Broadband over Power Lines

There was an interview printed in a recent issue of EDN Magazine with a member of the Universal Power Line Association (UPA) [1].  The complete interview is also printed online at EDN Magazine's web site.  The interview covers several interesting points about broadband data communication over power lines.  The first is that the UPA is working on an industry standard that will allow for coexistence between the two main types of this networking.  The first type is broadband internet service provided by the power company over the power lines.  The second type is local area networking within a home.  There are several competing companies with their own incompatible technology right now, mainly:

• DS2 (Associated with UPA) - the Author is from this company
• Homeplug
• HD-PLC (Associated with Panasonic)

Homeplug and HD-PLC are strictly focused on local area networking in the home, while DS2 is trying to come up with a standard through the UPA that takes both LAN and broadband internet service into account.  The current standard activity is in the IEEE P1901 standard.

The interview also covers some of the controversy surrounding broadband over power lines, mainly interference with other RF communications.  There is a link in the article to another article in the August 2006 issue of Computing Unplugged.  What it all boils down to is that there is a trade off between transmitted power and interference level - higher power equals more interference.  It should be possible to mitigate the interference problems by making a good trade off between transmitted power and interference.  When interference does exist, it can be mitigated by filtering and other means.

I'm very interested in communications technologies for the delivery of internet service, television service, and telephone service to the home, and within the home.  This technology is reaching data rates that are actually reasonable for these applications.  The current generation of DS2 technology is 200 Mbps peak, but the maximum data rate typically achieved is 95 Mbps.  The next generation of DS2 technology has been announced and it is 400 Mbps peak with a similar ratio of typical to peak.  This technology is compelling because it can achieve a higher throughput than wireless communications, but has a similar reach through out the house.  It is similar to wireless in privacy though because your network traffic will actually be broadcast out on the power lines for neighbors to eavesdrop on.  The technology also employs encryption similar to wireless networking for privacy concerns.  Overall I think the technology may be better suited to video distribution in the home than wireless.  I still would recommend to anyone building a new home to put in Cat 6 unshielded twisted pair cable because it is scalable up to 10 Gbps for most run lengths within a home.  For longer than 55 m runs, Cat 6a might be needed.  Wireless will not achieve this type of bandwidth for more than line of site short distances for a long time.

The engineering challenge of communicating at 400 Mbps over the really terrible transmission channel of a power line is very impressive.  As the interviewee stated in one of the linked interviews, it really comes down to trade offs in where the complexity is placed.  Generally engineers choose to specify a fairly well controlled transmission channel, especially for wired digital communications.  This removes much complexity from the transmitter and receiver and is good for overall system cost.  However in the case of communication over power lines, the transmission channel is fixed as a very uncontrolled low quality channel, so extra complexity is needed in the transmitters and receivers to compensate. 

[1] Dipert, Brian. December 14, 2007. "Voices: Chano Gomez on Powerline Networking's "Universal" Hope." EDN Magazine. Issue 26.