申論題

4. [15%] Define the functions as depicted in Figure 3(a).
  As shown in Figure 3(b), the input signal s(t)is multiplied by a carrier signal 2cos(2πf₀r) and then is passed through a nonlinear system y(t)=g(x(t)) to generate the output signal y(r). Suppose that the spectrum of s(t) is(f/6), the center frequency is f_o =10, and the nonlinear system is defined byy(t)=x(r)+0.3x²(t).

(a) Write the expression of the spectrum of y(t) in terms of.(10%)