Abstract: Signals carried inbound on an electricity distribution network are detected by extracting electrical current information from a waveform of the electricity distribution network, and digitally filtering the electrical current information, thereby forming a digital waveform, to extract signal information contained in the electrical current information. A reference waveform is constructed from a portion of the digital waveform, and the signal information is detected by comparing portions of the digital waveform with corresponding portions of the reference waveform.

Abstract: A communication system uses the current waveform of an electricity distribution network as a carrier, the signal being present as current pulses around four predetermined zero crossings. The current waveform is sampled around the voltage zero crossings to obtain a time-ordered set of waveform values. The ordered waveform values for each bit are examined to determine if the values fall within preset criteria indicative of a stable carrier. When the ordered waveform values for a particular bit all fall within the preset criteria, that particular bit is identified as a good bit. When at least some of the ordered waveform values for a particular bit fall outside the preset criteria, that particular bit is labelled as suspect. The ordered values of each suspect bit and of adjacent bits are tested to determine whether four successive values meets the preset stability criteria, and whether the four successive values indicating a stable carrier include at least two succesive values from the suspect bit.