Modeling and optimization of the access impedance of power line channels

Digital networks can be established using the same set of wires that is used to distribute the power signal through our homes, the power-line channel (PLC). This networks have no new wires. However, the PLC channel has highly varying characteristics that need to be taken into account, namely the equivalent transmission line characteristic impedance and input impedance. The impedance seen at the input of the power-line channel varies with frequency, time and from line to line. This means that for the same voltage signal the injected current will vary. The current flowing in the channel is the main source of radiated electromagnetic interference (EMI), and imposes limits on the injected signal. The amplitude of the current in the line is not equal to the input current. The current peaks in the line can be minimized by minimizing the current of the positive traveling wave and it will be shown that this can be accomplished if the transmitter is coupled through a matched resistor (to the line impedance) or adequate signal processing. The signal processing method allows to easily change the access impedance. At the output of the channel the signal to noise ratio is independent of charge resistance. A system with input impedance estimation and minimization of the positive wave amplitude was simulated.