Seeing the need for more upstream capacity fueled by the pandemic, Cox Communications is preparing to start field trials of "high-split" spectrum upgrades in January and accelerate its rollout of "mid-split" upgrades throughout 2022.

Speaking during a session at last week's virtual SCTE Cable-Tec Expo, Thomas "Tee" Harton, senior director of RF engineering for Cox, said the big US cable operator aims to begin high-split field trials in select regions where it needs more capacity and has already extended fiber deep into its hybrid fiber/coax (HFC) access network. He said Cox will gradually extend the high-split deployments to other areas throughout the year as it gets more comfortable with the upgrades and sees how they perform before going full-blast in 2023.

"So we'll start rolling it out and get a little bigger as we get into 2022 and beyond and position ourselves for a 2023 rollout," Harton said. "You'll see us starting to dip our toes in the water in a bigger way next year."

A high-split upgrade expands the amount of spectrum dedicated to the upstream in North American DOCSIS cable systems from the current range of 5MHz-42MHz (5MHz-65MHz on EuroDOCSIS networks) to a much greater range of 5MHz-204MHz, thereby enabling operators to offer upstream speeds as high as 1 Gbit/s and get ready for the multi-Gig world of DOCSIS 4.0. Currently, operators are tightly constrained in the upstream speeds they can offer because of bandwidth limitations.

However, cable operators must overcome some technology and operational challenges to carry out those upgrades to 204MHz. In particular, North American operators must contend with potential interference problems because their legacy set-top boxes tap into out-of-band signaling (used for set-top authorization and authentication) in a part of the spectrum that would be allocated to the upstream in a 204MHz high-split.

Acknowledging such challenges, Harton said Cox will tackle those and other issues during its forthcoming trials. "It's a process," he said. "You line up the hurdles and then you knock them down."

High-split trials will start in upgraded systems

If all goes according to plan, Cox will begin the high split field trials in its fiber-deep (N+0) systems where it has already removed all its amplifiers and upgraded all its network passive devices to 1.2GHz. The MSO then aims to extend the deployments to N+X systems as the new year goes on.

"We've got plans for high-split 1.0 as well as high-split 1.2 and beyond," Harton said. "So we believe we can exist in all these scenarios."

Cox is not the only major MSO eyeing high-split upgrades. Speaking on the same Expo session as Harton, Jay Lee, chief technology and strategy officer for ATX Networks, said one of his company's major cable customers is also preparing to start high-split trials shortly. Declining to name the operator, he said it plans to follow a similar course as Cox.

More mid-split mojo

At the same time, Cox is ramping up its rollout of "mid-split" spectrum upgrades to create more upstream capacity. A mid-split expands the amount of spectrum dedicated to the upstream in North American DOCSIS networks to a new range of 5MHz-85MHz, about doubling the HFC plant's current upstream capacity.

Harton said Cox, which started mid-split trials in 2018, will keep deploying mid-splits in areas where it needs more upstream capacity. In many cases, the cableco is pairing those spectrum upgrades with rollouts of remote PHY technology to further boost system capacity and deliver higher broadband speeds to customers. About 30% of the operator's nationwide network is now outfitted with remote PHY devices.

"Mid-split has been going well," he said. "It gets you a good amount of capacity ... It's easier for us to operationalize because it's more of the same of what we're used to doing on the HFC side."

Lee noted a number of other cable operators are also exploring mid-split upgrades now or "are in the throes" of deploying them.

Trying out OFDMA

In another move to free up more upstream bandwidth, Cox is also preparing to start field trials of OFDMA (orthogonal frequency-division multiple access) modulation technology in several cable systems. OFDMA, which relies on blocks of tiny subcarriers, is a more spectrum-efficient method than older, DOCSIS 3.0-era technologies that bond together multiple 6MHz-wide channels.

Harton said Cox will try out OFDMA in systems where it has already carried out mid-splits as well as systems where it has just relied on old-fashioned node splits to expand capacity. "We're just getting into that," he said. "It's still really early days at Cox for OFDMA deployments."

In addition, Cox is increasing its deployment of fiber-to-the-home (FTTH) lines in both its newbuild and existing territories. He noted that the MSO already passes "north of 600,000 to 700,000" homes with FTTH. "We'll see more fiber moving into the mix for us," he said.

But, like most cable technologists, Harton still sees a long life ahead for HFC plant and DOCSIS technology, projecting at least 20 years more for the combination. "It's hard to argue with an installed network," he said. "At the end of the day, the installed network continues to pay dividends."

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— Alan Breznick, Cable/Video Practice Leader, Light Reading