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8/2/2019 Video Transmission in 3G Telephony
1/6
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-
8/2/2019 Video Transmission in 3G Telephony
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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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