Regarding broadband power line (BPL)

Communication Power Line Carrier Systems over electric power transmission cables have been used by power companies from about 50 years. Originally these systems were used by the power companies for transmission of communication signals related to their own needs, especially for protection of high voltage power transmission lines; simple supervisory and control systems, and voice communication channels related to the operation of the electric system. Capacity and speed were relatively low, and carrier frequencies were typically below 2 or 3 MHz. Frequently, they were used over significant distances, using wave traps and coupling capacitors capable of sustaining the line voltages to isolate the electric cables at the carrier frequency.

In general, this kind of systems has been called Power Line Carrier Systems (PLC) or Broadband Power Line Carrier (BLC).

There are presently existing or projected modern BPL systems in many countries, with different levels of complexity used for the management and operation of electric systems, with these objectives, providing useful applications for the power companies within the required parameters, at competitive costs.

Recently, the development of modern modulation, coding and extremely robust error correcting techniques, have allowed to substantially overcome the limitations of the transmission medium, achieving transmission speeds in the range of 200 Mbps in normal conditions, with even higher expectations.

Systems aimed to the digitalization of household equipment should also be mentioned.

Electric power distribution systems have not been designed to carry communication signals, and power system conductors constitute one of the most hostile media for transmission of communication signals. The most important problems are time variant impulsive noise and colored noise related to the load condition of the power system, equipment and devices connected to it and maneuvers in the power system. Random noise sources related to corona effects and atmospheric discharges in medium and high voltage lines, transient in line currents and problems with ground connections in the power system are also present.

In spite of the picture above, BPL systems are presently one of the most promising high capacity communication transmission media, due to the much higher penetration of the electric service in comparison with communication services in all kinds of areas and communities of interest.

Communication channel characterization and the way to confront the problems of transmission are the most important challenges in the development of technologies capable to achieve high capacity, speed and availability in the in the systems. Some of the technologies and protocols used are OFDM, coded or not, multicarrier CDMA (MC-CDMA), Variable Gain Control and Dynamic Selection of Carriers according to transmission conditions in each of them, advanced ALOHA protocols, and others.

There are commercial systems existing today for transmission over low voltage (typically under 600 V) and medium voltage lines (normally between 5 and 35 KV) presently used in the electric power utilities. In these cases carrier frequency isolating impedances are not generally used, but, logically, inductive and capacitive coupling is used to couple the carrier to the electric conductors. In the case of high voltage lines, reactances are used to isolate the cables and couple the carrier signals to them.

There are BPL systems existing today in experimental and even commercial operation in some countries, under the regulations of operation of devices not subject to license requirements, by which the shall not cause harmful interference to other communication systems, belonging to licensed radio communication services, and with the obligation to solve interference situations that may arise.

Emission of non desired radiation of electromagnetic waves is produced when electric power conducting cables are used for the transmission of communication carrier signals, which may produce radiation and induction interference to radio communication systems. The use of BPL systems has to be studied from two points of view: Those related to the transmission of information itself, and those related to the interference they may produce to licensed radio communication systems operating in the same frequency bands used for the transmission of communication signals over the electric cables. Aspects of security in the design of materials and devices integrating these systems shall also be considered. There are existing institutions and institutions and organizations in different countries dedicated to the study of regulations for these issues.

Total independence and autonomy of the operation of the electric power system from the needs of the communication system is another important issue that has to be taken into account in the design of BPL systems. The operation of the electric power grid shall be continued to without consideration of the use of the conductors for transmission of BPL.

It is currently considered that the frequency spectrum convenient for operation of BPL systems is between 1.7 and 80 MHz, even though presently available systems have a upper limit around 40 MHz.

The common frequency spectrum presently used for transmission over medium voltage lines is approximately between 1.6 and 13 MHz, and 13 to 34 MHz for transmission over low voltage lines. This separation has important implications in the study of interferences that may be produced.

The IEEE has been interested in PLC (BPL) for about ten years, and has conducted multiple conferences and work meetings in which important studies have been presented for the development, use and regulation of these systems. The last of these meeting was the International Symposium on Power Line Communications (ISPLC) held in Orlando, Florida, at the end of March this year.

Likewise, the IEEE has created a Study Group on BPL for the study of the issue of compatibility with other communication systems that may receive harmful interference from it. This group has analyzed different scenarios of interference on radio services operating in the spectrum from 1.7 and 80 MHz, in special the Radio Amateur Service in specific bands in the 1.7 – 54 MHz frequency range; the HF broadcast Service in specific bands in the 5.9 – 21.850 MHz frequency range; the Standard Frequency and Time Signal Service in specific bands in the 2.95 – 20.010 frequency range, and the Citizens Band Services in specific bands in the 26.960 – 27.410 MHz frequency range. This Group is continuing studies in the indicated spectrum and is expected to produce new reports on the issue.

The IEEE-PLC Group has taken into consideration that potential of interference produced by BPL systems is related to the intensity of non desired emission it radiates and the signal levels being used by the radio services operating near the power lines carrying BPL signals. This depends on,

- Frequencies being used - Power levels of the BPL system - Radiation patterns and efficiency of the electric power line - Path attenuation between the power line and the antenna of the radio receiver. - Sensitivity and other characteristics of the radio receiving systems.

Among the criteria taken into consideration by the IEE-PLC Group, the principle that BPL systems will operate under the regulations of non-licensed equipment is outstanding. According to this rule, operation of BPL equipment is permitted under the condition that no harmful interference is produced on equipment of licensed services operating in specifically allocated frequency bands, and that problems of interference shall be solved by the operators of the BPL service.

It is generally considered that good engineering practice indicates that specific bands allocated to the Radio Amateur; HF Broadcasting and the Standard Frequency and Time Signal services should be excluded in areas where existence of operators of these services may be expected (normally in residential areas). Likewise, the group recommends the establishment of Coordinating Areas be established in bands allocated to certain critical services, for example specific bands allocated to the Aeronautical Mobile Service (R).

As a general measure, it is recommended that in any case compatibility problems shall de solved on a case-by-case basis by the operators of the BPL service.

The European Community has also advanced important work for the regulation of BPL. ETSI has produced the TR 102 324 V1.1.1 (2004-5) code, which describes the radiated emissions characteristics and associated method of measurements of powerline communications networks. The document also reports the radiated emission characteristics of powerline communication networks in the frequency range 1.605 MHz to 30 MHz. In April 2005 the EC issued a recommendation on BPL in which it recommends Member States to remove any unjustified regulatory obstacles, in particular from utility companies, on the deployment of broadband power line communications systems. The recommendation details how to apply the regulations of the directives on electromagnetic compatibility and requests reporting from the Member States on the standardization process.

It is important that interested world wide organizations, and Administrations of CITEL make efforts for the production of regulations on BPL systems and their subsequent harmonization, with the purpose that BPL systems can be established soon, in an orderly manner, with due protections to radio services that make use of the spectrum involved and technical regulations that would facilitate equipment interoperability.

CONATEL-Venezuela