The opportunity to provide Internet services, video-on-demand, and video streaming directly into the home or industrial building at cost effective prices and at a time when customers require such services is an opportunity not to be missed.

However, providing such services requires higher data rates and consequently higher bandwidths and operating frequencies. At the moment the frequency band 1MHz to 30MHz is being used for trial systems. Particular propagation problems are associated with transmitting at these frequencies, and these require investigation before a full commercial service can be implemented. The development of standards for these services will be considered with respect to current developments. 

The last ten years have seen electricity companies worldwide investigate and implement communication services using the 11kV, low voltage power distribution network. The driving force behind this commercial enterprise arises from the competition to introduce new services to a broad range of customers – industrial, commercial and residential. However, the limited bandwidth available on all types of communications services throughout the world is a matter of growing concern.

Low frequency transmission


The first power line carrier services concentrated on transmission and reception in the low frequency band. In Europe, the European Committee for Electrotechnical Standardisation, CENELEC, produced EN50065, a standard covering the communications requirements for transmitting and receiving signals over the low voltage distribution network, both to the building and in building communication, in the frequency range 3kHz to 148.5kHz. The USA frequency band covers the frequency range 45kHz to 450kHz. 

The services provided in this frequency range included remote meter reading of all types of utility meter, basic load and energy management. This type of service required only low data rates, which could be provided efficiently at these low frequencies. As the demand for more services into buildings grows, however, competition between the major cable companies intensifies. Because of the shortage of bandwidth, companies are exploiting other parts of the frequency spectrum in the range 1MHz to 30MHz. This allows them to enter into broadband services associated with high speed data services, such as the Internet.

Introducing such services places a demand on the technical requirements for conditioning the low voltage distribution network. Managing the increase in bandwidth from a few kilohertz for low data rates to several megahertz for these new services will require considerable ingenuity. In particular, the propagation of signals at these frequencies through the differential, and common mode signals leading not only to ground wave transmission but also sky wave propagation, requires thorough investigation.

High frequency transmission


Data transmission for broadband services takes place in the frequency band 1MHz to 30MHz. This frequency range is subdivided into the access band operating from 1MHz to 10 MHz, and the in-house frequency band which operates from 10MHz to 30MHz.

The transmission of power line systems in the high frequency range 1MHz to 30MHz gives rise to potential interference with a variety of well-established services throughout the world, including:

  • Broadcasting
  • Amateur radio
  • Mobile communications
  • Distress frequencies
  • Space research and radio astronomy 
  • Military communications.

In particular, operating in the frequency band 1MHz to 30MHz provides potential problems in the access band between the distribution sub-station and the building (whether residential, commercial or industrial) as well as in the in-house band, although this is limited to a smaller area. However, power line communication is not the only system operating at these frequencies that contributes to the interference with established communication services. The introduction of xDSL services through the use of the copper pairs in the ground in conjunction with the optical fibre allows some millions of users to have high speed Internet communication services. Further cable networks and LANs potentially contribute to the interference pattern.

The regulatory framework


In order to establish the same radiated emission level from all cable network communication systems operating in the high frequency band throughout the world, it is essential to have a single framework within which all users are able to operate. Due to the propagation characteristics associated with frequencies in the range 1MHz to 30MHz, any standard must follow international agreement.

The radio spectrum at an inter-national level is governed by the International Telecommunications Union (ITU). They set the frequency bands for particular services and the way those services are managed throughout the world. The direct management of the spectrum is then implemented by different regions. For example in Europe the conference of European post and telecommunications administrators (CEPT) manages the spectrum through the Electrical Communication Committee (ECC). A prime function of their work is the use of the spectrum and how it is protected from interference. 

However, the communication network has two key components – the equipment connected to the network and the communication network itself. The communication equipment for the European network is the responsibility of the European Telecommunications Standards Institute (ETSI) and the European Committee for Electrotechnical Standardisation, CENELEC. They have established working groups, ETSI PLT and CENELEC S/C205A working group 10, High Frequency Communications, to investigate high frequency radiated emissions from power cables. Between these two committees every aspect of communication using the power line, both on the access and in-house network, is being investigated. Other committees from CENELEC involved in developments are TC215 for telecommunication standards and TC209 for cable networks .

The establishment of electromagnetic compatibility (EMC) limits and allocations of the radio spectrum are carried out through the ETSI ERM committee, which acts as a focus for all the ETSI committees.

There are three permanent working groups within CEPT: frequency management, spectrum engineering (WGSE) and a conference developing proposals for world radio conferences. In particular, WGSE35 is active in determining the radiated emission limits for wired cable networks and their interference effects on established radio services. The committee is producing two reports covering cable communications and the effects on radio communication services, and the radiated emission levels from wired communication networks.

During 2001 the European Commission issued a mandate, M313, to CEN, CENELEC and ETSI requesting the establishment of harmonised standards for all telecommunication networks. The main thrust for this mandate is the establishment of harmonised standards for power line communication systems, coaxial cables and telephone lines. The emphasis is on the communication network and not on the equipment, although the latter should be in line with any standards being produced for the EMC of equipment. 

In particular these standards should take into consideration the limits set through the EN50083-8 standard, the German standard NB30, which has been withdrawn after one one year, and MPT1570, which covers the frequency range to 1.6MHz. Each of these standards has different radiated emission levels for cable systems, which therefore have to be unified into one single emission standard. 

In addition to these different emission standards there is the USA standard from the Federal Communication Commission (FCC) which is again different and which allows the highest emission levels of all the standards. It is therefore essential to establish limits, and a level playing field, for all cable networks and the level of radiated emissions emanating from them.

At the international level, the International Electrotechnical Commission (IEC) through CISPRE has established a number of committees for the investigation of radio interference. In particular CISPR22 has a number of working groups responsible for determining radiated emission limits for cable networks throughout the world. Their work is well established and recommendations will be forthcoming. 

Conclusions


The ability to provide PLT high frequency services to the residential home and office using the frequency band 1MHz to 30 MHz offers considerable potential. Services include Internet connection, video-on-demand and other applications, with the potential to be competitive compared to other communication providers. However, there are a number of potential problems to be resolved, in particular the radiated emission from the power line network. In order to set limits that all companies and utilities can work with, a series of measurements must be made to establish realistic radiation emissions and their interference effects on established radio services.