telecommunication

1. 1 | P a g e
Chapter 4
Analog and Digital communications
Chapter 4: Analog and Digital communications.
4.1. Differentiate between voice and data communications.
4.2. Modulation and their applications.
4.3. Explain the concepts of signal type and bandwidth.

2. 2 | P a g e
This page on Data Communication versus Voice communication describes difference between data communication and
voice communication.
Signal:
In electronics, a signal is an electric current or electromagnetic field used to convey data from one place to another. The
simplest form of signal is a direct current (DC) that is switched on and off; this is the principle by which the early telegraph
worked.
Bandwidth:
Bandwidth is measured as the amount of data that can be transferred from one point to another within a network in a
specific amount of time. Typically, bandwidth is expressed as a bitrate and measured in bits per second (bps). It refers to
the transmission capacity of a connection and is an important factor when determining the quality and speed of a
network.

3. 3 | P a g e
A transmitter is a group of electronic circuits designed to convert the information into a signal for
transmission over a given communication medium.
A receiver is a group of electronic circuits designed to convert the signal back to the original information.
The communication channel is the medium which is designed to transmit the electronic signal from one place
to another.

4. 4 | P a g e
We are living in an era of communication wherein we can easily transfer any 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 scenarios within the communication systems.
Modulation plays a key role in communication system to encode information digitally in 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.
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 carrier wave.
These modulation techniques are classified into two major types:
1- Analog.
2- Digita.

5. 5 | P a g e
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, in which, three parameters can be altered to get modulation – they are 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 lower frequency band, upper
frequency band and carrier frequency components. This type of modulation requires greater band width, more
power. Filtering is very difficult in this modulation.

6. 6 | P a g e
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 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.

7. 7 | P a g e
Digital Modulation
For a better quality and efficient communication, digital modulation technique is employed. The main advantages
of the 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.
Types of Digital Modulation:
Digital modulation is of several types depending 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 base band signal or message
signal, which is in digital format. It is used for low-band requirements and is sensitive to noise.
Digital Modulation
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.
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 communication system. And therefore, the
readers can share their ideas, suggestions and comments in the comment section below.