Low-density parity-check (LDPC) coded OFDM systems with M-PSK

Orthogonal Frequency Division Multiplexing (OFDM) is a very attractive technique to achieve the high-bit-rate transmission required for the future mobile communications. To improve the error rate performance of OFDM, forward error correction coding is essential. Recently, low-density parity-check (LDPC) codes, which can achieve the near Shannon limit performance, have attracted much attention. We proposed the LDPC coded OFDM (LDPC-COFDM) systems to improve the error rate performance of OFDM [1]. We showed that LDPC codes are effective to improve the error rate performance of OFDM on a frequency-selective fading channel. In mobile communications the high bandwidth efficiency is required, and thus the multilevel modulation is preferred. In [2], we proposed the decoding algorithm for the LDPC-COFDM systems with M-PSK on an AWGN channel. In this paper, we evaluate the error rate performance of the LDPC-COFDM systems with M-PSK using the Gray and the natural mappings on an AWGN channel, and that of the systems with M-PSK using the Gray mapping on a flat Rayleigh fading channel. We show that the LDPC-COFDM systems with M-PSK using the Gray mapping have better error rate performance than the systems using the natural mapping on an AWGN channel. We also show that the LDPC-COFDM systems with QPSK is more effective than the other systems on a flat Rayleigh fading channel.