A block diagram and a phasor diagram of an angle modulated communication system are shown in the figures. The additive white Gaussian noise n (t) is added to the modulated signal u(t) and the result is passed through a noise- limiting filter (the bandpass filter) whose role is remove the out-of-band noise, and therefore, it passed the modulated signal without distortion. However, it eliminates the out-of band noise and hence, the noise output of the filter is a bandpassed Gaussian noise denoted by n(t) = V(t) cos(2pfet + D(t)), where V(t) and (t) represent the envelope and the phase of the bandpass noise process, respective. The assumption that the signal (magnitude of the carrier) is much larger then the noise means that p(V(t)