Quaternary Message Passing Decoding of LDPC Codes: Density Evolution Analysis and Error Floor

We revisit a coarsely quantized message passing decoding algorithm for low-density parity-check (LDPC) code ensembles, named quaternary message passing (QMP). Particularly, we analyze the performance of unstructured LDPC codes under QMP decoding by means of density evolution. The impact of degree-2 and degree-3 variable nodes on the error floor performance is also discussed. We design a code for QMP that performs within 0.55 dB of the 5G LDPC code at a block error rate of 10−4.