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Periodic Signal vs Aperiodic Signal-difference between Periodic Signal,Aperiodic Signal

This page compares Periodic Signal vs Aperiodic Signal or Non-periodic Signal and mentions difference between Periodic Signal and Aperiodic Signal (i.e. Non-periodic Signal).

In data communication domain, there are two major types of signals viz. periodic analog signals and non-periodic or aperiodic digital signals. Periodic analog signals can be classified as simple or composite.

Periodic Signal

Definition: A signal is considered to be periodic signal when it is repeated over cycle of time or regular interval of time. This means periodic signal repeats its pattern over a period. The function f(x) can be periodic if it satisfies following equation.
➤f(x + p) = f(x)

Example:
The cosine signal is periodic with periodicity value of 2π.

Composite Periodic Signal

A simple periodic analog signal such as sine wave or cosine wave can not be decomposed into simpler signals. A composite periodic analog signal is composed of multiple sine waves. The figure-1 depicts typical composite periodic signal.

Composite Periodic Signal Time and Frequency domain decomposition

The frequency is rate of change with respect to time. The frequency and period are inverse of each other. Hence following can be implied.
➤ f = 1/T and T = 1/f,
The units such as seconds(s), milliseconds(ms), microseconds(µs), nanoseconds (ns) and picoseconds (ps) are used for time period while units such as Hz, KHz, MHz, GHz and THz are used for frequency. The figure-2 depicts time domain and frequency domain decomposition of the composite periodic signal. This is derived from the fact that a complete sine wave in the time domain can be represented by one single spike in frequency domain.

Aperiodic Signal | Non-periodic Signal

Definition: A signal is considered to be non-periodic or aperiodic signal when it does not repeat its pattern over a period (i.e. interval of time).

Aperiodic Signal time and frequency domain decomposition

The figure-3 depicts time domain and frequency domain decomposition of the composite aperiodic signal. Following are the two classic examples of aperiodic signal type.

Example#1:
Signal created by microphone or telephone when one or two words are pronounced. In this application, composite signal can not be periodic in nature. Hence it is referred as aperiodic signal.
Example#2:
Signal propagated by AM radio station or FM radio station

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