Serial Concatenation of LDPC Codes and Dieren tially Encoded Modulations
Michele Franceschini, Gianluigi Ferrari, R. Raheli, A. Curtoni · 2004
In this paper, we consider serially concatenated schemes with outer novel and ecien t Low Density Parity Check (LDPC) codes and inner modulations effective against channel impairments, or LDPC coded modulations. With a pragmatic approach, we show how to design LDPC codes tailored for simple and robust modulation formats, like Dier entially Encoded (DE) modulations. The LDPC codes are optimized through the use of a recently proposed analysis technique based on EXtrinsic Information Transfer (EXIT) charts. In particular, we optimize the degree distributions of the LDPC codes, obtaining signican t insights into the impact of such distributions on the performance of the proposed concatenated schemes. The EXIT chartbased optimization is conrmed by numerical simulations, considering Dieren tial M-ary Phase Shift Keying (DMPSK) at the transmitter side, and iterative demodulation/decoding at the receiver side. The obtained optimized codes show poor performance if not concatenated with the inner DE. The analysis of the optimized codes shows that the decoding complexity of these codes is lower, with respect to that of standard LDPC codes, i.e., optimized for the additive white Gaussian noise (AWGN) channel.