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Signal decoding method and apparatus

  • US 7,242,729 B1
  • Filed: 04/25/2005
  • Issued: 07/10/2007
  • Est. Priority Date: 04/26/2004
  • Status: Active Grant
First Claim
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1. A method of decoding a phase shift keying signal carried on a carrier frequency over a power line operating at a power grid frequency, the method comprising the steps of:

  • detecting a zero crossing of the alternating current on a first phase of the power line operated at the power grid frequency;

    converting at least a portion of a received analog signal carried on the carrier frequency to a set of digital samples, the portion corresponding to the analog signal during a sampling window established in relation to the detected zero crossing on the first phase of the power line;

    using the detected zero crossing as a trigger to create a set of digital values of an ideal cosine wave with a frequency substantially equal to the carrier frequency;

    using the detected zero crossing to create a set of digital values of an ideal sine wave with frequency substantially equal to the carrier frequency;

    multiplying a subset of digital samples with a subset of corresponding created digital values for the ideal cosine wave and storing the sum of the products as the In-Phase Component of the set of digital samples;

    multiplying a subset of digital samples with a subset of corresponding created digital values for the ideal sine wave and storing the sum of the products as the Quadrature component of the set of digital samples;

    obtaining a phase offset for the received analog signal from an ideal cosine wave by obtaining the Arctangent of the quotient of the Quadrature component divided by the In-Phase component; and

    using the obtained phase offset to decode the binary information conveyed by phase shift keying in the received analog signal.

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