General method for low-frequency data transmission on a power line
View Patent ↗A method for producing a set of inbound pulse patterns and detection vectors for lengths longer than 4 cycles in an AC waveform. These are used for generating inbound messages in a two-way automatic communication system (TWACS). The method uses Hadamard matrices adapted to generate a set of detection vectors by permuting rows of a matrix and removing certain columns of the matrix to meet system design requirements. The method can be extended to any length and modified to accommodate multiple pulses per half-cycle to support higher data rates.
1. A method of producing a set of pulse patterns and detection vectors for lengths longer than 4 cycles in an AC waveform for use in generating inbound messages in a two-way automatic communication system (TWACS) comprising:
selecting a Hadamard matrix of a size n×n where n is the number of rows and columns in the matrix;
manipulating rows and columns of the Hadamard matrix;
selecting a set of columns of the matrix as a set of detection vectors;
using the detection vectors to create pulse patterns representing logical “0” and “1”;
combining the transmitted pulse patterns with the set of detection vectors to create a detection matrix; and
generate inbound messages for the TWACS by applying the detection matrix to detect signals imposed on the AC waveform at predetermined locations.
2. The method of claim 1 in which the value n for determining the size of the Hadamard matrix is 1, 2, or an integer multiple of 4.
3. The method of claim 1 in which the Hadamard matrix is manipulated to generate the set of detection vectors by permuting rows of the matrix and by deleting selected columns of the matrix.
4. The method of claim 3 in which the Hadamard matrix is further manipulated to generate the set of detection vectors by inverting the sign of an entire row or an entire column in the matrix.
5. The method of claim 4 in which the resulting matrix is a sequency ordered Hadamard matrix.
6. The method of claim 5 in which the TWACS employs a set of channels for communications, and the method includes deleting rows from the Hadamard matrix which represent those channels in the set of channels on which an inbound message will be difficult to detect.
7. The method of claim 6 in which the deleted rows represent detection vectors for channels whose frequency content is concentrated near the AC frequency and odd harmonics thereof.
8. The method of claim 1 in which the design constraints include avoiding a DC component in the signal and further avoiding a frequency component in the signal that is at substantially the same frequency as the AC waveform.
9. The method of claim 5 in which the Hadamard matrix is ordered in sequency by indexing it using a Gray code with a bit-reversed order in which the most significant bit is incremented first.
10. The method of claim 9 in which, after sequency ordering, the detection vectors remaining in the Hadamard matrix are arranged in order of preference.