Bit Rate

The 5-Gigahertz Cable Network

5/18/2008 12:29 PM

The theoretical maximum amount of spectrum you could squeeze out of coaxial cable?

Somewhere around 5 Gigahertz, according to John Ulm, a fellow of the technical staff at Motorola, speaking on a panel at the Cable Show, "Expansion Plan: Where Bandwidth Goes from Here."

That’s at least five times the capacity most cable systems run at today. 

"It will take a long time to get there, and it will be incremental as we’ve seen with previous increases," Ulm said. "But we have a lot of headroom in the cable industry."

In a 5-GHz network, the conventional 6-Megahertz channel divisions will go away, replaced by much larger wideband channels, Ulm predicts. A 120-MHz chunk could deliver "gigabits of bandwidth," he said – "and suddenly cable looks pretty competitive with a 10-Gigabit PON."

Of course, it’s not gonna be cheap. Comcast CEO Brian Roberts, in the opening general session today, said the cable industry spent about $100 billion to upgrade from around 500 to 750 MHz.

The huge near-term opportunity to increase capacity is through analog reclamation — to reclaim 250 to 500 MHz from analog channels, Roberts said, will probably cost the industry less than $5 billion. (See Analog Zappers and Pace Talkin’ DTAs With Comcast.)

But as Comcast executive fellow Dave Fellows, who moderated the bandwidth panel, noted at the outset, "Just as you can never be too thin or too rich, you can also never have too much bandwidth."

One new bandwidth-hungry service Ulm mentioned that could go into that expanded network: 3-D high-defintion video, which the NBA for one has been experimenting with. "That’s going to be everywhere," he said.

March