Joint Demodulation and EMS Decoding Algorithm for Q-ary LDPC Codes

To reduce the high decoding complexity of q-ary LDPC codes, a joint-demodulation and extended min-sum (JD-EMS) decoding algorithm is presented in this paper. By utilizing the squares of the distances between signal and constellation points over constellation graph as the decoder input soft messages, the proposed algorithm not only facilitates the computations of the decoder initial messages, but also avoids the performance loss due to conversions between probabilities and log-likelihoodratios. The elementary check node (ECN) processing is also improved in JD-EMS algorithm, thus the number of real additions can be reduced. Moreover, we also give an upper bound of the number of comparison candidates in the sorter at each ECN step. Simulation results indicate that, while significantly reducing the number of real additions at check nodes, JD-EMS algorithm performs as well as EMS algorithm on both AWGN and Rayleigh fading channels.