PERFORMANCE EVALUATION OF HYBRID ARQ USING LDPC CODES

Abstract

Packet-oriented data transmission is gaining more and more importance in wireless communication systems. Typically, data transmission is not strictly delay-sensitive but requires a virtually error-free link. In order to provide such level of reliability over wireless channels, Automatic Repeat Request (ARQ) schemes can be combined with suitable Forward Error Correction (FEC) schemes, resulting in a Hybrid ARQ system. When fading varies slowly over the duration of a codeword, coding takes care of the channel noise while retransmissions take care of bad channel conditions. A desired level of performance can only be achieved if the FEC code is chosen properly. The LDPC code is one of the preferred choices for error correction in a Hybrid ARQ system, since it has the virtue of approaching the Shannon's limit. This dissertation examines the throughput achievable by both Type-I and Type-II HARQ schemes using LDPC codes over Additive White Gaussian Noise (AWGN) and flat Rayleigh fading channel with both the Go-Back N and the ideal Selective Repeat protocol. The results suggest that regular finite-length LDPC codes are very attractive for wireless communications based on HARQ schemes, as they outperform schemes based on other channel codes, including the capacity achieving Turbo codes.