Efficient construction of irregular codes with midterm block length and near-shannon performance

In this study, the authors propose a new method for constructing irregular low-density parity-check codes (LDPC codes) with midterm or short block lengths. It is a Monte-Carlo simulation-based optimisation procedure called downhill simplex which uses progressive edge growth method for Tanner graph construction in cost function evaluations. It outperforms the density evolution (DE) method in both efficiency and performance. The efficiency of the authors´ proposal mostly depends on the Monte-Carlo simulation time which owing to the midterm block lengths is relatively small compared to the time delay of the conventional DE method. Simulation results show that for block length of 3200 and a relatively low code rate 3/8, LDPC codes constructed using the authors´ proposal noticeably outperform those constructed with DE method by more than 0.2 dB in the entire signal to noise ratio (SNR) range under AWGN channel.