5 Broadband PLC systems for data transmission
5.2 Parameters of BPL

From the perspective of BPL signal transfer, two parameters are important:

As already stated, a power distribution network, considered as a transmission medium, represents a very problematic environment in terms of electromagnetic compatibility. Moreover, the conditions for the energy transfer vary every moment (due to operational handling and connecting/switching on appliances). It is therefore necessary to carefully select appropriate modulations in BPL, (but also coding methods and methods for detection and correction of errors). This, however, increases the necessary number of service bits, which actually decreases the effective transmission rate of user data.

Generally speaking, the higher the bit rate, the lower the immunity to errors, and therefore more transmission capacity must be reserved for error detection and correction. In systems with smaller transmission rates, the ratio of useful and redundant data is about 1: 1. In systems with a transmission rate of 200 Mbps, this ratio is about 1: 3 (thus only about 30% of the transmission capacity is accounted for useful data). The maximum achievable distance between two BPL modems depends mainly on the output power of BPL signal, its attenuation and also at the level of interference at the receiving side. Without repeaters, it can reach the distance of hundreds meters, but only in public electrical networks with outdoor or underground wires. For the inner part of the network with a variety of sources of interference, any average value of the span does not provide useful information, because different installation affects the reach of tens of meters in both directions. In indoor systems, the reachable distance is about 100 m.

A BPL modem can be attached to the power grid either directly or inductively. Direct conductive connection of the BPL modem by using the output power cable, of course, assumes that the capacitive coupling enabling to connect the modem to 230 V is its internal part.

While the narrowband PLC systems are designed based on the international standards, the standardization for broadband BPL systems is still unresolved internationally.

The electricity network in more developed countries offers 100% coverage of buildings, i.e. both households and companies. In less developed countries, BPL can substitute the lack of telecommunications infrastructure. One of the results of negotiations between manufacturers, electric utility companies, is the project entitled Open PLC European Research Alliance (OPERA), its main sponsor is the European Commission. OPERA project involved 37 companies and universities from ten European countries. OPERA was then officially launched in 2004 at the European BPL meeting, held in Madrid.

During the development of BPL systems there were a large number of manufacturers. Particular products can be classified based on the specific production generations, which differ mainly in terms of modulation type and achievable bit rate of transmitted data. In Europe, most modern BPL modems of the 3rd generation uses DS2 chip using OFDM modulation. Such BPL systems become competitive to conventional telecommunications technologies used in access networks.

Although BPL technology is still developing, one cannot ignore the fact that even after many years of technical development and testing, practical use of BPL is usually limited to a relatively small pilot projects, of which only some have the ambition to grow into a much larger scale. Probably the largest project about PLC/BPL system was run in Texas in the US companies ONCOR Texas, CURRENT Group, LLC. The goal was to implant these technologies within the framework of the project Smart Grid. At present, BPL systems can be commercially offered in the following application areas, e.g.: low area industrial networks, internet connectivity for local providers, supplementing the existing fixed networks in areas where they are not yet implemented, temporary solutions for exhibitions, seminars, training or presentations, construction of data networks in the areas with limited construction or reconstruction possibilities - e.g. historic buildings, museums, galleries; domestic LANs (e.g. linking PCs, printers, phones, fax), access network combined with the use of other telecommunication systems (fixed telephony and data networks, GSM, GPRS, WiFi radio networks, etc.), and finally the use in countries with less developed communications infrastructure in Asia, Africa and South America.

Observing current development of BPL systems, one can conclude that these systems are already part of telecommunications access networks, and their further development is related to the issues of standardization, which suggests lowering their prices due to larger production series, thus increasing the efficiency of their deployment. Future approach to the problem of their deployment in the electromagnetic environment of new intelligent buildings and modern management systems, especially in case of Smart Grids, is found to be very important.