Analog and Digital Communication Prepared According to R 2017
ANALOG AND DIGITAL COMMUNICATION
Prepared according to Anna university syllabus R-201
7 (Common to III semester-CSE/IT )
G. E lumalai , M.E.,(Ph.D)
Assistant Professor (Grade I) Department of Electronics and Communication Engineering Panimalar Engineering College Chennai.
Er. m. J aiGanEsh , M.E., Assistant Professor Department of Electronics and Communication Engineering
Panimalar Engineering College Chennai.
SREE KAMALAMANI PUBLICATIONS CHENNAI
sREE Kamalamani PuBliCaTiOns (P) l td.
Publised by SREE KAMALAMANI PUBLICATIONS. N o . AJ. 21, o ld N o . AJ. 52, P th th ew N lot No. 2614,
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1ST EdiTioN 2014
2Nd REViSEd EdiTioN 2016 Copyright © 2014, by Sree Kamalamani Publications.
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About the Author
G.Elumalai M.E., is working as an Assistant Professor (Grade – I)
in the Department of Electronics and Communication Engineering, Panimalar Engineering College, Chennai. He obtained his B.E. in Electronics and Communication Engineering; M.E. in Applied Electronics and Ph.D pursing in Wireless Sensor Network. His areas of interests are Communication System, Digital communication, Digital signal processing and Wireless Sensor Network. He has more than 13 years of experience.
M.Jaiganesh M.E., is working as an Assistant Professor in the
Department of Electronics and Communication Engineering, Panimalar Engineering College, Chennai. He obtained his B.E. in Electronics and Communication Engineering; M.E. in Computer and Communication. His areas of interests are Communication System, Digital communication, Optical Communication and Embedded system. He has more than 4 years of experience.
PREFACE
Dear Students,We are extremely happy to present the book “Analog and Digital Communication” for you. This book has been written strictly as per the revised syllabus (R2013) of Anna University. We have divided the subject into five units so that the topics can be arranged and understood proper- ly. The topics within the units have been arranged in a proper sequence to ensure smooth flow of the subject.
Unit I - Introduce the basic concepts of communication, need of
modulation and different types of analog modulation (Amplitude modu- lation, Frequency modulation and Phase modulation).
Unit II - Deals with basic concepts of digital communication which includes ASK, FSK, PSK, QPSK and QAM. Unit III - Discuss about concept of data communication and various pulse modulation technique. Unit IV - Concentrate on various techniques for error control cod- ing. Unit V – Describe about multiuser radio communication.
A large number of solved university examples and university questions have been included in each unit, so we are sure that this book will cater all your needs for this subject.
We have made every possible effort to eliminate all the errors in this book. However if you find any, please let we know, because that will help for us to improve further. G.Elumalai
M.Jaiganesh
EC8394 ANALOG AND DIGITAL COMMUNICATION L T P C 3 0 0 3
UNIT I ANALOG COMMUNICATION Noise: Source of Noise - External Noise- Internal Noise- Noise Calculation.
Introduction to Communication Systems: Modulation – Types - Need for Modulation.
Theory of Amplitude Modulation - Evolution and Description of SSB Techniques - Theory
of Frequency and Phase Modulation – Comparison of various Analog Communication
System (AM – FM – PM).UNIT II DIGITAL COMMUNICATION
Amplitude Shift Keying (ASK) – Frequency Shift Keying (FSK) Minimum Shift
Keying (MSK) –Phase Shift Keying (PSK) – BPSK – QPSK – 8 PSK – 16 PSK - Quadrature
Amplitude Modulation (QAM) – 8 QAM – 16 QAM – Bandwidth Efficiency– Comparison of
various Digital Communication System (ASK– FSK – PSK – QAM).UNIT III DATA AND PULSE COMMUNICATION
Data Communication: History of Data Communication - Standards Organiza-
tions for Data Communication- Data Communication Circuits - Data Communication
Codes - Error Detection and Correction Techniques - Data communication Hardware -
serial and parallel interfaces. Pulse Communication: Pulse Amplitude Modulation (PAM)
- – Pulse Communication System (PAM – PTM – PCM).
Pulse Time Modulation (PTM) – Pulse code Modulation (PCM) - Comparison of various
UNIT IV SOURCE AND ERROR CONTROL CODING
Entropy, Source encoding theorem, Shannon fano coding, Huffman coding,
mutual information, channel capacity, channel coding theorem, Error Control Coding,
linear block codes, cyclic codes, convolution codes, viterbi decoding algorithm.UNIT V MULTI-USER RADIO COMMUNICATION Advanced Mobile Phone System (AMPS) - Global System for Mobile Communica-
tions (GSM) - Code division multiple access (CDMA) – Cellular Concept and Frequency
Reuse - Channel Assignment and Hand - Overview of Multiple Access Schemes - Satellite
Communication - BluetoothTABLE OF CONTENTS TABLE OF CONTENTS
UNIT – I ANALOG COMMUNICATION
1.1 Introduction
1.2 Noise
1.3 Introduction to communication system
1.4 Modulation
1.5 Need for modulation
1.6 Classifications of modulation
1.7 Some important definitions related to communication
1.8 Theory of Amplitude modulation
1.9 Generation of SSB
- – 1.10 AM Transmitters
1.11 AM Super heterodyne receiver with its characteristic Performance
1.12 Performance characteristics of a receiver
1.13 Theory of Frequency and Phase modulation
1.14 Comparison of various analog communication system
Solved two mark questions
UNIT – II DIGITAL COMMUNICATION2.1 Introduction
2.2 Digital Transmission system
2.3 Digital Radio
2.4 Information capacity
2.5 Trade of between, Bandwidth and SNR
2.6 M-ary encoding
2.7 Digital Continuous wave modulation technique
Analog and Digital communication
2.8 Amplitude shift keying (or) Digital Amplitude Modulation (or) OOK – System
2.9 Frequency shift keying
2.10 Minimum shift keying (or) continuous phase frequency shift keying
2.11 Phase shift keying
2.12 Differential Phase shift keying
2.13 Quadrature Phase shift keying
2.14 8 PSK System
2.15 16 PSK System
2.16 Quadrature Amplitude modulation
16 QAM
- 2.17
2.18 Carrier recovery (phase referencing)
2.19 Clock recovery circuit
2.20 Comparison of various digital communication system
Solved two mark questions
3.1 Introduction
3.2 History of data communication
3.3 Components of Data communication systems
3.4 Standard organization for data communication
3.5 Data communication circuits
3.6 Data transmission
3.7 Configurations
3.8 Topologies
3.9 Transmission modes
3.10 Data communication codes
3.11 Introduction to error detection and correction techniques
3.12 Error detection techniques
3.13 Error correction techniques
TABLE OF CONTENTS
3.14 Data communication hardware
3.15 Serial interface
3.16 Centronics – Parallel interface
3.17 Introduction to Pulse modulation
3.18 Pulse Amplitude Modulation (PAM)
3.19 Pulse Width Modulation (PWM)
3.20 Pulse Position Modulation (PPM)
3.21 Pulse Code Modulation (PCM)
3.22 Differential Pulse Code Modulation (DPCM)
3.23 Delta Modulation (DM)
3.24 Adaptive Delta Modulation (ADM)
3.25 Comparison of various pulse communication system
3.26 Comparison of various source coding methods
Solved two mark questions
4.1 Introduction
4.2 Entropy (or) average information (H)
4.3 Source coding to increase average information per bit
4.4 Data compaction
4.5 Shannon fano coding algorithm
4.6 Huffman coding algorithm
4.7 Mutual information
4.8 Channel capacity
4.9 Maximum entropy for continuous channel
4.10 Channel coding theorem
4.11 Error control codings
4.12 Linear Block codes
4.13 Hamming codes
4.14 Syndrome decoding for Linear block codes
4.15 Cyclic codes
4.16 Convolutional codes
4.17 Decoding methods of Convolutional codes
Analog and Digital communication
Solved two mark questions
5.9 Earth station (or) ground station
Solved Two Marks Review Questions
Bluetooth
5.14
5.13 Satellite frequency plans and allocation
5.12 Satellite Elevation categories
5.11 Satellite Orbits
5.10 Kepler’s laws
UNIT – V MULTI-USER RADIO COMMUNICATION
5.4 CDMA
5.1 Introduction
5.2 Advanced Mobile Phone Systems (AMPS)
5.3 Global system for mobile - GSM (2G)
5.8 Satellite Link system Models
5.5 Cellular network
5.6 Multiple access techniques for wireless Communication
5.7 Satellite communication
NUMBER SYSTEM Noise: Source of Noise - External Noise- Internal Noise- Noise Calculation. Introduction to Communication Systems: Modulation – Types - Need for Modulation. Theory of Amplitude Modulation - Evo- lution and Description of SSB Techniques - Theory of Frequency and Phase Modulation – Comparison of various Analog Communication System (AM – FM – PM).
ANALOG AND DIGITAL COMMUNICATION ANALOG COMMUNICATION Unit
1
1.1 INTRODUCTION
Communication is the process of establishing connection (or link) between two points for information exchange. The science of communication involving long distances is called telecommunication ,the word tele stands for long distance The information can be of different type such as sound, picture, music computer data etc., The basic communication components are t A Transmitter t A communication channel or medium and t A receiver
1.1.1 Elements of communication system:
The block diagram of elements of communication system is as shown in figure 1.1
Destination Information Transmitter Channel Receiver Source
Noise and
Distortion
Figure 1.1 Block diagram of simple communication systemANALOG COMMUNICATION
The elements of basic communication system are as follows
1. Information or input signal
2. Input transducer
3. Transmitter
4. Communication channel
5. Noise
6. Receiver
7. Output transducer
Information or input signal
- The communication system has been developing for communicating useful information from one place to the other.
- This information can be in the form of a sound signal like speech or music, or it can be in the form of pictures or it can be data informa- tion coming from a computer.
Input transducer
The information in the form of sound, picture and data signals cannot be transmitted as it is. Input transducer is used to convert the information signal from source into suitable electrical signal . The input transducer used usually in the communication systems are microphones, TV camera etc..
Transmitter
The function of transmitter block is to convert the electrical equivalent of the information to a suitable form corresponding to communicate through communication medium (or) channel. The transmitter consists of the electronic circuits such as modulator, amplifier, mixer, oscillator and power amplifier.
ANALOG AND DIGITAL COMMUNICATION
In addition to that it increases the power level of the signal. The power level should be increased in order to cover a large range.
Communication channel
The communication channel is the medium used for trans- mission of electronic signal from one place to the other. The communication medium can be conducting wires, cables, optical fibre or free space. Depending on the type of communication medium, two types of communication systems will exist. They are:
- Wire communication (or) line communication
- Wireless communication (or) radio communication
Noise
Noise is an unwanted electrical signal which gets added to the transmitted signal when it is travelling towards the receiver Due to noise, quality of the transmitted information degrades. Once added, the noise cannot be separated out from the information.
Hence noise is a big problem in the communication systems. Even though noise cannot be completely eliminated, its effect can be reduced by using various techniques.
Receiver The reception is exactly the opposite process of transmission.
That is extract original signal form transmitted signal.
The receiver consists of the electronic circuits such as demodula- tor, amplifier, mixer, oscillator and power amplifier.
Output transducer
The output transducer converts the electrical signal at the output of the receiver back to the original form (i.e) Sound, picture and data signals.
The typical examples of output transducer are loud speakers, picture tube computer monitor etc.
ANALOG COMMUNICATION
1.2 NOISE
Noise is an unwanted signal that interferes with the desired message signal. In audio and video systems electrical disturbances are appearing as interference is called as noise. In general noise may be predictable or unpredictable (random) in nature.
Predictable noise
The predictable noise can be estimated and eliminated by proper engineering design. The predictable noise is generally man made noise and it can be eliminated easily.
Examples: power supply hum, ignition radiation pickup, spurious oscillations in feedback amplifiers, fluorescent lightening.
Unpredictable noise
This type of noise varies randomly with time, and we have no control over this noise. The term noise is generally used to represent random noise. Presents of random noise ,complicate the communication system
Sources of noise
1. Internal noise
2. External noise Internal noise may be classified as
1. Shot noise
2. Thermal Noise
3. Partition Noise
4. Flicker Noise
ANALOG AND DIGITAL COMMUNICATION
External Noise may be classified as
1. Natural Noise
2. Manmade Noise
1.2.1 Natural noise
This type of noise randomly occurs in atmosphere due to lightning, electrical storms and other atmospheric disturbances.
This noise is unpredictable in nature. This noise is also called as atmospheric noise (or) static noise
1.2.2 Manmade Noise
Manmade noise results from undesired pickups from electrical appliances, such as motors, automobiles and aircraft ignition etc.,
This type of noise can be eliminated by removing the source of the noise. This noise is effective in frequency range of 1 MHz - 500 MHz
1.2.3 Internal noise
Internal noise is created by active and passive components present within the communication system
1.2.3.1 Shot noise
Shot noise present in active devices due to random fluctuation of charge carriers crossing the potential barriers. In electron tubes, shot noise is generated due to random emission from cathodes.
In semi-conductor devices, it is caused due to random diffusion of minority carriers (or) random generation of recombination of electron hole. Shot noise is not normally observed during measurement of direct noise current, because it is small compared to the DC-
ANALOG COMMUNICATION
Shot noise has a flat response spectrum. The mean squared noise component is proportional to the DC-flowing and for most of the devices the mean square shot noise current is given by,
2 I = 2I q B
amperes ...(1)
n o e n
Where I = DC in amperes
- 19
q C)
= Magnitude of electron charge (1.6 x 10
e
B = Equivalent noise Bandwidth
n
1.2.3.2 Thermal noise
? This type of noise arises due to random motion of electrons in a conducting medium such as a resistor, and this motion in turn is randomized through collisions caused by imperfection in the structure of conductors. The net effect of motion of all electrons constitutes an electric current flowing through the resistor, causing the noise
This noise is also known as resistor noise (or) Johnson noise. ? The power density spectrum of the current contributing the thermal noise is given by
KTG
2 i ( ) ω = S 2 ...(2)
ω
1
-
α
Where,
T- Ambient temperature in degree kelvin
G- Conductance of the resistor in mhos K - Boltzman constant a - average number of collisions per sec per electron
ANALOG AND DIGITAL COMMUNICATION
1.2.3.3 Partition noise
? This noise is generated whenever a current has to divide between two (or) more electrodes and results from random fluctuation in the division. ? It would be expected therefore that a diode would be less noisy than a transistor, if third electrode draws current.
? For this reason, the input stage of microwave receiver is often a diode circuit. The spectrum of the partition is flat
1.2.3.4 Flicker noise (or) low frequency noise
Flicker noise occurs due to imperfection in cathode surface of electron tubes and surface around the junctions of semiconductor devices. In the semiconductor, flicker noise arise from fluctuation in the carrier density, which in turn give rise to fluctuation in the conductivity of the material. The power density of the flicker noise is inversely
1 proportional to frequency (ie) S (w) a . f
Hence, this noise becomes significant at very low frequencies (below a few KHz)
1.2.4 Calculation of noise i. Signal to noise Ratio (SNR)
It is defined as the ratio of signal power to noise power either input side (or) at output side of the circuit (or) device Signal power at the input
SNR =
i
Noise power at the input Output Signal power
SNR = Output Noise power
ii. Noise Figure
Noise figure is defined as, the ratio of the signal to noise power ratio supplied to the input terminals of a receiver (SNR ) to the signal
i
ANALOG COMMUNICATION
to noise power ratio supplied to the output terminal (or) load resistor (SNR ) Therefore,
(SNR)
i
Noise figure (F) = (SNR)
Calculation of Noise Figure Generator (Antenna) Amplifier (receiver)
Voltage gain A
V R R i L
Figure 1.1 (a) Block Diagram of calculation of noise figure Calculate noise figure consider a network shown in figure 1.1(a).The network has the following
1. Input impedance R
t
2. Output impedance R
L
3. An Overall voltage gain It is led from a source that is antenna of internal resistance R .
a
The internal resistance R , may or may not be equal to R . The figure
a t 1.1(a) shows the block diagram of such 4 terminals network.
The calculation procedures are as follows
Step 1: Determination of input signal power ‘P ’ st
and From the figure 1.1(a), we can obtain signal input voltage V
si
ANALOG AND DIGITAL COMMUNICATION
power P as
si
V R s t V = si
...(1)
R + R a t
2 V si
and P = ...(2) s R
t
Substituting equation (1) in (2) we get, 2 2 V .R si t P = si 2 (R + R ) . R a t t
Therefore,
2 V .R si t
P = ...(3)
si2
(R + R )
a t Step 2: Determination of input noise power ‘P ’ ni
Similarly the noise input voltage V and power P can be
ni ni
calculated We know that
V =
4KTBR
ni
= ...(4)
R R a t
4KTB
- R R a t 2
- R R a t
- R
- [ ]
- [ ]
- ( ) ( )
- Receiver 1 Transmitter + Receiver 2
V
ni
and P =
ni
R
t
Substitute V value here, we get
ni
R R a t
4KTB a t + R R
P =
ni R t
R a
4KTB = ...(5)
ANALOG COMMUNICATION Step 3 Calculation of input SNR
P
si
SNR =
i
P
ni
Using equation (3) and (5), we get
2
2
(V R /(R + R ) )
si t a t
SNR =
i
4KTB (R / R + R )
a a t
2 V .R si t
= ...(6)
4KTB. R (R + R )
a a t Step 4: Determination of signal output power P so
The output signal power will be given as,
2
2 V (AV ) so si
P = =
so
R R
L L
2
2 A .V si
P = ...(7)
so
R
L
Substitute equation (1) in (7), we get
2
2 A (V R / R R ) si t a t
P =
so
R
L
2
2
V .R
2 A
si t
P = ...(8)
so
2 R (R + R ) L a t Step 5 Determination of noise output power P no
The noise output power may be quite difficult to calculate for instance, it can be simply written as, P
= output noise power ...(9)
no Step 6 Calculation of the output SNR
The output signal to noise (SNR ) will be found as,
ANALOG AND DIGITAL COMMUNICATION
...(10)
SNR = P
so
P
no
Using equation (8) and (9) we get SNR =
P
so
P
no
= A
2 V si
2 R t
2
(R
t
)
3. Whether the system uses baseband transmission (or) uses some kind of modulation
2. Whether it uses an analog (or) digital information signal
Electronics communication system can be classified into various categories based on the following parameters
11 2 = This is the necessary equation.
4
...
. .
F R R R P KTB R R A a t L no a t .
=
4 .
2 2 2 2
=
V R KTB R R R A V R R R R P si t a a t si t a t L no
F
SNR Using eq uation (6) and (10), we get
i
SNR
Step 7 Calculation of Noise figure (F)
a
no
.P
2 R L
The general expression for noise figure is F =
1.3 INTRODUCTION TO COMMUNICATION SYSTEMS
1. Whether the system is unidirectional (or) bidirectional
ANALOG COMMUNICATION
Electronics communication systems
Technique of Unidirectional/ Nature of transmission
Bidirectional Information communication signal
Communication
Full Baseband
Simplex Half Analog Digital using Duplex transmission system duplex modulation
Figure 1.2 Classification of communication system
1.3.1 Classifications based on directions of Communication
Based on whether the system communicates only in one direction (or) otherwise, the communication systems are classified as,
1. Simplex system
2. Half duplex systems
3. Full duplex systems Communication System
Unidirectional Bidirectional (Simplex) (Duplex)
Half duplex Full duplex
ANALOG AND DIGITAL COMMUNICATION
Simplex system
In these systems the information is communicated in only one direction , they cannot receive. For example, the radio, TV-broadcasting and telemetry System of a satellite to earth.
Half duplex system
These systems are bidirectional they can transmit as well as receive but not simultaneously. At a time these systems can either transmit (or) receive, for example a trans-receiver (or)walky talky set.
Full duplex System
These are truly bidirectional systems as they allow the communication to take place in both the direction simultaneously. These systems can transmit as well as receive simultaneously , for example the telephone Systems.
Transmitter
Bidirectional flow
of information
Communication
link
1.3.2 Classifications based on the nature of Information signal
Based on nature of information signal, Communication system classified into two categories namely,
1. Analog Communication system.
2. Digital communication system.
ANALOG COMMUNICATION Analog Communication
In this communication technique, the transmitted signal is in the form of analog (or) continuous in nature through the communication channel (or) media.
Digital communication
In this communication technique, the transmitted signal is in the form of digital pulses of constant amplitude, frequency and phase.
1.3.3 Classification based on the technique of transmission
Based on the technique used for the signal transmission. we can categories into two namely,
1. Base band transmission.
2. Communication systems using modulation.
Base-band transmission
In this technique, the baseband signal (original information signals) are directly transmitted. Examples of these type of systems are telephone networks where the sound signal converted into electrical signal is placed directly on the telephone lines for transmission (local calls).
Another example of baseband transmission is computer data transmission over a Co-axial Cables in the computer networks (eg. RS 232 cables).
Thus , the base band transmission is the transmission of the original information signal as it is.
Limitations of Baseband transmission
The baseband transmission cannot be used with certain medium (eg) it cannot be used for the radio transmission where the medium is
ANALOG AND DIGITAL COMMUNICATION free space.
This is because the Voice signal (in the electrical form) cannot travel long distance in air. It gets suppressed after a short distance. Therefore for the radio
Communication of baseband signals a technique called “Modulation” is used.
Drawbacks of baseband transmission (without modulation) 1. Excessively large antenna heights.
2. Signals get mixed up.
3. Short range of communication.
4. Multiplexing is not possible and 5. Poor quality of reception.
Why modulation
The baseband transmission has many limitations which can be overcome using modulation. In radio communication, signals from various sources are transmitted through a common medium that is in open (free) space .This causes interference among various signals, and no useful message is received by the receiver.
The problem of interference is solved by translating the message signals to different radio frequency spectra. This is done by the transmitter by a process known as ”Modulation”.
1.4 MODULATION
Define: In the modulation process, two signals are used namely the modulating signal and the carrier signal.
ANALOG COMMUNICATION
(or) (or) Baseband signal Low frequency signal Modulating signal High frequency signal Carrier signal (or)
Modulating signal Modulator Modulated signal
Carrier signal
Modulation is the process of changing the characteristics of carrier signal (such as amplitude, frequency and phase) in accordance with the instantaneous value of modulating signal.
In simple, modulation is the process of mixing of modulating signal and carrier signal together. In the process of modulation , the baseband signal is translated (i.e) shifted from low frequency to high frequency.
1.5 NEED FOR MODULATION (OR) ADVANTAGES OF MODULATION
The advantages of modulation are, (1) Easy of radiation.
(2) Adjustment of bandwidth. (3) Reduction in height of antenna. (4) Avoids mixing of signals. (5) Increases the range of information. (6) Multiplexing and (7) Improves quality of reception.
1.5.1 Easy of radiation
As the signals are translated to higher frequencies, it becomes relatively easier to design amplifier circuits as well as
ANALOG AND DIGITAL COMMUNICATION antenna systems at these increased frequencies.
1.5.2 Adjustment of bandwidth
Bandwidth of a modulated signal may be made smaller (or) larger than the original signal. Signal to noise ratio (SNR) in the receiver which is a function of the signal Bandwidth can thus be improved by proper control of bandwidth at the modulating stage.
1.5.3 Reduction in antenna height
When free space is used as a communication media, messages are transmitted with the help of antennas. If the signals are transmitted without modulation, the size of antenna needed for an effective radiation would be of the order of the half of the wavelength, given as, c
λ =
...(1) 2f
2 In broadcast systems, the maximum audio frequency transmitted from a radio station is 5 KHZ. Therefore,the antenna height required is, 8
c
c 3 x 10 λ
= = 30 km = = = 3 3 2 2f 2 x 5 x 10 10 x 10
The antenna of this height is practically impossible to install. Now consider a modulated signal f=10 MHZ. The minimum antenna height is given by, c
λ Antenna height is =
= 2f
2 8
3 x 10
= 6
2 x 10 x 10
= 15 metre This antenna height can be practically achieved.
ANALOG COMMUNICATION
1.5.4 Avoid mixing of signals
Each modulating signal (message signal) is modulated with different carrier then they will occupy different slot in the frequency domain (different channels).Thus modulation avoids mixing of signals.
1.5.5 Increases the range of communication
The modulation process increases the frequency of the signal to be transmitted. Hence, increases the range of communication.
1.5.6 Multiplexing
If different message signals are transmitted without modulation through a single channel may causes interference with one another. (i.e) overlap with one another.
To overcome this interference means, we need n-number of channels for n-message signals separately. But different message signals can be transmitted over a same channel (single channel) without interference using the techniques
“Multiplexing”.
Simultaneous transmission of multiple message (more than one message) over a channel is known as “multiplexing”. Due to multiplexing, the number of channels needed are less. This reduces the cost of installation and maintenance of more channels.
1.5.7 Improves quality of reception Due to modulation, the effect of noise is reduced to great extent.
This improves quality of reception.
The two basic types of communications systems are analog and digital.
Message - continuous signal
Analog communication
Carrier - continuous signal Message - Digital (or) analog signal
Digital communication
Carrier - continuous signal (analog)
ANALOG AND DIGITAL COMMUNICATION
1.6 CLASSIFICATIONS OF MODULATION
Modulation
Analog modulation Digital modulation
Amplitude- modulation(AM)Angle modulation Continuous modulation
Analog pulse modulation DPCM DM ADM PCM PAM PWM PPM
Phase modulation (PM) Frequency modulation (FM)
Figire 1.4 Classifications of Modulation
Where, PAM - Pulse amplitude modulation.
PWM - Pulse width modulation. PPM - Pulse Position modulation. PCM – Pulse code modulation. DM – Delta modulation. ADM – Adaptive delta modulation. DPCM – Differential Pulse code modulation.
Linear modulation
The modulation system following the superposition
ANALOG COMMUNICATION theorem of spectra is known as linear modulation system. Non-linear modulation
The modulation system which does not follow the superposition theorem of spectra is known as non-linear modulation system.
1.7 SOME IMPORTANT DEFINITIONS RELATED TO COMMUNICATION
1.7.1 Frequency(f)
The frequency is defined as the number of cycles of a waveform per second. It is expressed in hertz (Hz). Frequency is simply the number of times a periodic motion, such as a sine wave of voltage (or) current, occurs in a given period of time.
Amp Time
1 Cycle
Figure 1.5 One cycle1.7.2 Wave length (
λ) Wave length (λ ) is defined as the distance between two points of similar cycles of a periodic wave.
Wavelength
Figure 1.6 WavelengthWavelength is also defined as the distance travelled by an
ANALOG AND DIGITAL COMMUNICATION electromagnetic wave during the time of one cycle.
1.7.3 Bandwidth
Bandwidth is defined as the frequency range over which an information signals is transmitted . Bandwidth is the difference between the upper and lower frequency limits of the signal.
Bandwidth (BW) = f f 2 1 2 – Where, f upper frequency 1 – f lower frequency BW
f f 1 2 Frequency
1.7.4 Transmission frequencies
The total usable radio frequency (RF) spectrum is divided into narrower frequency bands, which are descriptive names and several of these band are further broken down into various types of services.
The International Telecommunication Union (ITU) is an international agency is control of allocating frequencies and services within the overall frequency spectrum.
ANALOG COMMUNICATION F requency W avelength deSignation range F requency range Extremely High 30 - 300 GHZ
1mm - 1cm frequency (EFH) super High frequency 3 - 30 GHZ
1 - 10 cm (SHF) Ultra High 300MHZ -3GHZ
10cm - 1m Frequency (UHF) Very High frequency 30 - 300MHZ
1 -10m (VHF) High frequency(HF) 3 - 30MHZ 10-100m
100m-1km Medium frequency (MF) 300KHZ - 3MHZ Low frequency (LF)
30 KHZ - 300KHZ 1km - 10km
Table 1.1 The radio frequency spectrum Solved Problem1. Find the wavelength of a signal at each of the following frequencies.
(1) 850 MHZ (2) 1.9 GHZ (3) 28 GHZ.
Solution Given data
(1)f = 850 MHZ (2)f =1.9 GHZ and (3) f = 28 GHZ.
Velocity of light Wavelength ‘ λ ‘ =
Frequency
c
=
f
8
3 x 10 (i) l = = 0.35 M
6
850 x 10
8
3 x 10 (ii) l = = 0.158 m
9
1.9 x 10
ANALOG AND DIGITAL COMMUNICATION
8
3 x 10 (iii) l = = 0.0107 m
9
28 x 10
1.7.5 Frequency spectrum
Frequency spectrum is the representation of a signal in the frequency domain . It can be obtained by using either fourier series (or) fourier transform.
It consists of the amplitude and phase spectrums of the signal. The frequency spectrum indicates the amplitude and phase of various frequency components present in the given signal.
The frequency spectrum enables us to analyze and synthesize a signal.
1.7.6 Demodulation (or) Detection
The process of extracting a modulating (or) baseband signal from the modulated signal is called “demodulation”. In other words , Demodulation (or) detection is the process by which the message signal is recovered from the modulated signal at receiver.
1.8 THEORY OF AMPLITUDE MODULATION Definition
Amplitude modulation (AM) is the process by which amplitude of the carrier signal is varied in accordance with the instantaneous value (amplitude) of the modulating signal, but frequency and phase remains constant.
1.8.1 Mathematical Representation of an AM wave
Let us consider, The Modulating signal V (t) = V sinω t ...(1)
m m m
The Carrier signal V (t) = V t ...(2) sinω
c c c
Where,
ANALOG COMMUNICATION __
V Amplitude of the carrier signal (volts) c V _ Amplitude of the modulating signal (volts) m
_ Frequency of the modulating signal (HZ) ω
m