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BPL Discussion Points


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1) The official notice.

On July 30, 2005 the Government of Canada issued Notice SMSE-005-5 - Consultation Paper on Broadband over Power Line (BPL) Communication Systems:

http://canadagazette.gc.ca/partI/2005/20050730/html/notice-e.html

which states "The intent of this Consultation Paper is to seek comment on the deployment and regulation of BPL systems, including the specific equipment standards and operational requirements which address potential interference to radio services."


Some background material can be found at Industry Canada's BPL Web page:
http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/en/sf08432e.html


The Consultation Paper is available in PDF form at:
http://strategis.ic.gc.ca/epic/internet/insmt-gst.nsf/vwapj/bpl-e.pdf/$FILE/bpl-e.pdf


The Consultation Paper provides a brief description of various BPL systems and then goes on, in section 6, to Discussion and Proposals, including some suggested BPL system technical parameters.



2) What is BPL?

BPL is a system that would employ single or multi-phase AC power transmission wires to distribute and deliver high-speed (broadband) Internet signals to homes. The signals would be carried by medium or low voltage power distribution lines. In Europe, BPL is also known as PLT (power Line Telecommunications) and PLC (Power line Communications). A signal injector would produce the BPL signal and couple it to the power line(s). A BPL modem would be used to extract the network signal and provide bi-directional communication to connected computers, etc. BPL would use the frequency range between 1.705 and 80MHz to carry its signals. The Consultation Paper provides a good description of the various types of BPL systems and additional information can be found in the Web references.



3) Why should radio users be concerned?

Unlike cable systems that use shielded coaxial cable, or DSL/ADSL systems that use differentially driven closely-spaced line-pairs, BPL will employ a wiring system that was never designed to carry, and equipment that was never designed to deal with, signals in the proposed frequency range. The unavoidable and demonstrated consequence of this is radiation of the BPL signals. The important questions are:

  • what level of radiated signal should be permitted;
  • over what frequency range or ranges should this level be permitted.
In order to judge BPL's effect on radio reception one must look at the sensitivity of today's receivers and compare the strength of typical signals, and existing noise sources, to the interference produced by a BPL system. Our ability to hear a signal is determined by the relative strength of the desired signal compared to any environmental noise sources plus the receiver's internal noise. This determines the signal-to-noise ratio at which we hear a radio signal. In the HF band, in most cases, it is the external noise sources that dominate. The sources of this noise include cosmic and atmospheric noise, plus manmade noise.

Although it is the relative field strength values of the signal and noise sources that are the determining factors of the signal-to-noise ratio, the following analysis will be developed from the radio user's point of view. That is, the effects of BPL signals will be expressed in terms of received quantities - dBm, microvolts and S-units. It will be assumed that the antenna is a half-wave dipole in free space, the feed lines are lossless and the SWR is 1:1 at all points in the system.

The field strengths given as emission limits in section 6.2-a of the Consultation Paper were used to calculate the amplitude of a BPL signal in a receiver. The International Telecommunications Union has evaluated the typical noise environment in several different types of locations, from a noisy business area to rural and quiet rural sites, and has developed formulas that can be used to calculate the noise as a function of frequency. The first two graphs below show ITU noise spectra and BPL signal strengths as a function of frequency. The signal strengths are given in dBm in one graph and in microvolts in the other. Each of these graphs shows the ambient noise in four different locations (the four lower lines), the strength of a BPL signal at the emission limit given in the Consultation Paper (the second line from the top, labeled BPL @ SMSE-005-5) and the BPL signal, scaled as described below, to a BPL-line-to-receiving-antenna distance of 3m (the top line, labeled BPL 1/r extrapolated to 3m). The third graph will allow radio users to convert the signal amplitudes in the first two graphs from dBm or microvolts to more familiar S-units. Even a quick glance at the graphs shows that, depending upon location, BPL signal amplitudes are 30 to 60dB above ambient noise levels.

graph - BPL and noise in dBms
graph - BPL and noise in uV
graph - dBm and uV to S-units

Today's HF receivers have SSB/CW sensitivities of about 0.2 microvolts (-121dBm) and MDS (minimum discernable signal) levels that are in the region of 0.07uV(-130dBm) or lower. However natural and manmade noise sources will be the limiting factor when it comes to the reception of weak signals. These data are presented in the graph above, but we can get a feel for the numbers by picking a frequency in the middle of the 20 amateur band (14.150MHz). If we assume that amateur radio operators, short-wave listeners and other radio users will reside in quiet rural, rural or residential locations, we get noise levels of -120, -105 and -100dBm[1]. The results are summarized in the table below.

Non-BPL noise level (14.150MHz)
unitsQuiet RuralRuralResidential
dBm-120-105-100
uV0.221.22.2
S-units1.13.74.5


What is the strength of typical amateur radio and short-wave signals? Amateurs and other radio users frequently work with signals in the -107dBm (S-3) to -85dBm (S-7) range. Strong signals would have levels in the range of -73 (50uV, S-9) to -53dBm (500uV, S-9+20dB). While not of broadcast quality, amateurs have become adept at receiving weak signals and frequently achieve communications with signals that are close to the ambient noise level. Experienced CW operators can copy signals that are at, or even slightly below, the ambient noise level.

What about the strength of BPL signals? The amplitude of a BPL signal at 14.150MHz can be obtained from the graphs above. A BPL system, operating within the emission limits specified in the Consultation Paper and at an antenna-to-power-line separation of 30m, can produce a signal with an amplitude of -68.5dBm, or 84uV. This is 31.5dB above the background noise in a residential area and 36.5 and 51.5dB above the noise levels present in rural and quiet rural areas! If you have an S-meter on your radio, the BPL "signal" would be received with a signal strength of S-9+5dB. It is difficult to see how anything but the strongest signals would be heard under these conditions. Of what value is an emission limit that allows all but the stronest signals to be obliterated?

Is the 30m separation to a BPL line realistic for HF antennas? It must be realized that in any area with power distribution wires, it will be nearly impossible to locate an antenna at the 30m (98.4 foot) reference distance specified for the emission limits in the Consultation Paper. This would be particularly true in urban areas where lot dimensions will limit the separation that can be achieved between a back yard tower-mounted antenna and surrounding power lines. The situation will be even worse for apartment or condominium dwellers. With the dimensions of typical residential dwellings, which contain power wiring in the walls, floors and ceiling, a more realistic separation between radio antennas and BPL lines would be 1 to 3 metres. Even with tower-mounted antennas, the 30m separation is unrealistic except for radio users with large lots and antennas located far away from the house and any BPL-signal carrying line. A more realistic distance of 10m might be achievable for some tower-mounted antennas located in single-family homes on larger-sized lots. Of what use is an antenna-to-BPL-line reference separation that does not apply in any but exceptional cases?

What happens if your antenna is closer than 30m to a BPL line? The strength of a BPL signal varies in a complex fashion with distance from a BPL line and does not necessarily follow an inverse-square law. This is due in part to the fact that a power wire carrying BPL signals is an extended source of RF signals, several wavelengths long, and not a point source. Also, local objects will often be in the near field of the BPL cable and modify the field distribution. Even receiving antennas will often be in the near-field of the BPL cables. It is a difficult question to answer and the solution requires careful calculation and computer modelling, however, we can make a simplifying assumtion. The most optimistic extrapolation would assume a 10dB increase in BPL power when the distance is reduced by a factor of 10 (power varies as 1/distance). (Other studies have asssumed an inverse square-law dependence which would produce a 20dB increase in signal power for every factor of 10 reduction in distance from the source.) Applying a 1/distance factor to the 30m emission limit field strengths specified for the 1.705 to 30MHz portion of the BPL band will raise the interfering BPL signal power by an additional 4.8 dB for antennas that are located 10m from the BPL line, 10dB for antennas at 3m and 14.8dB for an antenna which is 1m from a BPL line. The effects are summarized in the table below. This would bring BPL signals to the level of high-power international broadcast stations and amateur stations running full legal power into large directional antennas. BPL on HF would truly be armchair copy.

Summary - 2 to 30MHz
 dBmuVS-units
ITU Rural noise-115 to -1000.4 to 2.22 to 4.5
Rcvr sensitivity-1210.21
MDS-1300.07below 1
Typical signals-103 to -791.6 to 254 to 8
Strong signals-73 to -5350 to 5009 to 9+20dB
BPL at 30m-68.5849+5dB
BPL at 10m-63.71469+10dB
BPL at 3m-58.52669+15dB
BPL at 1m-53.74629+20dB


Compare the amplitude of the BPL signal to the environmental noise values in the above table, it is difficult to see how any HF receiver located in the vicinity of a BPL system, that is in compliance with the emission limits given in the Consultation Paper, would hear anything except the interfering BPL signal. Of what value is an emission limit that would allow the short-wave bands to be blanketed by interference?

1: ITU-R Rec. P.372-6, found on p.3 of the BBC R&D White Paper WHP 013, "Emission Limits" Nov. 2001


4) What is being threatened?

BPL signals will appear in the top portion (1.705 to 3.0MHz) of the medium frequency (0.3 to 3MHz) band and throughout the high-frequency (3-30MHz) band. This frequency range has propagation characteristics not found elsewhere in the radio spectrum and is used for everything from regional to worldwide communication and broadcasting. Modern radio communications, in a very real sense, exists because of the technology, communication and broadcast services that were first developed and demonstrated in the HF bands.

The 30 to 80MHz range is used for television broadcasting, amateur radio, and various other mobile and fixed communication services. The 6m amateur radio band (50 to 54MHz) is within this frequency range and, without appropriate action, will also suffer interference from BPL systems.



5) Who would be affected by BPL?

The consultation Paper mentions the possibility of interference to "radiocommunication users" and "authorized radiocommunication services" which seems to exclude non-licensed users such as short-wave listeners and General Radio Service (CB) operators. Anyone who receives a signal in the 1.705 to 80MHz range of the radio spectrum is a radio user. The Consultation Paper should address all users of the 1.705 to 80MHz section of the radio spectrum, not just licensed users and services.



6) What can we expect?

Increased noise and interference levels between 1.705 and 80MHz. Experience in Europe and the U.S. has shown that BPL systems which would meet the emission limits contained in the Consultation Paper will be sources of wideband noise and greatly raise the noise level in areas served by BPL. If 1.705 to 80MHz BPL systems are widely installed in urban areas, and operated in the frequency range given in the Consultation Paper and in compliance with its emission limits, it will be difficult to find any area that will be free of BPL interference. While the density of BPL cabling might be lower in rural areas, the behaviour of BPL's radiated fields will ensure that its effects are felt far beyond the users it is intended to serve.



7) Does BPL comply with ITU regulations?

International Telecommunication Union regulations have the effect of a treaty on member nations and Canada is a member of the ITU. ITU Radio Regulation 15.12 states that

"administrations shall take all practicable and necessary steps to ensure that the operation of electrical apparatus or installations of any kind, including power and telecommunication distribution networks, but excluding equipment used for industrial, scientific and medical applications, does not cause interference to a radiocommunication service and, in particular, to a radionavigation or any other safety service operating in accordance with the provisions of these Regulations"
The ITU sets out protection limits that require the interfering signal amplitude to be below that of the intended signal by a protection ratio.

With the emission limits suggested in the Consultation Paper, a BPL system could be in compliance with the limits at the specified 30m distance and still produce an interfering signal with an amplitude 20 to 50dB+ above that of the ambient noise level. This interference would also have an amplitude well above that of many received signals. The result would be a negative protection ratio for all but the strongest signals, and place Canada in violation of ITU regulation 15.12.


8) Does BPL agree with European Community Directives?

Further guidance on electromagnetic compatibility issues can be found in European Community EMC guidelines, although it should be noted that EC directives have no force in Canada. Section 4.1.4 Article 4 states, with reference to interference producing equipment, that:

a: the electromagnetic interference it generates does not exceed a level allowing radio and telecommunication equipment and other apparatus to operate as intended.

b: the apparatus has an adequate level of intrinsic immunity to electromagnetic disturbance to enable it to operate as intended.

The key phrase is "...to operate as intended." (see section a: above). It is hard to see how BPL systems that produce interfering signals with amplitudes above that of the intended signal, and far above the ambient noise levels in urban and rural environments, could allow radio equipment to receive the weak or moderate strength signals it is designed to receive.


9) Will BPL work as a business?

If you go to a bank for a business loan or to investors for support, you are asked to show your business plan. Before you can get anywhere, you must present a plan that shows how you intend to fund your business, details of your management structure, provide estimates of your setup and operating costs, and convince people that your idea will work and show a profit. Should the Government of Canada put time and energy into something that has yet to show how it will work as a business?



10) Is BPL the right technology?

The expansion of DSL/ADSL and cable modem technology has extended these high-speed Internet services out from urban areas into rural locations. While BPL could technically provide high-speed Internet access, it is highly questionable whether, or not, it provides any advantages over the above technologies. DSL/ADSL and cable systems have a widely installed infrastructure employing a reliable and stable technology. Expansion of the networks would simply involve installing more of the existing hardware. BPL operators would be required to install the complete infrastructure needed for their systems. Considering the unsuitability of power lines as high-speed network signal carriers, BPL is, at best, a very poor alternative to DSL/ADSL and cable modem systems and a technology that is already at its limits.



11) What’s really in store for the future?

If anything, the future will come from two directions - wireless and fibre-optic networking. As far as cable-based systems, the limited channel capacity provided by BPL is greatly surpassed by fibre-optic network technology. Developed approximately 30 years ago, fibre-optic networks have grown in technical sophistication and capacity. Wireless systems operating in the gigahertz frequency range can provide channel capacity equivalent to, and surpassing, that of BPL. Wi-Fi, today’s technology, provides speed up to 2Mbits-per-second in short-range wireless hot-spots while emerging WiMAX systems will provide up 75Mbps at distances up to 10km.

Rogers and Bell announced on September 16, 2005 that they had formed a joint venture, called Inukshuk (www.inukshuk.ca), to deliver broadband high-speed to two-thirds of Canadians in less than three years. Inukshuk also plans to deliver high-speed services to "unserved and remote communities". (www.inukshuk.ca/anglais/20050916press.html)

Make the judgment yourself. Does the future course of Internet communications lie with a technology that, from inception, is at or close to its limits (bandwidth available on power line cables)? Or does it lie with fibre-optic systems with channel capacities in the gigabit-per second range and wireless systems that can have access to the spectrum space available in the microwave region? If resources, money and regulatory effort will be used to develop communications infrastructure for the future, is BPL an investment that will produce a network with the future potential of fibre-optic and wireless systems?



12) What can you do about it?

Industry Canada is asking for comments on Notice SMSE-005-5 - Consultation Paper on Broadband over Power Line (BPL) Communication Systems from interested parties, amongst which can be counted all users of the radio spectrum. The deadline for comments is 28 November 2005, and all comments submitted will be posted on Industry Canada's Spectrum Management and Telecommunications Web site at http://strategis.gc.ca/spectrum

Comments should be provided in electronic form (WordPerfect, Microsoft Word, Adobe PDF or ASCII TXT) with a note indicating the software, the version number and the operating system used to produce the comment. All submissions should cite the following:

Canada Gazette, Part I;
publication date 30 July 2005;
title Consultation Paper on Broadband over Power Line (BPL) Communication Systems;
notice reference number SMSE-005-05.
Submissions should be sent to the following email address: DGSE-BPL@ic.gc.ca. Non-electronic responses should be addressed to:
Director General,
Spectrum Engineering Branch,
Industry Canada,
300 Slater Street,
Ottawa, ON,
K1A 0C8


It would be helpful if you send a copy of your submission to RAC as well:
Joe Parkinson VE3JG, Chair
RAC BPL Response Committee,
720 Belfast Road, suite 217,
Ottawa, ON
K1G 0Z5




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The opinions expressed on this site are those of Leo Nikkinen, VE2SI
Page created on 12 November 2005, last revision November 21, 2005