Performance Analysis of Turbo Codes over Awgn and Rayleigh Channels Using Different Interleavers

I certify that this thesis satisfies all the requirements as a thesis for the degree of Master of Science. This is to certify that we have read this thesis and that in our opinion it is fully adequate, in cope and quality, as a thesis for the degree of Master of Science in Electrical and Electronic Engineering. Turbo codes are a new class of forward error correcting codes that have proved to give a performance close to the channel capacity as proposed by C. Shannon. A turbo code encoder is formed by the parallel concatenation of two identical recursive convolutional encoders separated by an interleaver. The turbo code decoder utilizes two cascaded decoding blocks where each block in turn share the a priori information produced by the other. The decoding scheme has the benefit to work iteratively such that the overall performance can be improved. In this thesis, a performance analysis of turbo codes is carried out over AWGN, and slow independent Rayleigh fading channels using different interleaving schemes. The performance of turbo codes is analyzed using small data frame sizes with the maximum size close to the GSM standard (456 bits). Two decoding techniques, namely, Log-maximum a posteriori probability (Log-MAP) algorithm, and the soft output Viterbi algorithm (SOVA), which uses log-likelihood ratio to produce soft outputs are used in the performance analysis. The effect of using different interleaving schemes is studied on both punctured and unpunctured codes. Finally, the performance of the two different decoding techniques is compared in terms of bit error rate. Results indicate that turbo codes outperform the well-accepted convolutional codes with same constraints for all used interleavers, however the best results are given by the unpunctured Log-MAP decoding of turbo codes. as Jury members. Many thanks to my department and fellow associates for their help and support during my course of study. Great thanks to all of my friends for their presence, as it enhanced my motivation by making me feel at home. Finally, I especially wish to thank my parents who have provided me with immeasurable support and encouragement during all my years in academic life.