Lowering LDPC Error Floors by Postprocessing

A class of combinatorial structures, called absorbing sets, strongly influences the performance of low-density parity-check (LDPC) decoders at low error rates. Past experiments have shown that a class of (8,8) absorbing sets determines the error floor performance of the (2048,1723) Reed-Solomon based LDPC code (RS-LDPC). A postprocessing approach is formulated to exploit the structure of the absorbing set by biasing the reliabilities of selected messages in a message-passing decoder. The approach converges quickly and can be efficiently implemented with minimal overhead. Hardware emulation of the decoder with postprocessing shows more than two orders of magnitude improvement in the very low bit error rate performance and error- floor-free operation below a BER of 10^-12.