Digital modulation can be used on PLC communication links to increase system capacity. The improved noise and interference capability of digital modulation can lead to reduced guard distances between co-channel users and can more than offset the additional bandwidth requirements of digital modulation. QAM-16 is proposed as a suitable modulation scheme. In the example given this modulation leads to a modest capacity improvement of 10% when ADPCM is used for voice coding. This improves dramatically with the use of more advanced voice coders. Simulations are performed on a 500 KV line to determine the effect of
reflections and modal propagation on the equalization requirements of the modem. The major distortions are caused by the applied filtering within the modem, and the reflections on the transmission path, the later are
particularly evident at low carrier frequencies, and when the line lengths are short. A PLC bandlimited modem, whose frequency is user selectable within the PLC spectrum has been designed and tested. Particular emphasis is placed on the adaptive equalisation algorithm, that is selected in the
modem design to combat distortions due to the imperfections of the modem and reflections on the power line. Most of the modem functions were implemented using DSP techniques.