Data Over Cable Services – Improving the BICM Capacity

The Data Over Cable Service Interface Specification (DOCSIS) provides Internet access via Hybrid Fiber Coax networks. The current version DOCSIS 3.1 and the planned next iteration DOCSIS 4.0 use Quadrature Amplitude Modulation (QAM) and Low-Density Parity Check (LDPC) codes for Bit-Interleaved Coded Modulation (BICM). This paper analyzes the BICM performance characteristics of the DOCSIS downstream. We find that there is a gap of approximately 3.5 dB between DOCSIS and the theoretical Shannon limit. To reduce this gap, we suggest the use of alternative LDPC codes and Non-Uniform Constellations (NUCs) as specified by the ATSC 3.0 standard. To adjust the ATSC 3.0 specification for cable networks, we introduce novel NUCs that target very high signal-to-noise ratios. The proposed BICM chain reduces the distance to the Shannon limit by up to 1 dB.