Frequency-division multiplexing, as shown in Fig. 9.19, is used to separate messages in the frequency domain and assign a distinct frequency slot to each message. Four messages, each with a bandwidth B of 4 kHz, are to be multiplexed by amplitude modulation (AM). For proper demultiplexing a guard band of 3 kHz is needed.
(a) If a low-pass filter with steeper cutoff characteristics could be used in demultiplexing, would the guard band have to be smaller or larger?
(b) Determine the lowest carrier frequencies to accomplish frequency-division multiplexing
(c) Determine the highest frequency component that the transmission system must be capable of propagating.