketheSoftwareCommunicationsArchitecture(SCA)CoreFramework,aswellasbetter
programmingtoolsfromelectronicdesignautomation(EDA)andsemiconductorcompanies.
Figure1.SuccessivegenerationsofSDRshavecometodominatetheradioindustryandwillcontinuetoevolve.
TheadvancementofRFICs,FPGAs,andEDAtoolswasasignificantfactorinenablingthesecond
generationofSDRsbeingdrivenby4GLTEinfrastructure.VirtuallyallLTEbasestationsweredeveloped
withRFICsandFPGAs.SomeofthelargerinfrastructurevendorswouldeventuallygotoASICs,buteven
then,thebasebandASICswerelargelyprogrammable,astheyusedprocessorscoupledtohardened
blockscalledhardwareacceleratorsforcompute-intensivefunctions,suchasturbodecoding,that
wouldtypicallyexceedtheperformanceorpowerlimitationsoftheprocessors.
Thenextmarketripple,showninthethirdgeneration,occurredwhen4GLTEhandsetsmoved
consistentlytoSDRarchitectures.Thisshiftwasenabledbylow-power,high-performanceDSPcores
optimizedforhandsetsofferedbycompaniessuchasCeva,Tensilica,andQualcomm.Likebaseband
ASICsforinfrastructure,thesecoreswouldbeintegratedintoapplication-specificstandardproducts
(ASSPs)orASICsformuchofthePHYprocessing,coupledwithhardwareaccelerators.Oncethis
changeoveroccurred,SDRsincreasedordersofmagnitudeinvolumeandreachtobecomethedefacto
industrystandardforradios.
TheFuture—NextGenerationofSoftwareDefinedRadios
What’snextforSDR?Astheubiquityof4GhandsetshaspropelledSDRs,theprospectsofemerging
technologiessuchas5G,theInternetofThings(IoT),andsensornetworkspromisetoagainincreasethe
volumeofSDRsbyanotherorderofmagnitude.WhatwillbethetechnologydriverliftingSDRtothese
loftyheights?AswithpreviousleapsinSDRadoption,itwilllikelybeacombinationofbothhardware
andsoftwaretechnologies.
Oneofthenexttechnologydriversinhardwarelookstobethecombinationofanaloganddigital
technologyontoasinglemonolithicchiptoreducecostandsize,weight,andpower(SWaP).For
infrastructure,thisdrivercouldbeFPGAswithintegratedanalog-to-digitalconverters(ADCs)anddigitalto-analogconverters(DACs).Forhandsetsandsensors,thiscouldbeapplicationprocessors,alsowith
integratedADCsandDACs.
Newinnovationsinhardwarewon’tbeveryuseful,however,ifthesoftwareandtoolsdon’tfollow.That
isthewholepointofSDR,afterall.Toenablethedevelopmentofthesechips,aswellasthewaveforms
andapplicationsoftwarerunningonthem,therewillbearequirementforbettersystem-leveltoolsthat
canbeusedtodesignanddebugacrosstheanaloganddigitaldomains.AsSDRsbecomeusedfor
increasinglycomplextasks,theyarebeingdesignedwithmorepowerfulFPGAsdesignedforintensive
DSP(Figure2).Asaresult,thereisaninevitablegrowingneedforFPGAtoolsthatcanhandlerapidly
increasingamountsofdataandcomplexity.
Figure2.ThenumberofDSPslicesineachsubsequentFPGAgenerationcontinuestogrowrapidly.
Whilegeneral-purposeprocessors(GPPs)haveservedtheSDRcommunitywellinthepast,theyare
strugglingtomeettheperformancerequiredforareaslike5GandMILCOM.Softwaretoolssuchasthe
LabVIEWFPGAModuleandRFNetworkonChip(RFNoC)offerastreamlineduserexperiencethatmakes
FPGAprogrammingvastlymoreefficient.
Ultimately,integrationwilldrivethenextgenerationofSDRs.Theintegrationofanaloganddigital
technologyintomixed-signalchipswillbekey,butSDRshavefundamentallyreachedapointwherethe
primarylimitationongrowthisinsoftware,nothardware.Withoutsoftwaredevelopment
environmentsthatcanseamlesslyprogrambothGPPsandFPGAs,theadditionalhardwarefeaturesof
next-generationSDRswillbeunderusedanddevelopmentwillstall.TheabilityoftoolslikeLabVIEW
FPGAtoenablewirelessengineerswhoarenotHDLexpertstodevelopandrapidlyiterateon
sophisticateddesignsofferthebestopportunitymovingforwardtounlockthenextgenerationofSDRs.
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