By Jay Zhu, Comcast; Maher Harb, Comcast; Jeff Howe, Comcast; Chad Humble, Comcast; Dan Rice, Comcast
In 2022, Comcast introduced a fresh perspective on optimizing the spectrum to achieve desired outcomes for product speeds, capacity, node segmentation, and cost-effectiveness by maximizing spectral efficiency via reallocation of data over cable service interface specification (DOCSIS) 3.0 (D3.0) single carrier-quadrature amplitude modulation (SC-QAM) channels to DOCSIS 3.1 (D3.1) orthogonal frequency division multiplexing (OFDM) channels while accounting for the utilization distribution [1]. Comcast also presented a virtual network function (VNF) concept to manage the balance automatically and dynamically between the SC-QAM and OFDM spectrum. As the penetration growth in D3.1 devices continues and the deployment of D4.0 devices comes to the horizon, such a VNF solution can ensure our network resources are utilized at their optimal efficiency and robustness during the transformation. At a high level, a requirement of this VNF solution is to consider each individual service group’s characteristics and constraints at scale and produce tailor-made recommendations as inputs into the automation layer where configuration change procedures, error handling and failover logic are implemented. A unified source of truth for the current state of the spectrum configuration is also maintained to support the VNF operations in the larger picture of the architecture. Based on these requirements, late last year, we continued to make progress on this initiative and designed and developed algorithms to effectively produce spectrum configuration recommendations based on the given real-world constraints and objectives. Using the analytical engine of the VNF service with baseline constraints, we estimated the average capacity gain that can be achieved across our distributed access architecture (DAA) footprint is 231 Mbps per service group at the time of measurement, accounting for strict constraints and without adding any new spectrum. This capacity increase is enabled by the ~44% capacity gain from our profile management application (PMA) VNF [2][3] while the SC-QAM spectrum is converted into OFDM spectrum when the constraints are satisfied. To demonstrate and test our work, we built an automation layer with a configuration manager and a closed-loop system in our lab that supports dynamic radio frequency (RF) spectrum changes using our virtual cable modem termination system (vCMTS) – remote physical layer (PHY) device (RPD)configuration application programming interfaces (APIs) without disconnecting the cable modems (CMs) on the service group. This demonstrates the ability of the system to make hit-less RF spectrum changes in an integration context. We also measured the peak throughput changes of the DOCSIS 3.1 CMs after the hit-less spectrum changes.