Tone rejection during synchronization in frequency shift keyed modulation systems

A method comprising:

• waiting for a preamble detection event to occur at a receiver;
• in response to occurrence of the preamble detection event, identifying a search window of carrier-frequency-offset-corrected samples in which a first intermediate output signal from a demodulator does not exceed a predetermined threshold;
• convolving a second intermediate output signal from the demodulator within the search window with a predetermined pattern to provide a convolution result;
• in response to an absolute peak of the convolution result exceeding a preamble pattern confirmation threshold, confirming the preamble detection event to provide a confirmed preamble detection event for a confirmed preamble pattern;
• and
• receiving a signal comprising the confirmed preamble pattern to provide a received digital signal extracted from the signal.

A receiver apparatus comprising:

• a demodulator comprising an input to receive a modulated signal, a first output to provide a demodulated output, a second output to provide a first intermediate signal of the demodulator, and a third output to provide a second intermediate signal of the demodulator;
• a preamble detector coupled to the demodulator to detect an occurrence of a preamble detection event;
• and
• a control circuit comprising
• a first preamble qualification module comprising an input coupled to the second output of the demodulator to identify, in response to the control circuit receiving an indication of the preamble detection event, a search window of carrier-frequency-offset-corrected samples for which the first intermediate output signal does not exceed a threshold;
• a second preamble qualification module comprising an input and an output,
• the input coupled to the third output of the demodulator to convolve the second intermediate output signal within the search window identified by the first qualification module with a predetermined pattern to provide a convolution result;
• the output to provide a confirmed preamble indicator in response to an absolute peak of the convolution result exceeding a preamble pattern confirmation threshold;
• and
• wherein the receiver is configured to provide a received digital signal extracted from the signal in response to receiving the confirmed preamble indicator.