| 摘要 |
A method and apparatus for selectively reducing the phase shift contributions caused by transmission impairments such as noise and phase jitter, takes advantage of the fact that for phase modulated data signals capable of assuming one of M discrete values, when the noise phase shift due to impairment in transmission is less than pi /M in a system capable of discriminating between discrete data encoded phase shifts of 2 pi /M. Accordingly, each received discrete signal of phase magnitude theta is multiplied by 2 pi /M. The integral portion of the product represents the phase shift of data whereas the fractional value represents the phase shift caused by impairments. The fractional value is multiplied by a parameter alpha and algebraically combined with a reference value. The reference value is subtracted from the discrete signal theta to reduce the phase shift of the transmission impairments. By varying the value of alpha , the type of demodulation can be altered. For example, for alpha =0, the demodulator is coherent, while for alpha =1 the demodulator operates differentially. The reference value is in effect a predictor of the noise contribution and its magnitude is modified by the algebraic addition of the product of the fraction part and the parameter alpha .
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