In data communications terminology, what does “baseband” transmission mean, and which description best fits the term in contrast to modulated carrier systems?

Introduction:
The term baseband distinguishes direct, unmodulated signaling from modulated carrier transmission (passband). Classic Ethernet on copper, for example, is baseband: the digital waveform is placed directly on the wire without up-conversion to a high-frequency carrier. This item asks you to pick the description that accurately captures baseband in communications contexts.

Given Data / Assumptions:

• We contrast baseband versus passband (carrier-modulated) systems.
• Baseband examples include early 10BASE-T/2/5 Ethernet and many serial links.
• We are looking for the most precise definition, not related but different concepts.

Concept / Approach:
Baseband transmission sends the original low-frequency (baseband) signal directly over the medium using a line code (e.g., NRZ, Manchester). No separate sinusoidal carrier is used for up/down conversion. In contrast, passband systems (radio, cable TV) modulate the baseband onto a carrier (AM, FM, QAM). While a baseband signal is indeed bandlimited, “bandlimited” is a more general term that applies to many signals (baseband or passband) and is not the definition of baseband itself. Likewise, “simultaneous transmission to many stations” describes broadcast/multicast behavior, not baseband.

Step-by-Step Solution:

Verification / Alternative check:
Standards documents label early Ethernet as “BASE” (baseband) in names like 10BASE-T, distinguishing it from broadband coax systems that carry multiple RF channels simultaneously via modulation.

Why Other Options Are Wrong:

• Bandlimited signal: true for many signals but not the definition of baseband.
• Simultaneous transmission: broadcast/multicast concept unrelated to baseband vs passband.
• All of the above: incorrect since the other items are not definitions of baseband.
• None of the above: incorrect because one option matches exactly.

Common Pitfalls:
Confusing “baseband” with “unfiltered DC content” (some line codes are DC-balanced); thinking baseband implies single-user only—multiple access can be achieved with time slots even at baseband.

Final Answer:
Transmission of signals without modulation onto a separate carrier.