The key difference between modulation and demodulation is that modulation is to transfer the message signal by adding it with the carrier signal while demodulation is the process of filtering out the actual message signal from the carrier signal.

In general, radio carrier generates at the transmission side of a telecommunication link. In transmission, it is necessary to send a signal a long distance. Usually, a high-frequency signal is capable of traveling a long distance. Therefore, the message signal or the information signal combines with a high-frequency signal called the carrier signal without affecting its original characteristics. This process of combining the message signal with the carrier signal is called the modulation. The demodulation process occurs at the receiving end.

CONTENTS

1. Overview and Key Difference
2. What is Modulation
3. What is Demodulation
4. Side by Side Comparison – Modulation vs Demodulation in Tabular Form
5. Summary

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What is Modulation?

Modulation is the process of putting the information that we need to transfer into a carrier signal. IEEE defines modulation as “a process whereby certain characteristics of a wave, often called the carrier, are varied or selected in accordance with a modulation function.”

There are various types of modulation. In Amplitude Modulation (AM) the amplitude of the carrier signal varies according to the amplitude of the message signal. Frequency Modulation (FM) changes the carrier signal frequency according to the message signal. Phase Modulation (PM) changes the carrier phase according to the message signal.

Figure 01: Communication System

Digital Modulation converts the analog signals to digital forms of 1s and 0s. There are various digital modulation techniques. Amplitude Shift Keying (ASK) represents the binary data in the form of variations in the amplitude of a signal. Frequency Shift Keying (FSK) changes the frequency of the carrier signal according to the discrete digital changes. Phase Shift Keying (PSK) changes the phase of the carrier signal by varying the sine and cosine inputs at a particular time.

Modulation of a sine waveform allows to transform a baseband message signal into a passband signal; for example, low-frequency audio signal into a radio-frequency signal (RF signal). In radio broadcasting and voice communication, this concept is highly utilized to shift baseband voice signal into a passband channel.

What is Demodulation?

Demodulation is the process of extracting an information signal from the carrier signal. Demodulation process should be exactly compatible with the modulation method otherwise, the destination end will not be able to extract the original information signal from the carrier signal. Therefore, the initial handshake should take place in a proper mechanism to negotiate the modulation and demodulation methods in advance, for a dynamic environment.

For an example, in mobile communications, modulation methods could change on the fly. Therefore, handshaking takes place before shifting from one method to another or uses special algorithms at the destination end to extract the information by identifying the original modulation method. All the modulation methods, such as AM, FM, PM etc. have their own demodulation methods to recover the original signal at the destination end.

Equipment that does both modulation and demodulation is called a modem. Modulation and demodulation processes mainly aim to achieve the transfer of information with the minimum distortion or corruption, minimum loss to the carrier signal, and efficient use of the spectrum. Even though there are a number of methods or schemes for modulation and demodulation process, they have their own advantages and disadvantages as well. For an example, AM is used in shortwave and medium wave radio broadcasting, FM is used in Very High Frequency (VHF) radio broadcasting, and PM is popular with the digital signal modulation.

What is the Difference Between Modulation and Demodulation?
Modulation is the process of impinging useful information on the carrier signal, while demodulation is the recovery of original information from the carrier signal. Usually, modulation occurs at the transmitter while demodulation occurs at the receiver.

Summary – Modulation vs Demodulation
The difference between the modulation and demodulation is that modulation is to transfer the message signal by adding it with the carrier signal while demodulation is the process of filtering out the actual message signal from the carrier signal. Both modulation and demodulation processes are equally important to transfer an information signal using a carrier signal. Therefore, the modulation method we use at the transmitter must be exactly compatible with the demodulation method at the receiver end to achieve a proper transfer of information from one location to another.

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