MoCA Challenges Wireless For Home Networking Dominance
Louis E. Frenzel
January 18, 2007
The Multimedia over Coax Alliance (MoCA) sponsors a home networking technology that's significantly growing in popularity thanks to the need to transport video and audio around the home between consumer electronics. Its goal is to ensure a reliable network with the simplicity, reliability, and quality of service to ensure triple-play delivery.
MoCA's technology is a closely held secret unless you pony up the $12,000 membership fee, though. Essentially, it uses the existing installed coax cabling that exists in over 90% of the estimated 110 million homes in the U.S. as the networking medium. While that cabling delivers video from the local cable supplier and/or the satellite receiver, the networking takes place over the cable bandwidth from about 860 to 1500 MHz.
The MoCA spec divides that bandwidth into 50-MHz channels and modulates the digital video using orthogonal frequencydivision multiplexing in each channel. Most coax wiring is RG-6, which is the 75Ωlow-loss cable that's more than able to handle signals in that frequency range over short distances within a home. If the satellite is using the spectrum above about 950 MHz, the MoCA system can squeeze the home networking channel between 860 and 950 MHz.
The MoCA standard relies on the ability of the splitters normally used in home cable installations to work in both directions for two-way communications between any nodes on the cable. Contrary to popular belief, the splitters (which are passive devices designed for one-way transmission) easily work in both directions. Any room with an F-connector jack will automatically be able to speak to any central video source or any other node.
What makes the MoCA solution so desirable to providers of high-definition video is that the cable provides a medium that can reliably deliver up to 270 Mbits/s of gross data speed and easily more than 100 Mbits/s of net speed that can handle multiple SDTV or HDTV streams uncompressed. Name one other home networking technology that can do that!
Other determined contenders can deliver the triple play everyone dreams about. 802.11 Wi-Fi is the most widely used method today. But even in its fastest current form, 802.11g, it can only deliver up to 54 Mbits/s peak, and that's rarely achieved.
More common is just less than half of that rate even under the best conditions. When walls, ceilings, floors, and other obstacles interfere, the signal level drops off and the data rate follows to maintain a link. Such speeds are more than adequate for Internet access but not good for quality video.
The new draft-n or pre-n Wi-Fi routers/ gateways use multiple input/multiple output (MIMO) to achieve higher speeds of up to about 100 Mbits/s. The final 802.11n standard products are expected to deliver even higher rates. A final standard isn't expected until 2008, so the pren products will fill that gap.
Wireless is tempting, since it is so easy to set up, and no new wires are needed. Yet it remains to be seen whether 802.11n will actually deliver the kind of performance and quality of service (QoS) that consumers expect for their video. Still, it's a prime contender.
Ultra-Wideband (UWB) easily provides up to 480 Mbits/s, but over a range of less than 10 m. It's not the best option for whole-house or room-to-room links. But for short-range interconnections between video boxes, it's a great low-cost winner. TZero has a version of UWB using MIMO and other techniques that can extend that range, but it too may not be the solution for every home.
The Home Phone Networking Alliance (HPNA) standard uses the existing builtin twisted-pair phone lines in a home to carry the video. It utilizes the bandwidth well above the voice frequencies used by the phone and hopefully above the bands used for DSL if it's used as the broadband connection.HPNA appears to work well, and claims of data rates to 240 Mbits/s have been made. Can it sustain multiple uncompressed HD streams reliably? Some say yes, while others are doubtful. In any case, some carriers who plan to offer inhome video on demand (VOD) and Internet Protocol TV (IPTV) seriously consider it an option. We shall see.
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