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PRINCIPLES OF
COMMUNICATION SYSTEMS
Lecture 1- Introduction Elements, Modulation,
Demodulation, Frequency Spectrum
Topic covered
• Introduction to subject
• Elements of Communication system
• Modulation
• General term used in communication
• Frequency spectrum and bandwidth
GENERAL INFORMATION
• You can find this PPT, Course plan, Assignments, reference material on course website.
• You can even ask doubts and give feedback on this website
• Link :- http://pcomextc.weebly.com
INTRODUCTION
What is communication?
Communication is the process of exchanging information.
INTRODUCTION
Methods of communication Face to face Signals Written word (letters) Electrical innovations: Telegraph Telephone Radio Television Internet (computer)
ELEMENTS OF A COMMUNICATION SYSTEM
• Basic components: • Transmitter • Channel or medium • Receiver
Noise degrades or interferes with transmitted information
ELEMENTS OF A COMMUNICATION SYSTEM
COMMUNICATION SYSTEM
Transmitter
• The transmitter is a collection of electronic components and circuits that converts the electrical signal into a signal suitable for transmission over a given medium.
• Transmitters are made up of oscillators, amplifiers, tuned circuits and filters, modulators, frequency mixers, frequency synthesizers, and other circuits.
Communication Channel
• The communication channel is the medium by which the electronic signal is sent from one place to another.
• Types of media include
• Electrical conductors
• Optical media
• Free space
• System-specific media (e.g., water for sonar).
COMMUNICATION SYSTEM
Receivers
• A receiver is a collection of electronic components and circuits that accepts the transmitted message from the channel and converts it back into a form understandable by humans.
• Receivers contain amplifiers, oscillators, mixers, tuned circuits and filters, and a demodulator or detector that recovers the original intelligence signal from the modulated carrier.
COMMUNICATION SYSTEM
Attenuation
• Signal attenuation, or degradation, exists in all media of wireless transmission. It is proportional to the square of the distance between the transmitter and receiver.
COMMUNICATION SYSTEM
Transceivers • A transceiver is an electronic unit that
incorporates circuits that both send and receive signals.
• Examples are: • Telephones • Fax machines • Handheld CB radios • Cell phones • Computer modems
COMMUNICATION SYSTEM
Noise
• Noise is random, undesirable electronic energy that enters the communication system via the communicating medium and interferes with the transmitted message.
We will study in more detail
COMMUNICATION SYSTEM
COMMUNICATION SYSTEMS
Digital
Analog
BASEBAND
Baseband Transmission • Baseband information can be sent directly and
unmodified over the medium or can be used to modulate a carrier for transmission over the medium.
• In telephone or intercom systems, the voice is placed on the wires and transmitted.
• In some computer networks, the digital signals are applied
directly to coaxial or twisted-pair cables for transmission.
MODULATION AND MULTIPLEXING
• Modulation and multiplexing are electronic techniques for transmitting information efficiently from one place to another.
• Modulation makes the information signal more compatible with the medium.
• Multiplexing allows more than one signal to be transmitted concurrently over a single medium.
MODULATION
Broadband Transmission • A carrier is a high frequency signal that is
modulated by audio, video, or data. • A radio-frequency (RF) wave is an electromagnetic
signal that is able to travel long distances through space.
Modulation • It is the process of changing one or more
properties of the analog carrier in proportion with the information signal.
MODULATION
Modulation at the transmitter.
WHY MODULATION IS NECESSARY?
• It is extremely difficult to radiate low frequency signals form an antenna in the form of electromagnetic energy.
• Information signals often occupy the same frequency band and if signals from two or more sources are transmitted at the same time, they would interfere with each other.
• Reduction in noise
ANALOG SIGNAL
3 Basic Parameters of analog signal 1. Amplitude 2. Frequency 3. Phase
TWO SIGNALS WITH THE SAME PHASE AND FREQUENCY, BUT DIFFERENT AMPLITUDES
FREQUENCY
• Frequency is the rate of change of cycle (Positive and Negative) with respect to time.
•Change in a short span of time means high frequency.
•Change over a long span of time means low frequency.
3 SINE WAVES WITH FREQUENCIES 0, 8 & 16
PHASE
Phase describes the position of the
waveform relative to time 0.
THREE SINE WAVES WITH THE SAME AMPLITUDE AND FREQUENCY, BUT
DIFFERENT PHASES
MODULATION AND MULTIPLEXING
Types of modulation. (a) Amplitude modulation. (b) Frequency modulation.
MULTIPLEXING
Multiplexing
• Multiplexing is the process of allowing two or more signals to share the same medium or channel.
• The three basic types of multiplexing are: • Frequency division
• Time division
• Code division
MULTIPLEXING
Multiplexing at the transmitter.
• Electronic communications are classified according to whether they are
1. One-way (Simplex) or two-way (Half duplex or Full duplex) transmissions.
2. Analog or digital signals.
TYPE OF COMMUNICATION
SIMPLEX
• The simplest method of electronic communication is referred to as simplex.
• This type of communication is one-way. Examples are:
• Radio
• TV broadcasting
HALF DUPLEX
• The form of two-way communication in which only one party transmits at a time is known as half duplex.
• Examples are:
• Police, military, etc. radio transmissions
• Walky Talky
• HAM radio
• Morse Code
FULL DUPLEX
• Most electronic communication is two-way and is referred to as duplex.
• When people can talk and listen simultaneously, it is called full duplex.
• Telephone
ANALOG COMMUNICATION
DIGITAL COMMUNICATION
DATA
• Data can be analog or digital.
• The term analog data refers to information that is
continuous.
• Digital data refers to information that has discrete
states.
• Analog data take on continuous values.
• Digital data take on discrete values.
FREQUENCY SPECTRUM
• Available range of frequencies for communication
• Starts from low frequency communication such as voice and progresses to high frequency communication such as satellite communication
• The spectrum spans the entire bandwidth of communicable frequencies
THE ELECTROMAGNETIC SPECTRUM
• The range of electromagnetic signals encompassing all frequencies is referred to as the electromagnetic spectrum.
THE ELECTROMAGNETIC SPECTRUM
Figure 1-13: The electromagnetic spectrum.
THE ELECTROMAGNETIC SPECTRUM
Frequency Ranges from 30 Hz to 300 GHz
• The electromagnetic spectrum is divided into segments:
Extremely Low Frequencies (ELF) 30–300 Hz.
Voice Frequencies (VF) 300–3000 Hz.
Very Low Frequencies (VLF) include the higher end of the
human hearing range up to
about 20 kHz.
Low Frequencies (LF) 30–300 kHz.
Medium Frequencies (MF)
300–3000 kHz
AM radio 535–1605 kHz.
ELECTROMAGNETIC SPECTRUM
Frequency Ranges from 30 Hz to 300 GHz
High Frequencies (HF)
(short waves; VOA, BBC
broadcasts; government and
military two-way communication;
amateur radio, CB.
3–30 MHz
Very High Frequencies (VHF)
FM radio broadcasting (88–108
MHz), television channels 2–13.
30–300 MHz
Ultra High Frequencies (UHF)
TV channels 14–67, cellular
phones, military communication.
300–3000 MHz
ELECTROMAGNETIC SPECTRUM
Frequency Ranges from 30 Hz to 300 GHz
Microwaves and Super High
Frequencies (SHF)
Satellite communication, radar,
wireless LANs, microwave ovens
1–30 GHz
Extremely High Frequencies (EHF)
Satellite communication, computer
data, radar
30–300 GHz
BA
N
D
Frequen
cy
range
Designations applications
2 30 Hz-
300 Hz ELF (
Extremely
low
frequencies)
Include AC power distribution signals (60Hz) and low telemetry
signals.
3 0.3 KHz –
3 KHz VF ( Voice
frequencies) Include frequencies generally associated with human speech.
Standard Telephone channels have a 300 Hz to 3000 Hz bandwidth
and are often called Voice Frequency of Voice band frequencies.
4 3 KHz –
30 KHz VLF( Very
low
frequencies)
Includes upper end of the hearing range. Used for Specialized
government and military systems like submarine communications
5 30 KHZ –
300 KHz LF (low
frequencies) Used for marine and aeronautical navigation
6 0.3 MHz
– 3 MHz Mf( MEDIUM
FREQUECNIE
S)
Used for commercial AM radio broadcasting (535 KHZ to 1605 KHz)
7 3 MHZ –
30 MHz HF ( high
frequencies) Referred as SHORT waves. Used in two way radio communications
, Voice of America and Radio Free Europe broadcast within the HF
band.
Amateur radio and citizens band (CB) radio are also use signals in
this range.
8 30 MHz -
300 MHz VHF( Very
high
frequency)
Used for mobile radio, marine and aeronautical communications,
commercial FM broadcasting ( 88 MHz to 108 MHz) and
commercial TV broadcasting of channels 2 to 13 ( 54 MHz to 216
MHz)
9 300 MHz
– 3 GHz UHF ( Ultra high
frequency) Used by commercial TV broadcasting of channels 14 to
83 , land mobile communications services, cellular
telephones, certain radar and navigation systems, and
microwave and satellite Radio systems. Frequencies
above 1 GHz are considered microwave frequencies,
which include the upper end of the UHF range.
10 3 GHz –
30 GHZ SHF( Super high
frequency) Used for microwave and satellite radio communications
systems.
11 30 GHz –
300 GHz EHF ( Extremely
high frequency) Seldom used for radio communication except in very
sophisticated expensive and specialized applications.
12 0.3 THz –
3 THz Infrared Light Not referred as radio waves. It refers to Electromagnetic
radiation generally associated with heat. Used in heat
seeking guidance systems, electronic photography , and
astronomy.
13 3 THz –
30 Thz Infra red light
14 30 THz –
300 THz Infra red light
15 0.3 PHz-
3 PHZ Visible light Includes electromagnetic frequencies that fall within the
visible range of humans . Light wave communications is
used with optical fiber systems.
16 3 PHz- 30
PHz Ultraviolet light Ultraviolet rays, X rays, Gamma Rays and cosmic rays
have little application to electronic communication.
ELECTROMAGNETIC FREQUENCY SPECTRUM
17 30 PHz – 300 PHz
X rays
18 0.3 EHz- 3 EHz
Gamma rays
19 3 EHz – 30 EHz
Cosmic rays
WAVELENGTH
• It is the length that one cycle of an electromagnetic wave occupies in space i.e. the distance between similar points in a repetitive wave.
• It is inversely proportional to the velocity of propagation.
WAVELENGTH
BANDWIDTH
• Bandwidth (BW) is that portion of the electromagnetic spectrum occupied by a signal.
• Channel bandwidth refers to the range of frequencies required to transmit the desired information.
BANDWIDTH
More Room at the Top
• Today, virtually the entire frequency spectrum between approximately 30 kHz and 300 MHz has been spoken for.
• There is tremendous competition for these frequencies, between companies, individuals, and government services in individual carriers and between the different nations of the world.
• The electromagnetic spectrum is one of our most precious natural resources.
BANDWIDTH
More Room at the Top • Communication engineering is devoted to making
the best use of that finite spectrum.
• Great effort goes into developing communication techniques that minimize the bandwidth required to transmit given information and thus conserve spectrum space.
• This provides more room for additional communication channels and gives other services or users an opportunity to take advantage of it.