PLC: Modem and communication link

Problems of present PLC technology, using duplex communication, can be divided into two parts, the modem itself and a communication link.

 Communication link

The communication link, in fact the power line, can be divided into two groups. To branched lines (high and low voltage) ones an branched low voltage lines with dynamic topology alteration. During signal distribution progress processing we can reliably draw from studies that was theoretically worked out and practically verified during HDO introduction and operation. Signal distribution mechanism and connections building needs a different principal theoretical attitude from the one of light-current lines for mostly multiwire asymmetric system is the point. Due to simplification a definition of distributed parameters was attended to where procedures for individuals sections of similarly same parameters are described resulting from theory of two-port networks. Each element notation exists in form of property matrix describing e.g. wave impedance, transmission, etc. Notation is given in a complex form.

A universal admittance method turned out for transmission properties analysis of network section which is defined as branched non-homogenous link and individual elements are described in form of matrix. This method can describe an analyzed system by a form of matrix and provides a branched non-homogenous link parameters by means of appropriate procedures. This calculation gives a static transmission image to which marginal conditions must be attached. The marginal conditions, however, has no negligible influence as they comprise dynamic behavior of the system itself (variation of transmission properties at variations of the system load and changes of electrical energy consumers manners respectively reaction to the system).

Modem

Demands on modem itself theoretically worked out as from the point of modulation and demodulation as the following procedures necessary for achievement of reliable communication. The physical modem itself is a result theoretical processes implementation. Since the actual communication runs over a communication link and number of dynamic properties influence the communicating modem (e.g. various interference with different internal impedances, link attenuation variations, transmission effects on the link, etc.) no property, that should be dominant, can be definitely preferred. A reliably functioning modem must be designed with parameters very well balanced.

ModemTec company has managed to transfer information in majority of instances from a concentrator to a terminal point without need of inserted repeaters (contrary to broadband PLC transmissions that have to use repeaters every 50-100m) in the area of single power supply. Both modem groups are able to operate terminal equipment without a special treatment in a given area.

Communicating modems parameters attested in the period of a long time (several years) as by pilot projects as routine projects observation. Selection of pilot projects was focused on different environment of power low voltage distribution systems. Even when the project proved nonexistence of two completely equal locations the company managed to prepare a technique for PLC transmission implementation in any environment. Based on practical experiences every modem has its own diagnostic serving to analyses of modem behavior as well as to communication link analysis.

PLC (Power Line Communicati on) technology uses existing power cables for data transfer. Our products are able to communicate over several kilometers distance within low voltage distribution network. Our customers thus save costs as they do not need to invest into cabling installation, and the whole project is thus speeded up and simplified. 
Our narrowband PLC communication is robust, reliable and operates also in disturbed environment with communicati on rate 10 kbit/s. 
ModemTec can effectively use newly introduced components. As for programmable logic arrays, significantly higher circuit integration enables to introduce more sophisticated products. New modems use transmission channel with higher intensity (multi -channel communicati on), and Turbo codes implementation increases ability to restore damaged data that are transferred over disturbed transmission channel. Maximum communicati on rate reaches up to 400 kbit/s, if the channel is extremely disturbed, the rate decreases to 40 kbit/s. Special compositi on of communicati on packet headers guarantee 1 Byte transfer even if distortion significantly increases signal level (transmission of mass messages with 255 choices) while CENELEC standards are used.