turbo for ocdma

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TURBO CODING FOR FFH-OCDMA

SYSTEM A SIMULATION STUDY

T N SUDHASHREE

(2009252041)

Project Guide

Mrs. G. GEETHAAssociate Professor

Department of Electronics andCommunication Engineering

Anna University, Chennai-25.


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Introduction

Optical Code Division Multiple Access(OCDMA)

The most promising multiple access

technique.

OCDMA offers several advantages:

Asynchronous access capability

User allocation flexibility

Security against unauthorized users

Anti-jamming capability


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Turbo codes

5

(a) PCCC and (b) SCCC


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Serial concatenated convolutional

code Encoder

input

SCCC

encoded

bits


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The MAP (Maximum A Posteriori)

algorithm

m)b(j ,j ,

1k

1

0j

m)b(j ,

1k

m

k

m)f(j,

1k

1

0j

mj ,

k

m

k

mi,

kk

i

kk

mi,

k vyux0.5exp

Forward state metric

Reverse state metric

Branch metric


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Graphical Representation for Calculating

and

m

k

m

k


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Log likelihood ratio

m

mf

k

m

k

k

m

m

mf

k

m

k

k

m

kdL

),0(

1

,0

),1(

1

,1

log)

(


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Decoder trellis an example


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Iterative decoding of SCCC

Inner MAP

Outer MAP


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Simulation Model

Communication System Model


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SCCC Encoder and MAP decoder

with trellis termination

without trellis termination

(equal probability initialization of beta)


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Serial Concatenated Convolutional

Coding With Trellis Termination


Code Encoder


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RSC ENCODER


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RSC Encoder


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SCCC iterative decoder


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Inner MAP decoder with trellis

termination


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Branch Metrics


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Inner MAP decoder with trellis

termination


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Outer MAP decoder with trellis

termination


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Coding Without Trellis Termination

Serial Concatenated Convolutional Code

Encoder


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Decision making device


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RSC Encoder


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SCCC iterative decoder


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Inner MAP decoder (without trellis

termination)


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Inner MAP decoder (without trellis

termination)


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Outer MAP decoder (without trellis

termination)


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Outer MAP decoder (without trellis

termination)


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Parameters Used For Serial Concatenated

Convolutional Coding

]


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SCCC with trellis termination


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SCCC without trellis termination


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Comparison


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Transmitted and received signal with

trellis termination


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Transmitted and received signal without

trellis termination


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Future work

Serial concatenated convolutional coding is to beincorporated into the existing FBG based FFH

OCDMA system.

The use of suitable serial concatenated

convolutional error correction codes to improve thesystem performance of FBG based FFH OCDMA

system is to be studied.


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References A.Stoke and E.H.Sargent, Role of Optical CDMA in access networks,

IEEE Communications Magazine, Vol.40, No.9, Sep 2002.

Isamu Saeki, Shouhei Nishi and Koso Murakami, All-Optical Code

Division Multiplexing Switching Network Based on Self-Routing

Principle, IEICE Trans,Commun., Vol E82-B, no.2.Feb 1999,pp 239-

245.

M.Meenashi and I.Andonovic, Effect of physical Layer Impairments onSUM and AND Detection Stratergies for 2D-Optical CDMA, IEEE

Photonics technology Letters, Vol.17, No.4, April 2005.

Henrik Lundqvist, Student Member, Ieee, And Gunnar Karlsson, Senior

Member, IEEE On Error-Correction Coding For Cdma Pon Journal Of

Lightwave Technology, Vol. 23, No. 8, August 2005.

M. Kulkarni, R. K. Sinha, and D. R. Bhaskar System Performance

Comparison of Turbo and Trellis Coded Optical CDMA Systems

International Journal of Signal Processing Summer 2007.

Jin Young Kim, Member, IEEE, and H. Vincent Poo, Fellow, Member,

IEEE, OSA Turbo-Coded Optical Direct-Detection Cdma System With

Ppm Modulation Journal Of Lightwave Technology, Vol. 19, No. 3,


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References G. D. Forney Jr., Concatenated Codes Cambridge, MA: MIT Press,

1966.

S. Benedetto, D. Divsalar, G. Montorsi, and F. Pollara Serial

Concatenation of Interleaved Codes: Performance Analysis, Design,

and Iterative Decoding TDA Progress Report 42-126, August 15, 1996.

Krishna R. Narayanan, Student Member, IEEE, and Gordon L. Stuber,

Senior Member, IEEE Selective Serial Concatenation of Turbo CodesIEEE Communications Letters, Vol. 1, No. 5, September 1997.

Horia Balta and Maria Kovaci A study on turbo decoding iterative

algorithms Transactions on Electronics and Communications Tom

49(63), a Fscicola 2, 2004.

E. Boutillon, C. Douillard, G. Montorsi Iterative Decoding ofConcatenated Convolutional Codes: Implementation Issues,

Proceedings of the IEEE. , No. 6, June 2007.

Bernard Sklar, Digital Communications-Fundamentals and

Applications, Second Edition S. Benedetto, D. Divsalar, G. Montorsi,

and F. Pollara Serial Concatenation of Interleaved Codes:

Performance Analysis, Design, and Iterative Decoding TDA Progress-


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