Multiplexing methods: which technique places each input signal on a distinct carrier frequency so multiple signals share the same medium simultaneously?

Introduction / Context:
Multiplexing allows several independent signals to share a single physical medium efficiently. Two foundational approaches are dividing by frequency (FDM) and dividing by time (TDM). This question checks whether you can correctly associate the technique that assigns different carrier frequencies to different signals so they can be transmitted at once without interference, given appropriate filtering and guard bands.

Given Data / Assumptions:

• The medium supports a band of frequencies broad enough for multiple channels.
• Signals are isolated using filters and guard bands.
• We contrast frequency-division versus time-division approaches.

Concept / Approach:
In Frequency-Division Multiplexing (FDM), each input occupies a unique sub-band centered around its own carrier frequency. These sub-bands are summed and transported together. Receivers use tuned filters to recover the intended channel. By contrast, Time-Division Multiplexing (TDM) interleaves signals across time slots on a single carrier or baseband; synchronous TDM preassigns slots, while statistical/asynchronous TDM assigns slots dynamically based on demand. Thus, only FDM fits the description of shifting each signal to a different carrier frequency.

Step-by-Step Solution:

Verification / Alternative check:
Broadcast radio and cable television are classical FDM systems; each station or channel occupies a specific frequency band. Telephone carrier systems historically used FDM before digital TDM came to dominate trunks.

Why Other Options Are Wrong:

• Synchronous TDM: fixed time slots on one carrier; no per-channel carrier shifting.
• Asynchronous TDM: dynamic time slots; still time, not frequency separation.
• All of the above: false because only FDM uses different carriers.
• None of the above: incorrect because FDM is correct.

Common Pitfalls:
Mixing up FDM with FDMA (access method naming); assuming OFDM is TDM—Orthogonal FDM is still frequency-division at its core, though with orthogonal subcarriers.

Final Answer:
FDM.