Concatenated space-time codes in Rayleigh fading channels.

Abstract

The rapid growth of wireless subscribers and services as well as the increased use of internet

services, suggest that wireless internet access will increase rapidly over the next few years.

This will require the provision of high data rate wireless communication services. However

the problem of a limited and expensive radio spectrum coupled with the problem of the

wireless fading channel makes it difficult to provide these services. For these reasons, the

research area of high data rate, bandwidth efficient and reliable wireless communications

is currently receiving much attention.

Concatenated codes are a class of forward error correction codes which consist of two or

more constituent codes. These codes achieve reliable communications very close to the

Shannon limit provided that sufficient diversity, such as temporal or spatial diversity, is

available. Space-time trellis codes (STTCs) merge channel coding and transmit antenna

diversity to improve system capacity and performance. The main focus of this dissertation

is on STTCs and concatenated STTCs in quasi-static and rapid Rayleigh fading channels.

Analytical bounds are useful in determining the behaviour of a code at high SNRs where

it becomes difficult to generate simulation results. A novel method is proposed to analyse

the performance of STTCs and the accuracy of this analysis is compared to simulation

results where it is shown to closely approximate system performance.

The field of concatenated STTCs has already received much attention and has shown

improved performance over conventional STTCs. It was recently shown that double concatenated

convolutional codes in AWGN channels outperform simple concatenated codes.

Motivated by this, two double concatenated STTC structures are proposed and their performance is compared to that of a simple concatenated STTCs. It is shown that double

concatenated STTCs outperform simple concatenated STTCs in rapid Rayleigh fading

channels. An analytical model for this system in rapid fading is developed which combines

the proposed analytical method for STTCs with existing analytical techniques for

concatenated convolutional codes.

The final part of this dissertation considers a direct-sequencejslow-frequency-hopped (DSj

SFH) code division multiple access (CDMA) system with turbo coding and multiple transmit

antennas. The system model is modified to include a more realistic, time correlated

Rayleigh fading channel and the use of side information is incorporated to improve the

performance of the turbo decoder. Simulation results are presented for this system and it

is shown that the use of transmit antenna diversity and side information can be used to improve system performance.