Signal decoding method and apparatus with dynamic noise threshold

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:

• using a zero crossing detector to detect a zero crossing of the alternating current on a first phase of the power line operated at the power grid frequency;
• using a receiver to receive a burst of received analog signal carried on a carrier frequency over a power line;
• converting at least a portion of the burst of received analog signal carried on the carrier frequency to a set of digital samples, the portion corresponding to the analog signal during a burst sampling window between zero crossings established in relation to the detected zero crossing on the first phase of the power line;
• creating a set of digital values of an ideal cosine wave with a frequency substantially equal to the carrier frequency;
• creating a set of digital values of an ideal sine wave with frequency substantially equal to the carrier frequency;
• multiplying a subset of digital samples from the burst 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 the subset of digital samples from the burst 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;
• discarding the In-Phase component and the Quadrature component if an energy level in the received analog signal does not exceed a threshold value;
• when the energy level in the received analog signal exceeds a threshold value, 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;
• using pairs of obtained phase offsets from adjacent bursts to decode the binary information conveyed by phase shift keying in the received analog signal;
• and
• dynamically adjusting the threshold value based on measurements of the energy level in the received analog signal.