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1. EDUCATION HOLE PRESENTS
ELECTRONICS ENGINEERING
Unit-V

2. Fundamentals of Communication Engineering ........................................................................ 3
Elements of a Communication System .................................................................................................................3
Elements of a communication system..................................................................................................................3
Need of modulation .........................................................................................................................4
(i) To separate signal from different transmitters ................................................................................................4
(ii) Size of the antenna .........................................................................................................................................4
Types of modulation.............................................................................................................................................4
Electromagnetic spectrum................................................................................................................5
Electromagnetic typical applications....................................................................................................................5
Radio Waves (communications).......................................................................................................................6
Satellite signals (Microwaves)...............................................................................................................................6
Infrared Radiation (remote controls, toasters).....................................................................................................6
Ultraviolet .............................................................................................................................................................6
X-rays ....................................................................................................................................................................7
Gamma Rays .........................................................................................................................................................7
Terminologies in communication systems........................................................................................7
(i) Transducer....................................................................................................................................................7
(ii) Signal ...........................................................................................................................................................7
(iii) Noise...........................................................................................................................................................8
(iv) Transmitter................................................................................................................................................8
(v) Receiver.......................................................................................................................................................8
(vi) Attenuation ................................................................................................................................................8
(vii) Amplification .............................................................................................................................................8
(viii) Range........................................................................................................................................................8
(ix) Bandwidth ..................................................................................................................................................8
(x) Modulation..................................................................................................................................................8
(xi) Demodulation.............................................................................................................................................9
(xii) Repeater ....................................................................................................................................................9
Basics of signal representation and analysis .....................................................................................9
Magnitude and Phase Information of the FFT......................................................................................................9
Fundamentals of amplitude ........................................................................................................... 10
Amplitude modulation basics......................................................................................................... 11
Amplitude modulation advantages & disadvantages...................................................................... 12
Fundamentals of angle modulation................................................................................................ 12
Modulation techniques.......................................................................................................................................13
Amplitude Phase Shift Keying (APSK)..................................................................................................................13
Orthogonal Frequency Division Multiplexing (OFDM)........................................................................................14
Determining Spectral Efficiency..........................................................................................................................15
Other Factors Affecting Spectral Efficiency ........................................................................................................16
Implementing Modulation And Demodulation ............................................................................... 17
Demodulation techniques ..................................................................................................................................17

3. Fundamentals of Communication Engineering
Elements of a Communication System
Elements of a communication system
The above figure depicts the elements of a communication system. There are three essential parts
of any communication system, the transmitter, transmission channel, and receiver. Each parts
plays a particular role in signal transmission, as follows:
The transmitter processes the input signal to produce a suitable transmitted signal suited to the
characteristics of the transmission channel. Signal processing for transmissions almost always
involves modulation and may also include coding. The transmission channel is the electrical
medium that bridges the distance from source to destination. It may be a pair of wires, a coaxial
cable, or a radio wave or laser beam. Every channel introduces some amount of transmission loss
or attenuation. So, the signal power progressively decreases with increasing distance. The
receiver operates on the output signal from the channel in preparation for delivery to the
transducer at the destination. Receiver operations include amplification to compensate for
transmission loss. These also include demodulation and decoding to reverse the signal procession
performed at the transmitter. Filtering is another important function at the receiver. The figure
represents one-way or simplex (SX) transmission. Two way communication of course requires a
transmitter and receiver at each end. A full-duplex (FDX) system has a channel that allows

4. simultaneous transmission in both directions. A half-duplex (HDX) system allows transmission
in either direction but not at the same time.
Need of modulation
(i) To separate signal from different transmitters
Audio frequencies are within the range of 20 Hz to 20 kHz. Without modulation all signals at
same frequencies from different transmitters would be mixed up. There by giving impossible
situation to tune to any one of them. In order to separate the various signals, radio stations must
broadcast at different frequencies.
Each radio station must be given its own frequency band. This is achieved by frequency
translation as a result of modulation process.
(ii) Size of the antenna
For efficient transmission the transmitting antennas should have length at least equal to a quarter
of the wavelength of the signal to be transmitted. For an electromagnetic wave of frequency 15
kHz, the wavelength λ is 20 km and one-quarter of this will be equal to 5 km. Obviously, a
vertical antenna of this size is impractible. On the other hand, for a frequency of 1 MHz, this
height is reduced to 75m.
Also, the power radiated by an antenna of length l is proportional to (l/λ)2
. This shows that for
the same antenna length, power radiated is large for shorter wavelength. Thus, our signal which
is of low frequency must be translated to the high frequency spectrum of the electromagnetic
wave. This is achieved by the process of modulation.
Types of modulation
A sinusoidal carrier wave can be expressed as
ec = Ec cos(ωc t + θ)
Its three distinct characteristics are
(i) Amplitude (Ec)
(ii) angular frequency (ωc)
(iii) phase angle (θ).

5. Either of these three characteristics can be varied in accordance with the modulating signal.
These result in three types of modulation.
(i) Amplitude modulation (AM)
(ii) Frequency modulation (FM)
(iii) Phase modulation (PM)
Electromagnetic spectrum
The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is energy
that travels and spreads out as it goes – the visible light that comes from a lamp in your house
and the radio waves that come from a radio station are two types of electromagnetic radiation.
The other types of EM radiation that make up the electromagnetic spectrum are microwaves,
infrared light, ultraviolet light, X-rays and gamma-rays.
Radio: Your radio captures radio waves emitted by radio stations, bringing your favorite tunes.
Radio waves are also emitted by stars and gases in space.
Microwave: Microwave radiation will cook your popcorn in just a few minutes, but is also used
by astronomers to learn about the structure of nearby galaxies.
Infrared: Night vision goggles pick up the infrared light emitted by our skin and objects with
heat. In space, infrared light helps us map the dust between stars.
Visible: Our eyes detect visible light. Fireflies, light bulbs, and stars all emit visible light.
Ultraviolet: Ultraviolet radiation is emitted by the Sun and is the reason skin tans and burns.
"Hot" objects in space emit UV radiation as well.
X-ray: A dentist uses X-rays to image your teeth, and airport security uses them to see through
your bag. Hot gases in the Universe also emit X-rays.
Gamma ray: Doctors use gamma-ray imaging to see inside your body. The biggest gamma-ray
generator of all is the Universe.
Electromagnetic typical applications
Wavelength of the ElectroMagnetic spectrum continually changes
• high frequency = short wavelength
• high frequency = high energy

6. • high energy = more dangerous
Radio Waves (communications)
• TV and FM radio (short wavelength)
• Direct line of sight with transmitter (do not diffract)
• Medium wavelength – travel further because they reflect from layers in the atmosphere
Satellite signals (Microwaves)
• Frequency of microwaves pass easily through atmosphere and clouds
Cooking (Microwaves)
• Microwaves are absorbed by water molecules.
• These water molecules become heated > heat food
• Dangers: microwaves are absorbed by living tissue Internal heating will damage or kill
cells
Infrared Radiation (remote controls, toasters)
• Any object that radiates heat radiates Infrared Radiation
• Infrared Radiation is absorbed by all materials and causes heating
• It is used for night vision and security cameras as Infrared Radiation is visible in daytime
or night-time
• Police use it to catch criminals, army use it to detect enemy
• Dangers: damage to cells (burns)
Ultraviolet
• Dangers:
o over-exposure to UVA and B damages surface cells and eyes and can cause
cancer.
 There is a problem with current sunscreens which protect against skin
burning from high UVB but give inadequate protection against free radical
damage caused by UVA.
 Dark skins are not necessarily safer from harm.
 Sun exposure for the skin is best restricted to before 11am and after 3pm
in the UK in summer months.
• Benefits:

7. o sanitary and therapeutic properties have a marked effect on architecture,
engineering and public health and have done so throughout history.
o UVC is germicidal, destroying bacteria, viruses and moulds in the air, in water
and on surfaces.
o UV synthesises vitamin D in skin, controls the endocrine system and is a
painkiller.
o Used in state of the art air-handling units, personal air purifiers and swimming
pool technology.
o Used to detect forged bank notes: they fluoresce in UV light; real bank notes
don’t. Used to identify items outside visible spectrum areas, known as 'black
lighting'.
X-rays
• X-rays detect bone breaks
• X-rays pass through flesh but not dense material like bones
• Dangers: X-rays damage cells and cause cancers. Radiographer precautions include
wearing lead aprons and standing behind a lead screen to minimise exposure
Gamma Rays
• Gamma Rays cause and treat cancers
• In high doses, gamma can kill normal cells and cause cancers
• Gamma can be used to kill mutated cells though too.
Terminologies in communication systems
(i) Transducer: Any device that converts one form of energy into another can be termed as a
transducer. In electronic communication systems, we usually come across devices that have
either their inputs or outputs in the electrical form. An electrical transducer may be defined as a
device that converts some physical variable (pressure, displacement, force, temperature, etc) into
corresponding variations in the electrical signal at its output.
(ii) Signal: Information converted in electrical form and suitable for transmission is called a
signal. Signals can be either analog or digital. Analog signals are continuous variations of
voltage or current. They are essentially single-valued functions of time. Sine wave is a
fundamental analog signal. All other analog signals can be fully understood in terms of their sine
wave components. Sound and picture signals in TV are analog in nature. Digital signals are those
which can take only discrete stepwise values. Binary system that is extensively used in digital
electronics employs just two levels of a signal. ‘0’ corresponds to a low level and ‘1’

8. corresponds to a high level of voltage/ current. There are several coding schemes useful for
digital communication. They employ suitable combinations of number systems such as the
binary coded decimal (BCD)*. American Standard Code for Information Interchange (ASCII)**
is a universally popular digital code to represent numbers, letters and certain characters.
(iii) Noise: Noise refers to the unwanted signals that tend to disturb the transmission and
processing of message signals in a communication system.
The source generating the noise may be located inside or outside the system.
(iv) Transmitter: A transmitter processes the incoming message signal so as to make it suitable
for transmission through a channel and subsequent reception.
(v) Receiver: A receiver extracts the desired message signals from the received signals at the
channel output.
(vi) Attenuation: The loss of strength of a signal while propagating through a medium is known
as attenuation.
* In BCD, a digit is usually represented by four binary (0 or 1) bits. For example the numbers 0,
1, 2, 3, 4 in the decimal system are written as 0000, 0001, 0010, 0011 and 0100. 1000 would
represent eight.
(vii) Amplification: It is the process of increasing the amplitude (and
consequently the strength) of a signal using an electronic circuit called the amplifier
Amplification is necessary to compensate for the attenuation of the signal in communication
systems. The energy needed for additional signal strength is obtained from a DC power source.
Amplification is done at a place between the source and the destination wherever signal strength
becomes weaker than the required strength.
(viii) Range: It is the largest distance between a source and a destination up to which the signal
is received with sufficient strength.
(ix) Bandwidth: Bandwidth refers to the frequency range over which an equipment operates or
the portion of the spectrum occupied by the signal.
(x) Modulation: The original low frequency message/information signal cannot be transmitted
to long distances because of reasons. Therefore, at the transmitter, information contained in the
low frequency message signal is superimposed on a high frequency wave, which acts as a carrier
of the information. This process is known as modulation. As will be explained later, there are
several types of modulation, abbreviated as AM, FM and PM.

9. (xi) Demodulation: The process of retrieval of information from the carrier wave at the receiver
is termed demodulation. This is the reverse process of modulation.
(xii) Repeater: A repeater is a combination of a receiver and a transmitter. A repeater, picks up
the signal from the transmitter, amplifies and retransmits it to the receiver sometimes with a
change in carrier frequency.
Basics of signal representation and analysis
Frequency-domain analysis is a tool of utmost importance in signal processing applications.
Frequency-domain analysis is widely used in such areas as communications, geology, remote
sensing, and image processing. While time-domain analysis shows how a signal changes over
time, frequency-domain analysis shows how the signal's energy is distributed over a range of
frequencies. A frequency-domain representation also includes information on the phase shift that
must be applied to each frequency component in order to recover the original time signal with a
combination of all the individual frequency components.
A signal can be converted between the time and frequency domains with a pair of mathematical
operators called a transform. An example is the Fourier transform, which decomposes a function
into the sum of a (potentially infinite) number of sine wave frequency components. The
'spectrum' of frequency components is the frequency domain representation of the signal. The
inverse Fourier transform converts the frequency domain function back to a time function. The
fft and ifft functions in MATLAB allow you to compute the Discrete Fourier transform (DFT) of
a signal and the inverse of this transform respectively.
Magnitude and Phase Information of the FFT
The frequency-domain representation of a signal carries information about the signal's magnitude
and phase at each frequency. This is why the output of the FFT computation is complex. A
complex number, , has a real, , and an imaginary part, , such that . The
magnitude of is computed as , and the phase of is computed as . You
can use MATLAB functions abs and angle to respectively get the magnitude and phase of any
complex number.
Use an audio example to develop some insight on what information is carried by the magnitude
and the phase of a signal. To do this, load an audio file containing 15 seconds of acoustic guitar
music. The sample rate of the audio signal is 44.1 kHz.
Fs = 44100;
y = audioread

10. Use fft to observe the frequency content of the signal.
NFFT = length(y);
Y = fft(y,NFFT);
F = ((0:1/NFFT:1-1/NFFT)*Fs).';
The output of the FFT is a complex vector containing information about the frequency content of
the signal. The magnitude tells you the strength of the frequency components relative to other
components. The phase tells you how all the frequency components align in time.
Fundamentals of amplitude
Amplitude modulation, AM tutorial includes:
• Amplitude modulation introduction
• AM theory & equations
• AM spectrum & bandwidth
• AM modulation index
• Amplitude modulation efficiency
• Single sideband modulation
• Single sideband suppressed carrier
In order that a steady radio signal or "radio carrier" can carry information it must be changed or
modulated in one way so that the information can be conveyed from one place to another. There
are a number of ways in which a carrier can be modulated to carry a signal - often an audio
signal and the most obvious way is to vary its amplitude.
Amplitude Modulation has been in use since the very earliest days of radio technology. The first
recorded instance of its use was in 1901 when a signal was transmitted by a Canadian engineer
named Reginald Fessenden. To achieve this, he used a continuous spark transmission and placed
a carbon microphone in the antenna lead. The sound waves impacting on the microphone varied
its resistance and in turn this varied the intensity of the transmission. Although very crude,
signals were audible over a distance of a few hundred metres. The quality of the audio was not
good particularly as a result of the continuous rasping sound caused by the spark used for the
transmission.
Later, continuous sine wave signals could be generated and the audio quality was greatly
improved. As a result, amplitude modulation, AM became the standard for voice transmissions.
Currently amplitude modulation is primarily used for broadcasting, but it is still used for some
forms of two way radio communications. Its main radio communications use is for local aviation

11. related VHF two way radio links. It is used for ground to air radio communications as well as
two way radio links for ground staff as well.
Amplitude modulation basics
When an amplitude modulated signal is created, the amplitude of the signal is varied in line with
the variations in intensity of the sound wave. In this way the overall amplitude or envelope of the
carrier is modulated to carry the audio signal. Here the envelope of the carrier can be seen to
change in line with the modulating signal.
Amplitude Modulation, AM
Amplitude modulation, AM is the most straightforward way of modulating a signal.
Demodulation, or the process where the radio frequency signal is converted into an audio
frequency signal is also very simple. An amplitude modulation signal only requires a simple
diode detector circuit. The circuit that is commonly used has a diode that rectifies the signal, only
allowing the one half of the alternating radio frequency waveform through. A capacitor is used to
remove the radio frequency parts of the signal, leaving the audio waveform. This can be fed into
an amplifier after which it can be used to drive a loudspeaker. As the circuit used for
demodulating AM is very cheap, it enables the cost of radio receivers for AM to be kept low.

12. Amplitude modulation advantages & disadvantages
Like any other system of modulation, amplitude modulation has several advantages and
disadvantages. These mean that it is used in particular circumstances where its advantages can be
used to good effect..
Advantages Disadvantages
• It is simple to implement
• It can be demodulated using a circuit
consisting of very few components
• AM receivers are very cheap as no
specialised components are needed.
• An amplitude modulation signal is not
efficient in terms of its power usage
• It is not efficient in terms of its use of
bandwidth, requiring a bandwidth equal
to twice that of the highest audio
frequency
• An amplitude modulation signal is prone
to high levels of noise because most
noise is amplitude based and obviously
AM detectors are sensitive to it.
In view of its characteristics advantages and disadvantages, amplitude modulation is being used
less frequently. However it is still in widespread use for broadcasting on the long, medium and
short wave bands as well as for a number of mobile or portable communications systems
including some aircraft communications.
Fundamentals of angle modulation
A sine wave carrier can be modulated by varying its amplitude, frequency, or phase shift. The
basic equation for a carrier wave is
ν = Vc sin(2Πft ± θ)
where Vc = peak amplitude, f = frequency, and θ = phase angle
Impressing an information signal on a carrier by changing its frequency produces FM. Varying
the amount of phase shift that a carrier experiences is known as phase modulation (PM). Varying
the phase shift of a carrier also produces FM. FM and PM are collectively referred to as angle
modulation. Since FM is generally superior in performance to AM, it is widely used in many
areas of communication electronics.

13. Modulation techniques
The main goal of modulation today is to squeeze as much data into the least amount of spectrum
possible. That objective, known as spectral efficiency, measures how quickly data can be
transmitted in an assigned bandwidth. The unit of measurement is bits per second per Hz
(b/s/Hz). Multiple techniques have emerged to achieve and improve spectral efficiency.
Amplitude Phase Shift Keying (APSK)
Amplitude phase shift keying (APSK), a variation of both M-PSK and QAM, was created in
response to the need for an improved QAM. Higher levels of QAM such as 16QAM and above
have many different amplitude levels as well as phase shifts. These amplitude levels are more
susceptible to noise. Furthermore, these multiple levels require linear power amplifiers (PAs)
that are less efficient than nonlinear (e.g., class C). The fewer the number of amplitude levels or
the smaller the difference between the amplitude levels, the greater the chance to operate in the
nonlinear region of the PA to boost power level. APSK uses fewer amplitude levels. It
essentially arranges the symbols into two or more concentric rings with a constant phase offset θ.
For example, 16APSK uses a double-ring PSK format (Fig. 5). This is called 4-12 16APSK with
four symbols in the center ring and 12 in the outer ring.
5. 16APSK uses two amplitude levels, A1 and A2, plus 16 different phase positions with an
offset of θ. This technique is widely used in satellites.

14. Two close amplitude levels allow the amplifier to operate closer to the nonlinear region,
improving efficiency as well as power output. APSK is used primarily in satellites since it is a
good fit with the popular traveling wave tube (TWT) PAs.
Orthogonal Frequency Division Multiplexing (OFDM)
Orthogonal frequency division multiplexing (OFDM) combines modulation and multiplexing
techniques to improve spectral efficiency. A transmission channel is divided into many smaller
subchannels or subcarriers. The subcarrier frequencies and spacings are chosen so they’re
orthogonal to one another. Their spectra won’t interfere with one another, then, so no guard
bands are required (Fig. 6).
6. In the OFDM signal for the IEEE 802.11n Wi-Fi standard, 56 subcarriers are spaced 312.5
kHz in a 20-MHz channel. Data rates to 300 Mbits/s can be achieved with 64QAM.
The serial digital data to be transmitted is subdivided into parallel slower data rate channels.
These lower data rate signals are then used to modulate each subcarrier. The most common
forms of modulation are BPSK, QPSK, and several levels of QAM. BPSK, QPSK, 16QAM, and
64QAM are defined with 802.11n. Data rates up to about 300 Mbits/s are possible with 64QAM.
The complex modulation process is only produced by digital signal processing (DSP) techniques.
An inverse fast Fourier transform (IFFT) generates the signal to be transmitted. An FFT process
recovers the signal at the receiver. OFDM is very spectrally efficient. That efficiency level
depends on the number of subcarriers and the type of modulation, but it can be as high as 30
bits/s/Hz. Because of the wide bandwidth it usually occupies and the large number of subcarriers,
it also is less prone to signal loss due to fading, multipath reflections, and similar effects
common in UHF and microwave radio signal propagation. Currently, OFDM is the most popular

15. form of digital modulation. It is used in Wi-Fi LANs, WiMAX broadband wireless, Long Term
Evolution (LTE) 4G cellular systems, digital subscriber line (DSL) systems, and in most power-
line communications (PLC) applications. For more, see “Orthogonal Frequency-Division
Multiplexing (OFDM): FAQ Tutorial.”
Determining Spectral Efficiency
Again, spectral efficiency is a measure of how quickly data can be transmitted in an assigned
bandwidth, and the unit of measurement is bits/s/Hz (b/s/Hz). Each type of modulation has a
maximum theoretical spectral efficiency measure (Table 2).
SNR is another important factor that influences spectral efficiency. It also can be expressed as
the carrier to noise power ratio (CNR). The measure is the BER for a given CNR value. BER is
the percentage of errors that occur in a given number of bits transmitted. As the noise becomes
larger compared to the signal level, more errors occur.
Some modulation methods are more immune to noise than others. Amplitude modulation
methods like ASK/OOK and QAM are far more susceptible to noise so they have a higher BER

16. for a given modulation. Phase and frequency modulation (BPSK, FSK, etc.) fare better in a noisy
environment so they require less signal power for a given noise level (Fig. 7).
7. This is a comparison of several popular modulation methods and their spectral efficiency
expressed in terms of BER versus CNR. Note that for a given BER, a greater CNR is needed for
the higher QAM levels.
Other Factors Affecting Spectral Efficiency
While modulation plays a key role in the spectral efficiency you can expect, other aspects in
wireless design influence it as well. For example, the use of forward error correction (FEC)
techniques can greatly improve the BER. Such coding methods add extra bits so errors can be
detected and corrected.
These extra coding bits add overhead to the signal, reducing the net bit rate of the data, but that’s
usually an acceptable tradeoff for the single-digit dB improvement in CNR. Such coding gain is
common to almost all wireless systems today. Digital compression is another useful technique.
The digital data to be sent is subjected to a compression algorithm that greatly reduces the
amount of information. This allows digital signals to be reduced in content so they can be
transmitted as shorter, slower data streams. For example, voice signals are compressed for digital
cell phones and voice over Internet protocol (VoIP) phones. Music is compressed in MP3 or
AAC files for faster transmission and less storage. Video is compressed so high-resolution
images can be transmitted faster or in bandwidth-limited systems.
Another factor affecting spectral efficiency is the use of multiple-input multiple-output (MIMO),
which is the use of multiple antennas and transceivers to transmit two or more bit streams. A
single high-rate stream is divided into two parallel streams and transmitted in the same
bandwidth simultaneously. By coding the streams and their unique path characteristics, the

17. receiver can identify and demodulate each stream and reassemble it into the original stream.
MIMO, therefore, improves data rate, noise performance, and spectral efficiency. Newer wireless
LAN (WLAN) standards like 802.11n and 802.11ac/ad and cellular standards like LTE and
WiMAX use MIMO. For more, see.”
Implementing Modulation And Demodulation
In the past, unique circuits implemented modulation and demodulation. Today, most modern
radios are software-defined radios (SDR) where functions like modulation and demodulation are
handled in software. DSP algorithms do the job previously assigned to modulator and
demodulator circuits. The modulation process begins with the data to be transmitted being fed to
a DSP device that generates two digital outputs, which are needed to define the amplitude and
phase information required at the receiver to recover the data. The DSP produces two baseband
streams that are sent to digital-to-analog converters (DACs) that produce the analog equivalents.
Demodulation techniques
Demodulation is the act of extracting the original information-bearing signal from a modulated
carrier wave. A demodulator is an electronic circuit (or computer program in a software defined
radio) that is used to recover the information content from the modulated carrier wave. These
terms are traditionally used in connection with radio receivers, but many other systems use many
kinds of demodulators. Another common one is in a modem, which is a contraction of the terms
modulator/demodulator. There are several ways of demodulation depending on how parameters
of the base-band signal are transmitted in the carrier signal, such as amplitude, frequency or
phase. For example, for a signal modulated with a linear modulation, like AM (Amplitude
Modulated), we can use a synchronous detector. On the other hand, for a signal modulated with
an angular modulation, we must use an FM (Frequency Modulation) demodulator or a PM
(Phase Modulation) demodulator. Different kinds of circuits perform these functions.
Many techniques—such as carrier recovery, clock recovery, bit slip, frame synchronization, rake
receiver, pulse compression, Received Signal Strength Indication, error detection and correction,
etc. -- are only performed by demodulators, although any specific demodulator may perform
only some or none of these techniques.