In telecommunications, the term “carrier” refers to which of the following definitions in the context of modulation and transmission?

Introduction / Context:
Analog and digital communication systems often use a high-frequency sinusoid called a carrier. Information (voice, data, video) is imposed on this carrier via modulation so it can propagate efficiently over media like air, coax, or fiber and be separated from noise and adjacent channels by filtering.

Given Data / Assumptions:

• We are discussing baseband-to-passband conversion using a carrier wave.
• Modulation may be amplitude, frequency, phase, or digital variants (ASK, FSK, PSK, QAM).
• Other options describe different networking terms.

Concept / Approach:
A carrier is a continuous wave (usually sinusoidal) with constant amplitude and frequency in the absence of modulation. By varying one or more parameters of this carrier according to the message signal, energy is shifted around the carrier frequency so that transmission and reception become practical using bandpass channels and tuned circuits.

Step-by-Step Solution:

Verification / Alternative check:
Consider AM radio: a program (message) modulates a carrier (for example, 1 MHz). A receiver tunes to that carrier and demodulates to recover the baseband audio—demonstrating the definition in practice.

Why Other Options Are Wrong:

• Common connection of devices: describes a bus.
• Attempting to use the same channel simultaneously: describes a collision or contention.
• Interconnected functional units providing service: describes a network.

Common Pitfalls:
Confusing “carrier” with “carrier sense” in CSMA/CD, or with a telecommunications service provider (a “carrier” in business terms) rather than the physical signal.

Final Answer:
a continuous frequency capable of being modulated or impressed with a second signal