Dr. Ali AbdelAziz
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Mail: aabdelaziz@aswu.edu.eg
Digital Communication Lecture 4 Sources
Dr. Ali AbdelAziz
email: aabdelaziz@aswu.edu.eg
Mob: +201090390213
September 2023
1
Before we start, Modulation in Analogue Transmission
When transmitting data over an analog transmission system, the choice between digital modulation and analog
modulation is influenced by various factors. Understanding the motivation behind these choices is crucial for
effective communication system design.
1.1
Nature of Original Data
• Digital Data: When transmitting digital data, such as computer data or digital voice, it’s typically
converted into an analog waveform using digital modulation. This conversion is essential since most
real-world transmission media, especially wireless channels, are inherently analog.
• Analog Data: For transmitting analog data, like voice or TV signals, the signal can be modulated
directly with analog modulation. However, in many modern systems, it’s beneficial to digitize the analog
data first (using ADCs) and then utilize digital modulation for transmission.
1.2
Efficiency and Robustness
• Digital Modulation: Techniques such as QAM, PSK, and FSK are more resistant to noise, interference,
and other distortions. They often provide superior performance in noisy channels compared to analog
modulation. Moreover, digital signals easily integrate with error correction codes, enhancing transmission
robustness.
• Analog Modulation: Schemes like AM, FM, or PM vary the amplitude, frequency, or phase of the
carrier signal directly according to the input analog signal. They might be less resilient against noise,
especially AM, but can be simpler for certain applications.
1.3
Transmission Medium Characteristics
Most real-world transmission channels, particularly wireless ones, are naturally analog. Thus, the transmitted
signal, regardless of data’s original form, will be analog. Modulation ensures the data is suitable for the medium.
1.4
Technological Advancements
• With technological evolution, digital systems, both in terms of data and modulation, are favored due to
their advantages in efficiency, bandwidth utilization, noise resistance, and integration with modern IT
systems.
• However, in certain scenarios where bandwidth efficiency isn’t paramount or where infrastructure is predominantly analog, analog modulation might persist.
1.5
Application Requirements
Specific applications might inherently prefer one modulation type over another. For example, AM radio employs
amplitude modulation due to its simplicity and historical prevalence. Conversely, digital cellular systems adopt
digital modulation for enhanced efficiency, capacity, and clarity.
Motivation and Approach in Data Transmission
Analog Transmission
Why use digital modulation for digital data in analog transmission?
Dr. Ali AbdelAziz
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• Most real-world transmission channels, especially wireless ones, are naturally analog. To transmit digital
data over these channels, we need to convert the digital data into an analog waveform. This is done
through digital modulation.
• Digital modulation schemes, such as QAM, PSK, and FSK, are designed to be more robust against noise,
interference, and other distortions. This makes them suitable for transmitting digital data over noisy
channels.
Why use analog modulation for analog data in analog transmission?
• Analog signals, like voice or TV broadcasts, can be directly modulated using analog modulation techniques,
such as AM, FM, or PM.
• Direct analog modulation can be simpler and more straightforward for specific applications and is historically rooted in certain systems like AM radio.
Digital Transmission
Why use encoding for digital data in digital transmission?
• Encoding is used to represent digital data in a specific format suitable for transmission. This might involve
converting the data into a series of signals (like high and low voltages) that represent binary values.
• Encoding can introduce redundancy, error-checking, and other features that ensure the transmitted data
can be correctly and efficiently decoded at the receiving end.
Why use Analog-to-Digital (A/D) conversion for analog data in digital transmission?
• To transmit analog data over a digital transmission system, the data first needs to be digitized. This is
done using Analog-to-Digital Converters (ADC).
• Once the analog data is digitized, it can benefit from the features of digital transmission, like error
correction and data compression.
• Digital systems, especially modern IT systems, are better equipped to handle, store, and process digital
data, making the digitization of analog data a necessity in many scenarios.
Data Transmission
The transmission of data refers to the process of sending data from a source to a destination. This transmission
can occur in various ways, depending on the nature of the data (analog or digital) and the method of transmission
(analog or digital signal). Given these variations, we can identify four primary scenarios:
1. Analog Transmission
a. Digital Data (Digital Modulation)
In this method, digital data, often represented in binary form (0s and 1s), is modulated to analog signals.
Digital Modulation techniques, such as Amplitude Shift Keying (ASK) or Frequency Shift Keying (FSK), are
used to change specific properties of the analog signal (like amplitude or frequency) in correspondence to the
digital data.
b. Analog Data (Analog Modulation)
Here, analog data (like voice or music) is modulated directly onto an analog signal. Classical modulation
techniques such as Amplitude Modulation (AM), Frequency Modulation (FM), or Phase Modulation (PM) are
used to embed the analog data onto an analog carrier signal.
2. Digital Transmission
a. Digital Data (Encoding)
When both the data and the signal are digital, an encoding scheme is used. This method involves representing
the digital data directly as sequences of voltage levels. Common encoding methods include Non-return to Zero
(NRZ), Manchester encoding, and others.
Dr. Ali AbdelAziz
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b. Analog Data (A/D Conversion)
In situations where the data is analog but needs to be transmitted over a digital signal, an Analog-to-Digital
(A/D) converter is used. This device samples the analog data at regular intervals and converts each sample
into its digital equivalent, allowing the data to be transmitted as a digital signal.
2
Slide 6: Motivation for Analogue Transmission
Although digital transmission has robust characteristics, there are specific scenarios where analog transmission
becomes necessary. This section discusses the motivation behind opting for analog transmission in certain
situations.
2.1
Band Pass Channels
If the available communication channel is a band pass channel, direct digital transmission isn’t feasible. In such
cases, the digital signal must first be converted into an analog signal before transmission.
2.2
Wireless Medium
Similarly, when the medium of transmission is wireless, digital data should be transformed into an analog signal
prior to transmission.
2.3
Modulation
The process of converting digital data or a low pass analog signal to a band pass analog signal is traditionally
termed as modulation.
Slide 9: Baseband Signals and Their Transmission Characteristics
In the context of signal processing and telecommunications, understanding the nature and limitations of baseband signals is vital. A baseband signal is one that has its frequency components centered around zero frequency
(DC or direct current component).
Nature of Baseband Signals
• The source of a communication system typically produces a low-frequency signal, often referred to as the
baseband signal.
• A baseband signal, being a low-frequency signal, has its spectrum situated close to direct current (DC)
or 0 Hz. For instance:
– Speech signals typically possess a spectrum ranging from 0 to 3.5 kHz.
– Video signals generally have a spectrum spanning from 0 to 4.3 kHz.
Limitations for Direct Transmission
• Baseband signals, due to their inherent low-frequency nature, are not well-suited for direct transmission
over band-pass channels.
• A band-pass channel is one that is designed to transmit signals within a specific frequency range, not
starting from 0 Hz. The low-frequency components of baseband signals, being close to DC, don’t match
well with these channels.
• Direct transmission of baseband signals over long distances can be prone to high levels of noise and
interference. It may also not be efficient in terms of spectrum utilization on shared mediums.
• Therefore, to transmit a baseband signal over such a channel, it must first be converted into a form that
fits within the channel’s usable frequency range. This conversion process is typically achieved through
modulation, where the baseband signal modulates a higher frequency carrier signal.
Dr. Ali AbdelAziz
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Dr. Ali AbdelAziz
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Slide 10: Transmitting Digital Data through Analog Transmission
When dealing with communication systems, there are times when digital data must be transmitted through
analog means. Two primary scenarios where this is required include:
1. The transmission channel is a band-pass channel.
2. The medium of transmission is wireless, such as microwave or radio systems.
Band-pass Channel
• A band-pass channel is designed to carry signals whose frequency components lie within a certain range,
excluding the frequencies close to zero (or DC). Digital signals, in their native form, are baseband signals
with frequencies centered around zero.
• To transmit digital data over a band-pass channel, it must first be converted to an analog form that fits
within the permissible frequency range of the channel. This is achieved using modulation techniques.
• Modulation allows the digital data to piggyback on a carrier signal, which is a high-frequency analog
waveform. The characteristics of this carrier waveform are varied according to the digital data to be
transmitted.
Wireless Transmission Systems
• Wireless mediums, such as radio or microwave systems, inherently operate at certain frequency bands that
are suitable for air transmission and reception by antennas. Direct transmission of baseband digital data
isn’t efficient or even feasible in many wireless scenarios.
• Similar to the band-pass channel scenario, modulation is used to convert the digital data into an analog
waveform suitable for wireless transmission.
• Furthermore, wireless channels are often noisy and can suffer from interference, multipath fading, and
other challenges. Modulating digital data onto an analog carrier can introduce resilience and improve the
chances of successful data reception at the other end.
In both cases, the reception end demodulates the received analog signal to retrieve the original digital
data. The necessity of converting digital data for analog transmission arises from the physical and operational
characteristics of the channel or medium in use.
Slide 11:12 Modulation
Modulation plays a critical role in communication systems, allowing signals to be transmitted over various media
efficiently. It is the mechanism that facilitates the transformation of information into a format optimal for the
transmission medium.
Definition
Modulation is the process of converting digital data or a low-pass analog signal into a band-pass (higher
frequency) analog signal.
• The primary goal is to transform the information to be transmitted into a format suitable for the utilized
medium.
• In analog transmission, signals are typically represented as sine waves characterized by three main parameters: amplitude, frequency, and phase shift.
Types of Modulation
1. General Modulation
It is the process of converting binary data or a low-pass analog signal into a band-pass analog signal.
2. Digital Modulation
Digital modulation, or digital-to-analog conversion, refers to the process of altering one of the characteristics of
an analog signal (amplitude, frequency, or phase shift) based on the information in digital data (represented by
bits 0 or 1).
Dr. Ali AbdelAziz
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Dr. Ali AbdelAziz
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3. Analog Modulation
Analog modulation involves converting a low-pass analog signal into a band-pass analog signal. This conversion
shifts the frequency spectrum of the analog signal from baseband to a higher frequency range suitable for
transmission over a particular medium.
Slide 14: Why We Need Digital Modulation
In the realm of data communication, especially in the wireless domain, transmitting pure digital signals is often
not feasible due to the constraints imposed by the medium. This calls for a mechanism to convert these digital
signals to a format that’s compatible with the medium, and this is where digital modulation comes into play.
Necessity for Digital Modulation
1. Compatibility with Medium: There are channels or mediums that primarily support analog transmission, such as band-pass channels. For transmitting digital data over such channels, a translation from
digital to analog is imperative.
2. Wireless Constraints: In wireless communication systems, transmissions are inherently in the form of
analog sine waves due to the nature of electromagnetic wave propagation. Pure digital signals would not
propagate efficiently over these mediums.
3. Efficiency and Bandwidth: Digital modulation techniques, especially modern ones, are designed to
make efficient use of available bandwidth, ensuring that more data can be transmitted over a given
channel without significant interference or loss of information.
The Process of Digital Modulation
• Digital modulation essentially translates digital data into an analog signal. This translated analog signal,
often referred to as the analog baseband signal, is then suitable for transmission over analog mediums.
• The term ”Shift Keying” denotes the modulation process wherein the digital data ’shifts’ or alters a
particular characteristic of the carrier wave. The carrier wave is typically a pure sine wave, and its
amplitude, frequency, or phase is changed (or keyed) in accordance with the digital data.
• Common forms of digital modulation include:
– Amplitude Shift Keying (ASK): The amplitude of the carrier wave is altered based on the digital
data.
– Frequency Shift Keying (FSK): The frequency of the carrier wave changes in line with the digital
data.
– Phase Shift Keying (PSK): The phase of the carrier wave is shifted according to the digital data.
Slide 15: Types of Digital-to-Analog Conversion
Digital-to-analog conversion involves translating digital data into analog signals suitable for transmission over
analog mediums. A sine wave, commonly used as the carrier wave in this context, can be described by three
primary characteristics: amplitude, frequency, and phase. By modulating these characteristics according to the
digital data, we can effectively represent the data in an analog form. The primary techniques utilized for this
purpose are:
1. Amplitude Shift Keying (ASK): In this method, the amplitude of the sine wave (carrier wave) is
altered in accordance with the digital data. Typically, a binary ‘0’ might be represented by a low amplitude
and a binary ‘1’ by a higher amplitude.
• Advantages: Simple implementation.
• Disadvantages: Susceptible to noise as noise can cause amplitude distortion.
2. Frequency Shift Keying (FSK): Here, different frequencies of the sine wave represent different binary
values. For instance, one specific frequency can signify a binary ‘0’, while another can denote a binary ‘1’.
• Advantages: Less susceptible to errors compared to ASK.
• Disadvantages: Requires a wider bandwidth than ASK.
Dr. Ali AbdelAziz
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Dr. Ali AbdelAziz
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3. Phase Shift Keying (PSK): In PSK, the phase of the sine wave is modified to represent digital data.
For example, a phase shift of 0 degrees might symbolize a binary ‘0’, while a shift of 180 degrees could
represent a binary ‘1’.
• Advantages: More bandwidth-efficient and less error-prone than both ASK and FSK.
• Disadvantages: More complex circuitry required for implementation.
Slide 16: Amplitude Shift Keying (ASK)
Amplitude Shift Keying (ASK) is a modulation technique used in digital communication where the amplitude
of a carrier wave is altered according to the binary data, while its frequency and phase remain constant. In the
simplest form of ASK, two amplitude levels are used.
Carrier Wave in ASK
In Amplitude Shift Keying (ASK), the binary data is represented by varying the amplitude of a carrier wave.
The carrier wave can be either a sine wave or a cosine wave. The choice between using a sine or cosine function
is based on the phase reference. Mathematically, the sine and cosine functions are phase-shifted versions of each
other, with a 90◦ or π/2 radians difference.
Representation using Sine
The modulated signal using a sine wave as the carrier can be represented as:
(
A sin(2πfc t) for binary ’1’
m(t) =
0
for binary ’0’
Representation using Cosine
Similarly, using a cosine wave as the carrier, the modulated signal can be represented as:
(
A cos(2πfc t) for binary ’1’
m(t) =
0
for binary ’0’
Features and Characteristics
• Bandwidth Efficiency: ASK is bandwidth efficient as it requires a minimal increase in bandwidth to
transmit the modulated signal.
• Susceptibility to Noise: ASK is highly susceptible to noise because the amplitude variations can easily
be interfered with, causing errors in detection of ’1’ and ’0’.
• Implementation: The circuitry for ASK is simple and less complex, making it easier to implement.
• Applications: ASK is often used in fiber-optic communication because light intensity can be easily
modulated.
Slide 17: Binary Amplitude Shift Keying (ASK)
Amplitude Shift Keying (ASK) is a modulation technique where the amplitude of a carrier wave is varied in
response to the incoming data signal. While ASK can have multiple amplitude levels to represent data, when
only two levels are used, it’s specifically referred to as Binary ASK or On-Off Keying (OOK).
Binary ASK (OOK)
Binary Amplitude Shift Keying, or On-Off Keying, is the simplest form of amplitude modulation. In OOK, the
presence of a carrier wave signal represents a binary ’1’, while its absence represents a binary ’0’.
Mathematically, the modulated signal can be represented as:
(
A sin(2πfc t) for binary ’1’
s(t) =
0
for binary ’0’
Where:
Dr. Ali AbdelAziz
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Dr. Ali AbdelAziz
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• s(t) is the modulated signal.
• A is the amplitude of the carrier wave.
• fc is the frequency of the carrier wave.
Advantages and Uses of OOK
1. Simplicity: OOK is simple to implement, as it only involves turning the carrier wave on or off.
2. Efficiency: Since the carrier is off half the time (for binary ’0’), OOK can be power-efficient.
However, OOK is more susceptible to errors in the presence of noise as compared to other modulation
schemes with more amplitude levels.
Slide 18: Implementation of Binary Amplitude Shift Keying (ASK)
Binary Amplitude Shift Keying (ASK) is a modulation technique where the amplitude of a carrier wave is
varied based on the digital data signal. For the case where digital data is represented using a unipolar NonReturn-to-Zero (NRZ) format, the implementation of ASK can be realized by modulating the carrier based on
the amplitude of this digital signal.
Unipolar NRZ and Binary ASK
Given a unipolar NRZ digital signal with a high voltage of I V (representing binary ’1’) and a low voltage of
0 V (representing binary ’0’), the Binary ASK can be implemented as follows:
1. The digital signal is multiplied by the carrier signal sourced from an oscillator.
2. When the digital signal’s amplitude is I V (binary ’1’), the carrier signal’s amplitude remains unchanged.
3. When the digital signal’s amplitude is 0 V (binary ’0’), the carrier signal’s amplitude becomes zero,
effectively turning off the carrier.
Mathematically, the modulated ASK signal, s(t), can be represented as:
s(t) = d(t) × c(t)
Where:
• d(t) is the unipolar NRZ digital signal.
• c(t) is the carrier signal from the oscillator.
Thus, during a binary ’1’ of the digital signal, s(t) is equivalent to the carrier c(t). During a binary ’0’, s(t)
is zero.
Carrier Frequency Selection for ASK Modulation
Given Data
The available bandwidth is given as 100 kHz which spans from 200 kHz to 300 kHz.
Slide 20: Carrier Frequency Calculation
For Amplitude Shift Keying (ASK) modulation, it’s customary to select a carrier frequency, fc , that lies in the
center of the available bandwidth. Mathematically, this can be represented as:
fc =
fstart + fend
2
Where:
• fstart is the starting frequency of the bandwidth.
• fend is the ending frequency of the bandwidth.
Substituting in the given values:
fc =
Dr. Ali AbdelAziz
200 kHz + 300 kHz
= 250 kHz
2
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Slide 21: Full Duplex Links in Data Communications
In data communications, full duplex links are often employed. These links facilitate communication in both
directions simultaneously. This is achieved by dividing the available bandwidth into two parts, and each part
is assigned its own carrier frequency.
Bandwidth Division
The total available bandwidth spanning from 200 kHz to 300 kHz is divided into two equal parts, each of 50
kHz. The two carrier frequencies, fc1 and fc2 , are centered within their respective bandwidths. Specifically,
they are positioned at 225 kHz and 275 kHz, respectively.
This division ensures that each direction of the communication link has an equal amount of bandwidth (50
kHz) and a distinct carrier frequency to avoid interference.
Slide 22: Amplitude Shift Keying (ASK)
Amplitude Shift Keying (ASK) is a modulation technique where the amplitude of a carrier signal is varied in
response to the incoming data signal.
Demodulation
In ASK, the demodulation process is straightforward. The receiver’s primary task is to detect the presence or
absence of a sinusoid within a specific time interval. This is because the data is represented by the amplitude
variations: the presence of the sinusoid corresponds to a binary ‘1’ and its absence to a binary ‘0’.
Advantages and Disadvantages
Advantage
• Simplicity: The ASK technique is simple to implement because it involves basic amplitude variations.
Disadvantages
• Noise Susceptibility: ASK is highly susceptible to noise. This is because noise, especially in electronic
communication, primarily affects the amplitude. Therefore, among all modulation techniques, ASK is the
most affected by noise.
Applications
ASK finds its application in transmitting digital data over optical fibers. This is because, in optical communication:
• Light in the ’ON’ state signifies a binary ‘1’.
• Light in the ’OFF’ state signifies a binary ‘0’.
This makes ASK not only simple but also highly efficient for optical communication.
Slide 23: Multilevel Amplitude Shift Keying (ASK)
Amplitude Shift Keying (ASK) can be extended to more than just two amplitude levels, leading to what is
known as Multilevel ASK.
Basics of Multilevel ASK
In standard binary ASK, data is modulated using two distinct amplitude levels, typically representing binary
‘0’ and ‘1’. However, with Multilevel ASK, we can use multiple amplitude levels to represent data. This means
that each symbol (amplitude level) can represent more than one bit.
Advantages
• Increased Data Rate: Since each symbol in multilevel ASK can represent multiple bits, it can achieve
a higher data rate compared to binary ASK for the same bandwidth.
• Efficient Use of Bandwidth: With multiple bits represented by each amplitude level, the bandwidth
utilization is more efficient.
Dr. Ali AbdelAziz
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Dr. Ali AbdelAziz
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Implementation
For instance:
• With 4 distinct amplitude levels, each level can represent 2 bits (00, 01, 10, 11).
• With 8 distinct amplitude levels, each level can represent 3 bits (ranging from 000 to 111).
• With 16 distinct amplitude levels, each level can represent 4 bits, and so on.
It’s worth noting that as the number of amplitude levels increases, the difference between successive levels
decreases. This makes the system more susceptible to noise since a small amount of noise can cause the signal
to be interpreted as a neighboring level.
Slide 24: Frequency Shift Keying (FSK)
Frequency Shift Keying (FSK) is a form of digital modulation where the frequency of the carrier signal is altered
to encode the binary data.
Basics of FSK
In FSK, two distinct carrier frequencies are used, one for binary ‘0’ and another for binary ‘1’. Unlike Amplitude
Shift Keying (ASK) where the amplitude of the carrier signal is varied, in FSK it’s the frequency that gets
changed based on the binary data to be transmitted.
Mathematically, the FSK signal, s(t), can be represented as:
(
A cos(2πf1 t) for binary 0
s(t) =
A cos(2πf2 t) for binary 1
Here:
• A represents the amplitude of the carrier signal, which remains constant.
• f1 and f2 are the two distinct frequencies used for representing binary 0 and 1 respectively.
• t represents time.
Characteristics
• Peak Amplitude: In FSK, the peak amplitude remains constant regardless of the data being transmitted.
• Phase: The phase of the carrier signal also remains constant in FSK.
• Frequency Variation: The carrier frequency switches between f1 and f2 based on the binary data being
sent.
Advantages
FSK is often used in systems where the signal-to-noise ratio is poor because changes in frequency are more
distinguishable than changes in amplitude. Therefore, FSK is more resistant to amplitude-based noise than
ASK.
Slide 26: Frequency Shift Keying (FSK) Demodulation
FSK demodulation is the process of decoding the original data from the received FSK signal. The main goal of
an FSK demodulator is to determine which of the two possible frequencies is present in the received signal at
a given time.
Demodulation Process
• The demodulator examines the incoming signal to detect its frequency.
• If the detected frequency matches f1 , it decodes a binary ‘0’; if it matches f2 , it decodes a binary ‘1’.
• This detection can be achieved using a combination of band-pass filters, discriminators, and decisionmaking algorithms.
Dr. Ali AbdelAziz
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Advantages
• Robustness against noise: FSK is inherently less susceptible to amplitude-based noise compared to
ASK. This is because FSK relies on frequency changes, and the receiver looks for specific frequency changes
over several intervals. Thus, short-lived voltage spikes or noise can be largely ignored.
Disadvantages
• Spectral Efficiency: The bandwidth requirement for FSK is greater than that for ASK. Specifically, the
FSK spectrum is approximately twice the ASK spectrum. This means FSK may require more bandwidth
for the same amount of data compared to ASK.
Applications
• FSK is commonly used over voice lines, especially in modems.
• It is also employed in high-frequency radio transmissions.
• Other applications include caller ID and emergency broadcasts.
Slide 27: Multilevel Frequency Shift Keying (FSK)
Multilevel FSK is an extension of the basic binary FSK modulation scheme where more than two frequencies
are used to represent data. Instead of transmitting one bit per symbol, as in binary FSK, multiple bits are
transmitted per symbol in multilevel FSK.
Mechanism
• In binary FSK, two distinct frequencies f1 and f2 are used to represent the binary values 0 and 1,
respectively.
• In multilevel FSK, multiple frequencies are used. For example, four frequencies f1 , f2 , f3 , and f4 can be
used to represent two bits at a time. This means:
f1 → 00
f2 → 01
f3 → 10
f4 → 11
• This technique allows for increased data rates since more than one bit is transmitted per symbol period.
Frequency Separation
• An essential consideration in multilevel FSK is ensuring that the chosen frequencies are sufficiently separated from each other. This is to prevent interference and to allow the receiver to distinguish between
them effectively.
• The minimum frequency separation depends on the modulation index, the bandwidth of the data signal,
and the characteristics of the channel (including its noise properties).
• As the number of levels increases, ensuring sufficient frequency separation can become challenging, potentially limiting the maximum number of levels that can be used practically.
Slide 28: Phase Shift Keying (PSK)
Phase Shift Keying (PSK) is a modulation technique where the phase of a carrier wave is altered based on the
data signal, while keeping other parameters like amplitude and frequency constant.
Mechanism
• In PSK, the phase of the carrier wave is changed based on the binary data being transmitted.
• Both the peak amplitude and frequency of the carrier remain constant during this modulation.
Dr. Ali AbdelAziz
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Dr. Ali AbdelAziz
Mob: +201090390213
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Binary PSK (BPSK)
Binary Phase Shift Keying (BPSK) is a simple form of PSK where only two phase states are used, corresponding
to the binary values 0 and 1.
• The carrier takes on one phase for a binary ‘0’ and a different phase for a binary ‘1’.
• In BPSK, the two phases used are typically 0◦ and 180◦ .
• Symbolically:
Binary 0 → 0◦ phase shift
Binary 1 → 180◦ phase shift
Advantages
• PSK, especially BPSK, is robust against noise and interference compared to other modulation techniques
like ASK and FSK.
• It provides a balance between complexity and performance, making it suitable for many wireless communication systems.
Slide 29: Phase Shift Keying (PSK)
In Phase Shift Keying (PSK), the phase of a carrier wave is altered based on the binary data signal. In binary
PSK (BPSK), two distinct phases are used to represent the binary values 0 and 1.
Given a carrier signal with frequency fc , the signal s(t) can be represented in the following manner:
Representation 1
(
s(t) =
A cos(2πfc t)
for binary 1
A cos(2πfc t + π) for binary 0
In this representation, a phase shift of π (180 degrees) is introduced for a binary 0, effectively inverting the
carrier wave.
Representation 2
(
s(t) =
A cos(2πfc t)
−A cos(2πfc t)
for binary 1
for binary 0
Here, instead of a phase shift, the amplitude of the signal is inverted for a binary 0.
Slide 30: Implementation of Binary Phase Shift Keying (BPSK)
Binary Phase Shift Keying (BPSK) is one of the simplest forms of phase modulation in which two phases are
used to represent the binary values 0 and 1. The implementation of BPSK can be understood in relation to
Amplitude Shift Keying (ASK).
BPSK vs. ASK
In BPSK, the signal element with a phase of 180◦ is essentially the complement of the signal element with a
phase of 0◦ . This characteristic simplifies the implementation of BPSK and draws parallels to ASK.
Implementation Approach
The key insight for BPSK implementation is to utilize a polar Non-Return-to-Zero (NRZ) signal rather than
the unipolar NRZ signal typically used in ASK. The steps for implementation are as follows:
1. Begin with the binary digital data that needs to be transmitted.
2. Convert this data into a polar NRZ signal. In this format, a binary ‘1’ is represented by a positive voltage,
while a binary ‘0’ is represented by a negative voltage.
3. Multiply the polar NRZ signal by the carrier frequency.
4. The resultant signal will have a phase starting at 0◦ for a positive voltage (binary ‘1’) and a phase starting
at 180◦ for a negative voltage (binary ‘0’).
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Slide 32: Phase Shift Keying (PSK) Demodulation
Phase Shift Keying (PSK) is a modulation technique where the phase of the carrier wave is changed according
to the input data. The demodulation process in PSK is crucial in correctly interpreting the received signals.
Demodulation
The main objective during PSK demodulation is to determine the phase of the received sinusoid with respect
to a reference phase. The demodulator must be capable of accurately detecting these phase shifts to correctly
interpret the transmitted data.
Advantages
• PSK is less susceptible to errors compared to Amplitude Shift Keying (ASK). This is because noise usually
affects amplitude rather than phase.
• PSK is superior to Frequency Shift Keying (FSK) as it doesn’t require two separate carrier signals.
• The bandwidth requirement for Binary PSK (BPSK) is the same as that for binary ASK, which means it
is efficient in terms of bandwidth utilization.
Disadvantages
• The signal detection and recovery process in PSK is more complex compared to ASK and FSK.
Baud Rate vs. Bit Rate
Baud Rate
Baud rate, also known as the symbol rate, refers to the number of signal units (symbols) transmitted per second.
A symbol can represent more than one bit of information.
Baud Rate (Bd) =
Number of Symbols
Time (seconds)
(1)
Bit Rate
Bit rate, often referred to as data rate, measures the number of bits (0s and 1s) transmitted per second.
Bit Rate (bps) =
Number of Bits
Time (seconds)
(2)
Relation between Baud Rate and Bit Rate
The relationship between bit rate and baud rate can be represented as:
Bit Rate = Baud Rate × Number of bits per symbol
(3)
For binary systems, where each symbol represents only a single bit (like Non-Return to Zero or NRZ
encoding), the baud rate is equal to the bit rate. However, in systems where each symbol can represent
more than one bit, the bit rate can be multiple times higher than the baud rate.
Example: In a system where each symbol can represent 2 bits (like Quadrature Phase Shift Keying or
QPSK), a baud rate of 1 Bd would result in a bit rate of 2 bps.
Slide 33: Quadrature Phase Shift Keying (QPSK)
Quadrature Phase Shift Keying, commonly known as QPSK, is a type of Phase Shift Keying (PSK) where two
bits are modulated at once, selecting one out of four possible carrier phase shifts. It is also sometimes referred
to as 4-PSK.
Basic Concept
In QPSK, the carrier signal undergoes phase shifts of either 0◦ , 90◦ , 180◦ , or 270◦ , which correspond to phase
shifts of 0, π2 , π, and 3π
2 radians respectively. This allows for the encoding of two bits per symbol.
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Bit to Phase Mapping
Given the 2-bit binary input data, the corresponding phase shift is:
• 00 → 0◦ or 0 radians
• 01 → 90◦ or
π
2
radians
• 10 → 180◦ or π radians
• 11 → 270◦ or
3π
2
radians
Advantages
• The symbol rate of QPSK is half the bit rate, allowing for higher data rates.
• QPSK is more bandwidth-efficient than Binary Phase Shift Keying (BPSK) because it transmits two bits
in each symbol.
• It provides a balance between bandwidth efficiency and resilience to interference.
Slide 34: Quadrature Phase Shift Keying (QPSK)
Quadrature Phase Shift Keying, abbreviated as QPSK, is an advanced form of phase modulation technique.
Unlike Binary Phase Shift Keying (BPSK) which uses two phases, QPSK uses four phases to transmit data.
Working Principle
In QPSK, each symbol consists of 2 bits, and hence four different phase angles are used to represent each
unique 2-bit combination. The carrier signal undergoes different phase shifts depending on the binary data to
be transmitted:

for binary 00

A cos(2πfc t),

A cos(2πf t + π ), for binary 01
c
2
s(t) =
A cos(2πfc t + π),
for binary 10



A cos(2πfc t + 3π
),
for binary 11
2
Where:
• A is the amplitude of the carrier signal.
• fc is the carrier frequency.
• t is time.
Advantages
• QPSK is bandwidth efficient: Since each QPSK symbol represents 2 bits, it effectively transmits two bits
for every change in phase.
• Resilient to noise: Due to the nature of phase modulation, QPSK can be more resilient to noise than
amplitude-based modulations.
Slide 35: Advantages of Quadrature Phase Shift Keying (QPSK)
Quadrature Phase Shift Keying (QPSK) is a type of phase modulation technique that offers several advantages
especially when compared to its binary counterpart, Binary Phase Shift Keying (BPSK).
1. Higher Data Rate
QPSK achieves a higher data rate than BPSK. In QPSK, two bits are transmitted in each symbol, allowing
the data rate to be doubled compared to BPSK. Even though it sends two bits per symbol, the bandwidth
occupancy remains the same as that of BPSK. This translates to:
• Effective utilization of the available bandwidth.
• Transmission of more information in the same time frame without requiring additional bandwidth.
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
2. Extensibility
QPSK can be easily extended to higher-order PSK like 8 PSK. This extensibility to n PSK means:
• It offers flexibility in choosing modulation schemes based on the application.
• It can achieve even higher data rates by increasing the number of phase shifts, thereby transmitting more
bits per symbol.
3. Equipment Limitations
While QPSK and higher-order PSK schemes can achieve greater data rates, they are constrained by the equipment’s ability to distinguish minor phase differences. As the number of phase shifts increases, the distinction
between each phase becomes finer. This requires:
• More precise reception equipment.
• Advanced error correction techniques to handle possible errors due to the inability to distinguish closely
spaced phase angles.
Slide 38: Why We Need Analog Modulation
Analog modulation refers to the process by which we change a carrier wave, which is a high-frequency analog
signal, based on the value of a lower frequency baseband signal. The need for analog modulation arises due
to various reasons and constraints posed by communication channels and the nature of the signals we wish to
transmit.
Analog to Analog Conversion
The fundamental idea behind analog modulation is the conversion of a low-frequency analog signal (baseband
signal) into a high-frequency analog signal that is suitable for transmission over a particular medium. This
process can be visualized as representing the original signal using a different analog format, one that is more
amenable to transmission over the intended channel.
Reasons for Analog Modulation
1. Bandpass Nature of the Medium: Many communication mediums, especially wireless channels, are
bandpass in nature. This means that they can only carry signals within a specific frequency range.
Modulation allows us to shift the spectrum of our baseband signal into this range, ensuring its successful
transmission over the medium.
2. Size and Antenna Matching: For efficient radiation of signals, especially in wireless systems, the size of
the transmitting antenna needs to be on the order of the wavelength of the signal. Modulating the signal
to a higher frequency reduces the wavelength, making the design of practical-sized antennas feasible.
3. Multiplexing: Modulation allows for the simultaneous transmission of multiple signals over the same
channel without interference, a technique known as Frequency Division Multiplexing (FDM).
4. Reduction in Interference: High-frequency signals are less susceptible to certain types of noise and
interference. By modulating a signal to a higher frequency, we can often achieve better transmission
quality.
Basic Analog Modulation Schemes
The primary analog modulation techniques include:
• Amplitude Modulation (AM): In this scheme, the amplitude of the carrier wave is varied in accordance
with the instantaneous value of the baseband signal.
• Frequency Modulation (FM): Here, the frequency of the carrier wave is changed based on the value
of the baseband signal.
• Phase Modulation (PM): In PM, the phase of the carrier wave is altered based on the baseband signal’s
value.
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Slide 40: Frequency Domain Representation of Modulation
The provided diagram depicts a signal in its frequency domain, both in its original (unmodulated) form and
after modulation.
Unmodulated Signal
• Signal: This is the original or baseband signal. It represents the actual information or message we wish
to transmit. As seen in the diagram, its spectrum is centered around low frequencies, close to 0 Hz.
• Carrier: The high-frequency signal without any modulation. It does not contain any information by
itself but serves as the signal that will be modulated by the baseband signal for transmission.
Modulated Signal
When the baseband signal is modulated onto the carrier, the resultant signal occupies a higher frequency band.
In the given diagram:
• The carrier remains at the same central frequency.
• The baseband signal, however, is now shifted (or translated) to frequencies around the carrier, resulting
in the modulated signal. This means the information in the baseband signal is now represented at these
higher frequencies.
Significance of Modulation: Modulation allows a signal to be transmitted over channels that might
not support the original baseband frequencies. For example, many communication channels (like radio waves)
operate at high frequencies. By modulating a baseband signal onto a high-frequency carrier, we can transmit
the information over these channels. In the diagram, modulation translates a signal from its baseband to the
operating range of the channel.
Slide 41: Types of Analog-to-Analog Modulation
Analog-to-analog modulation, often referred to as analog modulation, is the representation of a low-frequency
analog signal using a higher frequency analog signal. The primary objective of such modulation is to shift the
baseband analog signal to a higher frequency band suitable for transmission. There are three principal types of
analog modulation:
1. Amplitude Modulation (AM): In amplitude modulation, the amplitude of the high-frequency carrier
wave is varied in accordance with the instantaneous amplitude of the baseband signal. The frequency and
phase of the carrier remain unchanged.
2. Frequency Modulation (FM): Here, the frequency of the carrier wave is varied based on the instantaneous amplitude of the baseband signal. The amplitude and phase of the carrier remain constant. FM is
widely used in radio broadcasting due to its resistance to amplitude noise.
3. Phase Modulation (PM): In phase modulation, the phase of the carrier wave is altered based on
the instantaneous amplitude of the baseband signal. The amplitude and frequency of the carrier remain
unchanged.
Each of these modulation schemes has its own set of advantages, disadvantages, and applications, depending
on the requirements of the communication system and the nature of the transmission channel.
Slide 42: Amplitude Modulation (AM)
Amplitude Modulation, commonly abbreviated as AM, is one of the fundamental modulation techniques utilized
to transmit information, especially in audio broadcasting systems.
In AM:
• The amplitude of a high-frequency carrier wave is varied in accordance with the instantaneous amplitude
of the modulating signal (often an audio signal).
• The frequency and phase of the carrier wave remain unchanged during this modulation process.
• The modulating signal, which contains the information or message, determines the envelope of the modulated carrier wave.
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Dr. Ali AbdelAziz
Mob: +201090390213
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• As shown in the illustration, the amplitude of the carrier wave changes as per the modulating signal.
When the modulating signal’s amplitude is high, the carrier’s amplitude is high, and vice versa.
• The bandwidth of the AM signal is twice the bandwidth of the modulating signal.
The main advantage of AM is its simplicity, which makes it suitable for broadcasting. However, it is more
susceptible to noise compared to other modulation techniques since noise primarily affects amplitude.
Slide 43: AM Bandwidth
Amplitude Modulation (AM) is a modulation technique used in electronic communication. A significant aspect
of AM is its bandwidth, which directly impacts the frequency spectrum it occupies.
Key points regarding AM bandwidth:
• The spectrum of an AM signal consists of the carrier frequency (fc ) and sidebands that occur due to
modulation. These sidebands carry the information.
• The upper and lower sidebands contain identical information, making one of them redundant. Consequently, only one sideband is essential for the transmission of the information.
• However, in standard AM, both sidebands are transmitted. This results in a bandwidth (BAM ) that is
twice the bandwidth (B) of the modulating signal.
• Mathematically, the bandwidth of an AM signal is given by:
BAM = 2B
• The range of frequencies occupied by the AM signal is centered around the carrier frequency, fc .
Slide 44: Standard Bandwidth Allocation for AM Radio
Amplitude Modulation (AM) radio is a widely used broadcasting method, especially for long-distance communication. The allocation of bandwidth is crucial to ensure clear transmission and to avoid interference with
neighboring channels.
1. Audio Signal Bandwidth: The bandwidth (BW) of a typical audio signal, which may encompass speech
and music, is approximately 5 kHz. This means that the highest frequency in the audio signal is 5 kHz.
2. AM Bandwidth: Due to the nature of AM, where both the upper and lower sidebands are transmitted,
an AM radio station requires a bandwidth that is twice that of the modulating audio signal. Thus, for a
5 kHz audio signal:
AM Bandwidth = 2 × 5 kHz = 10 kHz
3. Carrier Frequency Range: AM radio stations are allocated carrier frequencies in the Medium Frequency
(MF) band. This ranges from 530 kHz to 1700 kHz.
4. Separation to Avoid Interference: To prevent interference between neighboring radio stations, there
is a mandated separation in their carrier frequencies. Each station’s carrier frequency must be separated
from its neighboring stations by at least 10 kHz (equivalent to one AM bandwidth). This separation
ensures that the broadcasts from one station do not interfere with those of adjacent stations.
Slide 45: Frequency Modulation (FM)
Frequency Modulation (FM) is a modulation technique in which the frequency of a carrier wave is altered
according to the instantaneous amplitude of the modulating signal. The core principle behind FM is that the
frequency deviation of the carrier is directly proportional to the instantaneous amplitude of the modulating
signal.
• Modulating Signal (Audio): This is the original signal that we wish to transmit, typically a lowfrequency audio signal.
• Carrier Frequency: A high-frequency signal that is modulated by the audio signal. It is the backbone
upon which the audio signal is carried and broadcasted.
• FM Signal: The resulting signal after the carrier’s frequency has been modulated by the audio signal.
As the amplitude of the audio signal changes, the frequency of the carrier wave changes correspondingly.
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Key Characteristics of FM:
1. The amplitude of the FM signal remains constant. This makes FM more resistant to amplitude noise
and is one of the reasons FM is popular for radio broadcasting, especially in environments with a lot of
potential interference.
2. Only the frequency of the carrier changes as per the modulating signal.
3. The phase of the carrier signal remains constant.
Slide 46: FM Bandwidth
The bandwidth of a Frequency Modulated (FM) signal is essential for understanding its behavior in a communication channel. In FM, the carrier frequency varies according to the instantaneous value of the modulating
signal. The range over which this frequency varies, known as the deviation, determines the bandwidth required
for transmission.
Given by the equation:
BF M = 2(1 + δ)B
Where:
• BF M is the bandwidth of the FM signal.
• δ is the modulation index, which is the ratio of the frequency deviation to the modulating frequency.
• B is the bandwidth of the modulating signal.
The equation suggests that the FM bandwidth, BF M , is directly influenced by both the bandwidth of the
modulating signal and the modulation index δ. Thus, FM bandwidth can become quite large, especially when
the modulating signal has a significant bandwidth and/or when a high modulation index is used.
It’s worth noting that the oscillator’s frequency changing according to the input voltage essentially means
that the instantaneous frequency of the carrier changes in proportion to the amplitude of the modulating signal.
This behavior defines FM and distinguishes it from Amplitude Modulation (AM).
Slide 47: Standard Bandwidth Allocation for FM Radio
FM (Frequency Modulation) radio broadcasting has a specific standard bandwidth allocation to ensure efficient
and interference-free transmission of signals. This standardization is crucial for the organization and quality
maintenance of radio broadcasts.
Audio Signal Bandwidth
For FM radio, especially those broadcasting in stereo, the bandwidth of an audio signal, which includes speech
and music, is approximately 15 kHz. This ensures that the audio quality remains high, covering the range of
human hearing.
Bandwidth of audio signal ≈ 15 kHz
FCC Bandwidth Allocation
The Federal Communications Commission (FCC) allocates a total bandwidth of 200 kHz (or 0.2 MHz) for each
FM radio station. With a modulation index (β) of 4, this allows for the necessary deviation caused by the
modulating audio signal and provides some extra space termed the ’guard band’ to prevent interference with
adjacent channels.
Total bandwidth per station = 200 kHz
β=4
Frequency Range for FM Stations
FM radio stations are allocated carrier frequencies in the VHF (Very High Frequency) range. Specifically, the
allocated range for FM stations lies between 88 MHz and 108 MHz.
88 MHz ≤ fc ≤ 108 MHz
Where fc represents the carrier frequency.
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg
Separation Between Stations
To avoid interference and ensure clarity of broadcasts, FM stations need to be separated by at least the allocated
bandwidth of 200 kHz. This separation ensures that the bandwidths of individual stations do not overlap,
thereby preventing interference.
Minimum separation between stations = 200 kHz
Slide 48: Phase Modulation (PM)
Phase Modulation (PM) is a modulation scheme wherein the phase of the carrier signal is altered according to
the instantaneous amplitude of the modulating signal. Unlike Amplitude Modulation (AM) where the amplitude
of the carrier varies, or Frequency Modulation (FM) where the frequency of the carrier is varied, in PM, it’s
the phase of the carrier signal that gets modulated.
Key Characteristics of PM
• The modulating signal, which can represent information like voice or music, determines the variations in
the phase of the carrier.
• During PM, the carrier’s peak amplitude and frequency remain constant. Only its phase varies.
• The phase changes are proportional to the instantaneous amplitude of the modulating signal. A higher
amplitude in the modulating signal results in a greater phase shift in the carrier signal, and vice versa.
In essence, the changing voltage level (or amplitude) of the modulating signal directly influences the phase
of the carrier signal in PM. This modulation technique is used in various communication systems due to its
resilience to noise and ability to carry information efficiently.
Slide 49: Analog Modulation
Analog modulation is a technique used in electronic communication wherein the properties of a carrier wave
(such as its amplitude, frequency, or phase) are altered or varied in accordance with the instantaneous values
of the message signal or the modulating signal. The main goal is to transmit an analog message signal over a
communication channel, typically over the airwaves or via cables.
Definition
Analog modulation can be formally defined as the process to impress an information-bearing analog waveform
onto a carrier waveform for the purpose of transmission. This ensures that the information contained in the
original signal can be transported over significant distances and can be received accurately on the other end.
Types of Analog Modulation
There are three primary types of analog modulation:
1. Amplitude Modulation (AM): The amplitude of the carrier wave is varied in proportion to the instantaneous amplitude of the modulating signal, keeping the frequency and phase constant.
2. Frequency Modulation (FM): The frequency of the carrier wave is varied in accordance with the
instantaneous amplitude of the modulating signal, while keeping amplitude and phase constant.
3. Phase Modulation (PM): The phase of the carrier signal is varied based on the instantaneous amplitude
of the modulating signal, keeping amplitude and frequency constant.
The choice of modulation scheme often depends on the specific requirements of the communication system,
such as the need for bandwidth efficiency, resistance to noise, or other system constraints.
Dr. Ali AbdelAziz
Mob: +201090390213
Mail: aabdelaziz@aswu.edu.eg