Optimum demodulation of multiple signals having overlapped spectra

Maximum a posteriori (MAP) receivers are derived for the optimum demodulation of multiple amplitude and angle-modulated signals with overlapping radio-frequency spectra. It is assumed that the signals have known frequencies and modulation formats. The received waveform is represented as a complex quantity leading to a receiver that eliminates unwanted "twice carrier-frequency" terms that can cause in-band foldover in sampled data systems. The MAP receiver is shown to employ demodulators matched to each known signal type; the output of each demodulator is remodulated and coherently subtracted from the input to every other demodulator except its own. Computer simulations show that the MAP receiver can successfully demodulate an amplitude and phase-modulated signal simultaneously or two spectrally overlapped phase-modulated signals simultaneously.