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How '1394 over coax' spec will work


Cable TV operators today distribute their MPEG-2 program signals via coaxial cable, with a cable set-top box at each TV receiver. Coaxial cables abound in most homes in the United States.

Taking advantage of this coax-friendly environment, IEEE 1394 proponents are developing a new spec called "1394 over coax" to connect clusters of devices, in different rooms of a house, on a 1394 bus by sending 1394 baseband signals over coaxial cable.

While the 1394 Trade Association has already defined specs for Category 5 copper, plastic optical fiber and glass optical fiber, coaxial cable has been one missing piece. The group will use ultrawideband (UWB) as a physical layer for the new 1394-over-coax spec. However, in this application, UWB shouldn't be confused with sending information wirelessly. "We use UWB to modulate the signal. But, once modulated, we keep the signal in coax. We don't radiate it," said Hans van der Ven, chairman of the 1394-over-coax working group. "By moving the signal way up high--3.3 to 4.7 GHz--through UWB, we can have lower signal amplitude and minimize interference."

In essence, UWB is used in coax as a waveguide to achieve higher accuracy and improve cable length. Further, the 1394-over-coax standard will use IEEE 802.15.3's media-access controller, just as UWB does.

The idea of a coax-based home network is already gaining some traction among cable operators. The Multimedia Over Coax Alliance (MoCA) is pushing its proposal to carry both analog TV programs and 100-Mbit/second Ethernet over coax with splitters. The 1394 proponents, however, think they can do better. At 400 Mbits/second for 1394 over coax, they claim a fourfold throughput advantage over MoCA's 95 Mbits/s.