A novel transmission scheme for irregular LDPC coded OFDM system

A novel and practical transmission scheme called degree distribution & reliability based (DD&R) LDPC-COFDM is proposed for irregular LDPC coded OFDM (LDPC-COFDM) system. Unequal protection of irregular LDPC codes and sub carriers´ reliability of OFDM are investigated and combined to enhance the transmission power efficiency. SNR of sub carriers is linearly quantized and defined as reliability. For the irregular LDPC block bits with higher degrees play more important role in the decoding process and hence need more protection during transmission. In the scheme, these important bits (with large degrees) are prior to be mapped to the sub carriers with higher reliabilities (SNR) in the Is´ transmission. When reception fails and repeat is needed, the bits carried on the less reliable sub carriers will be in high retransmission priority since it´s more likely to be error. Gaussian approximation (GA) scheme is employed to analyze asymptotic performance of the new scheme and some initial simulations are also considered. Both of the results reveal significant improvement compared with conventional method.