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Turbo Codes
Azmat Ali Pasha
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Goals of PresentationWhy Coding, Error Correction, etc?Basic terms and concepts
ethods of handling the noiseissues
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Error Control Coding!Channel
CodingWhat can you do in situations"here data is transmitted o#er anoisy channel?Adding redundancy to information
Chec$ codeCorrect Errors
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Transmission%& 'ata is digitally recorded and
compressed(& 'ata is encoded by error control
coding)& 'ata is modulated from digital
data to an analog signal
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*eception%& Analog signal is recei#ed and
demodulated bac$ to a digital signal(& 'ata is processed in the Error
Control 'ecoder*edundancy is used to chec$ for errors
and correct them)& 'ata is uncompressed and
presented
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Transmission Process "ith
CodingApplication +ayer
'ata Compression
Channel Coding
odulation
re-uency .p/con#ersionPo"er Ampli0cation
Application +ayer
'ata 'ecompression
Channel'ecoding
'emodulation
re-uency 'o"n/con#ersion
*ecei#er
Con#olutionalor
Turbo coding
1iterbior
Turbo decoding
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2ensiti#ity to ErrorMedia Sensitivity to Error
.ncompressed1oice +o" 2ensiti#ity
.ncompressed1ideo +o" 2ensiti#ity
Compressed 1oice 3igh 2ensiti#ityCompressed 1ideo 3igh 2ensiti#ity
'ata 3igh 2ensiti#ity
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*epetition Code2imple *epetition Code
4nformation 2e-uence 56%66%%7Code"ord 566 %% 66 66 %% %%7Code/rate 8 9
Problems "ith *epetitionBand"idth 4ncrease'ecrease the information rate
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Channel CodingWhen :;T to channel code bits are called parity
bitsParity bits used for error chec$ingand correcting
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Bloc$ Code =(' apping> higher minimum "eight
of code, higher theminimum "eightbet"een #alid code"ords higher "eight, better
decoder performance
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Con#olutional CodesContinuous or 2treamingcoding
1iterbi and 2oft ;utput 1iterbiare the most common
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Turbo Codesi@ bet"een Con#olutional and
Bloc$ codes*e-uire a Bloc$ code3;WE1E*, they use shift registersli$e Con#olutional Codes
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Turbo Codes =contd&>ost common is the
PCCC =ParallelConcatenatedCon#olutional Codes>Produce high "eightcode "ords4nterlea#er shu es
the input se-uence,u$, in such a "aythat it produces ahigh "eight
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Turbo Code 'ecoder4t re-uires a soft output decoder2oft/output
Assign a probability to decodedinformation =eg& % "ith a 6li$elihood>
;utperform hard decision algorithmsAP = a@imum A Posteriori>
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4terati#e 'ecoding
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Turbo 'ecodingCycle "ill continue until certainconditions are met
The decoder circulates estimatesof the sent data li$e a turbo enginecirculates air;nce the decoder is ready, thehard decision is made
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Error Corrections ;ld and:e"
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.sesCell Phone2atellite Communication'ial/up Communication* Communication =Auto4'? Wi i?>
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Duestions, Clari0cations, and
Comments Turbo Coding ethod?Business 4mplications?
*educed Po"er *e-uirements3igher Band"idth =lo"er redundancy>