Modulation plays a key role in communication system to encode information digitally in analog world. So, when a signal is to be transmitted to a distance, it should not affect any external disturbances, to avoid external disturbances it has to undergo a process called Modulation. It improves the strength of the signal without disturbing the parameters of the original signal.
A signal which carries a message gets transmitted over a distance and to maintain reliable communication, it requires high frequency signal to travel to longer distances as it is not possible for low frequency signals to travel to longer distances which should not affect the original characteristics of the message signal.
The any changes occur in the characteristics of the message signal, the message contained in it also alters. Hence, it is very important to take care of the message signal. A high frequency signal can travel up to a longer distance, without getting affected by external disturbances. That high frequency signal is called as a carrier signal that helps to transmit your message signal. Such a process is simply called as Modulation. So, whenever signal undergoes modulation then the parameters of the carrier signal are changed.
Modulation is the process of changing the parameters of the carrier signal, in accordance with the instantaneous values of the modulating signal. It is very important to modulate the signals before sending them to the receiver.
Baseband signals are inconsistent for direct transmission. For such signals it needs very high modulating frequency carrier wave so as to travel to longer distances. And this should not affect the parameters of the modulating signal.
If the signal does not undergo modulation process then the antenna used for transmission must be very large. The range of communication is restricted to limited as the wave signal cannot travel to longer distances without getting distorted.
Following are some of the advantages for implementing modulation in the communication systems.
Following are the three types of signals in the modulation process.
The signal which contains a message to be transmitted is called as a message signal. It is a baseband signal, which has to undergo the modulation process, to get transmitted. Hence, it is also called as the modulating signal.
Carrier signal is a high frequency signal which travels to longer distances constitutes a certain amplitude, frequency and phase but does not contain any information. It is called as an empty signal with no information and is used to carry the signal to the receiver after modulation.
The signal after completing the process of modulation is called as a modulated signal. This signal is a combination of modulating signal and carrier signal. Every signal has to be modulated before sending to the receiver.
There are many types of modulations. Depending upon the modulation techniques used, they are classified as shown in the following figure.
The types of modulations are broadly classified into continuous-wave modulation and pulse modulation.
In continuous-wave modulation, a high frequency sine wave is used as a carrier wave. This is further divided into amplitude and angle
In Pulse modulation, a continuous signal is converted into a sequence of rectangular pulses, which is used as a carrier wave. This is further divided into analog and digital modulation.
In analog modulation technique, if the amplitude or duration or position of a pulse is varied in accordance with the instantaneous values of the baseband modulating signal, then such a technique is called as Pulse Amplitude Modulation (PAM) or Pulse Duration/Width Modulation (PDM/PWM), or Pulse Position Modulation (PPM).
In digital modulation, the modulation technique used is Pulse Code Modulation (PCM) where the analog signal is converted into digital form of binary digits that is 1s and 0s so that modified analog signal can be transmitted through the digital communication network.Thus, the resultant is a coded pulse train, called as PCM. Here quality does not mean that importance. This is further developed as Delta Modulation (DM). These digital modulation techniques are discussed in our Digital Communications tutorial
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