Friday, December 3, 2010

An update on PLT, Power Line Telecommunications, in Europe.

Power Lines

Image by Manu_H via Flickr

Sometimes referred to as PLN (Power Line Networking), PLA (Power Line Adaptor), PLC(Power Line Carrier), or here in the US, BPL (Broadband over Power Line), the technology enables the distribution of digital communications through conventional power lines, making it easy to setup communications networks without the need to rewire, or use radio transmitters. As data rates of these devices increase, so does the potential for interference, thus much work is being done by stakeholders to develop uniform methods by which to assess products with this technology for compliance with the EMC directive, and prevent unwanted interference of incumbent services.

The CLC/ Technical Committee 210 on electromagnetic compatibility (or TC210) established a working group (WG11) to produce a two-part standard for emission requirements for PLT apparatus of all types, as follows:

EN 50XXX-1 Power line telecommunications modems - Radio disturbance characteristics – Limits and methods of measurement - Part 1: Modems for in-house networks

EN 50XXX-2 Power line telecommunications modems - Radio disturbance characteristics – Limits and methods of measurement - Part 2: Modems for access networks

A draft document for Part 1 has been prepared by TC210/WG11,

The document is being set for a 3 month enquiry under what is called the Unique Acceptance Procedure, or UAP, and then given over to WG 11 for update if necessary. After this, it will be issued for a 2 month vote.

Following is some background on the controversy over PLT.

Currently, no separate harmonized standard exists for testing PLT product specifically. Certain classes of PLT are incapable of complying with current emissions limits as is, thus; some manufacturers have been looking to EU Notified Bodies, some of which have been prescribing the use of alternative draft standards for testing purposes. Manufacturers have a couple of options for EMC compliance, one is a self certification, test and comply with harmonized standards and issue a declaration of such. A second method, when harmonized standards don’t exist or are not able to be applied, is to perform an EMC assessment and prepare a Technical Construction File, usually in consultation with a Notified Body, seeking the opinion of the Notified Body, to support claims of compliance with the essential requirements of the EMC directive. The bottom line however is that in the end, the product must comply with the essential requirements of the EMC directive, which is that, “the electromagnetic disturbance generated does not exceed the level above which radio and telecommunications equipment or other equipment cannot operate as intended”

An independent study, commissioned and published by Ofcom, the UK communications regulator responsible for enforcing aspects of the EMC regulations within the UK, was designed to examine the likelihood and extent of interference from PLT devices. This study was formed mainly due to claims that the use of PLC technology is disruptive to incumbent services, and, as a result, has attracted the attention of stakeholders, most notably, the amateur radio community and shortwave listeners.

As a result of this study, Ofcom advises that the conclusions indicate that the incorporation of mitigation techniques is important for the future of PLT technology. Ofcom expressed its concern that manufacturers should incorporate these features, to provide long term protection to the radio spectrum, and minimize potential for interference. The study can be found via Ofcom’s stakeholder web page

Controversy exists on whether mitigation techniques, such as smart notching or automatic level control go far enough to protect incumbent services. Real concern exists in the amateur radio community that many products on the market now do not implement mitigation techniques at all, and therefore are currently posing a problem for the amateur radio and shortwave listeners. The amateur radio community has been lobbying Ofcom, as the responsible authority for EMC enforcement within the UK, to remove such products from the marketplace. The Radio Society of Great Britain, or RSGB, has established a “Spectrum Defense Fund” to, as indicated in a Feb 2010 statement, “combat the threat of PLT/PLA”, as well as for the general protection of the spectrum for the amateur radio community.

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