By Greg White and Karthik Sundaresan, Cable Television Laboratories, Inc.
DOCSIS 3.1 OFDM Profiles provide a wide range of modulation choices that can be used to fine-tune the CMTS’s transmissions to get the best performance from the current network conditions. A well-designed, optimized set of modulation profiles allows a downstream channel to operate with a lower SNR margin, allowing a channel to operate at an overall higher throughput.
This paper describes methods for designing OFDM profiles and choosing the appropriate modulation orders for a profile. It answers the questions around which profile is appropriate for a CM and what is the optimal set of profiles to use across the an OFDM channel for a given set of CMs. This paper defines an objective function which can be used to calculate the gain in system capacity resulting from the use of multiple profiles, and then explores approaches to maximizing that objective function for a population of CMs. It proposes one such approach, which is referred to as the K-means Coalescation Algorithm, that appears to provide very good results with low computational complexity.