Pilot-assisted technique on LDPC-coded COFDM-CDMA in frequency-selective multipath fading channels

The low-density parity-check code is known for a superior signal reception capability in AWGN and/or flat fading channels with respect to increased encoding rates, however, its performance degrades when the communication channel becomes multipath fading. In this paper we have investigated a novel approach applying a pilot-assisted LDPC coding to a coded OFDM-CDMA system, which operates in a multipath fading mobile channel. In a typical multipath fading mobile channel with a SNR of 16 dB or lower, however, it is a challenging problem to obtain a BER lower than 1 out of I0⁵ when the LDPC encoding rate is about 1/4. In order to enhance the performance of the proposed system we have improve the LDPC decoding algorithm by incorporating the pilot information with the parity check bit. In contrast to the conventional 1/4-rate LDPC coded transmission symbol that is consisted of data bits and parity-check bits in 1 to 3 proportion, in the proposed method the same rate LDPC transmission symbol contains data bits, parity-check bits, and pilot bits in 1 to 2 to 1 proportion, respectively. The included pilot bits are effective not only for channel estimation and equalization but for LDPC symbol decoding by assisting the parity-check bits. The proposed system performance has been verified using computer simulations in multipath, Rayleigh fading channels, and the results show us usefulness of the proposed method over the conventional LDPC coding methods in terms of SNR vs BER measurements.