멀티레벨 변조방식에서 LDPC 복호 알고리즘

Abstract

Concatenate coding schemes are considered as being the best solution for powerful protection of digital information against nonlinear and fading noise. However, the performance of concatenate coding scheme is away from Shannon’s limit. The emergence of the turbo codes and iteration decoding algorithms for them has changed our view of the Shannon capacity, the capacity has become a practical benchmark for a coding system not only for power limited channels but also for bandwidth channels. The low density parity check(LDPC) codes have different characteristics compared with the turbo codes. The LDPC codes have better block error performance than that of the turbo codes. This is because the minimum distance of an LDPC code increases proportionally to the code length with high probability. Such a property is desirable for high-speed data transmission which requires very low frame error probability.

For LDPC decoding, received symbols are splitted bit by bit based using the received in-phase and quadrature components. The method of bit-splitting is affected on decoding performance because its method depend on distance over symbol constellation. This thesis proposes the bit split method using the sector information with sacrifice a little performance loss compared to Euclidean distance method. Futhermore DVB-S2 Digtal Video Broadcasting specification supports BC(Backward Compactible) mode which using the hierarchical modulation method, this thesis also analyze the decoding performance according to deviation angle of 8PSK constellation for various LDPC coding rates.