Which statement best describes a discrete-time signal?

Which statement best describes a discrete-time signal?

• A. A A signal defined for all real time
• B. B A signal defined only at discrete time instants
• C. C A digital code sequence
• D. D A signal with continuous amplitude

Answer: (B)

A discrete-time signal is defined only at a sequence of time instants, typically at t = nT, forming a sequence x[n]. This captures the essential idea that time has been sampled and we know the signal values only at those specific moments, rather than for every real time t. For example, sampling a sine wave at a fixed interval produces a series of samples x[0], x[1], x[2], and so on.

The other descriptions describe different ideas: a signal defined for all real time is continuous-time, not discrete-time; a digital code sequence is a specific digital representation of data and may be derived from a discrete-time signal but isn’t the defining feature; a signal with continuous amplitude refers to the magnitude of the signal, which isn’t about whether time is sampled or continuous.