| 摘要 |
Apparatus and method for estimating the angle-modulation imposed on a transmitted Radio Frequency (RF) or Intermediate Frequency (IF) carrier. The method estimates angle-modulation when communications channels add distortions such as noise to transmitted signals. The system provides reconstituted frequency modulation from a feedforward demodulator. The goal is to reduce the modulation index of a desired signal and to employ a narrower band-pass filter that passes this signal while rejecting the distortion that accompanies it. A plurality of stages, 1 through M, exist within the system. Stages 2 through M contain the same components, although filter coefficients and alignment delays may differ from stage to stage. Stage 1 of the demodulator differs slightly from the remaining stages, since the only input required by Stage 1 is a complex envelope signal that contains both the desired signal and the distortion added by the channel. The output of any particular stage of the demodulator consists of complex envelope signals and a real FM estimate. Each output from a stage p serves as input to stage p+1, for 2</=p+1<M. The phase modulation estimate can be an output of Stage M.
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