Figure P7.7-4a shows a scheme to transmit two signals m1(t) and m2(t) simultaneously on the same channel (without causing spectral interference). Such a scheme, which transmits more than one signal, is known as signal multiplexing. In this case, we transmit multiple signals by sharing an available spectral band on the channel, and, hence, this is an example of the frequency-division multiplexing. The signal at point b is the multiplexed signal, which now modulates a carrier of frequency 20,000 rad/s. The modulated signal at point c is now transmitted over the channel.
a. Sketch the spectra at points a, b, and c.
b. What must be the minimum bandwidth of the channel?
c. Design a receiver to recover signals m1(t) and m2(t) from the modulated signal at point c.