A decoder for a modulation scheme is configured to operate close to the radio noise floor. A correlation value may be constantly updated, in an effort to match to a signature to a preamble of a packet. A low clamp value may act as a floor to which a calculated correlation value is set, if it is less than the low clamp value. If a correlation threshold is exceeded, then the correlation value is examined to determine it is a peak value. If the peak is found, power of the preamble is compared to a power threshold that is relative to the radio noise floor. If the power threshold is exceeded, positive correlation is detected. A channel optimizer is used to remove the frequency misalignment. This enables the use of a filter that is approximately equal to the occupied bandwidth of the incoming signal, further rejecting noise and interference.