3. Bandlimited Baseband Modulation (18 points) Consider an M-ary PAM baseband communication system. The communication channel is an ideal lowpass filter with a cutoff frequency (or bandwidth) of W=8kHz. Let us denote the signal component at the output of the receiving filter as x(t) and its Fourier transform as X(f). Suppose the system is designed such that X(f) is a raised cosine spectrum: X(f)=T2T[1+cos(aT(f2T1))]00f212T1f2T1+f>2T1+ where 01, and the corresponding x(t) is x(t)=sinc(Tt)142t2/T2cos(t/T) Note: sinc(x)=xsin(x) (a) Suppose there is no inter-symbol interference (ISI), then what is the maximum symbol rate supported by the channel, and what is the symbol rate when a "true" (=1) raised cosine spectrum is used? (b) Determine and plot the shape of x(t) when the maximum symbol rate is used, identify the zero crossings, and explain why there is no ISI