Repeat--punctured turbo codes and superorthogonal convolutional turbo codes.

Abstract

The use of error-correction coding techniques in communication systems has become

extremely imperative. Due to the heavy constraints faced by systems engineers more

attention has been given to developing codes that converge closer to the Shannon

theoretical limit. Turbo codes exhibit a performance a few tenths of a decibel from the

theoretical limit and has motivated a lot of good research in the channel coding area in

recent years.

In the under-mentioned dissertation, motivated by turbo codes, we study the use of three

new error-correction coding schemes: Repeat-Punctured Superorthogonal Convolutional

Turbo Codes, Dual-Repeat-Punctured Turbo Codes and Dual-Repeat-Punctured

Superorthogonal Convolutional Turbo Codes, applied to the additive white Gaussian noise

channel and the frequency non-selective or flat Rayleigh fading channel. The performance

of turbo codes has been shown to be near the theoretical limit in the AWGN channel. By

using orthogonal signaling, which allows for bandwidth expansion, the performance of the

turbo coding scheme can be improved even further. Since the resultant is a low-rate code,

the code is mainly suitable for spread-spectrum modulation applications. In conventional

turbo codes the frame length is set equal to the interleaver size; however, the codeword

distance spectrum of turbo codes improves with an increasing interleaver size. It has been

reported that the performance of turbo codes can be improved by using repetition and

puncturing. Repeat-punctured turbo codes have shown a significant increase in

performance at moderate to high signal-to-noise ratios. In this thesis, we study the use of

orthogonal signaling and parallel concatenation together with repetition (dual and single)

and puncturing, to improve the performance of the superorthogonal convolutional turbo

code and the conventional turbo code for reliable and effective communications.

During this research, three new coding schemes were adapted from the conventional turbo

code; a method to evaluate the union bounds for the AWGN channel and flat Rayleigh

fading channel was also established together with a technique for the weight-spectrum

evaluation.