Cable's secretive 'NRoC' project explores way to run 5G on HFC

5G could become a core piece of cable's network strategy in a way that extends well beyond its use to deliver wireless signals. 5G, it appears, might also play a starring role in the industry's widely deployed hybrid fiber/coax (HFC) networks.

Charter Communications, Rogers Communications, CableLabs and select suppliers (Technetix is rumored to be among the vendor group) are collaborating on a way to vastly expand the capacity of their networks by overlaying 5G signals on HFC networks at higher frequencies – perhaps up to 4GHz or 5GHz, industry sources tell Light Reading.

In addition to increasing the capacity of the network and tapping into the global 5G technology ecosystem of chipmakers and other components and products, the project might also help operators push forward with their broader fixed/mobile network convergence strategies.

'NRoC' on the horizon

The project is known as "NRoC" for Next-Gen Radio over Coax or Next-Gen Radio over Cable (Light Reading has heard it called by both names), according to multiple industry sources. And it's still in the early stages, with expectations that commercial products tied to the project likely won't emerge for a year or more. A future goal is for NRoC to evolve into a bona fide set of CableLabs specifications, sources said.

Related:Broadcom's grip on DOCSIS 4.0 chips remains a concern

But hints of the work underway have been hiding out in the open. Last month, Rogers and CableLabs announced the establishment of "CableLabs North," with the goal to "develop new innovative applications and provide customers seamless connections in and out of the home or workplace." The announcement also noted that CableLabs North will develop technology to provide 5G using cable infrastructure to deliver "faster speeds and more capacity."

But the announcement didn't reference NRoC or any technical detail on how delivering 5G on cable networks might be accomplished.

"The idea is to overlay 5G on the coax," an industry source familiar with the project said. That approach, the person added, would also enable cable operators to take advantage of legacy HFC assets such as power and backhaul. "It's got everything that you need," the person added.

The general idea would be to run 5G as an overlay on HFC in spectrum above 1.2GHz – on up to 4GHz or 5GHz. DOCSIS would continue operate at 1.2GHz and below.

As a possible alternative to a distributed access architecture (DAA) that would pair a remote PHY device with a virtual cable modem termination system (vCMTS), the NRoC approach could match a traditional, integrated CMTS with a 5G radio deployed where a DAA node would typically be located.

Related:FWA is 'wireless substitution' and DOCSIS 'not done at 4.0' – Charter CEO

However, the approach would require a new type of amplifier. That amp, sources said, would operate traditional DOCSIS below 1.2GHz, and would operate above 1.2GHz using a Time Division Duplex (TDD) amplifier for the 5G radio. The customer premises equipment (CPE) on the customer side of the network would need to support DOCSIS as well as 5G by effectively squeezing in the guts of a mobile phone radio.

There are skeptics. Creating such an amplifier would be a "Herculean effort," a cable operator engineer said. "It's incredibly complex."

But if the NRoC project evolves into something real and deployable, it could provide a path toward a next-generation wireline network that would also fit with a broader convergence play because it would also work in tandem with 5G wireless/mobile coverage.

"That's what makes it exciting – it allows fixed and mobile to use the same platform," an industry source familiar with the idea said.

Tapping into a global 5G ecosystem

It's possible that NRoC could approach commercial readiness within a year to 18 months, given that it's using off-the-shelf 5G technologies and products. "We've passed feasibility and are discussing the potential to find and develop a system," a person familiar with the project said.

Related:DOCSIS 4.0 interop hits record 9-Gig downstream speeds

Charter recently conducted a demo with the CableLabs board of directors and it was "popular," a cable industry source said. A demo with the CableLabs technical committee should follow "soon," the person added.

Leaning on the 5G ecosystem could also have some benefits. While DOCSIS 4.0's silicon ecosystem is focused on two suppliers – Broadband and MaxLinear – there are many more sources for chips and components in the 5G market.

"You'd like to have Qualcomm or a MediaTek involved as convergence slowly moves forward through some of these initiatives," said Jeff Heynen, VP and analyst with Dell'Oro Group, who is focused on the broadband access and home networking markets.

NRoC could "dial cable into a technology that is a much bigger total revenue market in terms of multiple chip vendors, multiple radio vendors, multiple everything," a person familiar with the project said. "It effectively allows a much broader range of optionality for the future."

An idea resurfaces

The baseline idea isn't foreign to the cable industry. Using 5G radios to transmit signals over coax using TDD was explored for DOCSIS 4.0 back around 2014, but eventually discarded, multiple industry sources said. But it has been discussed as an option for future specs.

There are some technical compatibilities between the technologies. Notably, DOCSIS 3.1 and D4.0 and 5G use orthogonal frequency-division multiplexing (OFDM) channels, so the core would share some technical similarities. The big difference is that the latest iterations of DOCSIS use frequency division duplexing (FDD) or Full Duplex DOCSIS (FDX), and 5G uses TDD, hence the need for new, dual-capability amplifiers.

It's also possible that operators could explore using a 5G core to provision services on the network, but the approach would be incompatible with anything the industry has done to this point, an engineering exec with a top US cable operator said. "But it's not a bad idea," the exec said of the broader goals of the NRoC project.

Specifics being kept under wraps

Several of the parties known to be involved in NRoC said it is too early to provide much additional color on the project.

A Charter spokesperson confirmed that the operator is in the early stages of exploring the idea, but stressed that the company does not view it as an alternative or replacement for DOCSIS, including DOCSIS 4.0. Deployments of DAA, virtual CMTSs and DOCSIS 4.0 are part of Charter's multi-phase HFC network upgrade initiative.

One possible area of exploration is how the approach can help broaden 5G CBRS deployments at lower costs, the Charter official added.

Charter is starting to use CBRS to offload some mobile traffic onto its own network in high-usage areas to help it reduce MVNO costs. Charter has been rolling out CBRS to parts of Charlotte, North Carolina. The company plans to deploy CBRS in another market this year, CEO Chris Winfrey said last week at MoffettNathanson's investor event.

Offloading mobile traffic with 5G is a "reasonable way to start down the path toward some of these other advanced applications," Dell'Oro's Heynen said.

Heynen said a focus on 5G also fits with Charter's interest in the Generic Access Platform (GAP) node, which uses a standardized housing and standardized interfaces for service and compute modules. In addition to supporting DOCSIS and DAA, those GAP nodes could also be equipped with 5G small cells.

Meanwhile, Charter execs have suggested that DOCSIS has a long road ahead of it.

"DOCSIS is not done at 4.0," Charter CEO Chris Winfrey said in March 2023 at a Morgan Stanley event. "I think there'll be potential for that to expand both for the downstream and upstream in the future." Winfrey didn't elaborate on it at the time, so it's not clear if he was referring to the NRoC project or other work underway focused on expanding HFC spectrum to 3GHz.

Toronto-based Rogers didn't provide any specific plans it has for 5G on HFC, but said DOCSIS 4.0 remains squarely on its roadmap.

"As Canada's largest and most reliable wireless network operator, we are looking at new opportunities to leverage our coast-to-coast HFC and fibre networks to accelerate our industry-leading 5G wireless network to provide the best experience and seamless connectivity for our customers," a Rogers spokesperson said in a statement. "Working with CableLabs, our work at CableLabs North will focus on convergence technology developments while continuing on our roadmap to 10G by leveraging DOCSIS 4.0."

CableLabs declined to comment on the NRoC project. A CableLabs official said the organization, in general, is continually investigating or working on projects designed to evolve the network, and that it's always looking at potential technologies that can coexist with DOCSIS or serve as a future extension of DOCSIS.

What happens to DOCSIS 4.0?

Though Charter stressed that the 5G over coax project is not an alternative to DOCSIS 4.0, other industry sources familiar with the work underway with NRoC wonder how it might impact the path forward for some operators and put some additional strain on DOCSIS technology suppliers that are banking on 1.8GHz upgrades.

If, for example, the DOCSIS ceiling is set at 1.2GHz as 5G traffic operates above 1.2GHz with NRoC, it might cause some operators to reconsider upgrading the HFC network to 1.8GHz and implement the Extended Spectrum DOCSIS (ESD) option for DOCSIS 4.0.

Another possible wrinkle: Work is underway to extend the capabilities of Full Duplex DOCSIS (FDX), an option for D4.0 that uses an FDX band that allows upstream and downstream traffic to occupy the same block of spectrum. FDX, a focus of Comcast's DOCSIS 4.0 deployment, is currently targeted to HFC plant built to 1.2GHz. However, a revised spec being developed at CableLabs would extend FDX to 1.8GHz, an industry source said.