Signals and modulation: Demodulation is best described as which of the following processes?

Introduction / Context:
Communication systems use modulation to impress information onto a carrier and demodulation to recover it. Recognizing the basic transmitter/receiver functions is essential whether dealing with analog voice, digital data, or hybrid systems such as modems and radio links.

Given Data / Assumptions:

• At the transmitter, information is modulated onto a carrier suitable for the channel.
• At the receiver, the modulated signal must be demodulated to retrieve the baseband information.
• The baseband can be analog (audio) or digital (bitstream), depending on the system design.

Concept / Approach:

Modulation direction is “up” (baseband to passband); demodulation direction is “down” (passband to baseband). In data modems, demodulation recovers a digital bitstream from an analog carrier. In analog radio, it recovers an audio waveform. In all cases, demodulation extracts the original information from the received signal.

Step-by-Step Solution:

Verification / Alternative check:

Block diagrams of radios and modems consistently show the demodulator after the channel, producing the baseband output that feeds a decoder or audio stage.

Why Other Options Are Wrong:

a: Describes modulation (for example, DAC and modulator), not demodulation.

c: Describes multiplexing/aggregation, unrelated to demodulation.

d: Describes FDM (splitting bandwidth), not demodulation.

e: Not applicable because option b is correct.

Common Pitfalls:

Assuming demodulation always produces analog output; in digital systems, demodulation yields a digital symbol or bitstream. Also, confusing multiplexing techniques with modulation/demodulation functions is common.

Final Answer:

Converting analog signals to the original digital (or baseband) information at the receiver