Cable Techs Ponder A Wired 802.11 Link

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It sounds contradictory: Take a wireless home-networking transmission scheme and graft it onto a wire. But that's exactly what is happening, as such technology providers as Broadcom Corp. and Texas Instruments Inc. work to develop schemes that allow the 802.11 spec to ride on coaxial cable within a home broadband network.

It could strengthen the hold the Institute of Electrical and Electronics Engineers' spec has on the home-networking market, allowing consumers a single scheme that mixes wired and wireless connections to ship video and data around their homes. But the concept is still largely just that — and even supporters admit that more tests and a firmer business case are needed to link the product up.

In theory, 802.11-over-coax has its advantages. First, from the safety of a shielded coaxial cable, 802.11's reach can extend from about 150 feet to as much as 600 feet with better-sustained throughput. The signal is also far less vulnerable to interference from nearby appliances, such as microwave ovens and cordless phones.

"Here's another way to distribute information over a medium where wireless may not be able to cover the entire area that you are trying to cover," said John Gleiter, director of marketing for cable-modem and voice-over-Internet protocol products at Broadcom Corp.'s broadband communications business unit. "By putting it on the coax, you have a more solid communication path instead of through the air, where it may be compromised by interference or doesn't have the proper reach."

It's not regulated

At 2.4 gigahertz, 802.11b/g also fits well into the coax scheme, riding well above the frequencies cable uses for delivering video. Plus, it's free from federal-usage restrictions.

"The reason this is interesting is the 2.4 gigahertz for wired or over wireless is free-space spectrum," said Texas Instruments director of broadband strategy Peter Percosan. "It's not regulated, so there are no issues about remodulating or up or downconverting. Because of that, it doesn't interfere with the cable plant and also because there is no interference with the cable plant, anybody that meets the standard can participate in the space."

Since 802.11 is already an established technology, it could be relatively inexpensive to incorporate into cable modems and digital set-top boxes, and it could eliminate the need for other connection ports.

"It definitely simplifies it, if it becomes the standard interface that everyone wants to use, then obviously there are economies there," Gleiter said. "You get away from multiport Ethernet or HomePNA [Phone Networking Alliance], and you can use wireless if the connection is a short distance or you can go over coax."

At the recent Western Show, Broadcom demonstrated such a system, hooking up a digital video recorder-enabled box, based on its own reference design, to a low-cost set-top box. The reaction among cable operators was strong, according to Gleiter.

"They were really excited about this," he said. "The potential they see is enormous, to be able to leverage that wireless and bridging it over coax to either extend the network or provide an alternate way of distributing the information."

That said, there are still some sizable question marks. On the technical side, it isn't clear how 802.11 traffic will be affected by splitters, which are used to link additional set-top boxes to the coaxial cable in the home. Each splitter creates a certain amount of signal loss, which could affect 802.11's throughput.

"Right now the wild card in the home is the quality of the splitters and, more importantly, the number of splitters," Percosan said.

To determine that, the technology must graduate from the test bench to trials in real home networks. TI and Broadcom are already working to set up such tests with willing cable operators.

"We've identified the value. Now, we are working through the measurements to determine that we are not just hyping ourselves," Percosan said. "Unfortunately right now, we are solving a problem that we think is a cool problem, but it's still a luxury."

Installed base issue

And while 802.11-over-coax might work in a home that has the new digital cable boxes enabled to use it, it would face problems with digital set-tops already deployed. That's one reason why set-top box supplier Scientific-Atlanta Inc. is taking a wait-and-see attitude, according to subscriber networks center chief scientist Tony Wasilewski.

"We're talking about, in the U.S., around 30 million digital set-tops deployed," he said. "None of those set-tops have this capability in them, so if you wanted to use existing set-tops to do this you have to do something else."

S-A is looking at other ways to use the coaxial cable between boxes to shuttle content around, and that could involve elements of 802.11 technology. But for now it isn't the central focus.

"We don't reject it, because it could be useful," Wasilewski said. "But we will see how it unfolds."

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