UNIVERSITY
OF TRENTO
DEPARTMENT OF INFORMATION AND COMMUNICATION TECHNOLOGY
38100 Povo – Trento (Italy), Via Sommarive 14
http://www.dit.unitn.it
A Case Study in Performance Estimation and
Analysis for SDR: UMTS Data-Link Layer
Alena Simalatsar and Roberto Passerone
August 2007
forSDR: UMTSData-LinkLayer
AlenaSimalatsarandRobertoPasserone
DipartimentodiInformati aeTele omuni azioni
UniversityofTrento
fsimalats,robygdit.unitn.it
Abstra t
Theevolutionofte hnologyinthewirelessindustryhas
brought aproliferationofdifferent ommuni ation
proto- olsandstandards. Tosupportawiderrangeofservi es
andtosustainte hni alinnovation,proto ol
interoperabil-ityisessential. SoftwareDenedRadio(SDR)isemerging
as akeyintegrationte hnologyinthisarea. Deningthe
appropriatesystemar hite tureforSDRis,however,
om-plex,andrequiresextensiveanalysisandperforman e
eval-uation. Inthispaper,we onsiderUMTSas a ase-study
ofamobilestandardthatutilizesseveralhigh-layer
proto- olstoenablemultipleservi esdeliveryfor mobileusers.
WedevelopaSystemCfun tionalmodelforasubsetofthe
DataLinkLayerforUMTS,andanalyzeitsperforman eas
softwarerunningonseveralar hite tures.Theresultsarea
rststepinunderstandingthesystemrequirementsto
om-bineUMTS withotherwireless ommuni ationproto ols,
su hasWiFiandWiMax.
1.Introdu tion
The onstru tionofadistributed ommuni ation
infras-tru ture, andthe use of highly onne tedembedded
sys-tems, makes it possible todayto realizenewand
innova-tiveappli ationsandservi es,often ontext-aware,that an
leveragethemobilityaffordedbywireless onne tivity[5℄.
Whiletheseservi esareinterestingintheirownright,their
integration ouldpotentiallyleadtoamu hgreateradded
value. However,thewidevarietyofdifferent
ommuni a-tion requirements, togetherwiththe evolutionof
te hnol-ogy,haveresultedinaproliferationofmostlyin ompatible
andoften ompeting ommuni ationstandards, thatmake
integrationhardandexpensive. Theresultisthatusersare
for edto arrymultipledevi es,andmanuallysyn hronize
anddupli ateinformation,apotentiallyonerousand
error-pronetask.
Onesolution totheintegrationproblemistheuseofa
SoftwareDenedRadio(SDR)[19℄.InapureSDR,allthe
requiredpro essing,i.e.,tuning,modulationand
demodu-lationandthehandlingofthehigherlevelsoftheproto ols,
isdoneinthedigitaldomainbysoftwarerunningona
gen-eralpurposepro essor,whileaslimRFfront-endremains
intheanalogdomain. Be ausethetaskishighly
demand-ingin omputationpower,mostplatformsin ludededi ated
hardware omponentsthat anbe onguredandrewiredby
softwaretoadapttotherequiredfun tionality.These
ar hi-te turesareveryexibleandallowonetoswit hbetween
different ommuni ationstandardsbysimplyuploadinga
newversionofthe softwareinthedevi e,andpotentially
supportseveralproto olsatthesametime. Notonlydoes
thismakeintegrationsimpler,butitalsoallowsthedevi es
to be updated to support new standardsin a way that is
mostlytransparenttotheuser.
TheimplementationofaSDRrequiresthedevelopment
of highlyoptimized omputing platforms. However, the
tightreal-timerequirementsof ommuni ationsystems,
to-gether with onstraintson ost, physi al size and
perfor-man eofthedevi es,resultsinin reaseddesign
omplex-ityandsystemheterogeneitythatyieldalargedesignspa e.
ToolsbasedonRegisterTransferLevel(RTL)and
evalua-tionboardsaretoodetailedforaneffe tiveexplorationof
systemdesignalternatives,andaretypi allybiasedtowards
spe i implementationstyles. Inaddition,thela kof
ab-stra tionmakesthedesign,aswellasthevalidationpro ess,
dif ult.
Inthispaper,weproposetoraisethelevelofabstra tion
forthedesignofSDRplatformsusingthePlatform-Based
Design(PBD)[10,20℄methodology. PBDisbasedonthe
formationofdifferentlayers, alledplatforms,whi h
repre-sentdifferentlevelsofthedesignabstra tion.Ea hplatform
isawellseparatedlibraryof omputationaland
ommuni- ation omponents. Platformsathigherlevelsabstra tthe
details oflowerlevel platforms, and anbe usedforfast
ar hite turalexplorationandperforman eestimation. This
supportitsfutureextensions.Forthemethodologytowork,
ea hdomainandappli ationarearequiresthedevelopment
ofdistin tlibrariesof omponents,abstra tionlayers,and
thusar hite tural,performan eandfun tionalmodels.The
effe tivenessandthea eptan eofthePBDmethodology
isthereforetiedtotheavailabilityofthesemodelsandto
thedevelopmentofuse asesthat anprovetheira ura y.
In parti ular, in this paper, we strengthen the PBD
methodologyby developing,usingexistingtools[13,22℄,
appropriatefun tional andar hite tural models for SDR.
These modelare usedin a ase studytoexplorethe
im-pa tofhigherproto ollayersontheutilizationofageneral
purposeCPU,andderiveperforman emetri sthat anbe
usedtooptimizethe parametersofanar hite ture,based
ontheforseenmixof on urrentproto ols. Weshowthat
PBDisparti ularlywellsuitedforthedesignofSDR,sin e
therequirementsintermsofperforman eandadaptability
arehigh,andthedenitionofthebestar hite tureforthis
kindofsystemsishard.
This paper is organized as follows. After dis ussing
somerelatedworkinSe tion1.1,we giveanoverviewof
ourmethodologyandofthedomainofappli ationin
Se -tion2. Se tion3dis ussesindetailthefun tionaland
ar- hite turalmodel. Finally,simulationsandresultsare
dis- ussedinSe tion4.
1.1. Related Work
Theliteratureondesignspa eexplorationisvast.Inthis
se tion,wewilllimitourexpositiontotheworkthatappears
tobe losertoourdenedareaofappli ation.
Inthe areaofenablingte hnologiesforre ongurable
wireless terminals,the XiRis group ofthe Universityof
Bolognain ollaborationwithSTMi roele troni s[23℄
fo- usesonthe developmentofnextgenerationmobile
te h-nologiesbasedonre ongurableterminals[4,7℄.The
ar hi-te tureforre ongurableterminalspresentedbythisgroup
is able to support some important mobile te hnologies
(GSM, WCDMA,UMTS,WLAN andBluetooth)and
al-lowssoftwaredrivenswit hingbetweenthesete hnologies.
However,theaimofthisworkistoprovidean
appli ation-spe i ar hite ture, rather than a design methodology.
Nevertheless,thisar hite turemaybeapotentialtargetfor
ourdesignspa eexploration.
Bonietal.haveproposedate hniquefortheef ient
im-plementationofsupportve torma hine(SVM)algorithms
on dynami ally re ongurablesystems [8℄. Spe i ally,
they have proposed a re ongurable system to solvethe
inversemodelingproblemfortele ommuni ation
appli a-tionsbytheuseofSVMs. Whiletheydonotaddressthe
problemofdesignexplorationingeneral,thesolutions
pre-sentedintheirworkforthedynami mappingofalgorithms
inourfuturework.
Bonivento et al. are also working on several proje ts
related todesign spa e exploration,in luding the areaof
wireless ommuni ationintheformofwirelesssensor
net-works[9℄.Inparti ular,theyaredevelopinganew
method-ologyforthedesignofWirelessSensorNetworks(WSN)
applyingPBDprin iples,whi hiswell orrelatedwiththe
natureofourresear hwork. However,theyfo usonhigh
level operating system servi es, while we will fo us on
lowerlevelhardwarear hite tures.
Of parti ular interest for our resear h is the work of
Densmoreetal.whi hisfo usedmainlyonsystemlevel
ar- hite turemodelingbasedonthePBDmethodology.In
par-ti ular,theyareworkingonperforman eanalysisof
FPGA-basedar hite tures[12℄. Whilewe antakeadvantageof
theseresultsinourar hite turemodels,ourresear hwork
isnotjustfo usedonsu hkindofar hite turesandwewill
need to onsiderotheralternatives forar hite ture
imple-mentations.
Davare etal. proposea methodologyforenabling
au-tomated synthesis within PBD.Their work is mainly
fo- used on on urrentembeddeddesign formultimedia
ap-pli ations[11℄.Inthis ontext,theyproposefun tional
op-timization usingdesign spa e explorationfor multimedia
appli ationsbyapplyingthe pro essofmappingofthese
appli ations onto FPGA-based ar hite tures [14℄. To do
this, theyuse the Metropolisdesign framework [6℄. Our
approa hwillbesimilar. Whatdistinguishesourresear h
workfromtheirsisthatwewilldodesignspa eexploration
forar hite turesthat ansupport on urrentproto ols
in-steadofmultimediaappli ations.
Theresear hworkofMeyerowitzetal.isthemost
re-latedtoourproje t[18℄. Theirworkfo usesonhighlevel
modeling of embedded mi ro-ar hite tures retargetable
for different instru tion sets. The modeling of
mi ro-ar hite tural performan e is done within the Metropolis
framework. Re entpresentations suggest the use ofthis
te hniqueforSoftwareDenedRadio,anapproa hsimilar
toours (inSystemC)forar hite turedesignspa e
explo-ration [17℄. The la kofspe i publi ations inthisarea
fromtheauthors,however,makesa omparisondif ultat
this point. Nevertheless, the availability offuture results
willbeinstrumentaltovalidateourar hite tureexploration
methodologyandmodels.
2.Overview
A Software Dened Radio (SDR) is a te hnology in
whi hbothmodulationanddemodulationareperformedin
softwareorusingaprogrammabledevi e[19℄. Themajor
advantagesofanSDRisitsexibilityandeaseof
Pro-turers, who an rely on standardplatformsreused a ross
differentdomainsofappli ations.Atypi alar hite turefor
anSDRplatformisshowninFigure4.
Thedesignofreusableplatformsis,however,hard.The
designermust arefully onsiderseveraldifferents enarios
in the hoi eof the ar hite tural omponents, and inthe
waytheyare onne ted. Forinstan e,Shonoetal.report
thatthearrangementofCPUs,DSPsandFPGAsseriously
inuen es systemperforman e, andthat the software
as-signmenttoea hpro essorisdif ult[21℄.
Todeneaneffe tivesystemdesignowforSDR,we
applythePBDparadigm[20℄,byevaluatingdifferent
ar hi-te turesagainstthespe i ation onstraints,andby
map-pingthedesiredfun tionalityontheelementsofthe
plat-form.Themainobje tiveofthedesignexplorationpro ess
forea hparti ularar hite tureistodenewhatandhow
manyproto ols anbesupportedbytheplatform.To
fa il-itatethispro ess,itisimportanttoseparatethear hite ture
spe i ationfromthefun tionality. Thisway, hangesin
fun tionality(orinthe ar hite ture)willnot ausethe
re-designoftheentiresystem,andvi eversa.Inaddition,this
allowsustomodelfun tionandar hite tureattwodifferent
levelsofabstra tion, andenable fastannotated fun tional
simulationtoqui klyprovideperforman emetri sfora
va-rietyofdesign hoi es.
Ourparti ularimplementationoftheplatform-based
de-signmethodologyfollowsthestepspresentedinFigure1.
Werstbuildanabstra tSystemCmodelofthe
fun tional- !"#$"
Figure1.Designexplorationmethodology
ity,withnonotionoftime(theUntimedlevelinthegure),
whi hisusedtoverifyits orre tnessandtostudy
on ur-ren yissues. SystemCwas hosenbe auseitsupports
dif-ferentmodelsof omputationandallowsthedesignof
het-erogeneoussystems. Inaddition,itprovidesthepossibility
torenehighlevelspe i ationmodels(bothhardwareand
e utablemodels. Finally,be auseSystemC isbasedona
standardlanguage(C++),itiseasytosharemodelswiththe
othermembersoftheresear hgroup,su hasdevelopersof
appli ations,UIandbaseband.
Inorderto reateaSystemCperforman emodelfora
parti ularar hite tureweneedtoknowtheperforman eof
ea hfun tionalblo kexe utedonthisar hite ture. Todo
so,weextra ttheC odefromourSystemCmodelandrun
simulationsonseveralemulatedARMpro essorsusingthe
KeilARMDevelopmentTool[15℄. WeuseKeil's
embed-dedprolertoobtaininformationabouttheexe utiontime
ofea hfun tionrunonea hemulatedmi ro ontroller.Keil
implementsalowerlevelofabstra tion(theProlerlevel),
whi hweusetoextra ttherelevantperforman edata.We
then usethe timing informationtobuilda omplete
Sys-temCtimedmodel(theTimedlevel),whi hweuseto
deter-minetheperforman eoftheoverallsystem,andto ompute
theutilizationofthemi ro ontrollerfordatatransmission
withseveralbitrates.
Thiss hemehasseveraladvantagesovertheuseofthe
proleralone,whi hbyitself anprovidethesystem
per-forman e. First,thesimulationruninevaluationmodeare
verytime onsuminganddependonthe omplexityofthe
mi ro ontrollerar hite ture. In ontrast,SystemC
simula-tions arerelatively fastandindependentofthe
mi ro on-troller ar hite ture (see Se tion 4). Se ond, SystemC is
moreexibleandmakesiteasiertopartitionthe
fun tional-ityontodifferentpro essor ores,andto ombinetheir
per-forman e. Thisisessentialasplatformsevolvetoin lude
morepro essingelements. Thistrendalsorequiresthe
ex-ploration of different on urren ymodels, from dataow
tosyn hronizedexe ution,whi hisnativelysupportedby
SystemCbuttypi allynotbyar hite tureprolers.
In this paper we fo us on the UMTS ommuni ation
standard[2℄. Atthe toplevel,thenetworkar hite tureis
dividedintoaUser EquipmentDomainandan
Infrastru -tureDomain,whi h ommuni atethroughtheradio
inter-fa e.Wefo usontheUserEquipmentDomain,whi hisof
greaterinteresttomobiledevi eswhi haresubje ttomore
stringentimplementation onstraints.
Theproto olsta kfortheuserdomainisshownon
Fig-ure2,andisdividedintothreedifferentlayers,
orrespond-ing to the Physi al(PHY),the Data Link (DLL) andthe
NetworkLayer[3℄.Inadditiontotheusualaddressing
fun -tions,theNetworkLayer ontrolstheoperationsoftheData
LinkandofthePhysi alLayerbyrespondingto hangesin
thetransmissionparameters.TheDataLinkLayerperforms
generalpa ketformingandqualityofservi esupport.It
in- ludesaRadioLinkControl(RLC)andaMediumA ess
Control(MAC)sublayer.TheRLC ommuni ateswiththe
MACthroughdifferentlogi al hannels,todistinguish
! " #$ %& #$ '&%(&) # ( % *+ , -. /012 345 6 # 6 7 89:; ; < = # 7 89:; ; < > ?@!ABCAD B ECF
GD"F!ABCADB ECF HI B FJ ?I ADB E CF >K >L >M
Figure 2. Layer diagramfor theUser
Equip-mentDomainoftheUMTSproto ol
therequiredqualityofservi e,theMAClayermapsthe
log-i al hannelsintoasetoftransport hannels,whi harethen
passedontothePhysi alLayer.Finally,thePhysi alLayer
handleslowerlevel odingandmodulation,and
ommuni- ateswiththe radiointerfa ethroughaseriesofphysi al
hannels, ea hoptimizedtodifferenttimeand oding
re-quirements.
The ar hite tureofthe proto olsta kisvery omplex
dueto the highnumber ofdifferent logi alandtransport
hannels.Inthisworkwefo usonasubsetofthe
fun tion-ality,des ribedinthenextse tiontogetherwiththe
ar hi-te ture hosenforperforman eestimation.
3.Fun tionalandAr hite tureModel
Inthisse tion,wedes ribeinmoredetailthe
fun tional-ityofUMTSthatwemodeled,andthe lassofar hite tures
thatwehave onsideredastargetfortheperforman e
anal-ysis.Detailresultsarepresentedlater,inSe tion4.
3.1. Fun tional Model
Thesubsetoftheproto olsta kthatwehavemodeledis
these tionhighlightedonFigure2,and orrespondstothe
bidire tionalDedi ated Channelthat, inour ase, is
lim-ited topoint-to-pointuplinkuser data transmission. The
RLC is divided into three separate entities for
Transpar-ent(Tr),Una knowledged(UM)andA knowledged(AM)
transmissionmodes. Wehavelimited our analysistothe
Una knowledgedmode, orrespondingtothe UM-Entity,
sin ethisisasupersetoftheTransparentmode,and anbe
usedtoa ertaindegreetoestimatetheperforman eofthe
A knowledgedmode, whi h would otherwiserequirethe
downlinkmodel. Thus,theresultsofperforman eanalysis
oftheUM-Entity anallowustomakeapproximate
estima-tionsoftheperforman eofthe ompleteRLClayer.
Likewise,theMACsublayerisdividedintodifferent
en-titiesthathandlethemappingbetweenthelogi alandthe
transport hannels. Ofthese,we modeltheMAC-dentity
whi histhe onlyoneinvolvedwiththe baseline(not
en-han ed)Dedi atedChannel. Theotherblo ks,whi hwere
introdu edinmorere entversionsofthestandard,are
in-steadrequiredforhighspeedandqualityofservi esupport.
Our SystemC untimed fun tional model is shown on
Figure 3 and is omposed of seven modules, or a tors,
of a dataow pro ess network: four are related to the
UM RLC entity (i.e., Transmission Buffer,
Segmenta-tion/Con atenation,RLCHeader AddandCiphering)and
threetoMAC-d(i.e.,TransportChannelTypeswit h,C/T
MUX and Transport Format Combination (TFC)
sele -tion). 1 NOPQR STUV WXYWWYZV [\] ]^T _` Uab ^ c W ]T ZX dYed ^TfU g^TWh i^ eX ^ V c U c YZVj P ZV aU c^ V U c YZV klP d^ U R^T UR R P Y `d ^T YV e STUV W`ZTc a d UVV ^f WmY c a d PjS Nno STUV W`ZTc]ZTXUc W ^f^ a c YZV pYW`fU g _`Uab^ c cT UV WXYWWYZV c Z cd ^qrs h n V UabVZm f^R e ^R XZ R^ Z ]klP tutv tut v tu t v tutv tut v t u t v
Figure 3. Blo k diagram of the fun tional
model
Ea hblo ksignalstothenexttheavailabilityofapa ket
tobe pro essed, bydepositingit into aFIFO queuewith
blo kingreadand blo kingwrite. The s hedulingofthe
networkisthenlefttothesimulator.
SystemCtimedfun tionalmodelhasthesame
omposi-tionofblo k.Weassumethatalltheblo ksareexe utedon
thesamepro essor(ARMpro essor)thatmeansthanwhile
oneoftheblo ksisexe utedothersarewaitingforittobe
nished. Exe utionofea hpro esstakesaparti ulartime
whi hwe addtothe SystemCsimulation timewhile
pro- essingea hoftheblo ksandweassumethatthistimeis
alreadyknownfromrunningthefun tionalityonan
emula-torofexploredpro essor. Thisway,thebeginningandthe
1
MAC-dtypi allyin ludesalsoa ipheringmodule,butsin e
en ryp-tion isalreadydone attheRLClayer, thismoduleneednotbe
Thismodel anbeextendedbyin ludingmoreentities
oftheRLC andtheMACsublayerstoobtainmore
a u-rateresults.Ourfutureworkin ludesalsoextensionstothe
networklayerandhigherlevelappli ationsu hasMPEG
de odingandtheUserInterfa e(UI).
3.2. Ar hite ture Model
Todesignanoptimalar hite tureweneedtode idewhat
elements should be available on the platform to a hieve
the best trade-offbetween the metri s ofinterest. These
elements in ludegeneral-purposepro essors, Digital
Sig-nalPro essors(DSP),FieldProgrammingGateArrays
(FP-GAs),ortheirmix. Thisstepalsoin ludesidentifyingthe
kindofpro essorstobe used(andtheirperforman e),as
wellastheirnumberandgeneralinter onne tiontopology.
Tobeginwith,wesurveyedseveralar hite turesproposed
by the industry forSDR, and nally de ided totakethe
SmallFormFa torSDR(SFFSDR)DevelopmentPlatform
fromLyrte h[16℄asourbaselinemodel. We anthenuse
thear hite tureofthisplatformasastartingpointand
mod-ifyitforthedesignspa eexplorationofanSDR.
TheSFFSDRplatform onsistsofthreeseparate
mod-ules,theRadioFrequen y(RF),DataConversionand
Base-bandPro essingmodules, ombinedtogether,andisshown
inFigure4. Ea hofthesemodules anberepla edin
or-
Figure4.Blo kdiagramoftheSFFSDR
der tosatisfy therequirementsofthe target produ t. The
BasebandPro essingmoduleworksinthedigitaldomain,
and is the main fo us of our studies. This module
em-ploysaTMS320DM6446system-on- hip(SoC)fromTexas
Instruments and aVirtex-4 SX35 FPGA from Xilinx for
modulation. TheSoC onsistsofoneC64x+ TM
DSPand
oneARM926EJ-S
TM
general-purposepro essor.TheDSP
is typi ally used for pro essing the baseband, while the
general-purposepro essorisreservedfortheupperlayers
ofthe ommuni ationproto olsandotherhigherlevel
ap-pli ations.
Inthispaper,werestri tourattentiontotheARM
fam-ilyofpro essors,sin ethefun tionalitythatwearetesting
is limited toasubset ofthe UMTSDLL layer. We
on-siderlessperformingpro essorsthantheoneavailableon
theSFFSDRplatform(whi hweonlytakeasatemplate),
be auseofthelimitationsimposedbythe prolerthatwe
man eanalysistohigherperforman epro essors(su has
theoneusedontheSFFSDR),andintegratingthebaseband
pro essing, urrentlyunderdevelopment,whi hweassume
isrealizedpartlyontheFPGA,andpartlyontheDSP.
4.SimulationsandResults
Thisse tion is devotedtopresentingthe results ofthe
performan eanalysisfortheRLCandtheMACsublayers.
We usethree kinds ofmetri s to hara terizethe
perfor-man eofdifferentar hite tures,todeterminethe
distribu-tionofresour eswithintheproto olfun tion,andto
mea-suretheef ien yoftheperforman eanalysisitself.
Ourrstresults,depi tedinFigure5,showthe
per ent-age ofutilization (load)ofthe general-purposepro essor
underdifferenttransferrates,andfordifferentar hite tures.
WehaveanalyzedvedifferentARMmi ro ontrollersthat
LPC2119
LPC2194
STR912FW44 STR750FV2
STR736FV1
0
10
20
30
40
50
36 MHz
25 MHz
60 MHz
60 MHz
12.2 kbps
28.8 kbps
57.6 kbps
384 kbps
%
o
f
u
s
e
d
r
e
s
o
u
rc
e
s
60 MHz
Figure5.Ar hite tureperforman es
in lude theSTR912FW44, STR750FV2andSTR736FV1
fromSTMi roele troni s,andtheLPC2119andLPC2194
from NXP. These have been analyzed at their maximum
lo k frequen y (shown in Figure 5 under the name of
the ar hite ture),withthe ex eptionoftheSTR912FW44
andthe STR750FV2. The rst(STR912FW44)was
sim-ulatedat60MHz,insteadof96MHz,foran easierdire t
omparison with the NXP mi ro ontrollers. The se ond
(STR750FV2)wassimulatedat25MHz,insteadofits
max-imum60MHz,toobtainroughlythesameperforman e
re-sultsastheSTR736FV1,andthereforeshowthesavingsin
lo kfrequen y.
For ea h mi ro ontroller, we have omputed the
load for the four most ommon transmission data rates,
i.e., 12.2kbps for voi e ommuni ation, 28.8kbps and
57.6kbpsusedbymodemsandfaxes,and384kbpsforhigh
speeddatatransmission.Forea hdatarateweuseaxed,
modemsandfaxes,andof336bitsforhighspeeddata
trans-mission[1℄. Ea hpa ket hasa16-bit overheadfor RLC
andMACheaders.Inadditiontothat,informationdata
de-liveredbytheDedi atedTransportChannels(DTCHs)are
a ompaniedby ontrolpa ketsdeliveredthroughthe
Ded-i atedControlChannels(DCCHs). Inoursimulations,we
haveassumedthatea hDTCHpa ketisa ompanied by
oneDCCHpa ket.Forabitrateofxkbps,theloadis
om-putedastheratiobetweenthea tualtimeittakestotransmit
xbits,andonese ond,themaximumtimeallowedforthe
transmission.Formally,wehave
L= (T dp +T p )x=8 P dp +P p 1 1s 100%; whereT dp andT p
isthetimetotransmitadataanda
on-trolpa ket,andP dp
andP
p
isthe size,inbytes, ofdata
and ontrolpa kets,respe tively.Forthe ontrolpa ketwe
haveassumeda onstantsizeof100bits.
The resultsofthe analysispresentedinFigure 5show
onsiderablevariability,botha rossar hite tures, and,as
expe ted,fordifferentdatarates. Thisanalysisgivesusa
measureofthe residual omputingpoweravailabletothe
rest of the proto ol, to potential other proto ols running
on urrently,andtohigherlevelappli ations,whi hisan
essentialinformationforthe orre tar hite ture hoi eand
sizingofthe system. Inthe aseoftheSTR736FV1and
STR750FV2, theloadfor384kbpsex eeds100%,andis
thereforenotshownonthegure.
A se ond lassof resultsis devotedtothe analysis of
theresour esrequiredbyea hofthefun tionsofthemodel
showninFigure6.TheseresultsarefortheSTR912FW44
Cip
her
ing
RL
Ch
ead
erA
dd
C_
T_M
UX
Se
gm
en
tat
ion
Tr_
bu
ffe
r
TrF
orm
atS
el
TrC
hS
wit
ch
0
10
20
30
40
50
60
70
80
%
o
f
u
s
e
d
r
e
s
o
u
rc
e
s
b
y
e
a
c
h
f
u
n
c
ti
o
n
Figure6.Resour edistributionbyfun tion
ARM9 mi ro ontrollerfrom STMi roele troni s and the
pa ketsizeof70bytes,whi hwehavetakenas
representa-tive,sin etheanalysisfortheotherar hite turesandpa ket
sizesarequalitativelyandquantitativelysimilar. The
fun -tionsonFigure6aresortedbytheamountofresour esthat
fun tion isingeneral themost resour e onsuming
fun -tion. Thiskindofresult isveryusefulfortakingthe
pre-liminaryde ision about resour edistributionbetweenthe
fun tions.
Ourlastgroupofresultsis on ernedwithameasureof
theef ien yofthe performan eanalysis. InTable1,we
show,forea har hite ture,thetimeinse ondsrequiredto
simulatethe transmissionof7,000pa kets, withapa ket
size of70 bytes, forboththe Keil proler andSystemC.
ThesimulationswereperformedonaPentium R
M
pro es-sor runningat1.70GHz,with512MBofRAM.For
Sys-temC,we haveusedthe referen eimplementationversion
2.1.v1,availableattheSystemCwebsite[22℄.
Ar hite ture Keil SystemC Speed-up
LPC2119 28.1 4.2 6.7 LPC2194 25.8 4.2 6.1 STR912FW44 25.5 4.2 6.1 STR750FV2 26.6 4.2 6.3 STR736FV1 25.9 4.2 6.2 Average 26.4 4.2 6.3
Table1.Ef ien yofperforman eanalysis
Theperforman eoftheSystemCsimulationis
indepen-dentfromthear hite ture,sin eitisreferredtothesame
model. In ontrast, Keil showsvariability depending on
the mi ro ontroller. The last olumn ofthe table shows
thespeed-upobtainedbyusingthemoreabstra tSystemC
models. Onaverage,theSystemCsimulationismorethan
6timesfasterthantheproler,whi hjustiestheuseofthe
prolerfordatagathering,andtheuseoftheabstra t
simu-latorforperforman eanalysis.Thismethodologybe omes
evenmore ompellingas the omplexityofthe model
in- reases, and severalproto ols are run on urrently,sin e
thesimulationtimewill orrespondiblyin rease. The
per-forman eoftheSystemCsimulation anpotentiallybe
in- reasedbyusinganoptimizedsimulatorratherthanthe
ref-eren eimplementation.
5.Con lusionsandFutureWork
Wehavepresenteda asestudyofadesignspa e
explo-rationproblemforaSoftwareDenedRadio.Wehave
se-le tedasubsetoftheDataLinklayeroftheUMTS
ommu-ni ationstandard,andevaluateditsperforman eonseveral
ar hite tures,andfordifferentdataratesandpa ketsizes.
Our methodologyuses separatedfun tional and
ar hite -turalmodels. Thefun tionalmodelsrunatahighlevelof
abstra tion,and anbeusedforfun tionalveri ationand
annota-forman edata,andusesaprolertosimulatetheexa t
be-haviorofthear hite ture.Theanalysisshows onsiderable
variabilityinperforman e,bothas afun tionof
ar hite -ture, andasafun tionofdatarate. Thisjusties the use
ofthePBDapproa htodesignthiskindofsystems,whi h
mustbenetunedtobeabletosupportdifferentstandards.
Our future work is fo used towards on retizing the
PBDapproa hintoaspe ializedmethodologyforthe
de-signspa e explorationof ommuni ationhardware
ar hi-te tures. Thisin ludesautomatingthepro essof
annota-tionthroughtheuseofdedi ated omponents,abletoalso
determinethe shareofCPU inthe aseofmulti-threaded
exe ution. Inaddition, we will developintera tion
om-ponentsforthe estimation of ommuni ationoverheadin
multi- omponentar hite tures,whi hare ommoninSDR
toa hievethedesiredperforman e. Ourfutureworkalso
in ludestheextensionofthefun tionalmodeltointegrate
thebasebandpro essing(ontheDSP),higherlevelsofthe
proto ol, and otherproto ols ofinterest su has WiMax,
WiFiandGSM.
6.A knowledgments
The authors wouldalso like tothank Fernando
Piane-gianiandFabrizioStefaniforstimulating dis ussionsand
suggestions. Thiswork was supportedinpart by agrant
fromArsLogi a,s.r.l.
Referen es
[1℄ 3 rd
GenerationPartnershipProje t. Channel ondingand
multiplexingexamples. Te hni alSpe i ationTS25.944,
3GPP,June2001.
[2℄ 3 rd
GenerationPartnershipProje t. Generaluniversal
mo-bile tele ommuni ations system (UMTS)ar hite ture
(re-lease6).Te hni alSpe i ationTS23.101,3GPP,
De em-ber2004.
[3℄ 3 rd
GenerationPartnershipProje t.Radiointerfa eproto ol
ar hite ture(release7).Te hni alSpe i ationTS25.301,
3GPP,Mar h2006.
[4℄ F. Agnelli, G. Albasini, I. Bietti, A. Gnudi, A. La aita,
D.Manstretta,R.Rovatti,E.Sa hi,P.Savazzi,F.Svelto,
E. Temporiti, S.Vitali, andR. Castello. Wireless
multi-standardterminals: systemanalysisanddesignofa
re on-gurablerffront-end.IEEECir uitsandSystemsmagazine,
Spe ialIssueonWirelessRe ongurableTerminals,6(1):38
59,2006.
[5℄ C.Andersson. GPRSand3GWirelessAppli ations. John
Wiley&Sons,April2001.
[6℄ F.Balarin, L.Lavagno, C. Passerone,A. L.
Sangiovanni-Vin entelli, M. Sgroi, and Y. Watanabe. Modeling and
designing heterogeneous systems. In J. Cortadella and
A.Yakovlev,editors,Advan esinCon urren yandSystem
Design.Springer-Verlag,2002.
eri,L.Lavagno,A.Lodi,P.Mal ovati,andM.Toma.
Base-band analog front-end and digital ba k-end for
re ong-urablemulti-standardterminals.IEEECir uitsandSystems
magazine,Spe ialIssueonWirelessRe ongurable
Termi-nals,6(1):828,2006.
[8℄ A. Boni, F. Pianegiani, and D. Petri. Inverse modeling
withSVM-based dynami allyre ongurable systems. In
Pro eedingsoftheIEEEInstrumentationandMeasurement
Te hnologyConferen e (IMTC),pages20362040, Como,
Italy,May2004.
[9℄ A. Bonivento, L. P. Carloni, and A. L.
Sangiovanni-Vin entelli. Platformbaseddesignforwirelesssensor
net-works. MONET,11:469485,2006.
[10℄ L. P. Carloni, F. D. Bernardinis, A. L.
Sangiovanni-Vin entelli,andM.Sgroi.Theartands ien eofintegrated
systemsdesign.InPro eedingsofthe28 th
European
Solid-StateCir uits Conferen e, ESSCIRC 2002, Firenze, Italy,
September2002.
[11℄ J.Chong,A.Davare,andK.Lwin. Con urrentembedded
design formultimedia: JPEG en oding on Xilinx FPGA
asestudy. Te hni alReportUCB/EECS-2006-40,
Univer-sityofCalifornia,Berkeley,April162006.
[12℄ D.Densmore,A.Donlin,andA.L.Sangiovanni-Vin entelli.
FPGAar hite ture hara terizationforsystemlevel
perfor-man eanalysis. InPro eedings ofthe Conferen e on
De-sign,Automation and Test in Europe (DATE06),Muni h,
Germany,Mar h610,2006.
[13℄ T.Gr¨otker,S.Liao,G.Martin,andS.Swan.SystemDesign
withSystemC.KluwerA ademi Publishers,Norwell,MA,
2002.
[14℄ S.Kakita,Y.Watanabe,D.Densmore,A.Davare,andA.L.
Sangiovanni-Vin entelli. Fun tionalmodelexplorationfor
multimediaappli ationsviaalgebrai operators.In
Pro eed-ingsofthe6 th
InternationalConferen eonAppli ationof
Con urren ytoSystemDesign,Turku,Finland,June2630,
2006.
[15℄ Keil.http://www.keil. om.
[16℄ SFFSDRdevelopmentplatform. Te hni alspe i ations,
Lyrte h,February2007.
[17℄ T.Meyerowitz,R.Chen,A.L.Sangiovanni-Vin entelli,and
J.Harnish. Modelingaheterogeneous multipro essorfor
softwaredenedradio. InPresentationsoftheCHESS
re-viewmeeting,Berkeley,CA,February2006.
[18℄ T.C.MeyerowitzandA.L.Sangiovanni-Vin entelli. High
levelCPU mi ro-ar hite turemodels using Kahnpro ess
networks.InSRCTe hCON,Portland,Oregon,O tober24
252005.
[19℄ J.Mitola.Thesoftwareradioar hite ture.IEEE
Communi- ationMagazine,33(5):2638,May1995.
[20℄ A.L.Sangiovanni-Vin entelli.Deningplatform-based
de-sign.EEdesign,February2002.
[21℄ T.Shono,Y. Shirato,H.Shiba,K.Uehara, K.Araki,and
M. Umehira. IEEE 802.11 wireless LAN implemented
onsoftwaredenedradiowithhybridprogrammable
ar hi-te ture. IEEETransa tionson WirelessCommuni ations,
4(5):22992308,September2005.
[22℄ SystemC.http://www.system .org.
