Deploying PMA-Enabled OFDMA in Mid-Split and High-Split (2022)

By Maher Harb, Dan Rice, Kevin Dugan, Jude Ferreira, Robert Lund; Comcast

Comcast has deployed DOCSIS 3.1 (D3.1) orthogonal frequency division multiple access (OFDMA) in the mid-split (MS) and high-split (HS) bands of the upstream (US) spectrum on our virtual cable modem termination system (vCMTS) platform. D3.1 OFDMA allows higher modulation levels with up to 2x efficiency increases, with 2048-QAM today and anticipating 4096-QAM in the near future, compared to single carrier-quadrature amplitude modulation (SC-QAM) of 64-QAM. More importantly, D3.1 US technology allows configuring the modulation per 400 KHz mini-slot, enabling adaptation to the ingress and distortions discovered in the network. Several ingress and impairment sources that have the potential to degrade capacity and customer experience have been identified; examples include off-air very high frequency (VHF) broadcast, linear distortions, in-home analog TV modulators, frequency modulation (FM) radio, NOAA weather radios, and pre-equalization stability. As we deployed OFDMA initially on the network we quickly realized that in order to take full advantage of the capabilities OFDMA has to offer, most notably delivery of hundreds of Mbps US product speeds, a profile management application (PMA) system is required similar in concept to the one deployed downstream for managing orthogonal frequency division multiplexing (OFDM) profiles, which we reported on in previous SCTE contributions [1-4]. This paper presents the initial results from adapting the OFDM PMA system for OFDMA and testing in both lab systems and production field deployments. We share some examples of spectrum impairments, characterization methods, our thinking around how profiles are constructed based on devicelevel MER measurements, and the validation of the profiles against the vCMTS internal PMA function. We also comment on some of the intricacies of expanding upstream spectrum that warrant revisiting the core algorithm in the future.

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