On the Design of Analog VLSI Iterative Decoders

217 Pages·2000·1.91 MB·English

by  Felix Lustenberger

Series in Diss.ETHNo13879
Signal and
Information
Processing
Volume 2
On the Design of
Analog VLSI
Iterative Decoders
Adissertationsubmittedtothe
SwissFederalInstituteofTechnology,Zürich
forthedegreeof
DoctorofTechnicalSciences
presentedby
Felix Lustenberger
Ing.enMicrotechniquedipl.EPFL
bornonMay31,1969
citizenofKriens(LU)andHonau(LU)
acceptedontherecommendationof
Prof.Dr.GeorgeS.Moschytz,examiner
Hartung
Prof.Dr.Hans-AndreaLoeliger,co-examiner
Prof.Dr.DavidA.Johns,co-examiner
Gorre
Konstanz November2000

Series in Diss.ETHNo13879
Signal and
Information
Processing
Volume 2
On the Design of
Analog VLSI
Iterative Decoders
Adissertationsubmittedtothe
SwissFederalInstituteofTechnology,Zürich
forthedegreeof
DoctorofTechnicalSciences
presentedby
Felix Lustenberger
Ing.enMicrotechniquedipl.EPFL
bornonMay31,1969
citizenofKriens(LU)andHonau(LU)
acceptedontherecommendationof
Prof.Dr.GeorgeS.Moschytz,examiner
Hartung
Prof.Dr.Hans-AndreaLoeliger,co-examiner
Prof.Dr.DavidA.Johns,co-examiner
Gorre
Konstanz Hartung-GorreVerlag,Konstanz,November2000

FürRita,SimonundDavid
ii
Acknowledgements
First of all I would like to thank my doctoral father Prof. Dr.
GeorgeS.Moschytzforhisconfidenceinmeandmyworkby
givingmealargescientificfreedomandforalwayshavingthe
door of his office open in case of doubts and setbacks. I very
much admire his human kindness to create a fruitful working
environmentwithintheSignalandInformationProcessingLab-
oratory.
IamdeeplyindebtedtomymentorandfriendProf.Dr.Hans-
AndreaLoeligerwhosettheinitialsparktothisfascinatingre-
search project. With his never ending enthusiasm he led me
safely through all the periods of frustration and exhaustment
whicharecommontoambitiousresearchprojects. Iverymuch
appreciatedthelongtechnicalandsometimesalsophilosphical
discussionsthatbroadenedmyunderstandingofcodingtheory,
datacommunicationsandsignalprocessing.
Many thanks also to Prof. Dr. David A. Johns from the Uni-
versity of Toronto, Canada, for having accepted to serve as a
competentco-examinerforthepresentdoctoraldissertation.
MyspecialthanksgotoMarkusHelfensteinandFelixTarköy
ofourresearchteam. Theirmaturity,bothtechnicallyandper-
sonally,substantiallyaddedvaluetotheresultsofthisinterdis-
ciplinaryresearch. Itwasandstillisagreatpleasureformeto
shareideasanddreamstogether.
Allthecolleaguesatthelaboratoryalwayshelpedtocreatean
intellectually very stimulating and familiar working environ-
ment. I especially wish to thank my roommates and friends
HanspeterSchmidandPascalVontobel,butalsoDieterArnold,
MarcelJoho,DanielLippuner,HeinzMathis,andStefanMoser
for the time they invested into long and profound discussions
onmanydifferenttopics. Ialsoenjoyedandlearnedalotfrom
the collaboration with Georg Fromherz and Ermanno Schinca
whosediplomaworkIsupervised.
iv
Iwouldalsosay‘thankyou’toMaxDünki,whokeepsourSun
workstation cluster constantly running and up-to-date. With
great pleasure I also acknowledge the assistance with the de-
signofprintedcircuitboardsandmeasurementsetupprovided
bythetechnicalstaffofthelaboratory,inparticular,FelixFrey,
PatrickSchweizer,andThomasSchärer.
Whenevertherewereproblemsthatwewerenotabletosolveat
thelaboratory,Ialwaysfoundkindpersonswhithinthedepart-
mentofelectricalengineeringwillingtohelpme. Thefollow-
ing persons (in alphabetical order) provided me with practical
solutionstomanyproblems: ChristophBalmer,HubertKäslin,
Ruedi Köppel, and Andreas Wieland from the Design Center;
ArminDeiss,NorbertFelber,ClemensHammerschmied,Hans-
peter Mathys, Michael Oberle, Dirk Pfaff, and Robert Reute-
mannfromtheIntegratedSystemsLaboratory(IIS);DidierCot-
tetandMichaelSchefflerfromtheElectronicsLaboratory(IfE);
Geert Bernaerts and Etienne Hirt from Art of Technology, a
spin-off of IfE. Thank you very much to all of you for your
help.
My deepest gratitude goes to my wonderful family. My wife
and best friend Rita always supported me during the time of
workingonthisdissertation,whichisjustsimplyashardasdo-
ing the research itself. For months, my little sons Simon and
Davidhadtosharetheirfatheronweekendsonly. Iwouldalso
thank my parents who taught me in my younger years the cu-
riosityandthepassiontoknowhowthingswork. Allofthem
gavemethecouragetofinishthework.
ThisworkwasfinanciallysupportedbytheSwissNationalSci-
ence Foundation under Grants 21-49619.96 and 20-55761.98,
andbyETHZurichunderGrant41-2639.5.
Abstract
The rapidly growing electronic networking of our society has
createdtheneedforahigh-speedandlow-powerdatacommu-
nications infrastructure. Both voice and data communications
have been made available for the mobile user. Additionally,
more complex coding schemes and decoding algorithms have
beenintroducedtoprotecttheuserdatafromcorruptionduring
the transmission over a communications channel. The aim of
all these new coding and decoding approaches is to meet the
theoretical channel capacity limit to make a better use of the
signalpowerandchannelbandwidth. Theiterativeprobability-
propagation-type algorithms that are used to decode state-of-
the-artcodessuchasTurbocodesandlow-densityparity-check
codes create the need for a tremendous computational power.
Often, the computational complexity can not be implemented
with a traditional digital design approach and a given power
budget.
Thisthesisdiscussestheefficientimplementionofhigh-perfor-
mance decoding algorithms in analog VLSI technology. The
buildingblocksareverysimpleanalogtranslinearcircuitsthat
implementvectormultiplierswithbasicallyonlyonetransistor
perelementoftheouterproductoftwodiscreteprobabilitydis-
tributions. The presented analog probability propagation net-
works made of these buildingblocksare a directimage of the
underlying sum-product algorithm. The design of these ana-
lognetworksfollowsaheavilysemiconductor-physics-centered
bio-inspired design approach, that exploits, rather than fights
against, the inherent nonlinear behaviour of the basic semi-
conductor devices. By using such a bio-inspired design ap-
proach, the performance of these networks in terms of speed
or power-consumptionor bothis increasedby atleast a factor
of100comparedtodigitalimplementations. Despitetheuseof
very-low-precision circuit devices, a remarkable system-level
accuracy can be achieved by such a large, highly-connected
analognetwork.
vi
The first part of the thesis discusses the background of chan-
nelcodinganddecodingandthetheoreticalfoundationsoffac-
tor graphs and the sum-product algorithm, which operates by
messagepassingonsuchgraphs. Thispartprovidesabriefin-
troduction to the information-theoretic aspects of the interdis-
ciplinaryresearcheffort.
The second part of the thesis is devoted to the actual transis-
tor level implementation of the sum-product algorithm using
verysimpleanalog-VLSIcomputationalbuildingblocks. This
partdiscussesthedesign-orientedaspectsoftheresearch,how-
ever,itreliesheavilyontheinformation-theoreticconceptsin-
troducedinthefirstpart.
Finally,wepresentpracticaldesignsanddesignstudiesofsev-
eral decoding networks. Algorithmic simulations, circuit sim-
ulations, and, whereavailable, measurementresultsoftheim-
plemented decoding networks are presented. Two of the de-
coderexampleswereactuallyfabricatedina0.8mmBiCMOS
process. Additionally,application-specificdesignproblemsare
discussed.
The thesis is finished with a summary of the achieved results
andapresentationoffutureresearchpropositionsinthefieldof
analogdecoding.
Keywords:Iterativedecoding,low-densityparity-check(LDPC)
codes,repeat-accumulate(RA)codes,trelliscodes,Turbocodes,
maximum-aposterioriprobability(MAP)decoder,maximum-
likelihood (ML) sequence detection, sum-product algorithm,
Viterbi algorithm, probability propagation, factor graphs, ana-
logVLSItechnology,bio-inspirednetworks.