Impedance Modelling, Profiling and Characterisation of the Powerline Communication Channel

The ever-increasing demand for telecommunication services and the already established power line network makes power line communication (PLC)a very attractive mode of data transmission. However, the power line cables are designed for the transmission of high voltage at low frequencies, which is contrary to the low voltages, and high frequencies needed for the transfer of data signals. Moreover, the power line network is randomly loaded. This in turn results in impedance mismatch with considerable noise and high attenuation. The variant nature of input impedance requires impedance profiling of the PLC network. It is with this profiling that impedance adaptive techniques can be designed and applied to both the input and output of PLC modems, which tend to operate at 50 Ω. If the behaviour of PLC network impedance can be modelled, then the characteristics of the power line network can be known. This will in turn ensure the design of more efficient and effective impedance matching networks. This paper describes modelling of input impedance in a power line channel using parallel resonance circuits. TR5048 Vector Network Analyzer was used to obtain impedance measurements for a frequency range of 1-30 MHz at the power line communication laboratory at the University of KwaZulu-Natal, Durban, South Africa for different test network topologies and configurations considering the extreme cases that include open-circuit and short-circuit terminations. It is observed that the position of the maximum values of impedance depends on the number of branches, the length of the branch and the terminating load impedance. The model shows a good agreement with measurement. The impedance measured was then profiled into minimum, average and maximum bounds.