DESIGN OF LOW-DENSITY PARITY-CHECK CODES FOR AUTOMATIC REPEAT-REQUEST BLOCK-FADING CHANNEL

Abstract

Many practical communication systems such GSM, EDGE or system using orthogonal frequency division multiplexing (OFDM) can be modeled as the block fading channel. Communication over the block fading channel is particularly challenging because the transmitted codeword undergoes only a finite number of fading blocks making the channel non-ergodic. Hence there is a non-zero probability (called the outage probability) with which the communication is not possible. One practical way of reducing the outage probability is the use of adaptive technique such as ARQ systems. Subject to no delay constraints, outage can be avoided. In practice however, most system are subject to delay constraint imposed. Design of coding systems for ARQ system with delay constraint is considered in this thesis. The Low-Density Parity-Check (LDPC) code is used as a mother code. The LDPC codes are specifically designed to achieve the maximum diversity in a fixed rate transmission system. A novel algorithm to design Root-Check LDPC codes based on Progressive Edge Growth (PEG) techniques for block-fading channels is proposed, which outperform codes constructed by the existing techniques .The concept of the check splitting to the LDPC code is extended to provide an incremental redundancy coding scheme specifically for the block fading channel in this thesis. By construction, the proposed coding scheme achieves the outage probability, high level of the diversity and effectively adapts the transmission rate to the instantaneous channel conditions.