Introduction:
Discrete-time signals are signals that are defined at distinct points in time. They are commonly used in digital signal processing and are represented in various ways to facilitate analysis and processing. This question asks us to identify the representation of discrete-time signals that is NOT one of the standard representations.

Explanation:
The various representations of discrete-time signals are as follows:

a) Sequence representation:
A sequence is a discrete-time signal that is represented by a set of numbers arranged in a specific order. It is the most fundamental representation of a discrete-time signal and provides the actual values of the signal at each point in time.

b) Graphical representation:
Graphical representation involves plotting the values of a discrete-time signal on a graph, with time on the x-axis and signal amplitude on the y-axis. This representation helps visualize the signal and can provide insights into its characteristics and behavior.

c) Analytical representation:
Analytical representation refers to expressing a discrete-time signal in terms of a mathematical function or equation. This representation is often used when the signal can be described by a known mathematical model or when analyzing the signal using mathematical techniques.

d) Tabular representation:
Tabular representation involves presenting the values of a discrete-time signal in a table format, with time and corresponding signal values listed in rows or columns. This representation is useful for organizing and comparing the values of the signal at different points in time.

Conclusion:
Among the given options, the representation of discrete-time signals that is NOT standard is the 'Analytical representation'. While sequences, graphical representation, and tabular representation are commonly used to describe and analyze discrete-time signals, analytical representation is not a commonly employed method.