What is meant by each of the following terms: modulation, modulating signal, carrier signal, modulated signal, and demodulation? Explain the following types of signal modulation giving an application for each case:
(a) Amplitude modulation
(b) Frequency modulation
(c) Phase modulation
(d) PWM
(e) Pulse-frequency modulation
(f) Pulse-code modulation
How could the sign of the modulating signal be accounted for during demodulation in each of these types of modulation?