TurboCodes Ali

8/9/2019 TurboCodes Ali

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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>

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