Power-line digital communication system

Apparatus for decoding a signal received over a power line, the signal having been transmitted as a sequence of groups, each group encoding a data-carrying symbol, having one of a finite number of possible values, and consisting of N successive bursts of alternating signal, whereby each burst has been assigned one of M possible frequencies, the apparatus comprising:

• at least one signal generator operative to produce a reference signal for each of the M frequencies;
• at least one correlator for each of the M frequencies, operative to correlate the received signal with a corresponding reference signal, and to thus yield a correlation value at the end of each burst;
• an adder for each possible symbol value, operative to add corresponding correlation values from a plurality of correlators, obtained at a plurality of bursts, and to thus yield a symbol score;
• a selection logic, operative to select from among the outputs of said adders the one with the highest symbol score;
• a circuit to convert the received signal into a binary received signal;
• and
• a clock pulses generator;
• and wherein:
• said at least one reference signal generator is operative to generate a binary reference signal;
• and
• said at least one correlator includes:
• a XOR gate, receptive to said binary received signal and a binary reference signal, and
• an up-down counter, operative to count pulses, obtained from said clock pulses generator, up or down according to the output of said XOR gate.

A lighting control system, for controlling lamps by means of signals transmitted over a power line, the signals carrying encoded control commends, the system comprising:

• at least one encoder, operative to encode control commands as a sequence of symbols, each symbol having one of a finite number of possible values, and to encode each symbol into a corresponding group of N successive bursts of alternating signal, whereby each burst is assigned one of M possible frequencies;
• and
• at least one decoder, which includes:
• at least one reference signal generator, operative to generate a reference signal for each of said M frequencies,
• at least one correlator for each of said M frequencies, operative to correlate the received signal with a corresponding reference signal, and to thus yield a correlation value at the end of each burst,
• an adder for each possible symbol value, operative to add corresponding correlation values from a plurality of correlators, obtained over a plurality of bursts, and to thus yield a symbol score,
• a selection logic, operative to select the highest symbol score,
• a circuit to convert the received signal into a binary received signal, and
• a clock pulses generator;
• and wherein:
• said at least one reference signal generator is operative to generate a binary reference signal;
• and
• said at least one correlator includes;
• a XOR gate, receptive to said binary received signal and a binary reference signal, and
• an up-down counter, operative to count pulses, obtained from said clock pulses generator, up or down according to the output of said XOR gate.

A method for transmitting data over power lines, the data being represented by a series of symbols, each symbol having one of a finite number of possible values, the method comprising:

• encoding the series of symbols into a corresponding sequence of groups, each group consisting of N successive bursts of alternating signal, whereby each burst is assigned one of M possible frequencies;
• and
• decoding a group of said successive bursts, upon reception, whereby the decoding includes:
• providing M reference signals, each having a unique one of said M frequencies, and correlating each of said bursts with said M reference signals, resulting in M correlation values for each burst,
• for each possible symbol value, selecting for each burst the correlation value that corresponds to the frequency assigned to that symbol value and adding all selected correlation values together, to yield a symbol score, and
• selecting the highest symbol score to indicate the decoded symbol value;
• whereby said correlation, with respect to each of said M reference signals, includes:
• providing the reference signal as a pair of binary valued reference signals, each having the corresponding frequency and being in mutual phase quadrature;
• converting the received signal into a binary valued received signal;
• performing a XOR operation between the binary valued received signal and each of the two binary valued reference signals;
• providing a continuous train of clock pulses;
• counting said clock pulses up or down according to the results of each of the two XOR operations, resulting, at the end of each burst in corresponding two count values;
• and
• adding together the absolute values of said two count values.