Turbo equalisation algorithms for full and partial response modulation

Yeap, Bee Leong (2000) Turbo equalisation algorithms for full and partial response modulation. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This Thesis is based on the research of joint channel equalisation and channel decoding algorithms, known as turbo equalisation. Initially, the performance of independent channel equalisation and decoding was studied in the context of Gaussian Minimum Shift Keying (GMSK) modulation. A low-rate 1.9 Kbps GMS-like speech system was constructed with the aim of studying the potential of using convolutional-based turbo codes for low-delay systems. The results confirmed that turbo codes did not outperform conventional convolutional codes in low-delay speech systems, but were advantageous for data transmission systems that can tolerate longer transmission delays.

Subsequently, iterative joint channel equalisation and channel decoding techniques were investigated for the above convolutional-coded GMSK scheme, for convolutional-coding based turbo-coded systems and for block-based Bose-Chaudhuri-Hocquengham (BCH) turbo-coded GMSK schemes. Our results showed that the convolutional-coded GMSK system outperformed the convolutional-coding based turbo-coded scheme and the BCH-coding based turbo-coded system by a margin of 1.0 dB and 0.8 dB, respectively, for the transmission over a five-path Rayleigh fading channel at BER = 10^-4. This performance trend was confirmed by deriving the theoretical Maximum Likelihood bound upon invoking the union bound approach.

Turbo equalisation for full-response Binary Phase Shift Keying (BPSK) systems was also researched. Three classes of codes, namely convolutional codes, convolutional-coding based turbo codes and BCH-coding based turbo codes were employed. The objective was to compare the turbo equalisation performance of these codes for high code rates of R = ³/₄ and R = ⁵/₆. It was observed that the turbo-equalised convolutional-coding based turbo-coded system was the most robust scheme. Finally, turbo equalisation was explored in the context of multi-level Quadrature Amplitude Modulation schemes. A novel reduced complexity trellis-based equaliser, known as the In-Phase/Quadrature-phase Equaliser (I/Q EQ), was proposed based on equalising the in-phase and quadrature-phase components of the transmitted signal separately. The I/Q EQ was capable of achieving the same performance as the conventional turbo equaliser, while achieving a complexity reduction by a factor of 2.67 and 16 for 4-QAM and 16-QAM, respectively.