Communiqué

Whatever Happened to Power Line Communications?

Power line communications (PLC) is the technology that uses the ac power line as the medium for the transmission of digital data.  It has been around for decades and is now a highly developed wired communications alternative.  I have not heard much about it lately and wondered what was happening.

A while back, PLC was considered as an alternative to DSL and cable TV for high speed Internet connectivity.  It not was widely implemented because it was never fast enough to really compete successfully.  It was eventually abandoned because of the massive interference it caused to the ham radio and short wave listening bands (3-30 MHz).  Today, PLC is primarily a home networking technique.

There are several aspects to home networking.  The one we all know and use is Wi-Fi as it is what connects our smartphones, tablets and laptops to the home router connected to the Internet via cable TV or DSL.  It also connects our TV sets to Netflix by way of an Apple TV, Roku, or other over the top (OTT) TV box.  Wi-Fi is even increasingly used in connecting things to the Internet like home thermostats, video cams and some appliances.  Where PLC comes in is connecting multiple TVs, DVRs, DVDs, or other devices scattered around the home to the Internet.  Another technology that does the same thing is MoCA (Multimedia over Cable Alliance) that uses the existing home cable TV coax wiring.

The most widely used PLC technology is HomePlug (HP).  It is a standard of the HomePlug Alliance that was established in 2000.  The latest version of HP is AV2 that uses OFDM over the frequency range of 2 MHz to 86 MHz on the ac line.  Using modulation to 4096QAM it can achieve a raw data rate to 1 Gb/s or 500 Mb/s considering overhead.  This is useful for transporting HD video around the home.

I spoke with HomePlug President Rob Ranck who said sales of HP products were good.  They are not as visible as Wi-Fi products, but they are on the shelves at Best Buy and other retail outlets.  Usage is probably greater in Europe where Internet providers build in PLC to their modems and routers.  PLC gives better coverage than Wi-Fi in Europe where housing and building construction is harder for Wi-Fi to penetrate.  In the U.S. PLC helps whole home coverage by extending Wi-Fi coverage with re-broadcasters in a hybrid arrangement.  More and more, HP is being integrated into set top boxes, OTT routers, Internet TVs and other devices.  In any case, HP is alive and well and makes a great alternative for home connectivity.  Check out the resources at www.homeplug.org.

The other major PLC technology is G.hn.  This is a newer standard by the ITU designated G.9960 and G.9961.  It was designed so that it can use any available wired medium like existing telephone twisted pair, cable TV coax or the ac line.  It too uses OFDM to achieve data rates to 1 Gb/s as well.  There does not seem to be many commercial products available for the home networking market.  At least I could not locate any here in the U.S.  My inquiry to the Home Grid Forum was not answered in time for this article but you may want to check out their site at www.homegridforum.org.  My guess is that there is more activity in Asia than in the U.S.  It is an excellent technology that may have come too late for the U.S. market where HomePlug is the only PLC source.

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