By Karthik Sundaresan, Jay Zhu & Mayank Mishra, CableLabs; James Lin, Kyrio/CableLabs
DOCSIS 3.1 OFDM/A Profiles provide a wide range of modulation choices that can be used to fine-tune the CMTS downstream and CM Upstream transmissions to get the best performance from the current network conditions. A well-designed, optimized set of modulation profiles allows a channel to operate more robustly against ingress noise and also enables an overall higher user throughput.
This paper will discuss the D3.1 Profile Management Application and how it is used by operators in deployment with D3.1 CMTSs and CMs to create Downstream profiles and Upstream IUCs/Profiles. The paper will share our experiences from creating such an application. It will discuss the effect of noise on the choice of a profile assigned to a CM. We share results on how the number of FEC code words corrected vary with the noise, and at different modulation orders. We also talk about the gain in the network capacity seen by smart Profile creation algorithms versus using a flat profile and simply assigning CMs to the least common denominator profile which fits the CM.
The paper will also describe MAC layer state machine and interactions between the CM & CMTS when a profile fails. The interaction between CM-STATUS messages from a CM (for flagging failures and recovery on a profile) and the CMTS response to that message in changing the profile used, results in “Profile Flapping”. This paper recommends on how to design CM and CMTS MAC Layer settings to make the system be robust when these interactions take place in the D3.1 system.
D3.1 OFDM/A channels can have interference in parts of the channel and different modems experience this differently. Deploying well designed profiles for each channel will decrease the number of errors seen on the channel, reducing trouble calls. It could also unlock a solid 200~400 of Mbps of capacity gain on each channel.