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8.1Sub-blockandSlidingWindowSegmentation
Architecture
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Figure95.MAPUnitBlockDiagram
TheTCP2canenableordisablethemaxstarfunctionbymodifyingtheE_MAX_STARbitintheTCPIC3
register.
•E_MAX_STAR=0=Enablemaxstar
•E_MAX_STAR=1=Disablemaxstar
Log-mapalgorithmisimplementedinahighlyparalleledmannerusingtheslidingwindowprinciple.The
max-log-mapalgorithmisimplementedwithaprioriscaledpriortothemapdecoder.
TheMAPunitsplitstheframe(instandalonemode)orthesub-frame(insharedprocessingmode)into
sub-blocks.
IfthesizeoftheframeisnandthenumberofstatesintheencodertrellisisS,thenbetastatesmustbe
storedinthebetamemory.Toreducetheamountofmemoryrequiredtostorethebetastates,thesliding
windowtechniqueisused.Thistechniquedividestheframesizenintoseveralsmallerpiecesofsizer
(reliabilitysection).Becausethestartingstateisunknown,aprologsectionisadded.Theinitialstateof
thestartinglocationoftheprologsectionisunknown.Afterprocessingtheprologstatesandtheconstraint
length,thevaluesofthelastprologstateshaveahighprobabilityofbeinginthesamestatesasifthe
stateswereknownfromthestart.Eachsub-blockconsistsof1or2slidingwindows.Eachslidingwindow
consistsofthreeportions:
•Alphaprologportion
•Reliabilityportion
•BetaPrologportion
TMS320C6457Turbo-DecoderCoprocessor2 60SPRUGK1–March2009
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