Method and apparatus for removing the effects of co-channel interference from the message on a dominant frequency modulated carrier and for recovering the message from each of two co-channel carriers

摘要

Method and apparatus for improving an estimate of a message being carried by a frequency modulated dominant carrier in the presence of co- channel interference from a subdominant carrier. An envelope detector provides an envelope signal E(t). A frequency demodulator provides a demodulated frequency signal F(t). In one embodiment, a comparator compares the envelope signal to a threshold voltage V.sub.T. A switch is operated when the envelope signal is less than V.sub.T. The signal F applied to the switch is held by a holding circuit while the switch is open. Interpolation and lowpass filtering improve the quality of the output signal. In another embodiment of the invention, the frequency demodulated signal F is summed with an unfiltered signal to provide a first summed signal. The first summed signal is summed with an unfiltered signal to provide a second summed signal which is an estimate of the message on a co-channel subdominant carrier. Summing the filtered message on the subdominant carrier with a filtered message on the dominant carrier provides an estimate of the message on the dominant carrier. In this manner, neither recovered message experiences crosstalk. In another embodiment, digital signal processing means and apparatus are used to sample E and F. In this manner an estimate of the message on the dominant carrier which is free of the effects of interference is obtained. In addition, the messages on each of two co-channel carriers can be recovered from appropriate samples of F.