Video Transmission in 3G Telephony

8/2/2019 Video Transmission in 3G Telephony

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AbstractVideotransmissionin3Gwirelessenvironments

isachallengingtaskcallingforhighcompressionefficiencyaswell as a network friendly design. Theseare themaingoals of the new ITU-TH.26L standardization effort ad-dressingconversational(i.e., videotelephony)andnon-conversational(i.e.,storage,broadcast,orstreaming)appli-

cations. The video compression performance of H.26Ls

VideoCodingLayertypicallyyieldsafactoroftwoormoreinbit-ratesavingswhencomparingagainstallpreviousin-ternationalvideocodingstandardsandthereforeprovidesasignificant improvement towards this end. The network-

friendlydesigngoaloftheH.26LprojectisaddressedviatheNetworkAdaptationLayerthatisbeingdevelopedtotrans-

portthecodedvideodataoverexistingandfuturenetworkssuchas circuit-switchedwirednetworks, IPnetworkswithRTPpacketization,and3Gwirelesssystems.Theerrorresil-

iencefeaturesandappropriatetestmodelextensionsaten-coderanddecoderareintroducedin thispaper.Addition-ally,selectedresultsshowingthepotentialsofthesefeaturesarepresented.

I. INTRODUCTION

H.26L[1]isthecurrentprojectoftheITU-TVideoCod-

ingExpertsGroup(VCEG)agroupofficiallychartered

as ITU-T Study Group 16 Question 6. Just recently, a

JointVideoTeam(JVT)wasformedconsistingofVCEG

andMPEG(ISO/IECJTC1/SC29/WG11:MovingPic-

tureExpertsGroup).ThecharteroftheJVTistofinalizetheH.26LprojectofVCEGastechnicallyalignedITU-T

RecommendationandISOStandardcalledJVTCoding.The primary goals of theJVT projectare improved

codingefficiency,improvednetworkadaptationandsim-

ple syntax specification. The syntax of JVT Coding

should permit an average reduction in bit rate by 50%

comparedtoallpreviousstandardsforasimilardegreeof

encoder optimization.Recentresultsshowthat thisper-

formanceisalmostachieved[3].ThismakesJVTCoding

anattractivecandidateforwirelessvideotransmission,as

the resourcebit-rate is extremely costly inmobileenvi-ronments.However,toallowtransmissioninmobileenvi-

ronmentsinadditiontocodingefficiency,anetworkad-aptationlayeranderrorresiliencefeaturesareveryimpor-

tant.Relatingissuesexaminedseriouslyforthefirsttime

intheH.263andMPEG-4projects[2],[4]arebeingtaken

further in JVT Coding. The scenarios emphasized are

primarilyforInternet,LAN,andthird-generationmobile

wireless channels.Finally, thedesignofJVTCoding is

strongly intended tolead toa simple and cleansolution

avoiding any excessive quantity of optional features or

profileconfigurations.

Thispaperisorganizedasfollows.Wewillbrieflyin-

troduce video transmission in 3Gnetworks andpresent

the test conditions used in the JVT Coding project to

evaluate rate-distortion performance.Thenwewill pro-

videa shortoverviewofJVTCodingwithprimaryfocus

ontheerrorresiliencefeatures.Encoderanddecodertest

modelextensionsarediscussedthatallowtheuseoftheprovidedfeaturesinanoptimizedway.Selectedsimula-

tion results arepresented and discussed and somecon-

cludingremarksareprovided.

II. VIDEOTRANSMISSIONIN3GNETWORKS

A. Overview

Videotransmissionformobileterminalswillbeamajor

applicationintheupcoming3Gsystemsandmaybeakey

factor for their success. Thedisplay of videoonmobiledevicespavestheroadtoseveralnewapplications.Three

major service categories areidentified in theJVTstan-

dardization process [5]: 1) conversational services for

video telephonyandvideo conferencing,2) liveorpre-

recordedvideostreamingservices,and3)videoinmulti-

mediamessagingservices(MMS).

In general, mobile devices are hand-held and con-strainedinprocessingpowerandstoragecapacity.There-

fore,amobilevideocodecdesignmustminimizeterminal

complexitywhileremainingconsistentwiththeefficiency

androbustnessgoalsofthedesign.Inaddition,themobileenvironmentischaracterizedbyharshtransmissioncondi-

tionsintermsoffadingandmulti-userinterference,which

resultsintime-andlocation-varyingchannelconditions.

Manyhighlysophisticatedradiolinkfeatureslikebroad-

bandaccess,diversity techniques,fastpowercontrol,in-

terleaving,forwarderrorcorrectionbyTurbocodes,etc.,

are used in 3Gsystems to reduce thechannel varianceand,therefore,thebiterrorrateandradioblocklossrate.

Entirely error-free transmission of radio blocks isa

generally unrealistic assumption although with RLCretransmission methods, delay insensitive applicationslikeMMScanbedeliverederror-freetothemobileuser.

In contrast, conversational and streaming serviceswith

real-timedelayandjitterconstraintsallowforonlyavery

limitednumberofretransmissions,ifany.Inaddition,ina

cellularmulti-userenvironmentthetransmissioncapacity

withineachcellislimited.Therefore,ifnewusersenter

JVT/H.26LVIDEOTRANSMISSIONIN3GWIRELESSENVIRONMENTS

THOMASSTOCKHAMMER,TOBIASOELBAUM

InstituteforCommunicationsEngineering(LNT)MunichUniversityofTechnology(TUM)

D-80290Munich,Germany

THOMASWIEGAND

ImageProcessingDepartmentHeinrichHertzInstitute(HHI)

D-10587Berlin,Germany


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thecell,activeusersmustshareresourceswithnewusers

andifusersexitthecell,theresourcescanbere-allocated

tothe remaining users.Thewell-designed3G airinter-

facesallowdatarateswitchinginaveryflexiblewayby

assigningappropriatescramblingorchannelcodingrates.

This results in aneedforvideocodecs tobecapableof(forexample)doublingorhalvingvideodatarateevery5-

20seconds.Hence,dueto thetime-varyingnatureofthe

mobilechannel,thevideoapplicationmustbecapableofreactingtovariablebit-rate(VBR)channelsaswellasto

residualpacketlosses.Finally,theprioritizationandqual-ityofservicedesignformobilelinksisanongoingstan-

dardizationandresearchactivity.Systemssupportingpri-

oritizedtransmissionshowimprovedperformanceifvideo

standardsallowgeneratingdatawithdifferentpriorities.

B. CommonTestConditionsfor3GMobileVideo

IntheJVTstandardizationprocesstheimportanceofmo-

bilevideotransmissionhasbeenrecognizedbyadopting

appropriatecommontestconditionsfor3Gmobiletrans-missionforcircuitswitchedconversationalservicesbased

on H.324M [6] and for packet switched conversational

andstreamingservices[7].Thesetestconditionsallowforselectingappropriatecodingfeatures,totestandevaluate

errorresiliencefeaturesandtoproducemeaningfulanchor

streams. In the following we will focus on packet-switchedapplicationsandthecorrespondingcommontest

conditions,asthisseemstobemoreimportantinnowa-

days IP-based world. Additionally, the packetization

scheme as well as the performance for H.324M based

videotransmissioniscomparabletoIP-basedschemes.

The common test conditions define video test se-

quenceswiththeappropriatetemporalandspatialresolu-tion. Additionally, a simplified offline 3GPP/3GPP2simulationsoftware[8]isavailableincombinationwith

appropriateparametersettings.Forsimulatingradiochan-

nelconditions,bit-errorpatternsareusedthatwerecap-turedindifferentrealoremulatedmobileradiochannels.

The bit-error patterns aremeasured above the physical

layerandbelowtheRLC/RLPlayer,suchthatinpractice

theyactasthephysicallayersimulation.

NALpacket

IP

Framing,ROHC

Linklayer

Physicallayer

UDP RTP NALpacket RTP/UDP/IP

RoHCPPP

frameRLP frameRLP

PhysicalframeLTU

frameRLP

PhysicalframeLTU CRCCRC

.

Figure1Packetizationthrough3GPP2protocolstack

AccordingtoFigure1thesoftwaresimulatorassumesa

JVT Network Adaptation Layer Packet (NALP) to be

encapsulated in an IP/UDP/RTP packet at the input.

NALP usually contain a single slice packet (SSP)ora

data partition. Formoredetailswe referto [11].In the

following we briefly examine the user plane protocolstackfor3GPP2CDMA-2000.The3GPPUMTSstackis

verysimilar.AfterRobustHeaderCompression(RoHC),

the IP/UDP/RTP packet is encapsulated into one

PDCP/PPPpacketthatwillbecomeanRLC-SDU.Video

packetsare in generalof varying length,soRLC-SDUs

willbeofvaryinglengthaswell.InthecasethatanRLC-

SDUislargerthananRLC-PDU,theSDUissegmentedintoseveralPDUs.The flowofvariable sizeRLC-SDUs

iscontinuoustoavoidpaddingbits.RLC-SDUswithone

ormoreRLC-PDUs thatcontainpart of theRLC-SDUhave not been received correctly are discarded. The

RLC/RLP layer can perform re-transmissions. The re-transmissionschememaybesetupwithdifferentlevels

of persistency. The common test conditions specify 12

anchors with different video sequences, radio bit error

patterns,transmissionbit-ratesandretransmissionmodes.

III. JVTCODINGSTANDARD

A. OverviewCodingAlgorithm

Although thedesignof theJVTcodec basically fol-lowsthedesignofpriorvideocodingstandardsasMPEG-

2,H.263, andMPEG-4, it containsmany new features

that enable it to achieve a significant improvement in

termsofcompressionefficiency.Wewillbrieflyhighlight

those.Formoredetailswe refer to [1] and [3]. In JVT

Coding, blocks of 4x4 samples are used for transform

coding,andthusaMB(MB)consistsof16luminanceand

4blocksforeachchrominancecomponent.Conventional

picture types knownas I-and P-pictures aresupported.

Furthermore, JVTCodingsupportsmulti-framemotion-

compensated prediction. That is, more than one prior

coded picture can be used as reference for the motion

compensation.Encoderanddecoderhavetostorealreadycoded pictures in a multi-frame buffer. A generalized

frame-buffering concepthasbeen adoptedallowingmo-

tion-compensated prediction not just from previous

frames but also from future frames.For that, a flexible

andefficientsignalingmethodhasbeenadopted.Inaddi-

tion, JVT Coding permits so-called multi-hypothesis

(MH)pictures,whichsimilartoB-Picturesallowtwopre-

dictionsignalsperblockbutreferencemorethanonepic-

ture.Therefore, thesimpleB-picture functionalityis in-

cludedwithMH-pictures.

AMBcanalwaysbecodedinoneofseveralINTRA-

modes. There are two classesof INTRAcodingmodes,

onewhichbasicallyallowstocodeflatregionswithlow

frequencycomponentsandonewhichallowstocodede-

tailsinaveryefficientwayutilizingpredictioninthespa-

tialdomain by referring neighboring samplesofalready

coded blocks. In addition to the INTRA-modes, various

efficient INTER-modesare specified in JVTCoding.In

addition to theSKIP-mode that means justcopyingthe

contentfromthesamepositionfromthepreviouspicture,


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seven motion-compensated coding modes are available

for MBs in P-pictures. Eachmotion-compensatedmode

corresponds toa specific partition of theMB intofixed

sizeblocksusedformotiondescription.Currently,blocks

withsizesof16x16,16x8,8x16,8x8,8x4,4x8,and4x4

samples aresupported by thesyntax,and thusupto16motionvectorsmaybetransmittedforaMB.

TheJVTCodingsyntaxsupportsquarter-andeighth-

sampleaccuratemotioncompensation.Themotionvector

components aredifferentiallycodedusingeithermedian

or directional prediction from neighboring blocks. The

chosen prediction depends on the block shape and the

positioninsidetheMB.JVTCodingisbasicallysimilarto

otherpriorcodingstandardsinthatitutilizestransform

codingof thepredictionerror signal.However, in JVT

Coding the transformationis applied to4x4blocksand,

insteadoftheDCT,JVTCodingusesaseparableinteger

transform with basically the same properties as a 4x4

DCT.Sincethe inversetransformisdefinedbyexactin-teger operations, inverse-transform mismatches are

avoided.AppropriatetransformsareusedtothefourDC-

coefficientsof eachchrominancecomponent(2x2 trans-

form)andtheINTRA16x16-mode(repeated4x4).

For the quantization of transform coefficients, JVT

Coding uses scalarquantization. The quantizersarear-

rangedinawaythatthereisanincreaseofapproximately

12.5%fromonequantizationparameter(QP)tothenext.

Thequantizedtransformcoefficientsarescannedinazig-

zag fashion and converted into codingsymbolsbyrun-

lengthcoding(RLC).AllsyntaxelementsofaMBinclud-

ingthecodingsymbolsobtainedafterRLCareconveyed

byentropycodingmethods.

JVTCodingsupports twomethodofentropycoding.

The first one called Universal VariableLengthCoding

(UVLC) uses one single infinite-extend codeword set.

InsteadofdesigningadifferentVLCtableforeachsyntax

element, onlythemapping to thesingleUVLC tableis

customizedaccordingtothedatastatistics.Theefficiency

ofentropycodingisimprovedifContext-AdaptiveBinary

ArithmeticCoding(CABAC)isusedthatallowstheas-

signmentofnon-integernumbersof bits toeachsymbol

ofanalphabet.Additionally,theusageofadaptivecodes

permits theadjustmenttonon-stationarysymbolstatistic

andcontextmodelingallowsforexploitingstatisticalde-pendencies between symbols. For removing block-edge

artifacts, the JVT Codingdesign includes a deblocking

filter.TheJVTCodingblockedgefilterisappliedinside

themotionpredictionloop.Thefilteringstrengthisadap-

tivelycontrolledbythevaluesofseveralsyntaxelements.

B. ErrorResilienceFeatures

Forenhancederrorresilience,thetestmodelallowsinter-

ruptingspatial,temporalandsyntacticalpredictivecoding

onaMBbasis.Theprinciplesofeachoftheadoptedfea-

turesarereasonablywellknownfrompriorvideocoding

work, particularly from the H.263+, H.263++, andMPEG-4projects.However,thesefeaturesaretakenabit

furtherintheJVTCodingdesign.

Temporal resynchronization within a JVTvideobit-

streamcanbeaccomplishedbyuseofintrapicturerefresh

(stopping allprediction of data fromone picture toan-

other),whereasspatialresynchronizationissupportedbyslicestructuredcoding(providingspatially-distinctresyn-

chronizationpointswithinthevideodataforasinglepic-

ture).Inaddition,theusageofintraMBrefreshandmul-

tiple reference frames allows the encoder to introducewell-selectedintraupdatesreferenceframeselection.Ad-

ditionally,thepacketlengthcanbeadaptedbyappropriate

groupingofMBs.Fastrateadaptationcanbeaccomplishedbyswitching

thequantizationfidelityonaMBbasissuchthatareal-

time encoder can react immediately tovaryingbit rate.

For streaming of pre-coded sequences, well-designed

buffering can deal reasonablywellwith varyingbit-rateconditions.Still, bufferoverflows inVBRenvironments

may not be completely avoidable. For this reason JVT

Codingdefinesnewpicturetypes,SP-frame[10]andSI-

frames, toallowswitchingbetweenversionsofa streamwithoutintroducingtheefficiencylossassociatedwithan

I-frame. Additionally, a syntax-based data partitioning

schemewithatmost3partitionsperslicewasintroduced

in[11]allowinglessimportantinformationtobedropped

intheeventofabufferoverflowortobeusedinconjunc-tionwithnetworkprioritizationorunequalerrorprotec-

tiontosupportqualityofserviceconceptsinnetworks.

IV. TESTMODELEXTENSIONS

A. Overview

In theprevious section, thecoding and error resilience

toolsofJVTCodinghavebeenpresented.Ingeneral,thestandarddefinesonlytheappropriatesyntaxforeachin-

cluded feature. The selection ofappropriate options for

each application isupto theimplementer.However,in

ordertojudgeadoptedandproposednormativefeatures,

appropriate non-normative mechanisms in the encoderanddecodertestmodelarealsoincluded.TheJVTCod-

ingprojecthascarefullyadopteddifferentnon-normative

features in the testmodel software to improveperform-

anceintermsofcodingefficiencyanderrorresilience.

Theapproachofrate-distortionoptimizedencodingis

used in theencoder testmodelto selectthe appropriate

codingoptions.Thismethodiswellknowntoimprovethecodingefficiencysignificantlyincaseofencodersprovid-


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ing many coding options [12]. In JVT Coding, rate-

distortion optimized coding is used for selecting MB

modes,referenceframesandmotionvectors.Inaddition,

ifwehaveknowledgeofcertainchannelcharacteristics,

e.g.,apacketlossorbiterrorratemodel,thiscanalsobe

usedintheencoderaswillbediscussedinmoredetailsinthesubsectionBandC.Althoughthesemethodsingen-

eral require some knowledge on the expected channel

conditions,theyarerobustinawaythatonlyaroughes-timateonthechannelcharacteristicsissufficient.

Moreover,thedecoderincludesinadditiontoasimplepreviousframeerrorconcealment(EC)andanadvanced

ECschemewhichusescorrectlyreceivedinformationto

estimatethelostinformationinarecursiveway[13].For

I-pictures a weighted pixel value averaging is applied

whereas forP-picturesboundary-matching-basedmotion

vectorrecoveryisutilized.

B. OptimizedMBModeandReferenceFrameSelection

ThenumberofintracodedMBsperpicturecanbedeter-minedattheencoderbyvariousmeans.Fortransmission

in error-free environments, typically the algorithm for

rate-distortion optimization might sometimes select anintra MB due tocompressionefficiency. In error-prone

environments,itmaybedesirabletoincreasethenumber

ofintraMBstolimitthetemporalpropagationofanyer-roroccurred.Thecurrentencodertestmodelonlyallows

updating an entire row of MBs periodically. However,

intra codedMBs in generalshowbadcoding efficiency

andtheiruseshouldthereforebelimited.

Error-pronetransmissionshowsrandomlossesmaking

thedecodingresultarandomvariableaswell.Therefore,

theencodingdecisionsareoptimizedwithregardstotheexpectedvaluesofthedecodingrandomvariable.Hence,a rate-constrainedMBmode and referenceframe selec-

tionbasedon theexpectedmeansquareerrordistortion

andtherateisutilized.ThisschemeselectsintraMBup-dates very carefully by trading of distortion versus rate

givenaprobabilityofchannelerrors.Theexpecteddecod-

ingdistortionisestimatedbycomputingthesampleaver-

ageofthedecodingrandomvariableviarunning Nchan-

nel-decoderpairsintheencoderinparalleltosimulatethe

statistics of the channel and its impacton thedecoded

video.Thisprovidesan estimateoftheexpecteddecoder

distortionintheencoder.Inourimplementation,thesta-

tisticalprocessofloosingapacketismodeledindepend-

entlyforeachoftheNdecoders.Thepacketlossprocessforeachdecoderisalsoassumedtobei.i.d.,andtheslicelossprobabilitypisassumedtobeknownattheencoder.

Tobemoreprecise, let usdefine thesetof possible

combinationsofMBmodesand referenceframesasSMB

includingtheoptiontocodeaMBinINTRA,i.e.without

temporalerrorpropagation,orinINTER,i.e.,withtempo-

ralerrorpropagationbuthighercodingefficiency.Then,

foreachMBtheMBmodemisselectedaccordingto

!

" #

$

withDmbeingthedistortioninthecurrentMBwhense-

lectingMBmodemandRmbeingthecorrespondingrate,i.e.thenumberofbits.ThedistortionDmiscomputedas

% & '

( (

0

1 2

3

4 5 5 6

4

6 5

8 9 9

@ A

B C

D D

withfibeingtheoriginalpixelvalueatposition iwithin

theMBandE E

G H I Q

S

beingthereconstructedpixelvalueat

positioniforcodingMBmodeminthesimulatedchan-

nel-decoder pair n. Thedecoder in theencoder applies

simplepreviousframeECandthereforeservesasanup-

per bound on the expectedMBdistortion.Accordingto

[14]theparametershoulddependonthequantization

parameterqas=5exp(0.1q)(q+5)/(34-q).Obviouslyfor

largeN theencoderhas a good estimateof theaveragedecoder distortion.However,with increasingN alinear

increaseofstorageandcomputationalcomplexityinthe

encoderisobvious.Therefore,thismethodmightnotbe

practical in real-time encodingprocesses. Less complex

algorithms with similar performance are known [15].

However, the applications of these algorithms are not

straightforward due to sub-pelmotion estimation, loop-

filtering and intraMBprediction inJVTCoding.Addi-

tionally, for thepurposeof standardization, this simple

solutionprovidesflexibilityasnewfeaturesinthedecoder

arejustcopiestotheencoder.Inaddition,anyothererror

resiliencetoolscanbetestedandanestimationoftheex-

pecteddecoderdistortioncanbeobtainedintheencodereasily.

C. PacketLengthSelection

Anothercriticalparameteristheselectionofthepacket

length. the JVT Coding standard allows to group any

numberofMBsintoonesliceorNALpacket.Nospatial

predictionoversliceboundariesisallowed.Therefore,a

newsliceallowsresynchronizationwithinoneframe.Inmobileenvironments,theprobabilitythatshorterpackets

arehitby abit error istypically smaller thanforlarger

packets.Inaddition,shorterpacketsprovidemoreresyn-

chronizationpossibilitiesand, therefore,arefavorablein

termsoferrorresilience.Butsmallerpacketsalsoresultin

efficiency loss due to the restrictedspatialpredictioninsmallerslicesandtheintroducedsliceheaderandnetwork

overheadforeachpacketandduetotheinterruptionofthe

prediction at the source coder at the packet boundary.

Thoughtheheadersizescouldbereducedbytheintroduc-

tionof parameter sets [11]and RoHC, they arestillnotnegligible.Hence,acarefulselectionofthepacketlength

adaptedtochannelandvideoconditionsisvital.


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TheJVTCodingtestmodelencoderallowschoosing

theslicesizeindifferentmodes.ThenumberofMBsin

eachslicecanbespecified.Therefore,thepacketsusually

differinlength.Especiallypacketscontainingintrainfor-

mationor highmotionareasresult in bigger size,and,

therefore,aremoresusceptibletobiterrors.Therefore,ina different mode themaximum numberof bytes in one

packet canbe specified. This assures thatpackets have

similarlengthand,therefore,arealmostequallysuscepti-ble tobit errorsand resultinglosses.Thepacket length

canbeadaptedsothatthelossprobabilityisbelowacer-tainthresholdifthechannelconditionsareknownatthe

encoder.Obviously,anindividualpacketlengthselection

adaptedtovideocontentanderrorcharacteristicssimilar

tothepreviouslypresentedadaptiveintraupdatecanhelp

totradeoffoverheadversuscompressionefficiencyinan

optimizedway.Thistopicispartofongoingresearch.

V. SELECTEDSIMULATIONRESULTS

A. SimulationParameters

Wewillbrieflypresentsimulationsforselectedparame-

ters.AnIPbasedconversationalserviceatamobilespeed

of3km/hat64kbit/sissimulated.Weassumeinteractiveserviceswithasmallend-to-enddelayandtherefore,no

radioretransmissionsareapplied.Thebearerbiterrorrate

is at about510-4. TheQCIF videotest sequences Fore-

man (10s, 300 frames) and Hall Monitor (10s, 300

frames)aretransmittedataframerateof7.5fpsand15

fps, respectively [7]. Since no rate control is currently

present in the JVT video encoder, a fixed quantization

parameter is selected so that the total video bit-rate

includingthepacketizationoverheaddoesnotexceed64kbit/s.Foreachsequence,50decodingrunsareperformed

where each run starts at a different predefined starting

positionin thebiterror file.Thepacketlossprobability

obviouslydependsonthepacketlength.Anevaluationofthebiterrorpatternfileshowsforexamplethattheloss

probabilityofa packet of length200bytesis about2%,

whereas for a packet of length 500bytes itincreasesto

about5%.

B. SimulationResults

Different experiments have been carried out. We only

reportonaselectedsubsetandshowthebenefitsofdif-

ferent JVTCoding errorresilientmodesand testmodel

extensions. The entropy coding method applied in allcasesisthesimplerUVLC.NotethatapplyingCABACwould result in even better results for all experiments.Extensivesimulation resultsaswell asselected decodedvideosequencesareavailable

1.Forbothvideosequences,

wereportforeachinvestigatedcasetheluminancePSNR

averagedoverall framesand all runs (av)foradvanced

1Availableathttp://www.ei.tum.de/~stockhammer

EC(AEC).AdditionallyforForeman,theaverageoverall

framesfortheworst-case(wc)runarereported.Further-

more,resultsforpreviousframeEC(PFEC)aregivenas

well,sinceforthissequence,the twoconcealmentmeth-

odsprovidequitedifferentresults,whiletheconcealment

itselfdependsonthenumberofMBswithinaslice.Theresults for different encoder and decoder settings are

showninTable1.

Table1ResultsinPSNR(indB)forForeman(FM)and

HallMonitor(HM)fordifferentencoder/decodersettings

Exp QP PFECFM AECFM HM

FM HM av

PSNR

wc

PSNR

av

PSNR

wc

PSNR

av

PSNR

1 17 13 26.441 15.607 26.441 15.607 32.683

2 19 19 29.380 24.781 29.380 24.781 34.110

3 23 16 30.094 28.637 30.094 28.637 35.398

4 20 18 29.641 22.436 30.519 24.025 33.158

5 22 25 30.436 28.911 30.701 29.463 30.0366 23 19 30.131 26.168 30.377 28.677 33.887

7 21 16 30.974 29.215 31.169 30.046 35.628

8 22 16 30.719 29.152 30.762 29.890 35.625

InExperiments1,2and3anentireframeistransmit-

ted in onepacket. Therefore,bothECschemesperform

identically as theAEConlyexploitsspatial correlationswithin one frame. In experiment 1 no error resilience

toolshavebeenapplied.TheresultsfortheaveragePSNR

areacceptableasfortheForemansequencetheR-Dopti-

mized mode selection selects the intraMB mode quite

frequently.However,theworst-caseperformanceisvery

poor indicating that without error resilience encoding

methods,averybaddecodingqualitymightoccurocca-sionally.Inexperiment2,theintroductionofregularintraupdates (periodically 1 row of MBs is updated every

frame) providesa significant improvement. Even better

results canbeobtainedby adaptiveintraupdatesas ap-pliedinexperiment3.Especiallytheworst-casePSNRis

increasedsignificantlyand,therefore,thevarianceofthe

receiverquality is reduced.A frame loss rateof 10%is

assumedcausingalargenumberintraMBupdates.Please

notethatalsothequantizationparameterisincreaseddue

tothelowercodingefficiencyofINTRAcoding.Itcanbe

seenthattheadaptivecodingschemealsoadaptstheQP

appropriately.FortheForemansequencemanymoreintra

MBsareusedfortheadaptiveintraupdatecomparedto

theregularintraupdate.TheQPmatchingtherequiredbitrateismuchhigherforexperiment3comparedtoexperi-ment 2.For theHallMonitor sequence this isdifferent

thoughthechannelstatisticsareequivalent.Therefore,it

is obvious that the redundancy necessary to copewith

packetlossisadaptednotonlytothechannelstatisticsbut

alsotothevideocontent.Thisshowsthevalidityandim-

portanceoftherate-distortionapproach.


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Inexperiments4-8sliceshavebeenintroducedtoob-

tain shorter packets. In these experiments,typically the

AEC provides gains as spatial correlations within one

frame canbeexploitedat thedecoder.Experiment4is

equivalenttoexperiment1exceptthateachrowofMBsis

transmittedinaseparateslice.Thisallowsfrequentresyn-chronization,butalso reducescodingefficiency.These-

lectedQPinthiscaseis20fortheForemansequence,18

for theHall Monitor sequence. The performance com-paredtoexperiment1isslightlyincreased,especiallyfor

theAEC. Introducing regular intra updates as done inexperiment5doesimprovethequalitysignificantlyfor,

butnot for theHallMonitorsequence.FortheForeman

sequencetheamountofintraupdatesforexperiment4fits

quitewellthevideocontentandchannelstatistics.

Inexperiments6,7and8thecombinationofadaptive

intra updatesand the slicefeature is investigated. Inall

cases it canbe seen thattheAEC canimprove thede-

coded quality, especially in theworst scenarios. In ex-

periment 6 the slice loss probability at the encoder is

assumedtobe3%andtheslicelengthwasthesameasinexperiment4and5,i.e.onerowofMBsinoneslice.Thegains in this case are significant compared to allothernon-adaptivecases,forPFECaswellasforAEC.Againit

canbeobservedthatfortheForemansequencethesetting

in experiment5 iswellmatchedand theadaptive intra

updateisslightlyworseforexperiment6.Thisis,asthe

channel statistics cannot be modeled accurately in the

encoderwithanindependentpacketlossmodel.However,

fortheHallMonitorsequencethisexperimentshowssig-

nificant gainscomparedto experiment5. Therefore,the

robustness of adaptive intra updates is obvious. In ex-

periment7,theslicelengthissetto33MBssowehave3packetspervideoframe.Alossprobabilityof5%isas-sumedattheencoder.Theresultsofthisexperimentout-

perform all other experiments as thetradeoff of packet

overhead,intraupdatesandlossrateiswellmatched.The

AECimprovestheresultsslightlyasspatialcorrelations

canbeexploitedifnotallpacketsofoneframearelost.

Finally,inexperiment8,themaximumpacketlength

islimitedto256bytesandthelossprobabilityassumedat

theencoderis5%.Theperformanceisverysimilartothe

resultsinexperiment7.However,ingeneraltheapproachlimitingthepacketlengthratherfixingthenumberofMB

canprovidebetterresult.

VI. CONCLUSIONSANDOUTLOOK

The JVT Codingprojectpromises somesignificant ad-

vances in the state-of-the-artof standardizedvideocod-

ing,includingkeyaspectsdesignedwithmobileapplica-tionsin mind. In addition toexcellent codingefficiency

with halving thebit-ratecompared to all existing stan-

dards, the JVT Coding project also takes into account

networkadaptationintheinherentdesign.Thisincludes

the definitionof appropriatemobile testconditions, the

integrationofnetworkrelatedanderror-resilientfeatures

inthestandardand,finally,theextensionofthetestmodel

software tofullyexploit theintegratedfeatures.This al-

lowstoprovideappropriatejudgmentofadoptedandpro-

posedfeatures andto finally cometoa standard,whichwill help toimprovethe quality of lowbit-ratevideoin

3Gmobileenvironmentssignificantly.Furtherworkwill

beconductedwithintheJVTtoimprovecodingefficiencyas well as network and application friendliness and to

provideastandardsuitablefordifferentapplicationsandnetworkswithspecialfocusonmobilevideoapplications.

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Documents

Video Transmission in 3G Telephony