Turbo coding for mobile radio applications

Pao Yue-kong Library Electronic Theses Database

Turbo coding for mobile radio applications

 

Author: Qi, Feng
Title: Turbo coding for mobile radio applications
Degree: M.Phil.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Mobile communication systems
Wireless communication systems
Signal processing -- Digital techniques
Coding theory
Department: Dept. of Electronic and Information Engineering
Pages: vi, 117 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1682347
URI: http://theses.lib.polyu.edu.hk/handle/200/63
Abstract: Mobile communication systems require channel coding techniques that protect digital data from errors and improve the link performance in radio environments. Turbo coding, a channel coding scheme introduced in 1993, achieves near Shannon-limit error correction performance and has been proposed for the 3rd generation mobile communication systems. The objective of the thesis is to investigate new schemes that improve the performance of turbo codes and enable turbo coding applications in mobile communications. We undertake a comprehensive study of the characteristics of turbo codes' bit error rate performance, which enables us to choose proper design parameters in ac-cordance to specific performance requirements. By analyzing the union bound and weight spectrum of turbo codes, we propose the concept of "divisibility of information sequences". Based on this concept, we derive the design criterion of interleavers for turbo codes. We also propose the concept of "optimal period interleaver" and design a class of novel interleavers for turbo codes and successfully obtain effective short turbo codes for mobile communications. An order of magnitude improvement in bit error rate was achieved compared with the conventional short turbo codes under the middle or high signal to noise ratio environment. This is particularly of interest to turbo coding applications in mobile communications where short frames are typical. The mobile radio channel is particularly dynamic due to multipath fading and Doppler spread, and these effects have strong negative impact on the bit error rate of any modulation technique. Equalization is an important approach to compensate for intersymbol interference (ISI) in mobile fading channel. However, conventional equalizers will fail in decreasing the ISI when the channel experience the deep fading. Our research work focuses on the combination of turbo coding and equalization. We successfully apply the turbo codes obtained in a code-aided equalizer over a mobile radio fading channel. We use the short turbo codes obtained to implement the turbo code-aided adaptive equalizer. The simulation results show that the turbo code-aided equalizer is very effective compared with the conventional adaptive equalizer. The improvement is due to the soft-decision decoding nature of the turbo code and due to the effective short turbo code itself.

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