Ethernet-class networks over standard home power links are coming, thanks to ASIC-based signal processing advances that keep a lid on the interference and transfer function degradations that compromise the power line transmission medium.
The vision of the networked home has driven many a business plan, but product offerings to date have been too limited in capability or in market potential to achieve the dream. Advances in ASIC density, however, enable the use of sophisticated signal-processing techniques at price points that are making Ethernet-class home networks via wireless, phone lines, and now power lines a cost-effective reality.
Home networking is a different animal than networking in the workplace. The applications are different, the traffic patterns are different, and the media available to carry the data are different. Certainly home networking users will want to transfer files between their computers and share peripherals such as printers. They will want gateways to broadband access so they can share their Internet connection between multiple devices.
Users will also want other services, such as voice-over-IP (VoIP), streaming media for entertainment, and support for multiplayer networked games. And while some newer houses are wired with Cat5 cable suitable for Ethernet, most are not. The choices for the physical medium - phone wiring, wireless, and power line - all present a mixed bag of attributes.
The power line is certainly the most difficult medium of these three, but it does have two appealing attributes. First, as with phone lines, no RF conversion hardware is needed, so the cost can be low compared to wireless solutions.
But more importantly, power outlets are almost everywhere someone might want to use a networked device at home.
Aiming to stem consumer confusion and market fragmentation, a group of industry leading companies formed the HomePlug Powerline Alliance to create an industry standard for high-speed home networking via power lines. An extensive field trial is planned to validate the v1.0 specification beginning in the first quarter of 2001.
The power line medium is a harsh environment for communication. The channel between any two outlets in a home has the transfer function of an extremely complicated transmission line network with many stubs having terminating loads of various impedances. Such a network has an amplitude and phase response that varies widely with frequency.
At some frequencies the transmitted signal may arrive at the receiver with relatively little loss, while at other frequencies it may be driven below the noise floor. Worse, the transfer function can change with time. This might happen because the homeowner has plugged a new device into the power line, or if some of the devices plugged into the network have time-varying impedances (which can be the case with switching power supplies or motors).
