In receiver using coherent detection, the sinusoidal wave generated by the local oscillator suffers from a phase error (t) with respect to the carrier

In receiver using coherent detection, the sinusoidal wave generated by the local oscillator suffers from a phase error θ (t) with respect to the carrier wave cos (2πƒct). Assuming that θ (t) is a ample function of a zero-mean Guassian process of variance σ2o, and that most of the time the maximum value of θ (t) is small component with unity, find the mean-square error of the receiver output for DSB-SC modulation. The mean-square error is defined as the expected value of the squared difference between the receiver output and the message signal component of the receiver output.