The Different Technical Approaches to PLC

While power line communications vendors all agree PLC has huge potential in light of the ubiquity of the power grid, these companies differ significantly in the approaches they take to enable communications services over these wires.

One of the more interesting approaches comes from Amperion Inc., which pairs its medium voltage Connect power line technology with Wi-Fi access. The decision to use Wi-Fi technology to provide access was made because it is the safest and most effective mechanism to deliver broadband to the widest range of customers, according to the company. "PowerWi-Fi access enables us to deliver broadband quickly and inexpensively," says Philip Hunt, CEO of Amperion. "The proven flexibility and economies of scale offered by Wi-Fi, combined with the pervasiveness of power lines, gives us an inherently safe means of delivering broadband to the widest number of families and businesses."

Employing 802.11b Wi-Fi as the customer interface also delivers economies of scale, lowest cost per home passed and broad availability, says Amperion, which augments Wi-Fi with its own layer of privacy and security. The Amperion Connect product line is one of the few technologies to provide sufficient backhaul throughput and reach to support multiple 802.11b networks, according to the company. The system, which is designed to serve multiple customers per transformer, delivers data at 20mbps, or 45mbps raw speed, says Hunt.

Components of the Connect power line system -- which can use other methods of access besides Wi-Fi -- include an injector, a repeater and an extractor. The devices just clamp on to one electric line, explains Hunt. "This is truly a bird on the wire," he says, noting it doesn't matter what the voltage is on the wire since it's just a piggyback architecture.

Other PLC vendors use the low-voltage power lines in place to get from electrical transformers to customer locations. Seth E. Libby, senior analyst with The Yankee Group, explains that medium voltage lines on the network side of neighborhood transformers feed numerous arteries of low voltage into homes and businesses. "To make that transition from medium to low [voltage] you need a transformer to step down the voltage," Libby explains. "From a networking standpoint that creates a hurdle. The transformer blocks or interferes with the signal. So what do you do? You can amplify the signal so it's so loud that it can move through the transformer. The problem with that is it can create RF interference" with TVs in the area, with military frequencies and the like, he says. Or, Libby explains, a non-conducting physical coupling device can work with the transformer. That would convert that signal to fiber or coax into the home or to another device on the medium voltage power line, which then converts the signal back to low voltage, he says.

PLC vendor Main.net employs technology something like the first example Libby mentions. Jeff A. Norman, vice president of sales at the Reston, Va.-based vendor doesn't want to apply the word "amplification" to the company's Plus, Power Line Ultimate System. "Refresh is the word I would use," says Norman. "FCC Part 15 [defines] how strong a signal we can put on the grid. The signal never comes out of the modem any higher than it comes into it. When signal strength is not strong enough, Main.net repeats the signal indefinitely -- recreates it." Main.net's product is the only PLC solution on the market that's FCC Part 15 certified, Norman adds.

Components of the Main.net system include a concentration head end unit, which Norman says is akin to a DSLAM; RF repeating units at transformers, which Norman says are the solution's differentiating feature; in-home Ntplus network termination devices or modems; and a network management system.

Amperion offers two product lines. The Falcon 1000 MV (above) is designed to operate in overhead power distribution networks. The Lynx 1000 MV (below) is designed for underground systems. Amperion's solution includes devices to send, receive and repeat high-speed signals over power lines. The product lines consist of an injector, an extractor, and a repeater/extractor. The Amperion Connect system provides up to 18mbps of delivered throughput per injection point depending on line quality and equipment spacing.

Share this article: Email, Slashdot, Digg, Del.icio.us, Yahoo!MyWeb, Windows Live Favorites, Furl
Add this article feed to: RSS, My Yahoo, Newsgator, Bloglines