Modulation

Introduction

  • As we know that in normal communication, signals loose its strength/energy slowly as they travel to the medium upto a large distances. To send these transmitting message signals effectively for long distances, we use modulation technique. At the receiver end, after receiving the signal, we finally convert into the original frequency band (baseband)
    through demodulation.
  • Carrier Signal :
    • The carrier signal conveys the data/message/information.
    • It is an electromagnetic wave or pulse having steady frequency.
    • Carrier signals are high frequency signals in sinusoidal pulses form.
    • Carrier signal is modulated by the modulating or the information signal.
  • Message/Modulating Signal :
    • It is the original signal/message we want to sent/modulated with carrier signal.
    • In another words, it is the signal which contains a message to be transmitted.
    • Modulating signals are usually low frequency signals. 
  • Modulated Signal :
    • It is the mixing signals of both carrier and modulating signal using modulation process.
    • This signal has new property which is different from carrier and modulating signal .

Definition

  • Modulation is one of the most important data transmission technique which helps to transmit a data from source to destination through a medium. 
  • It is process of changing some physical characteristics (such as amplitude, frequency or phase) of a carrier wave in accordance with the intensity of the signal is known as modulation.

Features

  • It helps in data transmission usually for long distance through an analog medium (air/cables).
  • Modulation is used to transmit data mainly  in air/telephone line/optical fibers medium.

Advantages

  • Modulation process can shift the frequency spectrum of a message/modulating signal near to a band which is better suited to the channel for easy transmission.
  • Modulation permits the use of multiplexing in data communication.
  • Modulation (frequency modulation) can provide some control over noise and interference. 
  • Modulation is usually done without loss of information.

Disadvantages

  • It is an extra process implemented on analog/digital data during communication.
  • It requires/uses an extra device.

Types of Modulation

(A) On the basis of type of output/signal produced after modulation, it is broadly classified into two categories –

(a) Analog Modulation 

  • Analog modulation is the simplest form of the modulation.
  • Analog modulation is done by a device called ‘Modem’ through a process of Modulation. Modem performs/modulation consists of two process called Modulating and Demodulating by Modulator and Demodulator components of Modem.
  • In analog modulation, the modulation is applied continuously in response to the analog information signal.
  • Analog modulation shifts original signal’s baseband frequency into the broadband frequency.
  • Analog modulation is mostly suitable for data transmission in analog medium/environment.
  • Analog modulation is done through two ways  –

(I) Analog Data ———————> Analog Signal = This is done by 2 ways – (i) AM (ii) Angle Modulation.

(II) Digital Data ———————> Analog Signal = This is done by 4 ways – (i) ASK (ii) FSK (iii) PSK (iv) QAM.

 (I) Analog Data ———————> Analog Signal  

(i) Amplitude Modulation (AM) 

Definition

      • Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a high frequency carrier wave.
    • Features
      • AM works by varying the strength/amplitude of the transmitted signal in relation to the information being sent.

Advantage

      • The transmission coverage area of AM Receiver is wider than FM because atmospheric propagation.
      • AM supports long distance propagation because of its high power.
      • AM circuit is the cheapest and least complex.
      • AM can be easily demodulated using a Diode Detector.

Disadvantage

      • It is very much sensitive to noise and hence the quality & performance is very weak.
      • Signal of AM is not stronger than FM when it propagates through an obstacle.
      • Only one sideband of AM transmits Information Signal, so it loses power on other sideband and carrier. Hence the power efficiency of the Amplitude Modulation is very poor.

(ii)Angle Modulation  

    • The main characteristic of the angle modulation is that the amplitude of the carrier frequency is maintained constant, whereas the frequency or phase is changed.
    • Angle Modulation has two forms –
(i) Frequency Modulation (FM)

Definition

        • Frequency modulation is the technique in which, the frequency of the carrier wave is changed (remaining amplitude and phase constant) in accordance with the amplitude of the modulating signal.

Features

        • FM is widely used in a variety of radio communication’s applications.

Advantage

        • This technique has resilient towards noise (noise hater) hence utilized by the broadcasting industry.
        • Using this technique, stereophonic transmission is possible.
        • This technique does not require linear amplifiers in the transmitter because only frequency changes are required to be carried in this. Hence, no need of  amplifiers in the transmitter.
        • It has comparatively greater efficiency than many other modes.

Disadvantage

        • It requires larger bandwidth.
        • It needs to be operated at very high frequency bands.
        • The process of demodulation in this process is complex hence require more complicated demodulator hence more expensive.
(ii) Phase Modulation(PM) 

Definition

        • In the phase modulation, the phase of the carrier wave is changed (remaining amplitude and frequency constant) in accordance with the amplitude of the modulating frequency.

Features

        • Phase modulation is a form of analog modulation.
        • Phase modulation works by modulating the phase of the signal, i.e. changing the rate at which the point moves around the circle.
        • when phase modulation is applied to a signal there are frequency changes and vice versa. Phase and frequency are inseparably linked as phase is the integral of frequency. Due to these reason, frequency modulation can be changed into phase modulation when required.

Advantage

        • Its modulation and demodulation process is comparatively easy than frequency modulation.

Disadvantage

        • PM is not very widely used for radio transmissions because it tends to require more complex receiving hardware and there can be ambiguity problems in determining whether, for example, the signal has changed phase by +180° or -180°.

Use/Application

        • This method is used for producing radio signals used in a variety of radio communications applications.
        • PM is used in digital music synthesizers such as the Casio CZ synthesizers, or to implement FM Synthesis in digital synthesizers such as the Yamaha DX7.

 (II) Digital Data ———————> Analog Signal  

(i) Amplitude Shift Keying (ASK) 

Definition

Features

Advantage

Disadvantage

Use/Application

(ii) Frequency Shift Keying (FSK) 

Definition

Features

Advantage

Disadvantage

Use/Application

(iii) Phase Shift Keying (PSK)

Definition

Features

Advantage

Disadvantage

Use/Application

(iv) Quadrature Amplitude Modulation (QAM) 

Definition

Features

Advantage

Disadvantage

Use/Application

(b) Digital Modulation/Encoding 

Introduction

    • Digital modulation is done by a device called ‘Codec’ through a process of Encoding. Codec performs/encoding consists of two process called Coding and Decoding by Encoder and Decoder components of Codec respectively.

Definition

Features

    • Digital modulation is suitable for data transmission in digital medium/environment.

Advantages

Disadvantages

Types of Encoding

    • Digital modulation is performed through two ways –

(I) Analog Data  ———————> Digital Signal = This is done by 2 ways – (i) PCM (ii) DM.

(II) Digital Data  ———————> Digital Signal = This is done by 3 ways – (i) Unipolar (ii) Polar (iii) Bipolar.

(I) Analog Data ———————> Digital Signal

(i) Pulse Code Modulation (PCM)

Definition

Features

Advantage

Disadvantage

Use/Application

(ii) Delta Modulation (DM)

Definition

Features

Advantage

Disadvantage

Use/Application

  

(II) Digital Data ———————> Digital Signal  

(i) Unipolar

Definition

Features

Advantage

Disadvantage

Use/Application

(ii) Polar

Definition

Features

Advantage

Disadvantage

Use/Application

(iii) Bipolar

Definition

Features

Advantage

Disadvantage

Use/Application

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