Construction of SeIRA QC-LDPC codes with low error floor

We investigate the construction method of structured extended irregular repeated-accumulate quasi-cyclic low-density parity-check (SeIRA QC-LDPC) codes with short to moderate length. A new metric is proposed that jointly considers both circle length and circle connectivity, which aims to improve the error correcting performance in the error floor region. Meanwhile, iterative searching method is proposed that increase the possibility of finding out good solution based on the new metric. At last, we apply our construct method to design codes with different length by expanding them from the same mother matrix. Simulation results show that FER of the codes constructed by this method outperform the corresponding codes in the 802.16 standard expanded from the same mother matrix by 0.15~0.4dB at FER around 10^-5.