Toward low LDPC-code floors: a case study

While LDPC codes have been widely acclaimed in recent years for their near-capacity performance, they have not found their way into many important applications. For some cases, this is due to their increased decoding complexity relative to the classical coding techniques. For other cases, this is due to their inability to reach very low bit error rates (e.g., 10^-12) at low signal-to-noise ratios (SNRs), a consequence of the error rate floor phenomenon associated with iterative LDPC decoders. In the present paper, we make strides in the low-floor problem by identifying the weaknesses of the code under study and applying compensatory counter-measures. These counter-measures include: modifying the code itself, modifying the decoder, or adding a properly designed outer algebraic code. Our results demonstrate that each of these techniques can successfully lower an LDPC code´s floor, and that, for the code under study, an outer BCH code appears to be particularly effective. All of our results are based on FPGA decoder simulations and so they are reliable and repeatable.