Subchannel Ordering Scheme for LDPC-Coded OFDM Transmission Over Selective Channels

OFDM modulation seems to be a good choice to deal with highly distorted transmission channels, and LDPC error correction codes allow the system performance to get close to the Shannon capacity. Performance improvement of the LDPC-coded OFDM system can be accomplished by use of irregular binary LDPC codes along with an appropriate match between the bits of the codeword and the OFDM subchannels. Non-binary LDPC codes over high order finite fields GF(q) are an additional booster in case of short to moderate codeword lengths. In this paper, a simple practical method of the subchannel ordering for OFDM modulation with non-binary LDPC codes is proposed. The method exploits some special structural properties of the LDPC code parity check matrix generated based on the PEG (Progressive-Edge-Growth) algorithm. A noticeable improvement was achieved for regular codes when the column weights of the parity check matrix is equal to 2.