Thursday, June 24, 2010

UK Ofcom Publishes Key PLT/PLC Report

A long-awaited report from PA Consulting Group, as commissioned by the UK Office of Communications (Ofcom), has been released.

The report is entitled "The Likelihood and Extent of Radio Frequency Interference from In-Home PLT Devices." It carries a publication date of "21 June 2010."

This is a dense, highly detailed document with 156 pages. However, its conclusions are clearly written and easy to understand.

Basically, if nothing changes in the design of the home network adapters sold to the public, the UK can expect significant degradation of many radio systems and some hardwired services such as DSL, by 2020. Affected radio comm spectrum would include nearly all of HF outside amateur bands, and most of VHF.

PA, however, remains hopeful that design changes can reduce such interference.

Here are the most relevant parts from the conclusions in the summary at the beginning. Those wanting to read more and make their own conclusions can get the entire document at this link.

Page 1:

1 Executive summary

Power Line Telecommunications (PLT) devices are used for data distribution in the home

Power Line Telecommunications (PLT) is the collective term for various forms of communication over wiring used for supplying electricity (termed the 'mains' wiring throughout this report). The most recent developments in PLT devices address the consumer market for in home connectivity as an alternative to WiFi or data cabling. It is these in-home PLT devices that are the specific focus of this study. In-home PLT devices are growing in popularity and, in particular, their use in BT Vision installations in the UK has made the UK one of the biggest users of in-home PLT devices in Europe.

Ofcom has received complaints of interference caused by PLT devices and has requested this study The majority of PLT devices on the market today operate at HF frequencies and, while they are not intended to radiate, there is evidence of interference to other HF users which has resulted in a number of complaints to Ofcom. While most of these complaints have been resolved, Ofcom is concerned that the problem may grow as the number of PLT devices deployed increases over time. Higher data rate PLT devices operating up to 300MHz have also started to emerge in the UK market and so potential interference at VHF is also a concern.

Ofcom has asked PA to assess the likelihood and impact of RF interference from in-home PLT devices over the next 5 to 10 years.

Our results show that users of sensitive radio systems may increasingly suffer interference from PLT devices

In this study we have taken a statistical approach to quantifying the probability of interference occurring as PLT devices become more commonplace. We have concluded that if uptake increases in line with our market forecasts, there will be a high probability of interference to some existing spectrum users at both HF and VHF by 2020 if PLT device features do not change from those currently implemented.

However, within this timescale, in addition to the existing practice of notching International Amateur Radio Union (IARU) bands, interference mitigation features such as power control and smart notching are expected to have been implemented in PLT devices. Our results indicate that the introduction of these features will be enough to reduce interference to negligible levels in the majority of these cases. The exception to this is the safety critical aeronautical bands which we recommend are notched by default rather than by smart notching. [Smart notching only responds to very strong and persistent signals like SWBC, not weak USB comm. -Hugh]

And Page 3:

It is important that mitigating features are implemented in future PLT devices.

The majority of PLT devices in the UK to date have been issued as part of the BT Vision package; however, there is churn in this market, and it should not be assumed that the existing installed base is traceable or could be updated to incorporate these features. We do however assume that the current practice of PLT devices being upgraded in cases where they have been identified by Ofcom as sources of interference will continue and ensure that the existing installed base is gradually replaced where needed.

While power control and smart notching are already part of the product roadmaps of the PLT vendors that we consulted as part of this study, we recommend that where possible the introduction of these features is formalised to ensure that their introduction can be relied upon.