What is Modulation and Different Types

As we are living in an era of communication wherein we can easily transfer any form of information (video, audio, and other data) in the form of electrical signals to any other device or destined area. Although it is common in our perceptual experience that sending or receiving signals or data is simple, but it involves quite complex procedures, possibilities, and involved scenarios within the communication systems. So, in the scope of communication systems, modulation plays hold crucial responsibility in the communication system to encode information digitally in the analog world. It is very important to modulate the signals before sending them to the receiver section for larger distance transfer, accurate data transfer, and low-noise data reception. To be clear, let us dive into the detailed concept of knowing what is modulation, different types in it, and what are the types of modulation techniques used in communication systems.

What is Modulation?

Modulation is a process of changing the characteristics of the wave to be transmitted by superimposing the message signal on the high-frequency signal. In this process video, voice and other data signals modify high-frequency signals – also known as the carrier wave. This carrier wave can be DC or AC or pulse chain depending on the application used. Usually, a high-frequency sine wave is used as a carrier wave signal.

These modulation techniques are classified into two major types: analog and digital or pulse modulation. Prior to discussing further the different types of modulation techniques, let us understand the importance of modulation.

Why Modulation is Used in Communication?

• In the modulation technique, the message signal frequency is raised to a range so that it is more useful for transmission. The following points describe modulation’s importance in the communication system.
• In signal transmission, the signals from various sources are transmitted through a common channel simultaneously by using multiplexers. If these signals are transmitted simultaneously with a certain bandwidth, they cause interference. To overcome this, speech signals are modulated to various carrier frequencies in order for the receiver to tune them to the desired bandwidth of his own choice within the range of transmission.
• Another technical reason is antenna size; the antenna size is inversely proportional to the frequency of the radiated signal. The order of the antenna aperture size is at least one by a tenth of the wavelength of the signal. Its size is not practicable if the signal is 5 kHz; therefore, raising frequency by modulating process will certainly reduce the height of the antenna.
• Modulation is important to transfer the signals over large distances since it is not possible to send low-frequency signals for longer distances.
• Similarly, modulation is also important to allocate more channels for users and to increase noise immunity.

To start to know about detailed information of modulation techniques, let us know regarding the types of signals in the modulation process.

Modulating Signal

This signal is also termed as a message signal. It holds the data that has to be transmitted and so this termed as message signal. It is considered as the baseband signal where it undergoes a modulation process to get broadcasted or communicated. Because of this, it is the modulating signal.

Carrier Signal

This is the high range of frequency signal which is with specific amplitude, frequency, and phase levels, but it does not hold any data. So, it is termed as carrier signal as it is an empty one. This is simply utilized to transmit the message to the receiver section after the process of modulation.

Modulated Signal

The consequential signal that is obtained after the procedure of modulation is called a modulated signal. This is the product of both the carrier and modulating signals.

Different Types of Modulation

The two types of modulation: analog and digital modulation techniques have already been discussed. In both the techniques, the baseband information is converted to Radio Frequency signals, but in analog modulation, these RF communication signals are a continuous range of values, whereas in digital modulation these are prearranged discrete states.

Analog Modulation

In this modulation, a continuously varying sine wave is used as a carrier wave that modulates the message signal or data signal. The Sinusoidal wave’s general function is shown in the figure below, in which, three parameters can be altered to get modulation – they are mainly amplitude, frequency, and phase, so the types of analog modulation are:

• Amplitude modulation (AM)
• Frequency modulation (FM)
• Phase modulation (PM)

In amplitude modulation, the amplitude of the carrier wave is varied in proportion to the message signal, and the other factors like frequency and phase remain constant. The modulated signal is shown in the below figure, and its spectrum consists of a lower frequency band, upper-frequency band, and carrier frequency components. This type of modulation requires greater bandwidth, more power. Filtering is very difficult in this modulation.

Frequency modulation (FM) varies the frequency of the carrier in proportion to the message or data signal while maintaining other parameters constant. The advantage of FM over AM is the greater suppression of noise at the expense of bandwidth in FM. It is used in applications like radio, radar, telemetry seismic prospecting, and so on. The efficiency and bandwidths depend on the modulation index and maximum modulating frequency.

In phase modulation, the carrier phase is varied in accordance with the data signal. In this type of modulation, when the phase is changed it also affects the frequency, so this modulation also comes under frequency modulation.

Analog modulation (AM, FM, and PM) is more sensitive to noise. If noise enters into a system, it persists and gets carried till the end receiver. Therefore, this drawback can be overcome by the digital modulation technique.

Digital Modulation

For better quality and efficient communication, the digital modulation technique is employed. The main advantages of digital modulation over analog modulation include permissible power, available bandwidth, and high noise immunity. In digital modulation, a message signal is converted from analog to digital message and then modulated by using a carrier wave.

The carrier wave is keyed or switched on and off to create pulses such that the signal is modulated. Similar to the analog, here the parameters like amplitude, frequency, and phase variation of the carrier wave decides the type of digital modulation.

The types of digital modulation are based on the type of signal and application used such as Amplitude Shift Keying, Frequency Shift Keying, Phase Shift Keying, Differential Phase Shift Keying, Quadrature Phase Shift Keying, Minimum Shift Keying, Gaussian Minimum Shift Keying, Orthogonal Frequency Division Multiplexing, etc., as shown in the figure.

Amplitude shift keying changes the amplitude of the carrier wave based on the baseband signal or message signal, which is in digital format. It is used for low-band requirements and is sensitive to noise.

In frequency-shift keying, the frequency of the carrier wave is varied for each symbol in the digital data. It needs larger bandwidths as shown in the figure. Similarly, the phase shift keying changes the phase of the carrier for each symbol and it is less sensitive to noise.

Frequency Modulation

In order to create a frequency modulated wave, the frequency of the radio wave is varied in accordance with the amplitude of the input signal.

When the audio wave is modulated with that of the radio frequency carrier signal, then the generated frequency signal will change its frequency level. The variation by which the wave moves upward and downward is to be noted. This is termed as deviation and is generally represented as kHz deviation.

As an instance, when the signal has a deviation of either + or – 3kHz, then it is represented as ±3kHz. This means that the carrier signal has up and downward deviation of 3kHz.

Broadcasting stations that need very high-frequency range in the frequency spectrum (in the range of 88.5 – 108 MHz), they need certainly a large amount of deviation which is nearly ±75 kHz. This is called wide-band frequency modulation. The signals in this range hold the ability to assist the high quality of transmissions, whereas they require higher bandwidth too. In general, 200kHz is permitted for every WBFM. And for narrowband FM, a deviation of ±3 kHz is enough.

While implementing an FM wave, it is more beneficial to know the effectivity range of the modulation. This stands as the parameter in stating factors such as knowing the type of signal whether wide band or narrow band FM signal. It also helps in making sure that the whole receivers or transmitters that are in the system are programmed to adapt to the standardized range of modulation as this shows an impact on the factors such as the channel spacing, bandwidth of the receiver, and others.

So, to signify the modulation level, modulation index and deviation ratio parameters are to be determined.

The different types of frequency modulation include the following.

Narrow band FM

• This is termed as the type of frequency modulation where the modulation index value is too minimal.
• When the modulation index value is < 0.3, then there will be an only carrier and corresponding sidebands having bandwidth as twice the modulating signal. So, β ≤ 0.3 is called narrow band frequency modulation.
• The maximum range of modulating frequency is of 3 kHz
• The maximum frequency deviation value is 75 kHz

Wide band FM

• This is termed as the type of frequency modulation where the modulation index value is large.
• When the modulation index value is > 0.3, then there will be more than two sidebands having bandwidth as twice the modulating signal. When the modulation index value increases, then the number of sidebands gets increased. So, β > 0.3 is called narrow band frequency modulation.
• The maximum range of modulating frequencies is in between 30 Hz – 15 kHz
• The maximum frequency deviation value is 75 kHz
• This frequency modulation needs a higher bandwidth range which is almost 15 times ahead of the narrow band frequency modulation.

The other types of modulation techniques used in the communication system are:

• Binary phase shift keying
• Differential phase-shift keying
• Differential quadrature phase shift keying
• Offset quadrature phase shift keying
• Audio FSK
• Multi FSK
• Dual-tone FSK
• Minimum shift keying
• Gaussian minimum shift keying
• Trellis coded type of modulation

Advantages of Various Types of Modulation

For transmission purposes, the size of the antenna has to be very large before the modulation technique was not proposed. The level of communication gets restricted as there will be no long-distance communications having zero levels of distortions.

So, with the development of modulation, there are many benefits of utilizing communication systems. And the advantaged of modulation are:

• The size of the antenna can be lessened
• There happens no kind of signal consolidation
• The range of communication is enhanced
• There will be the possibility of multiplexing
• One can adjust bandwidth as per the requirements
• The quality of reception gets increased
• Better performance and effectivity

Applications of Various Types of Modulation

There is an extensive range of various modulation techniques and those are:

• Implemented in music mixing, and magnetic tape recording systems
• To track EEG monitoring for newly born children
• Used in telemetry
• Used in radar
• FM broadcasting techniques

To avoid making this article complex, some mathematical equations and in-depth information about digital communication systems have been exempted from it. However, the efforts put in to bring forth this article ensure basic information on different types of modulation in the communication system. Also, it is more important to have a clear idea of what are the disadvantages of modulation and how it shows an impact on other concepts?