Devices, systems, and methods for composite signal decoding

摘要

A method is provided for decoding a composite signal which includes receiving a composite signal including a pilot signal at a pilot signal frequency, and first and second information modulated with a subcarrier at a harmonic of the pilot frequency. The composite signal is sampled at a preselected sampling frequency. The sampled composite signal is mixed down with a reference signal of approximately the same frequency. The mixed down pilot signal is extracted from the mixed down composite signal, the amplitude and sign of the mixed down pilot signal proportional to the phase difference between the pilot signal and the reference signal. The phase of the reference signal is adjusted as a function of the amplitude and sign of the mixed down pilot signal such that the reference signal is approximately 90 DEG out of phase with the received pilot signal. The sample of the composite signal taken closest to the start of a period of the pilot signal is identified. Samples representing substantially the first and second information from the digitized composite signal are selected by selecting those samples of the digitized composite signal taken at point in time when the sine of the phase angle of the composite signal is substantially plus and minus one, the point in time determined from the sampling frequency and the samples of the composite signal taken closest to the start of each period of the pilot signal.