DC-free (d, k) constrained low density parity check (LDPC) codes

Recently, turbo codes and low-density parity check (LDPC) codes with iterative soft decoding have been heavily investigated as potential candidates for low-SNR, high-density data storage systems. However, relatively less attention has been devoted to the investigation of (d, k) run-length limited (RLL) constrained LDPC codes, although run-length constraints are generally employed in data storage channels due to channel nonlinearities and timing recovery issues. In this paper, we propose an extended bit insertion technique to construct DC-free (d, k) constrained LDPC codes. As an example of the proposed method, we construct a DC-free (1,7) LDPC code, and report its performance in an optical storage channel.