MODULE 6

Introduction to Communication Systems: Evolution of communication systems – Telegraphy to 5G.

Radio communication: principle of AM & FM, frequency bands used for various communication systems,
block diagram of super heterodyne receiver, Principle of antenna – radiation from accelerated charge.
Mobile communication: basic principles of cellular communications, principle and block diagram of
GSM.

Introduction to Communication Systems

Communication is the transfer of information from one point in space and time to another point.
The block diagram of a communication system is shown in Figure

Transmitter – It is the device which converts the source signal into a suitable form for
transmission through the channel.
Channel – It is defined as the channel connecting the transmitter and the receiver is a physical
medium. The channel can be in the form of wires, cables or wireless.
Receiver – It is the equipment in which due to noise and other factors, the corrupted version of
the signal arrives at the receiver. The receiver is that device which is used to reconstruct the
signal into a recognizable form of the original message for delivering it to the user. The signal at
the receiver forms the output.

 Depending on the communication channel, the communication system is categorized as

follows:
1. Wired (Line communication)

 Parallel wire communication

 Twisted wire communication
  Coaxial cable communication
 Optical fibre communication
2. Wireless (Space communication)

 Ground wave communication

 Skywave communication
 Space wave communication
 Satellite communication

 The Two basic types of communication systems are

(i) Analog.

(ii) Digital.

 In Analog Systems: Both the information and the carrier are analog signals.

 In Digital Systems: The digital pulses are transferred between two or more points
in a communication system.

Evolution of communication systems – Telegraphy to 5G (study from the handout)

Principle of AM and FM
 Frequency spectrum of AM wave:
  Total power of AM

PRINCIPLE OF FM
 Mathematical representation of FM
  Modulation Index

 Bandwidth

COMPARISION BETWEEN AM AND FM

Sl
AM FM
No
The abbreviation AM stands for Amplitude Frequency Modulation (FM) is
1
Modulation the abbreviation for FM
In AM modulation, amplitude of the signal is In FM modulation, frequency
varied, and frequency and phase are kept of the signal is varied, and
2
constant. amplitude and phase are kept
constant.
AM has two sidebands FM has infinite number of
3
sidebands
Modulation index in AM varies from 0 to 1. Modulation index in FM is
4
always greater than one.
AM is more noisy since the AM receivers do not Noise in FM can be reduced
have amplitude limiters. by employing amplitude
5 limiters to remove the
amplitude variations caused
by noise.
AM has narrow channel bandwidth which is 2 fm. The bandwidth in FM is much
6 higher, up to 10 times as that
of AM.
AM broadcast operates in the medium frequency FM broadcast operates in the
(MF) and high frequency (HF). upper VHF and UHF range,
7
where noise effects are
minimal.
The design of AM transmitter and receiver is not The design of FM transmitter
complex for the modulation and demodulation and receiver is relatively
8
purpose. complex for the modulation
and demodulation purpose.

ADVANTAGES OF FM
1. The amplitude of the frequency-modulated wave does not get affected.
2. Frequency Modulation decreases the noise; hence, there is a significant increase in the signal to noise ratio.
3. We can also reduce the noise by increasing the frequency deviation.
4. It also reduces the interference by the adjacent channels through guard bands.
5. It operates in a very high frequency called VHF.
6. It is resistant to single strength variations.
7. It does not require a linear amplifier in the transmitter.
RADIO RECEIVERS
In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an
electronic device that receives radio waves and converts the information carried by them to a usable form.
In view of the huge difference in requirements and performance levels needed, many different types of
radio can be seen these days.
 AM SUPER HETERODYNE RECEIVER
  FM SUPERHETERODYNE RECEIVER

ANTENNA
Definition:

An Antenna is a transducer, which converts electrical power into electromagnetic waves and vice versa.
An Antenna can be used either as a transmitting antenna or a receiving antenna.
 A transmitting antenna is one, which converts electrical signals into electromagnetic waves and radiates
them.
  A receiving antenna is one, which converts electromagnetic waves from the received beam into electrical
signals.
 In two-way communication, the same antenna can be used for both transmission and reception.

How Does An Antenna Work?

Telecommunication requires two antennas, a transmitter, and a receiver. First, the information is converted into an
electric current, which is sent to the transmitter. Next, the transmitter sends the electric current through the
transmitter's antenna. When the antenna conducts this electric current, it sends out electromagnetic radio waves.
Then, radio waves are detected by the receiver's antenna, which absorbs incoming radio waves, making the electrons
in the antenna vibrate. The antenna conducts this electric current to the receiver of the radio, TV, or other device.
Finally, the signal is converted into sound, TV images, or whatever other information is being transmitted.

PRINCIPLE OF ANTENNA-RADIATION FROM ACCELERATED CHARGE

 A stationary charge will create an electric field around it
 If charge is moving . magnetic field is created
 By changing magnetic field electric field is created
 By mutual interaction of electric field and magnetic field produces electromagnetic field.
 The time varying electric and magnetic field are perpendicular to each other
 This produces EM waves that propagate at the speed of light
TYPES OF ANTENNA

MOBILE COMMUNICATION

Mobile communications refers to a form of communications which does not depend on a physical
connection between the sender and receiver. It facilitates the users to move from one physical
location to another during communication.

CELLULAR COMMUNICATION

Introduction of cellular system helped to improve the user capacity of mobile communication
in the allowed spectrum. In cellular system, high power transmitters are replaced by a large
number of low power transmitters. Each of these transmitters constitute a cell that can
accommodate a large number of users over a geographical area. The frequency used in one cell
can be reused in another cell which is at a sufficient distance. This property helps in
communication between large number of stations using a limited spectrum. This is the basic
principle behind cellular communication.

BASIC CELLULAR SYSTEM

A cellular system consists of 4 basic components

1. Mobile unit: Mobile handset used by the user.
2. Cell site: Cellular service areas are divided into small regions called cell site. Each of
these has control unit, radio cabinet, antennas, power plant and data terminals.
3. Base station: It is a fixed point of communication which is connected to the antenna that
receives and transmits the signals on cellular networks to the customer phones.
4. Mobile Telephone Switching Office (MTSO): The base stations are controlled by
mobile switching centre. It coordinates all the cell sites. It contains cellular processor
and cellular switch. It controls call processing and handles billing services.
 Roaming
Global System For Mobile Communication(GSM)

Principle and Block diagram:

The figure shows the key functional elements in the GSM system. The boundaries at Um, Abis
and A refer to the interfaces between functional elements.