Could Coax Hit 20 Gigabits Per Second?

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There’s estimated to be around 5 Gigabits per second of total capacity in a 750-MHz cable system.

But if you crank up the frequencies to operate at up into the 3-Gigahertz range, “you could get up to 20 Gigs over the RF plant,” says SCTE chief technology officer Daniel Howard.

That’s not symmetrical — that would be overall capacity — and it would be shared among all subscribers in a serving group. But whew… that is a ton of bandwidth that could still be wrung out of good ol’ coax. It’s why cable tech types like Comcast CTO Tony Werner suggest there may never be a need for MSOs to run fiber-to-the-home (see Fiber to the Home? Maybe Never, Says Comcast’s Werner).

The more urgent issue for MSOs is to increase the upstream capacity, which today is usually locked into the 5-42 MHz band (see Big Upstream Upgrades). Howard sees cable operators being able to offer 1-Gbps upstream connections in the next 8-10 years (i.e., two cycles of plant upgrades) by redeploying the upstream/downstream frequency split.

“We don’t have to get there overnight,” he said.

Howard should know whereof he speaks — he co-authored CableLabs’ DOCSIS 1.1 and 2.0 specifications, and at Broadcom was a lead developer on the company’s primary DOCSIS 3.0 patent.

That 20 Gbps estimate, by the way, is just a ballpark. Note that CableLabs is working on a next-generation broadband project to make delivering data over coax even more efficient, using advanced media access control (MAC) and physical-layer (PHY) components that would do away with the traditional 6-MHz channel divisions (see CableLabs Next-Gen Broadband Project Envisions Multigigabit Speeds).