Construction of Irregular QC-LDPC Codes in Near-Earth Communications

—High-speed, high-reliability requirements and strict power limitation of near-earth communications yield that the channel coding must have high coding gain and lower error floor. In this paper, an irregular quasi-cyclic low-density paritycheck (QC-LDPC) code for specific use in near-earth communications is proposed. In order to eliminate the impact of short-cycles and further improve the performance of codes, a base matrix with girth at least 8 is employed. Then dualdiagonal structure is adopted in parity check matrix to reduce encoding complexity. Besides, circulant permutation matrices and zero matrices with different sizes are used to fill the nonzero positions and zero positions of the base matrix so as to remove the complexity of the selection of cyclic shift coefficients. The adoption of circulant permutation matrices with different sizes ensures that the parity check matrix is full rank, which makes the code rate controllable. Finally, simulation results are given to demonstrate the performance of the constructed codes by comparing with several existing codes.