ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I Digital modulation techniques

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION
Introduction
 Advanced Digital Communication refers to the sophisticated methods and techniques
employed in the transmission and reception of digital information over communication
channels.
 Advanced Digital Communication represents the application of sophisticated
technologies and methodologies to optimize digital communication systems for higher
data rates, improved reliability, and adaptability to dynamic network conditions.
 It plays a crucial role in the development of modern communication networks
supporting applications ranging from wireless communications and satellite systems to
broadband internet and beyond.

Fundamentals of Communication

I. Communication
 Communication refers to the process of exchanging information, ideas, thoughts, or
feelings between individuals or groups. It involves a sender encoding a message,
transmitting it through a chosen channel, and a receiver decoding and interpreting the
message.
 Effective communication is crucial in various aspects of human interaction, including
personal relationships, business, education, and more.

 Example: A person sending a text message to a friend to make plans for the weekend is
an example of communication.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

II. Modulation and Demodulation
Modulation and demodulation are fundamental concepts in communication systems.

a) Modulation
 Modulation is the process of changing one or more characteristics (Amplitude, Frequency
and Phase) of the high-frequency carrier signal in accordance with message signal
(Analog or Digital).

 In modulation, there are typically two signals involved: the message signal and the
carrier signal.

i) Message /Information Signal:
 This is the signal that carries the information we want to transmit. It could be an
analog signal representing things like sound or a digital signal carrying data.
 For audio signals (voice, music): Typically, the range is between 20 Hz to 20 kHz.
This is the audible frequency range for the human ear.
 For data signals (digital communication): The frequency range can vary widely
depending on the data rate and the type of information being transmitted. It can
range from a few kilohertz (kHz) to megahertz (MHz) for digital signals.
ii)Carrier Signal:
 The carrier signal is a high-frequency signal that acts as a carrier for the message
signal. It's like a vehicle that carries the information through a communication
channel.
 In radio communication, carrier frequencies can range from kilohertz (kHz) to
gigahertz (GHz).
 In cellular networks, for instance, frequencies may range from hundreds of
megahertz (MHz) to several gigahertz (GHz).

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 If the message signal is continuous signal, then modulation is called Analog Modulation.
Example: AM, FM and PM.

1.Amplitude Modulation (AM): In AM, the amplitude of the carrier signal is varied in
proportion to the instantaneous amplitude of the message signal. This is commonly used
in broadcasting for transmitting audio signals.

2.Frequency Modulation (FM): FM involves changing the frequency of the carrier
signal based on the instantaneous frequency of the message signal. FM is often used for
high-quality audio transmissions.

3.Phase Modulation (PM): PM modifies the phase of the carrier signal according to the
instantaneous phase of the message signal. PM is utilized in certain communication
systems and radar applications.

 If the message signal is discrete signal, then modulation is called Digital Modulation.
Example: ASK, FSK, and PSK.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

1. Amplitude Shift Keying (ASK): The amplitude of the carrier signal is altered to
represent digital data.
2. Frequency Shift Keying (FSK): Digital information is encoded by changing the
frequency of the carrier signal.
3. Phase Shift Keying (PSK): Digital data is represented by altering the phase of the
carrier signal.
 The electronic circuit used for modulation is known as Modulator, Modulation done at
the transmitter.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Need of Modulation in Communication
 Modulation is a fundamental process in communication systems, where a low-frequency
signal, known as the message signal, is combined with a high-frequency carrier signal.
 This modulation process yields several crucial advantages during transmission given
below.
1. Reduction in the height of antenna
2. Avoids mixing of signals
3. Multiplexing can be done
4. Compatibility with Transmission Medium
5. Efficient Bandwidth Utilization
6. Noise Immunity
7. Security
1. Reduction in the height of antenna
 The height of an antenna is often related to the wavelength of the transmitted signal.
λ = c /f
where c: is the velocity of light(3x10
8
)
f: is the frequency of the signal to be transmitted
 In radio communication, the ideal height of an antenna is typically a fraction or multiple
of the wavelength. Reducing the height may lead to inefficient radiation and reception,
potentially impacting the range and quality of communication.
Example:
 The minimum antenna height required to transmit a m signal of f = 10 kHz is
calculated as follows :

 This 7.5 km antenna of this height is practically impossible to install.
 Now, let us consider a modulated signal at f = 1 MHz . The minimum antenna height
is given by,

 This 75 meters’ antenna can be easily installed practically. Thus, modulation reduces
the height of the antenna.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

2. Avoids mixing of signals
 If baseband sound signals are transmitted without modulation by multiple transmitters,
they would share the same frequency range (0 to 20 kHz), causing signal mixing.

 Modulation assigns each signal to a different carrier, placing them in distinct frequency
slots (channels) and preventing interference, ensuring signal separation at the receiver.

3. Multiplexing can be done
 Modulation enables multiplexing, which is the simultaneous transmission of multiple
signals over the same communication channel.

 This is essential for combining various information sources, such as different audio
channels or data streams.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

4. Compatibility with Transmission Medium
 Different transmission mediums have different characteristics. Modulation allows for
the adaptation of the signal to suit the specific requirements of the medium, whether it's
free space, optical fiber, or conductive cables.

5. Efficient Bandwidth Utilization
 Efficient use of available bandwidth is essential, especially in scenarios where the
frequency spectrum is limited. By modulating a carrier signal, multiple signals can
share the same frequency band without interfering with each other.

6. Noise Immunity
 Modulation helps in improving the Signal-to-Noise Ratio(SNR). By spreading the
information across a wider frequency range, the signal is less susceptible to interference
and noise during transmission.

7. Security
 Modulation techniques can also contribute to the security of communication. Spread
spectrum modulation, for instance, can make signals less susceptible to interception or
jamming.

b) Demodulation
 Demodulation is the process of extracting the original message signal from a modulated
carrier signal.

 It is the reverse process of modulation and is crucial for retrieving the transmitted
information accurately.
 The electronic circuit responsible for demodulation is known as a demodulator, and
demodulation is typically performed at the receiver.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Difference Between Modulation and Demodulation
 Modulation combines a weak signal with a strong carrier for long-distance
transmission, while demodulation extracts the original information from the transmitted
signal.

 They work together: modulation at the sender's end and demodulation at the receiver's
end, ensuring effective communication between devices.

Characteristic Modulation Demodulation
Purpose Prepares a signal for transmission
by encoding information onto a
carrier signal.
Extracts the original message signal
from a modulated carrier signal.
Process Alters carrier signal characteristics
(amplitude, frequency, or phase)
based on the message signal.
Recovers the original message
signal from the modulated carrier by
undoing the modulation process.
Location Typically performed at the
transmitter.
Typically performed at the receiver.
Devices Modulator is used. Demodulator is used.
Frequency Involves a high-frequency carrier
signal.
Deals with the modulated carrier
signal, which may still be at a high
frequency.
Objective Facilitates efficient transmission
and reception of information.
Ensures accurate retrieval of the
original message from the
transmitted signal.
Examples
(Analog)
AM (Amplitude Modulation), FM
(Frequency Modulation), PM
(Phase Modulation).
Corresponding demodulation
techniques for AM, FM, and PM.
Examples
(Digital)
ASK (Amplitude Shift Keying),
FSK (Frequency Shift Keying),
PSK (Phase Shift Keying).
Corresponding demodulation
techniques for ASK, FSK, and PSK.
Signal
Transformation
Converts low-frequency message
signal to a high-frequency carrier
signal.
Reverts the high-frequency
modulated carrier signal back to the
original message signal.
Multiplexing Allows multiple signals to share
the same transmission medium.
Helps separate and extract
individual signals from the
combined transmission.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

III. Electronic/Analog Communication:
 Electronic communication involves the transmission of information using electronic
signals.

 Analog communication uses continuous signals to convey information. In analog
communication systems, the signal varies smoothly and continuously over time.

 Example: Traditional landline telephones use analog communication. The sound waves
produced by the speaker's voice are translated into electrical signals, which are then
transmitted over the phone lines as continuous electrical variations.

Block Diagram of Analog Communication System
The elements of basic analog communication system are input signal or information, input
transducer, transmitter, channel, Noise, Receiver, Output transducer.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

1.Information or Input signal:
 The information is transmitted from one place to another.
 This information can be in the form of a sound signal like speech, or it can be in the
form of pictures or it can be in the form of data information.

2.Input transducer:
 The information in the form of sound, picture or data signals cannot be transmitted as
it is.
 First it has to be converted into a suitable electrical signal.
 The input transducer block does this job.
 The input transducer commonly used are microphones, TV etc.

3.Transmitter:
 The function of the transmitter is to convert the electrical equivalent of the information
to a suitable form so that it can transfer over long distance.
 Basic block in transmitter are: Amplifier, Oscillator, Mixer.

4.Channel:
 The communication channel is the medium used for transmission of electrical signal
from one place to other.
 The communication medium can be conducting wires, cables, optical fibres or free
space.
 Depending on the type of communication medium, two types of communication system
exists.
 Line/Wired Communication: The line communication systems use the
communication medium like the simple wires or cables or optical fibres. Eg: Telephone,
Cable TV.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 Radio/Wireless Communication: The radio communication systems use the free
space as their communication medium. The transmitted signal is in the form of
electromagnetic waves. E.g. Mobile communication, satellite communication.

5.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 information gets degrade.
 Once added the noise cannot be separated out from the information

6.Receiver:
 The receiver always converts the modulated signal into original signal which consist of
Amplifier, Oscillator, Mixer.

7.Output transducer:
 Output transducer converts electrical signal into the original form i.e. sound or TV
pictures etc.
 E.g. Loudspeaker, data and image convertor.

IV. Digital Communication:
 Digital communication involves the transmission of information using discrete signals,
typically in the form of binary code (0s and 1s).

 Digital communication systems encode information into digital signals, which are more
resistant to noise and can be easily processed and manipulated by electronic devices.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 Example: Sending an email is an example of digital communication. The text of the email
is converted into digital data, transmitted over the internet in the form of packets, and then
reassembled into the original message by the recipient's device.

Block Diagram of Digital Communication System

It consists of an input transducer, source encoder, channel encoder, digital modulator,
communication channel, digital demodulator, channel decoder, source decoder, and output
transducer connected in series. Let's discuss the function of each component in the digital
communication system.

1. Information Sourer and Input transducer:
 The source of information is generally analog in nature for example voice signal and
video signal. These signals are non-electrical quantities and hence cannot be
processed directly in a digital communication system. the input transducer converts
this non-electrical quantity into electrical quantity. Ex: Microphone
 Source of Information Source can be classified into two categories based the nature
of their output
a) Analog Information Sources (Source Emit Continues Amplitude Signals.)
Examples: Microphone actuated by a speech, TV Camera scanning a scene,
continuous amplitude signals.
b) Digital Information Sources (Source that has only finite set of symbols)

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Examples: These are teletype or the numerical output of computer which consists of
a sequence of discrete symbols (0s and 1s)
 An Analog information is transformed into a discrete information through the process
of sampling and quantizing.

2. Source Encoder:
 The source encoder is used to compress the data into minimum number of bits. This
helps in effective utilization of the bandwidth.
 It removes the redundant bit’s or unnecessary excess bits, i.e., zeroes. from the input
data.
Example:
 Original Data: 10100100
 Source Encoder Compressed Data: 11001

3. Channel Encoder
 The information in the signal may get altered due to the noise during the
transmissions.
 The channel encoder works as an error correction method. It adds redundant
bits to the binary data that helps in correcting the error bits.
 The examples of error correction codes commonly employed in channel encoding
are Hamming Code, Convolutional Code, Turbo Codes.
 It enhances the transmission quality of the signal and the channel.
Example
 Original Compressed Data: 11001
 Channel Encoder Encoded Data: 11001+101=11001101

4. Digital Modulator:
 A digital modulator is a device or a component in a communication system that
converts digital data into a modulated signal suitable for transmission over a
communication channel.
 The process of modulating a digital signal involves varying the properties of a
carrier signal, such as amplitude, frequency, or phase, based on the digital data.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

This modulation allows the digital information to be transmitted efficiently over a
communication medium.
 Example: Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and
Phase Shift Keying (PSK).

5. Electrical Communication Channel:
 The communication channel is the physical medium that is used for transmitting
signals from transmitter to receiver.
 It can be categorized into wired and wireless types.
a) Wired Channel: Uses pairs of wires to transmit signals in electrical form.
Example: Traditional Telephone network.

b) Wireless Channel: No physical media between transmitter and receiver;
utilizes electromagnetic waves.
Example: Mobile communication
6. Noise:
 Noise is an unwanted signal or disturbance that is added to the original signal during
transmission.
 It can be caused by various factors, including electronic components, atmospheric
conditions, and external electromagnetic interference.
 Noise can degrade the quality of the transmitted information and make it more
challenging for the receiver to correctly interpret the intended message.
 Due to noise in the channel, the transmitted data may get altered.
 Transmitted Data (with noise): 1100110111111101

7. Digital Demodulator:
 This is the first step at the receiver end. The received signal is demodulated as
well as converted again from analog to digital.
 The digital demodulator reverses this process, recovering the original digital
information from the modulated signal.
 The demodulation process depends on the modulation scheme used in the
transmitter.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

8. Channel decoder
 The channel decoder, after detecting the sequence, does some error corrections.
The distortions which might occur during the transmission, are corrected by
adding some redundant bits. This addition of bits helps in the complete recovery
of the original signal.
 Channel Decoder detects and corrects errors:
 Decoded Data: 11001101

9. Source Decoder:
 The source decoder performs the inverse operations applied by the source encoder.
This may include processes like error correction, decompression, or any other
encoding technique used during transmission.
 Source Decoder recreates the original source output:
 Original Data: 1100100

10. Output Transducer:
 This is the last block which converts the signal into the original physical form,
which was at the input of the transmitter.
 It converts the electrical signal into physical output for example: loud speaker.

V. Advanced Communication:
 "Advanced communication" is a broad term that can encompass various sophisticated
and cutting-edge methods of exchanging information. This may involve the integration
of advanced technologies, high-speed data transfer, artificial intelligence, or other
innovative approaches to enhance the efficiency and capabilities of communication
systems.

 Example: Video conferencing using virtual reality (VR) technology could be
considered an advanced communication method. Participants can engage in virtual
meetings, feeling as if they are physically present in the same space, even if they are
geographically distant. This represents a more immersive and sophisticated form of
communication compared to traditional video calls.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Differences Between Digital Communication and Analog Communication

Feature Digital Communication Analog Communication
Representation Uses discrete signals (bits: 0s and
1s)
Uses continuous signals (varying
voltage or frequency)
Signal Quality Resistant to noise and distortion;
clear signal quality
Susceptible to noise and
distortion; degrades over distance
Bandwidth Efficiency More efficient use of bandwidth Less efficient use of bandwidth
Data Transmission Easily multiplexed and transmitted
over long distances
Limited multiplexing and shorter
transmission distances
Error
Detection/Correction
Robust error detection and
correction methods
Limited error detection and
correction capabilities
Switching Speed Faster switching speeds Slower switching speeds
Modulation Techniques Various modulation schemes
(ASK, FSK, PSK, QAM, etc.)
Modulation schemes like AM,
FM, PM
Security Easier to encrypt and secure data Less secure due to ease of
intercepting and tampering
Equipment Cost Digital equipment can be costlier Analog equipment may be less
expensive
Storage and Processing Easily stored and processed
digitally
Analog signals may require
additional processing
Common Applications Internet communication, digital
TV, mobile phones
Traditional telephony, AM/FM
radio
Advantages - Resistant to noise and distortion
- Efficient use of bandwidth
- Error detection and correction
capabilities
- Ease of encryption and security
-Simplicity and ease of
implementation
- Suitable for audio signals
-Analog signals can be less
complex to process
Disadvantages -Can be more complex to
implement
-Analog-to-digital conversion
introduces quantization error
- Susceptible to noise and distortion
- Limited bandwidth efficiency
-Limited error detection and
correction capabilities

Keep in mind that these generalizations may vary based on specific applications and
technological advancements. Both digital and analog communication systems have their
advantages and disadvantages, and the choice between them often depends on the requirements
and characteristics of the particular communication scenario.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Classification of Electronic Communication

1. Technique of Transmission:
a) Baseband transmission (Without Modulation): In baseband transmission, the
signal occupies the entire bandwidth of the transmission medium without modulation.
Example: Ethernet communication over a twisted pair cable. The digital signals
representing data are sent without modulation directly over the cable.

b) Passband/Broadband transmission (Modulation): Passband transmission
involves modulating a carrier signal with the information signal, allowing for efficient
use of bandwidth.
Example: FM (Frequency Modulation) radio broadcasting. In FM, an audio signal
modulates a carrier wave, allowing the signal to be transmitted efficiently over the
airwaves.

2. Nature of Information Signal:
a) Analog communication: Analog communication involves the transmission of
continuous signals, typically representing analog data such as voice or music.
Example: Traditional AM (Amplitude Modulation) radio broadcasting. The audio
signal is analog, and its amplitude modulates the carrier wave.

b) Digital communication: Digital communication involves discrete signals (bits),
representing digital data.
Classification of Electronic Communication Based on
1) Technique of
Transmission
a)Baseband
transmission(Without
Modulation)
b) Passband
transmission(Modulation)
2)Nature of Information
Signal
a) Analogcommunication
b) Digital communication
3)Direction of
Communication
a) Unidirectional (Simplex)
b) Bidirectional(Half
Dupex/Full Duplex)
4)Connectivity
a)Wired
b) Wireless

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Example: Digital TV broadcasting. Digital signals carrying video and audio
information are transmitted using modulation techniques like QAM (Quadrature
Amplitude Modulation).

3. Direction of Communication:

a) Unidirectional (Simplex): In unidirectional communication, information flows in one
direction only, from the sender to the receiver.
Example: Television broadcasting. TV signals are sent from the broadcasting station to
the viewers, and there is no direct communication back to the station.

b) Half-Duplex: In half-duplex communication, information can be transmitted in both
directions, but not simultaneously. Participants can switch between sending and
receiving, but not at the same time.
Example: Walkie-talkies are a classic example of half-duplex communication. When
one person is talking, the other person needs to listen, and vice versa. The
communication channel is shared and switches between transmission and reception.

c) Full-Duplex: In full-duplex communication, information can be transmitted in both
directions simultaneously. Participants can talk and listen at the same time, creating a
more natural and real-time communication experience.
Example: Mobile phone calls are a common example of full-duplex communication.
Both parties can speak and listen simultaneously, allowing for a more interactive
conversation. Similarly, traditional telephone networks also operate in full-duplex
mode.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

4. Connectivity:
a) Wired: Wired communication uses physical media, such as cables or fiber optics,
for signal transmission.
Example: Telephone communication over a landline. Voice signals are transmitted
using electrical signals over physical copper wires.

b) Wireless: Wireless communication involves transmission without the need for
physical cables, utilizing radio waves, microwaves, or other wireless technologies.
Example: Wi-Fi communication. Data is transmitted wirelessly between devices using
radio frequency signals, allowing for wireless connectivity in homes and businesses.

DIGITAL MODULATION TECHNIQUES

Digital Modulation
Digital modulation is the process in which one or more characteristics (amplitude, frequency,
or phase) of a high frequency carrier signal is varied in accordance with the instantaneous value
of the modulating signal consisting of binary or multilevel digital data.

Performance Measure of Digital Modulation
 The performance of digital modulation schemes is assessed using various measures that
provide insights into different aspects of their effectiveness and efficiency.
 Factors that influence choice of digital modulation techniques are given below
1.Bandwidth
2.Bit rate and Baud rate
3.Probability of Error(Pe) or Bit Error Rate(BER)
4.Power Spectral Density (PSD)
5.Power and Bandwidth efficiency

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

1. Bandwidth
 Definition: The range of frequencies occupied by the modulated signal.
 Importance: Efficient use of bandwidth is crucial for effective communication and
spectrum utilization.

Bandwidth=Highest Frequency Component−Lowest Frequency Component
Example:
If a signal occupies frequencies from 1 kHz to 5 kHz,
Bandwidth = 5kHz−1kHz=4kHz.

2. Bit rate and Baud rate
Bit Rate:
 Definition: The number of bits transmitted per unit of time (usually measured in bits
per second, bps).
 Importance: Reflects the data transmission capacity of the system. Bit Rate bps = Baud Rate×Number of Bits per Symbol

 If each symbol represents one bit (binary modulation), then the bit rate is equal to the
baud rate.
 However, if each symbol represents more than one bit (e.g., in higher-order
modulation), then the bit rate is higher than the baud rate.

Baud Rate:
 Definition: The number of signal changes (symbols) per second in a communication
channel.
 Importance: Baud rate is relevant for modulation schemes where one symbol
represents multiple bits (e.g., in the case of modulation schemes like QPSK, where each
symbol represents 2 bit

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

( / )


Bit Rate bps
Baud Rate bits symbol
Number of Bits per Symbol

Example:
For a QPSK modulation with a baud rate of 1000 symbols per second and each symbol
representing 2 bits,
 Bit rate=1000 symbols/s×2 bits/symbol=2000 bps
 Baud rate=2000 bps/2 bits/symbol=1000 symbols/s

3. Probability of Error (Pe) or Bit Error Rate (BER):
 Probability of Error (Pe):
 Definition: The likelihood that a received bit will be in error.

 The probability of the detector making an incorrect decision is termed the
probability of symbol error (Pe) , When transmitting data from one point to
another, either over a wireless link or a wired telecommunications link, the key
parameter is how many errors will appear in the data that appears at the receiver
end.
 Bit Error Rate (BER):
 Definition: The ratio of the number of bits received in error to the total number of
bits transmitted.
 Importance: BER provides a quantitative measure of the quality of
communication, with lower values indicating better performance.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24
Number of Bits Received in Error
BER =
Total Number of Bits Transmitted

 Let's consider an example to illustrate the calculation of BER. Suppose you transmit
1000 bits, and during the transmission, 10 bits are received in error. 10
BER = = 0.01
1000

 So, the Bit Error Rate in this example is 0.01 or 1%. This means that, on average, 1%
of the bits transmitted were received incorrectly.
4. Power Spectral Density (PSD):
 Definition: The power distribution of a signal with respect to its frequency.

Importance:
 PSD is crucial for regulatory compliance and interference analysis, as it characterizes
how the power of a signal is distributed across the frequency spectrum.
 It provides a way of representing the distribution of signal frequency components
which is easier to interpret visually.
 The formula for calculating PSD (S(f)) is

Power at f
S f =
Bandwidth
 Example: Assume we have a signal with a bandwidth of 4 MHz, composed of four
frequency components: 10 MHz, 11 MHz, 12 MHz, and 13 MHz. The power levels
measured for these frequencies are 4W, 5W, 6W, and 7W, respectively.
 For f=10MHz: 4W
S 10MHz = = 1W / MHz
Mhz
()
4

 For f=11MHz:

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24
5W
S 11MHz = = 1.25W / MHz
4 hz
()
M

5. Power and Bandwidth Efficiency:
A desired modulation scheme
i. Should provide low bit-error rates (Power efficiency)
ii. Should occupy minimum channel bandwidth (Bandwidth efficiency)

 Power Efficiency(Powerη ):
 Definition: The ratio of the signal power to the total power (including unwanted
components like noise).
 Power efficiency measures how efficiently power is used to transmit information.
It is the ratio of the bit energy to the total energy per bit. r
Signal Power
Power Ef c
To
e
t
i
a
n
l
y
P
f c =
owe
i

 Example:
If a system has a signal power of 10 W and a total power of 15 W, the power
efficiency is 10/15=0.671510 =0.67 or 67%.

 Bandwidth Efficiency(bwη ):
 Definition: Ability of a modulation scheme to accommodate data within a limited
bandwidth.
 Importance: These measures help in evaluating how efficiently the available
power and bandwidth are utilized for communication.

 Example: Let's consider a digital communication system with a bit rate of 10,000 bps
and an occupied bandwidth of 5 kHz. 10
2 /
5
kbps
Bandwidth Efficiency kbps kHz
kHz


So, the bandwidth efficiency in this example is 2 kbps/kHz2kbps/kHz. This means that for
every kilohertz of bandwidth, the system can transmit 2,000 bits of information per second. B
z
Bit R
B
ate
t
Oc
f
cu
c
p
n
i
y
e

d
d

i
B
d
a
a
n

d
i
w
e
i
c
d
η
t
w
h
n h E f i : = bps / H

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Classification of Digital Modulation
 Digital modulation techniques are categorized based on how digital information is
encoded onto analog signals for transmission.
 This classification is primarily divided into two main categories: Signalling Scheme
and Phase-Recovery.

I. Signaling Scheme
 A signaling scheme refers to the method or strategy used to represent digital
information in the analog domain for transmission over a communication channel.
 It defines how binary or multilevel symbols are mapped onto analog signals, such as
carrier waves, to facilitate the transmission of information between sender and
receiver.
 The two primary categories of signaling schemes are binary modulation and M-ary
modulation.

1.Bi-nary Modulation
Digital Modulation Technique
I.Signaling Scheme
1. Binary
Modulation
a) BASK
b)BFSK
c)BPSK
d)DBPSK
2.M-ary
Modulation
a)QPSK/8PSK
M-ary PSK
b)QAM/M-ary
ASK
c)M-ary FSK
II.Phase-Recovery
1.Coherent
Modulation
Ex:PSK
2. Non Coherent
Modulation
Ex:DBPSK

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 The word binary represents two-bits. They send communication signals at only 2
levels – 0 and 1

 Each symbol in binary modulation corresponds to a single bit of digital data.
 In binary signaling, we can represent two voltage or signal levels by using a single bit.
 Single bit has value either logic 0 or logic 1 where logic 0 represent ‘0’ volt and logic
1 represent ‘5’ volt.

 In binary signaling, where each bit corresponds to one of two signal levels, the bit rate
(number of bits transmitted per second) is the same as the baud rate (number of signal
level changes per second). This is because each bit represents a change in the signal
level, resulting in an equal number of signal transitions and bits transferred within a
second.
 Examples include Binary Amplitude Shift Keying (BASK), Binary Frequency Shift
Keying (BFSK), and Binary Phase Shift Keying (BPSK).

2.M-ary Modulation
 M-ary modulation involves the use of more than two discrete symbols, allowing
each symbol to represent multiple bits of information.
 In multi-level signaling, there are more than two voltage or signal levels

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 To represent those signal levels, we require more than one bit. Number of bits required
to represent voltage levels is obtained by using following formula.

Where N = number of bits necessary
M = number of conditions, level or combinations
 Assume in the above figure, Number of bits transferred per second are 9600 and there
are 4 voltage or signal levels[0V, 2V, 4V, 5V].
 To represent those 4 voltage or signal levels we required at least 2 bits (using
2=log2(4)).
 Assume 00 represents 0V, 01 represents 2V, 10 represents 4V and 11 represents 5V.
 M-ary modulation enables higher data transmission rates by conveying multiple bits
per symbol.
 Examples include Quadrature Phase Shift Keying (QPSK), 8PSK, and Quadrature
Amplitude Modulation (QAM), M-ary ASK, FSK, PSK.

MN
2log

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Comparison between Binary and M-ary modulation

Aspect Binary Modulation M-ary Modulation
Number of
Symbols
Two symbols: 0 and 1

More than two symbols (M
symbols), where M > 2
Modulation
Exa,ples
BASK,BFSK,BPSK QPSK,QAM,M-ary
ASK,FSK,PSK.
Bit
Representation
Each symbol represents one bit
(0 or 1)
Each symbol represents multiple
bits
Efficiency Lower spectral efficiency Higher spectral efficiency
Data Rate Limited data rate Higher potential data rate
Complexity Simpler
modulation/demodulation
Higher complexity, especially with
larger M
Bandwidth Usage Generally wider bandwidth
usage
More efficient use of bandwidth
Applications Simple applications with low
data rates
High data rate applications, e.g.,
broadband

II. Phase-Recovery
 In digital communication systems, the process of encoding and transmitting digital
information often involves modulating a carrier signal.
 Phase-recovery modulation schemes are a category of modulation techniques that
focus on how the receiver extracts and recovers the phase information from the
received signal.
 The goal is to accurately reconstruct the original digital data by recovering the phase
characteristics imparted during modulation.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

1. Coherent Modulation
 In coherent modulation schemes, the receiver is designed to have knowledge of the
phase of the carrier signal. This coherent detection allows for more accurate
demodulation.
 The job of the phase recovery circuit is to keep the oscillators supplying locally
generated carrier wave at the receiver; in synchronism to the oscillator supplying carrier
wave at the transmitting end.
 This technique employs coherent detection, the local carrier wave which is generated
at the receiver is phase locked with the carrier at the transmitter.
 Hence both the oscillators (carrier waves) are synchronized in both frequency and
phase.
 Requires a replica carrier wave of the same frequency and phase at the receiver.
 Applicable to: PSK, ASK, FSK

Example: Phase Shift Keying (PSK)
 PSK modulates the phase of the carrier signal to represent different symbols. Coherent
PSK requires the receiver to synchronize with the carrier phase for accurate
demodulation.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Advantages of Coherent Modulation:
1. Better Performance:
 Coherent modulation provides higher performance in terms of error rate,
making it suitable for applications with stringent requirements.
2. Optimized for High SNR:
 Particularly effective in scenarios where the signal-to-noise ratio is high.
3. Suitable for Advanced Modulation Schemes:
 Coherent modulation is often used in advanced modulation schemes such as
QAM, which require accurate phase information.
Disadvantages of Coherent Modulation:
1. Complex Receiver Design: Coherent modulation requires more complex receiver
designs compared to non-coherent schemes. Precise synchronization with the carrier
phase adds complexity to the receiver architecture.
2. Sensitive to Phase Noise: Coherent modulation schemes can be sensitive to phase
noise in the communication channel. Any deviation from the expected phase can result
in demodulation errors.
3. Higher Implementation Cost: The added complexity in coherent modulation systems
often leads to higher implementation costs, making them less cost-effective in certain
applications.
4. Challenging for Mobile Communication: Coherent modulation can be challenging
for mobile communication systems where there are rapid changes in channel
conditions, and maintaining precise phase synchronization becomes difficult.
Applications of Coherent Modulation:
1. High-Capacity Communication Systems:
 Coherent modulation is well-suited for high-capacity communication systems,
such as those used in broadband and high-speed data transmission.
2. Optical Communication:
 In optical communication, coherent modulation is commonly used to achieve
high data rates and efficient use of the optical spectrum.
3. Digital Broadcasting:
 Coherent modulation is employed in digital broadcasting systems where
accurate demodulation is essential for reliable signal reception.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

2.Non Coherent Modulation
 Non-coherent modulation schemes do not require the receiver to have phase
knowledge. i.e. there is no need for the two carriers (at transmitter and receiver) to be
phase locked.
 Requires no reference wave; does not exploit phase reference information (envelope
detection), Phase is Unknown
 Applicable to: Differential Phase Shift Keying (DPSK), FSK, ASK

Example: Non-coherent Amplitude Shift Keying (ASK), DPSK
In non-coherent ASK, the receiver does not require precise phase synchronization. It modulates
the amplitude of the carrier signal based on the input data, making it suitable for scenarios
where simplicity in receiver design and robustness to phase variations are essential.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Advantages of Non-Coherent Modulation:
1. Simplicity in Receiver Design: Non-coherent modulation schemes require less
complex receiver designs since they do not rely on maintaining precise phase
synchronization.
2. No Phase Synchronization: Non-coherent modulation does not require the receiver to
synchronize with the carrier phase, simplifying the receiver design.
3. Robust in Mobile Communication: Well-suited for mobile communication scenarios
where rapid changes in channel conditions can make phase synchronization
challenging.
4. Better Performance in Low SNR: Non-coherent modulation may perform better than
coherent schemes in low signal-to-noise ratio (SNR) environments, as they are less
sensitive to phase noise.
Disadvantages of Non-Coherent Modulation:
1. Lower Performance in High SNR: In high SNR environments, non-coherent
modulation schemes may not achieve the same level of performance as coherent
schemes.
2. Limited for Advanced Modulation: Non-coherent modulation may be limited in
supporting advanced modulation schemes that require precise phase information for
transmitting multiple bits per symbol.
3. Less Efficient Spectrum Utilization: In certain applications, non-coherent modulation
may result in less efficient use of the available spectrum compared to coherent
modulation.
4.
Applications of Non-Coherent Modulation
1. Low-Power Devices:
 Employed in low-power devices and applications where minimizing the complexity of
receiver circuits is essential for energy efficiency.
2. Short-Range Communication:
 Suitable for short-range communication systems, such as radio-frequency identification
(RFID) applications, where simplicity and robustness are prioritized over high data
rates.
3. Mobile Communication:

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 Well-suited for mobile communication systems where rapid changes in channel
conditions and mobility can make maintaining precise phase synchronization
challenging.
4. Underwater Communication:
 Applied in underwater communication systems where the underwater environment
introduces challenges such as multipath fading and signal distortion, making non-
coherent modulation more resilient.

Comparison between Coherent Modulation and Non-Coherent Modulation
Aspect Coherent Modulation Non-Coherent Modulation
Synchronization
Requirement
Requires precise
synchronization with carrier
phase
Does not require precise
synchronization with carrier phase
Receiver Complexity More complex receiver
design
Simpler receiver design
Performance in High
SNR
Generally performs well in
high SNR environments
May not perform as well as
coherent in high SNR
Robustness to Phase
Noise
Sensitive to phase noise More robust to phase noise
Advantages - Higher performance in
optimal conditions
- Suitable for high-capacity
communication systems
- Effective in advanced
modulation schemes

- Simpler receiver design
- More robust in scenarios with
unpredictable phase variations
- Well-suited for mobile
communication and short-range
applications

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Disadvantages - Higher receiver complexity
- Sensitivity to phase noise
- Challenging for mobile
communication
- Greater implementation cost
in certain scenarios
- Lower performance in optimal
conditions compared to coherent
Limited performance in high SNR
environments
- May have lower data rate
compared to coherent schemes
- Less efficient spectrum utilization
in some applications

Applications - Higher performance in
optimal conditions
-Advanced modulation
schemes (QAM, PSK)
- Optical communication
- Digital broadcasting
- Mobile communication systems
- Wireless sensor networks
- Underwater communication
- Low-power devices

Binary Modulation Techniques

I. Binary Amplitude Shift Keying (BASK)
 Definition: BASK is a form of binary digital modulation technique in which the
amplitude of the high frequency sinusoidal carrier signal is varied accordance with the
input binary data stream by keeping frequency and phase of the high carrier are
constant is called ASK.
 ASK is sometimes known as On-Off(OOK) keying because the carrier wave swings
between 0 and 1 according to the low and high level of input signal respectively.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

BASK Modulation Waveforms

The following observations can be made from ASK signal waveform:
 For every change in the input binary data stream, either from logic 1 to logic 0 or vice-
versa, there is corresponding one change in the ASK signal waveform.
 For the entire duration of the input binary data logic 1 (high), the output ASK signal is
a constant amplitude, constant-frequency sinusoidal carrier signal.
 For the entire duration of the input binary data logic 0 (low), the output ASK signal is
zero (no carrier signal).
BASK Modulator
BASK modulation, or Binary Amplitude Shift Keying, involves varying the amplitude of a
high-frequency carrier signal in accordance with a binary data sequence, employing a balanced
modulator and Band Pass Filter for digital communication.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Here's a step-by-step Working of BASK Modulator
Binary Data Sequence (Input):
 binary data sequence, which is a series of 1s and 0s representing digital information.
This sequence is the input to the BASK modulator.
Sinusoidal Carrier Signal:
 A high-frequency sinusoidal carrier signal is generated. The frequency of this carrier
signal is typically much higher than the frequency of the binary data sequence.
Balance Modulator:
 The binary data sequence and the sinusoidal carrier signal are fed into the two inputs of
a balanced modulator. A balanced modulator is a device that multiplies the two input
signals.
 For BASK modulation, the carrier signal is multiplied by the binary data sequence. The
output of the balanced modulator is a signal whose amplitude is determined by the
binary data. If the binary data is 1, the amplitude is high; if it's 0, the amplitude is low.

??????&#3627408534;&#3627408533;&#3627408529;&#3627408534;&#3627408533;=&#3627408488;??????⋅[&#3627409359;+&#3627408526;(&#3627408533;)]⋅??????&#3627408528;&#3627408532;(&#3627409360;??????&#3627408519;??????&#3627408533;)
Where:
 Ac is the amplitude of the carrier signal.
 m(t) is the message signal (binary data sequence in the context of BASK).
 fc is the carrier frequency.
 t is time.
 The term 1+m(t) is used to represent the modulation index, which allows for variations
in both the positive and negative directions of the carrier signal.
 When m(t) is equal to 1, the term 1+m(t) becomes 2, and when m(t) is equal to -1, the
term 1+m(t) becomes 0. This ensures that the modulation covers both the positive and
negative peaks of the carrier signal.
 If we were to use just m(t), it would only allow for positive modulation, and the negative
side of the carrier would not be properly represented.

Bandpass Filter (BPF):
 The output of the balanced modulator contains both the original carrier frequency and
sidebands produced by the modulation process. To extract the desired modulated signal
and filter out unwanted components, a Bandpass Filter (BPF) is used.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 The BPF allows only the frequency band around the carrier frequency to pass through,
filtering out other frequency components.

Output Signal:
 The final output of the BASK modulator is a modulated signal with variations in
amplitude corresponding to the binary data sequence.
??????&#3627408534;&#3627408533;&#3627408529;&#3627408534;&#3627408533; &#3627408489;??????&#3627408527;??????&#3627408531;?????? ??????&#3627408518;&#3627408530;&#3627408534;&#3627408518;&#3627408527;??????&#3627408518;={&#3627409358;,&#3627409359;,&#3627409358;,&#3627409359;,…}

BASK Demodulator
There are two types BASK demodulation possible

a) Coherent BASK Demodulator.
b) Non-Coherent BASK Demodulator.

a) Coherent BASK Demodulation.
 Coherent ASK demodulation retrieves binary data from an ASK-modulated signal by
maintaining precise synchronization between a local oscillator's carrier signal and the
received signal.
 Achieved through a balanced modulator, an integrator, and a decision-making device,
this ensures accurate retrieval of modulated information.

Here's a step-by-step working of BASK Coherent BASK Demodulator
1. Received ASK Signal:
 The received signal is an ASK-modulated signal that has been transmitted over
a communication channel.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 It is a carrier signal whose amplitude has been modulated based on a binary data
sequence.
 The received ASK signal can be represented as: ( ) ( ) ( )r t =Ac×m t ×cos 2πfct

where:
 Ac is the amplitude of the carrier signal.
 m(t) is the binary data sequence.
 fc is the carrier frequency.
 t is time.
2. Sinusoidal Carrier Signal from Local Oscillator:
 A local oscillator generates a sinusoidal carrier signal at the same frequency as
the carrier used in the modulation process.
 The local oscillator generates a sinusoidal carrier signal as: LO
)s t = ×cos 2( ) ( πfctA

where:
A LO is the amplitude of the local oscillator signal.
 In coherent ASK demodulation, the local carrier signal is precisely synchronized in
both frequency and phase with the carrier signal used in the ASK modulator. Two
essential synchronization aspects ensure optimal operation:
 Phase Synchronization: This aligns the phase of the locally generated carrier signal
with that of the carrier used in the ASK modulator, ensuring coherence during
demodulation.
 Timing Synchronization: This synchronization ensures accurate timing for decision-
making in the ASK demodulator, aligning with the switching instants between 1 and 0
in the original binary data.

3. Balanced Modulator:
 The received ASK signal and the sinusoidal carrier signal from the local
oscillator are fed into the two inputs of a balanced modulator. The balanced
modulator multiplies these two signals. )ut( ) ( )=r ×s(tt

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 The multiplication process involves both positive and negative frequency
components, ensuring that the demodulation process is coherent and can
properly recover the original binary data.

4. Integrator:
 The output of the balanced modulator, which contains the product of the ASK
signal and the local oscillator signal, is then passed through an integrator. 0
bT

v t = u t d( ) ( )t

 The integrator integrates the product signal over time, smoothing out rapid
fluctuations and emphasizing the variations in amplitude caused by the ASK
modulation.

5. Decision-Making Device (Comparator):
 The integrated signal is then fed into a decision-making device, often a
comparator. The comparator compares the integrated signal with a certain
threshold(5v).

()0
()1if v t Threshold
if v t Threshold



 
Output =
 If the integrated signal is above the threshold, the comparator decides that a '1'
was transmitted.
 If the integrated signal is below the threshold, it decides that a '0' was
transmitted.

6. Output:
 The output of the comparator represents the recovered binary data.
??????&#3627408534;&#3627408533;&#3627408529;&#3627408534;&#3627408533; &#3627408489;??????&#3627408527;??????&#3627408531;?????? ??????&#3627408518;&#3627408530;&#3627408534;&#3627408518;&#3627408527;??????&#3627408518;={&#3627409358;,&#3627409359;,&#3627409358;,&#3627409359;,…}
 The decision-making device outputs a binary sequence that closely resembles
the original binary data sequence used for modulation.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

b) Non-Coherent ASK Demodulator.
Non-coherent Amplitude Shift Keying (ASK) demodulation is a method used to recover the
original binary data from a received ASK-modulated signal without the need for phase
synchronization between the local oscillator and the carrier signal.

Here's a step-by-step working of BASK Non-Coherent BASK Demodulator

1. Received Binary ASK Signal:
 The received signal is an ASK-modulated signal that has been transmitted over
a communication channel. It is a carrier signal whose amplitude has been
modulated based on a binary data sequence. ( ) ( ) ( )r t =Ac×m t ×cos 2πfct

2. Bandpass Filter (BPF):
 The received ASK signal is first passed through a Bandpass Filter (BPF). ]xF( ) [=BP r(t)t

 The BPF allows only the frequency band around the carrier frequency to pass
through, filtering out unwanted frequency components and noise.
3. Envelope Detector (Rectifier + LPF):
 The filtered signal is then fed into an Envelope Detector, which typically
consists of a rectifier and a Low-Pass Filter (LPF). ]y t =LPF Recti( ) [ [ (f er x t)]i

 The rectifier converts the alternating current (AC) signal into a pulsating direct
current (DC) signal, and the LPF smoothens the pulsations to extract the
envelope of the signal.
 The envelope represents the variations in amplitude caused by the ASK
modulation, effectively demodulating the signal.

4. Decision Device (Comparator with Preset Threshold):

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 The output of the envelope detector, representing the recovered signal, is then
compared to a preset threshold level by a Decision Device, often implemented
as a comparator.
()0
()1if y t Threshold
if y t Threshold



 
Output =

 If the amplitude of the recovered signal is above the threshold, the comparator
decides that a '1' was transmitted. If the amplitude is below the threshold, it
decides that a '0' was transmitted.
 The threshold is set based on the expected amplitude levels of the modulated
signal, and it acts as a reference point for distinguishing between binary
symbols.

5. Output:
 The output of the decision device is the recovered binary data.
??????&#3627408534;&#3627408533;&#3627408529;&#3627408534;&#3627408533; &#3627408489;??????&#3627408527;??????&#3627408531;?????? ??????&#3627408518;&#3627408530;&#3627408534;&#3627408518;&#3627408527;??????&#3627408518;={&#3627409358;,&#3627409359;,&#3627409358;,&#3627409359;,…}
 The decision-making process is based on the amplitude information extracted
from the envelope of the received ASK signal.

Performance Measure of BASK

1. Bit Rate (Rb) and Baud Rate (Rbaud)
a) Bit Rate (Rb)
 Bit rate refers to the number of bits transmitted per unit of time. It is measured in bits
per second (bps).
 For BASK, each bit corresponds to one modulation symbol. Therefore, the bit rate is
equal to the symbol rate. Rb=
1
Tb

where Tb is the duration of one bit (symbol)
b) Baud Rate (Rbaud)
 Baud rate refers to the number of signal changes (symbols) per unit of time. It is
measured in baud.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 For binary modulation schemes like BASK, where each symbol represents one bit, the
baud rate is equal to the bit rate. Rbaud= Rb

Therefore, the rate of change of the ASK signal (expressed in baud) is the same as the rate of
change of the binary input data (expressed in bps). i.e. bit rate= baud rate

Note: For all binary modulation techniques (BASK, BFSK, BPSK, bit rate= baud rate)

2.Bandwidth (B)
Bandwidth is the frequency range occupied by a signal and is a critical parameter for
communication system design.

For BASK, the bandwidth is related to the bit rate by : BASK = 1(+r)×Rb

Where, r is a parameter related to the modulation process, where 01r
Rb is the bit rate
 Minimum Bandwidth: BASK minimum =Rb (when r=0)
 Maximum Bandwidth: BASK maximum=2×Rb (when r=1) 11
( ) ( )fc fc
Tb Tb
    
BASKBW
( ) ( )fc Rb fc Rb    
BASKBW = 2Rb

3.Power Spectral Density (PSD)
 The power spectral density represents the distribution of power with respect to
frequency.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 The ASK signal is basically the product of the binary digital data sequence and the
sinusoidal carrier signal.
 It has a power spectral density (PSD) same as that of the baseband binary data signal
but shifted in the frequency domain by ± fc, where fc is the carrier signal frequency.

 The PSD for BASK can be expressed as ]
Pavg
S f = δ f -fc +( ) [ ( δ f +( fc
2
))

Where,
P avg is the average power of the BASK signal.
fc is the carrier frequency.
δ(f) is the Dirac delta function

Derivation of Probability of Error(Pe) or Bit Error Rate(BER) of BASK

 The Probability of Error (Pe) or Bit Error Rate (BER) is important in digital
communication systems, indicating the likelihood of a transmitted bit being received
incorrectly.

 In digital communication, bits are encoded and transmitted over a channel, where
factors like noise can lead to errors.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 Pe, especially in the presence of additive white Gaussian noise (AWGN), assesses the
probability of making incorrect decisions about transmitted symbols.

Received Signal: (1)( ) ( ) (r t = A×m t +n t)

where:
 A is the amplitude of the carrier signal.
 m(t) is the binary data sequence with values of +1 or -1.
 n(t) is AWGN with zero mean and power spectral density N0/2.

To derive the probability of error (Pe) or Bit Error Rate (BER) for Binary Amplitude
Shift Keying (BASK)

 In BASK two signals,1c
)so( ) (t = A c s 2πfct and 2
s(t)=0

The energy difference (Ed) between the two symbols 
2
12
Tb
0
Ed= s t s t dt( )- ( )∣∣

2
c
Tb
0
Ef ()d= A cos 2π ct dt∣∣

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

22
c
Tb
0
Ed= A cos 2 c)πf dt(t

2 1+ cos 2θ
2
()
cθ()os =




Tb Tb2
00
Ac
1dt + cos 4πf( ) ]ct dt
2
Ed=






b
Tb2
0
Ac
Ed= T + cos 4 πf(]dt
2
)ct

1
cos ax dx =()
a
()sin ax

b
0
T
4πfc
1
sin 4 ct)πf( ∣

b
1
4πfc
()sin 4πfcT

bb
2
sin 4πfcT
4πf
)
c
1
(
Ac
Ed= T +
2




b
2
Ac T
Ed=
2




d
0
E
Pe=Q
2N




b
2
0
Ac T1
Pe= erfc
2 4N

we can express Pe in terms of Eb and 0N 




b
e(BASK)
o
E1
P = erfc
2 4N

where ,
Eb is the energy per bit
0N is the power spectral density of the noise.
erfc is probability of errors due to noise

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Advantages of BASK
1. Simplicity: BASK is a simple modulation technique, both in terms of implementation
and demodulation.
2. Bandwidth Efficiency: Compared to some other modulation schemes, BASK can be
bandwidth-efficient.
3. Ease of Detection: Demodulation of BASK signals is relatively straightforward,
requiring simple envelope detection in some cases.
4. Cost-Effective: BASK implementations can be cost-effective due to the simplicity of
the modulation and demodulation processes.

Disadvantages of BASK
1. Susceptibility to Noise: BASK is sensitive to noise, which can lead to a higher
probability of errors, especially in low signal-to-noise ratio (SNR) environments.
2. Limited Spectral Efficiency: BASK may not be as spectrally efficient as other
modulation techniques, and it may not make optimal use of the available bandwidth.
3. Inefficient Power Usage: BASK may not be power-efficient, particularly in situations
where constant-amplitude transmission is not necessary.
4. Limited Data Rate: The modulation scheme may have limitations on achievable data
rates compared to more advanced modulation techniques.

Applications of BASK
1. Low-Cost Applications: BASK is suitable for low-cost applications where simplicity
and cost-effectiveness are critical factors.
2. Short-Range Communication: BASK may be used in short-range communication
systems where the simplicity of the modulation and demodulation processes outweighs
its limitations.
3. Wireless Data Transmission: In applications where moderate data rates and spectral
efficiency are acceptable, BASK can find use in wireless data transmission.
4. Telemetry Systems: BASK is employed in telemetry systems for transmitting simple
binary data over short distances.
5. Remote Controls: BASK is commonly used in simple remote control systems, such as
those for home electronics, where low-cost implementation is essential.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

II. Binary Frequency Shift Keying (FSK)
 Definition: BFSK is a form of binary digital modulation technique in which the
frequency of the high frequency sinusoidal carrier signal is varied accordance with the
input binary data stream by keeping amplitude and phase of the high carrier are
constant is called BFSK.
 Mathematically, BFSK signal can be expressed as:

Where,
o Vc is the amplitude of the carrier signal
o f1 and f2 are the two different carrier frequencies (f1 > f2) used for binary 1
and binary 0, respectively

BFSK Waveforms

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

The following observations can be made:
 When the input binary data changes from a binary logic 1 to logic 0 and vice versa,
the BFSK output signal frequency shifts from f1 to f2 and vice versa (f1 > f2).

BASK Modulator
 Binary Frequency Shift Keying (BFSK) is a modulation technique used in digital
communication systems.
 It involves modulating a carrier signal with two different frequencies to represent binary
data.

 The modulator can be implemented using various components like a Bipolar NRZ
encoder, balance modulators (M1 and M2), an adder, and a Bandpass Filter (BPF).


1. Binary Data Sequence (Data): The binary data sequence is the input data that needs to
be transmitted. Let's represent it as a sequence of binary symbols, such as 0s and 1s. }Data= d1,d2,d3,…,dn{

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

2. Bipolar NRZ Encoder:
 The Bipolar Non-Return-to-Zero (NRZ) encoder is responsible for converting the
binary data into a bipolar signal.

 In this encoding, '0' is represented by one voltage level, and '1' is represented by
the opposite voltage level.
 Let A be the amplitude of the signal. 


A, if di=1
NRZ di =
-A, if
)
0
(
di=

3. Balance Modulator M1:
 The balance modulator M1 multiplies the bipolar NRZ signal with the carrier
signal of frequency f1.
 Let s(t) be the NRZ signal, and c1(t) be the carrier signal. )Mt()1 t =s ×(c1(t)

 The carrier signal can be represented as 1)c1 t =cos(( πf) 2 ×t

4. Balance Modulator M2:
 Similar to M1, the balance modulator M2 multiplies the inverted bipolar NRZ
signal with the carrier signal of frequency f2.

 The inversion of the signal before modulating with f2 helps in achieving a clear
distinction between the two frequencies. This inversion ensures that when the
input data is '0,' it gets modulated by the carrier frequency f1, and when the input

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

data is '1,' it gets modulated by the inverted signal with carrier frequency f2. This
separation in frequencies helps in the demodulation process, making it easier to
distinguish between the two binary states at the receiver.
 Let s′(t) be the inverted NRZ signal. '
( ) ( )× ( )M2 t =s t c2 t

 The carrier signal can be represented as 22 )c t =cos 2(πf( ×t)

5. Adder:
The outputs from M1 and M2 are added together. )At ()dder M (Output = 1 t +)2(Mt

6. Bandpass Filter (BPF):
 The combined signal from the adder is passed through a bandpass filter to select
the desired frequency components. ]BPF Output t =Filter Adder O) utpu( t(t[)

 The bandpass filter helps filter out unwanted frequency components and focuses on the
desired frequency band.
 The resulting modulated BFSK signal is then suitable for transmission over a
communication channel.

a) Coherent BFSK Demodulator
 A Coherent Binary Frequency Shift Keying (BFSK) Demodulator is used to
demodulate received BFSK signals with reference carrier signal.
 It involves the use of two correlators (Correlator 1 and Correlator 2), a subtractor, a
decision device, and a detected output.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

1. Received BFSK Signal (r(t)):
 The received BFSK signal is denoted as r(t) and can be expressed as a combination of
the two modulated signals with frequencies f1 and f2. '
12 )r t =A×s t ×cos 2πf t +A×s t ×( cos) 2) π) ( ( ( f( t)

where:
 A is the amplitude of the signal.
 (s(t) is the bipolar NRZ signal.
 s′(t) is the inverted bipolar NRZ signal.
 f1 and f2 are the carrier frequencies.

2. Correlator 1(Balance Modulator (BM1) + Integrator1)
 A correlator is a signal processing device used to measure the similarity between two
signals.
 Balance Modulator (BM1): Multiplies the received signal with the carrier signal. 11
( ) ( )BM out= r t ×c t

 Integrator1: Integrates the product over a bit duration Tb

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

b
T
1
0
C1 = BM out dt

3. Correlator 1(Balance Modulator (BM2) + Integrator2)
 Balance Modulator (BM2): Multiplies the received signal with the carrier signal. 22
( ) ( )BM out=r t ×c t

 Integrator2: Integrates the product over a bit duration Tb 2
b
T
0
C1= BM out dt

4. Subtractor
 The Subtractor takes the outputs of Correlator 1 (C1) and Correlator 2 (C2) and
computes the difference 12S =C -C

 The subtractor essentially quantifies the correlation strength between the received
signal and the local carrier frequencies f1 and f2.

5. Decision Device:
 The Decision Device compares the output of the Subtractor (S) to make a binary
decision:  
1 S > 0
Detected Output =
0 S 0

 The final output of the Coherent BFSK Demodulator is the binary decision made by
the Decision Device.
 This output is indicative of the binary data that was originally modulated and
transmitted.

b) Non-coherent BFSK Demodulator
 A non-coherent Binary Frequency Shift Keying (BFSK) demodulator is designed to
demodulate a BFSK signal without the need for a reference carrier signal.

 It typically employs two bandpass filters (BPF1 and BPF2), envelope detectors (ED1
and ED2), sampling switches, a comparator.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

1. Received BFSK Signal (r(t)):
The received BFSK signal is typically a sum of two modulated signals with frequencies f1
and f2: '
12 )r t = A×s t ×cos 2πf t +A×s t ×( cos) 2) π) ( ( ( f( t)

2. Bandpass Filters (BPF1 and BPF2):
 BPF1 filters out the component at f1, and BPF2 filters out the component at f2.
 Let x1(t) be the output of BPF1 and x2(t) be the output of BPF2. 11
22
(x t =r t ×cos 2πf)) t( ( )
( ) ( ) ( )x t =r t ×cos 2πf t

 Separate the signal components at f1 and f2 to isolate them for further processing.

3. Envelope Detectors (ED1 and ED2) [Rectifier+LPF]
 Extract the envelope of the filtered signals. The rectification and low-pass filtering help
in obtaining a representation of the amplitude variations. 22
11
y t = x t
y=
( ) ( )
( ) ( )t x t
∣∣
∣∣

4. Sampling Switches (at t=Ts)
 Sample the outputs of the envelope detectors at the symbol rate (Ts) to capture the
variations corresponding to the binary symbols. 11
22
)
z = y Ts
z=
()
(y Ts

5. Comparator
 Compares the sampled outputs and makes a binary decision based on the amplitudes.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24




1 if z > z
12
Detected Output =
0 if z z
12

6. Detected Output: Represents the detected binary data based on the comparison made by
the comparator.

Performance Measure of BFSK

1. Bit Rate (Rb) and Baud Rate (Rbaud)
a) Bit Rate (Rb)
 The bit rate is the number of bits transmitted per unit of time. 1
Rb=
Tb

b) Rate (Rbaud)
 The baud rate is the number of signal changes per second (symbols per second). Rbaud
1
=
Tb

2.Bandwidth(BW)
 Bandwidth is the range of frequencies required to transmit the signal without significant
loss.

 In BFSK, two frequencies (f1 and f2) are used to represent binary 0 and 1.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 The frequency separation between f1 and f2 is often chosen to be approximately equal
to the bit rate (Rb) to avoid intersymbol interference.

 Minimum Bandwidth Requirement: To accurately represent the binary data, the
minimum bandwidth required is approximately equal to the bit rate (Rb).
 Minimum Frequency Separation:For BFSK, the minimum frequency separation
between f1 and f2 is typically 2Rb to accommodate the transitions between the two
frequencies within one bit period. BFSK
BW = Rb+ 2Rb+ Rb= 4Rb

BFSK 1 2BW = f +f = 2Rb+2Rb= 4Rb

3. Power Spectral Density (PSD)
 Power Spectral Density is a measure of how the power of a signal is distributed across
different frequencies. 2
]
A
PSD f = δ f -f1 +( ) [ ( δ f -( f2
2
))

Derivation of Probability of Error(Pe) or Bit Error Rate(BER) of BFSK

 The Probability of Error (Pe) or Bit Error Rate (BER) is important in digital
communication systems, indicating the likelihood of a transmitted bit being received
incorrectly.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

 In digital communication, bits are encoded and transmitted over a channel, where
factors like noise can lead to errors.
 Pe, especially in the presence of additive white Gaussian noise (AWGN), assesses the
probability of making incorrect decisions about transmitted symbols.

Received Signal: (1)( ) ( ) (r t = A×m t +n t)

where:
 A is the amplitude of the carrier signal.
 m(t) is the binary data sequence with values of +1 or -1.
 n(t) is AWGN with zero mean and power spectral density N0/2.

To derive the probability of error (Pe) or Bit Error Rate (BER) for Binary Frequency
Shift Keying (BFSK)

 In BFSK two signals are, c11s t = A cos 2πf t for '0'( ) ( ) and 2 c 2
s t = A cos 2πf t for '1'( ) ( )

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

The energy difference (Ed) between the two symbols:

b
T
2
12
0
E ()d= s t -s)t dt(∣∣


b
c 1 c 2
T
2
0
Ed= A cos 2πf t -A cos 2πf t dt( ) ( )∣∣

(

b
2
c 12
T
2
0
Ed= cos 2 πf t -cos 2π(f t d)t()A

2 2 2
(a - b = a - 2ab + b)


b
22
1 1 2 2
2
c
T
0
Ed )= cos 2 πf t -2cos 2πf t cos 2πf t +cos 2( ( ) ( ( ) πf)td) t(A


b
22
1 1 2 2
2
c
T
22
cc
0
( ( ) ( )E ( )dd= cos 2 πf t dt-2A cos 2πf t cos 2πf t +A c tt ( ))os 2πf dtA

For the first term: 1
b
2
T
0
(cos 2πf t d( ))t

2 1+cos 2x
c
2
(
x()os
)
=



1
b
T
0
1+cosπf t
2
(4 )
dt


bb
TT
1
00
11
=
22
1dt cos πf t d(4 )t

The integral of 1
)c(4osπf t over one period is zero (because it completes one full cycle and
integrates to zero over that interval) 
b
1
+0
2
T


b
1
2
T

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

For the second term, use the trigonometric identity: )2cos A cos B = cos A - B +) co( ) ( ( ) s A + B(
12
2
c t-2A cos 2πf t co f( 2π)( t)ds
 
b
Tb
1 2 1 2
0
2
c
T
0
cos 2π f +f)t dt( ( )cos 2π f - d() t(f)t-A
0

For the third term, similar to the first term:

b
1
2
T





bb2
c
TT
22
Ed=A


2
Ed= A T
cb





d
0
E
Pe=Q
2N

2






2
cb
0
AT
Pe=Q
N






b
e(BFSK)
o
E1
P = erfc
2 2N

Advantages of BFSK

 It has lower probability of error (Pe).
 It provides high SNR (Signal to Noise Ratio).
 It has higher immunity to noise due to constant envelope. Hence it is robust against
variation in attenuation through channel.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Disadvantages of BFSK

 It uses larger bandwidth compare to other modulation techniques such as ASK and
PSK. Hence it is not bandwidth efficient.
 The BER (Bit Error Rate) performance in AWGN channel is worse compare to PSK
modulation.

Applications of BFSK:
1. Wireless Communication:
 Utilized in wireless systems for low-data-rate
applications.
 Commonly employed in devices like remote
controls and sensor networks.
2. Digital Modems:
 Found in digital modems for data
transmission.
 Suitable for scenarios where simplicity and
moderate data rates are sufficient.
3. RFID Systems:
 Used in Radio-Frequency Identification (RFID) systems.
 Applied for communication between RFID tags and readers, particularly in
applications with lower data rate requirements.

III. Binary Phase Shift Keying (PSK)
 Definition: BPSK is a form of binary digital modulation technique in which the Phase
of the high frequency sinusoidal carrier signal is varied accordance with the input binary
data stream by keeping amplitude and frequency of the high carrier are constant is
called BPSK.
 BPSK is also called biphase modulation or phase reversal keying or 2-PSK
 BPSK uses two phase states (0 and 180 degrees) to represent binary 1 and 0.
 The phase of the carrier signal is changed between 0° and 180° by the binary data.
 Mathematically, BPSK signal can be expressed as:

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24
0
1
for binary
for binary





 

c
BPSK
c
( ) '1'V Sin 2πfct
V
π( ) 'V 0'
=
Sin 2 fct

 Phase for '1' bit (ϕ₀): 0 degrees
 Phase for '0' bit (ϕ₁): 180 degrees

BPSK Waveforms

The following is observed.
• When the input binary data changes from 1 to 0 or vice versa, the BPSK output signal phase
shifts from 0° to180° or vice versa.

Constellation Diagram
 A constellation diagram is a graphical representation used in digital communication
systems to visualize the complex-valued symbols that are transmitted over a
communication channel.
 Each point in the diagram represents a symbol, and the position of the point corresponds
to the amplitude and phase of the symbol.
 In BPSK, there are two possible phase states for the carrier signal: 0 degrees and 180
degrees. These two states represent the binary values 0 and 1, respectively. Therefore,

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the constellation diagram for BPSK consists of two points in the complex plane, the
constellation diagram is relatively simple.

Forms of Phase Shift Keying
1. Binary Differential Phase Shift Keying (DBPSK)(Non-Coherent):
 In DBPSK, the phase of the current symbol is compared with the phase of the previous
symbol to determine the information. The phase difference between consecutive
symbols represents a binary 0 or 1.
2. Quadrature Phase Shift Keying (QPSK or 4-PSK):
 QPSK uses four phase states (0, 90, 180, and 270 degrees) to represent two bits per
symbol.
3. Differential Quadrature Phase Shift Keying (DQPSK) (Non-Coherent):
 DQPSK extends the concept of DPSK to quadrature modulation. Instead of using two
phase states as in DBPSK, DQPSK uses four phase states (0, 90, 180, and 270 degrees).
4. 8 Phase Shift Keying (8PSK):
 8PSK uses eight phase states to represent three bits per symbol.
5. 16 Phase Shift Keying (16PSK):
 16PSK uses sixteen phase states to represent four bits per symbol.
6. Quadrature Amplitude Modulation (QAM):
 QAM combines both amplitude and phase modulation. It uses a grid of points in the
complex plane to represent multiple bits per symbol.
7. 16 Quadrature Amplitude Modulation (16QAM):
 16QAM uses a 4x4 grid in the complex plane to represent four bits per symbol
8. Minimum Shift Keying (MSK):

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 MSK is a continuous-phase frequency-shift keying (CPFSK) modulation scheme with
a constant amplitude.
9. Gaussian Filtered Minimum Shift Keying (GMSK):
 GMSK is a form of MSK where the signal is filtered with a Gaussian filter to control
the bandwidth and reduce inter-symbol interference.

BPSK Modulator
The BPSK modulation process involves several stages, including binary data sequence
encoding, Bipolar NRZ encoder, Balanced Modulator, BPSK signal, and Bandpass Filter
(BPF).

1. Binary-data Sequence:
 The binary-data sequence is the digital data that we want to transmit. It consists of a
series of binary values (0s and 1s).
2. Bipolar NRZ Encoder:
 Represent binary data using bipolar Non-Return-to-Zero encoding.
 A '0' bit is represented by a positive or negative voltage, and a '1' bit is represented by
the opposite voltage.

 For example, '0' could be represented by +V and '1' by -V.

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
+v for ’0’ bit
-v for ’1’ bit
=)t(v

3. Balanced Modulator:
 The balanced modulator stage involves multiplying the bipolar NRZ signal with a
carrier signal to generate a BPSK signal.
 This multiplication results in phase inversion for '1' bits. )s t = v t ×cos 2) π( ( ( fct)

Where, s(t) is the modulated signal.
v(t) is the bipolar NRZ signal.
fc is the carrier frequency.
4. BPSK Signal:
The result is a BPSK-modulated signal where the phase of the carrier is shifted between 0
and 180 degrees based on the input binary data. ( ) ( )S t = Acos 2πfct +

Where:
 A is the amplitude of the BPSK signal.
 ϕ is the phase, which alternates between 0 and π based on the encoded data.

5. Bandpass Filtering (BPF):
 Filter the BPSK signal to remove unwanted frequency components.
 The BPF allows only the desired frequency (carrier frequency) to pass through.

Coherent BPSK Demodulator
A Coherent Binary Phase Shift Keying (BPSK) demodulator is designed to extract the original
binary data from the received BPSK signal. The process involves several stages, including
bandpass filtering, correlation, and decision-making.

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1. Received BPSK Signal:
The received BPSK signal, denoted as R(t), contains the modulated information. ( ) ( )R t = Acos 2πfct +

Where:
 A is the amplitude of the BPSK signal.
 fc is the carrier frequency.
 ϕ is the phase, representing the encoded binary data.
2. Bandpass Filtering (BPF):
The received signal is passed through a Bandpass Filter (BPF) to isolate the desired
frequency component. filtered
( ) ( ) ( )R t = R t *h t

Where:
 Rfiltered(t) is the filtered received signal.
 h(t) is the impulse response of the Bandpass Filter.

3. Correlation (Balanced Modulator + Integrator):
The correlation stage involves multiplying the filtered signal with a locally generated carrier
signal and then integrating the result over a bit period. 0
0
)
T
dtfiltered
Cτ = R t ×c t( ) ( os 2π(c) f+

Where:
 C(τ) is the correlation function over the bit period.
 τ is the time delay.
 T is the bit period.
 ϕ0 is the assumed phase reference.
4. Decision Device:
The decision device compares the correlation output to a threshold and makes a decision
about the transmitted bit. 
1 if Cτ > Threshold
Decision =
0 Otherwis
()
e

5. Detected Output:
The detected output represents the estimated binary data based on the decision device's
output.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Non Coherent BPSK Demodulator
In practical communication systems, coherent demodulation is commonly preferred for BPSK.
Coherent demodulation, involving the accurate tracking and correction of the carrier phase at
the receiver, offers enhanced robustness, particularly in the presence of noise.

1. Challenges in Noncoherent Demodulation:
 Noncoherent demodulation of BPSK can be challenging, especially in the presence
of noise.
 BPSK relies on phase information, and when the carrier phase is corrupted by noise,
recovering the correct phase becomes difficult without coherent demodulation.
2. Impact of Phase Shifts in Noisy Conditions:
 In the presence of noise, significant phase shifts in the BPSK signal can occur.
 Envelope detection becomes less accurate when the signal experiences substantial
phase shifts due to noise.
3. Higher Bit Error Rate (BER):
 Noncoherent demodulation, especially using envelope detection, may result in a
higher bit error rate (BER) in noisy conditions.

Performance Measure of BPSK
1. Bit Rate (Rb) and Baud Rate (Rbaud)
a) Bit Rate (Rb)
 The bit rate is the number of bits transmitted per unit of time. 1
Rb=
Tb

b) Rate (Rbaud)
 The baud rate is the number of signal changes per second (symbols per second). Rbaud
1
=
Tb

2.Bandwidth(BW)
 Bandwidth is the range of frequencies required to transmit the signal without
significant loss.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

11
( ) ( )fc fc
Tb Tb
    
BPSKBW
( ) ( )fc Rb fc Rb    
BPSKBW = 2Rb

3. Power Spectral Density (PSD)
]
Pavg
S f = δ f -fc +( ) [ ( δ f +( fc
2
))

Derivation of Probability of Error(Pe) or Bit Error Rate(BER) of BPSK

 The Probability of Error (Pe) or Bit Error Rate (BER) is important in digital
communication systems, indicating the likelihood of a transmitted bit being received
incorrectly.

 In digital communication, bits are encoded and transmitted over a channel, where
factors like noise can lead to errors.

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 Pe, especially in the presence of additive white Gaussian noise (AWGN), assesses the
probability of making incorrect decisions about transmitted symbols.

Received Signal: (1)( ) ( ) (r t = A×m t +n t)

where:
 A is the amplitude of the carrier signal.
 m(t) is the binary data sequence with values of +1 or -1.
 n(t) is AWGN with zero mean and power spectral density N0/2.

To derive the probability of error (Pe) or Bit Error Rate (BER) for Binary Phase Shift
Keying (BPSK)

 In BPSK two signals are , 1
)s t = Ac() s(oωt and 2
 )s t = Aco( s(ωt)
ω is the angular frequency of the signal.

The energy difference (Ed) between the two symbols:

b
T
2
12
0
E ()d= s t -s)t dt(∣∣

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
b
T
2
0
E ω( ( ))d= 2Acos t dt

b
22
T
0
(E )d= cos ωt dt4A
2 1+cos 2x
c
2
(
x()os
)
=
 
b
2
T
0
s((d )+ )E = 2 1 co 2 ωt dtA

1
cos ax dx =()
a
()sin ax




b
T
2
0
Ed= 2A
1
T+ sin )2ωt(
2ω




2 1
T+ sin 2 -((ωT sin 0
2ω
( ) ))Ed= 2A



2 1
T+ si )n2ωT
2ω
(Ed= 2A

Now, for BPSKb
T
2π
ω= 


2 4
T
πT
En ()d=2A T+ si T
π



2 T
Ei (4 )d=2A T+ s n π
π



2
×0
T
Ed=2A T+
π

b
2
TEd=2A




d
0
E
Pe=Q
2N





2
cb
0
2A T
Pe=Q
2N

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



b
0
E
Pe= Q
N





b
e(BPSK)
o
E1
P = erfc
2N

Advantages of BPSK
 Bandwidth Efficiency: BPSK provides better bandwidth efficiency compared to some
other modulation schemes, allowing for more data to be transmitted in a given
bandwidth.
 Less Power Consumption: BPSK consumes power compared to alternative methods
making it advantageous for battery powered devices.
 Compatible: BPSK serves as a building block for complex modulation schemes like
QPSK (Quadrature Phase Shift Keying) and higher order Quadrature Amplitude
Modulation (QAM).

Disadvantages of BPSK
 Sensitivity to Phase Ambiguity: BPSK is sensitive to phase ambiguities, which can
lead to decoding errors if not properly addressed.
 Limited Error Correction: BPSK does not provide as much inherent error correction
capability as more complex modulation schemes, therefore, error correction needs to
be added separately, which can increase system complexity.

Applications of BPSK
1. Wireless Communication: BPSK is commonly used in wireless communication
systems, such as Wi-Fi and Bluetooth.
2. Satellite Communication: BPSK is employed in satellite communication for its
simplicity and robustness against noise.
3. RFID Systems: BPSK is used in Radio-Frequency Identification (RFID) systems for
data transmission between tags and readers.
4. Underwater Communication: BPSK is suitable for underwater acoustic
communication due to its ability to handle the challenges of the underwater channel.

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4.Differential Binary Phase Shift Keying (DBPSK)
 Definition: DBPSK is alternative form of BPSK where the binary data information
is contained in the difference between the phases of two successive signaling
elements rather than the absolute phase. 
() nnDBPSK t
()s = Acos 2πfct+ - -1

Where:
 ϕn is the phase of the current symbol.
 ϕn−1 is the phase of the previous symbol.
DBPSK combines two key concepts:
a) Differential Encoding: The encoding process involves representing binary 1s and 0s
based on the phase difference between the current and previous bits.
b) Phase Shift Keying (PSK): It modulates the binary data onto the carrier signal by
shifting the phase.

 DBPSK is a no coherent modulation scheme, meaning that the receiver doesn't need a
phase reference from the transmitter to demodulate the signal. It relies on changes in
phase rather than absolute phase values.i.e., Non-coherent version of BPSK

DBPSK Waveforms

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DBPSK Modulator
Differential Binary Phase Shift Keying (DBPSK) is a type of digital modulation where the
phase of the carrier signal is shifted to represent binary data differentially.

Binary Data Sequence (Input):
 A binary data sequence, denoted as bk, is the input information to be transmitted. Each
bk can be either 0 or 1.

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Encoder or Logic Circuit (XNOR):
 The binary data sequence is processed by an encoder or logic circuit, typically an
XNOR gate.
 The output of the encoder is a signal sk representing the XNOR of the current bit and
the previous bit: 1
kkk
s b b  

 If the current bit (bk) is the same as the previous bit (bk−1), the output sk is 1.
 If the current bit (bk) is different from the previous bit (bk−1), the output sk is 0.

Delay (Tb):
 The signal sk is then delayed by one bit period (Tb), creating a delayed version sk−1.

Bipolar NRZ Line Encoder:
 The delayed signal sk−1 is used to modulate the amplitude of the carrier signal.
 A Bipolar Non-Return-to-Zero (NRZ) line encoding is often used, where 0 is
represented by negative voltage, and 1 is represented by a positive.

Balance Modulator:
 The bipolar NRZ signal is multiplied by the carrier signal to introduce phase shifts
based on the encoded data.
 The balance modulator output is given by: k )Ac×s -1×co(s2πfct

where Ac is the carrier amplitude, fc is the carrier frequency, and t is time.

Bandpass Filter (BPF):
 The output of the balance modulator is passed through a bandpass filter to filter out
unwanted frequency components and shape the signal.

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DBPSK Signal (Output):
 The filtered signal represents the DBPSK-modulated signal y(t), given by: 
k
+)y t =Ac×s -1×cos 2π(ct() f

where ϕ is the phase corresponding to the differential encoding.
 This signal can then be transmitted through the communication channel.

DBPSK Demodulator(Non-Coherent)
The non-coherent demodulation of Differential Binary Phase Shift Keying (DBPSK) involves
recovering the original binary data from the received signal without the need for a phase-locked
loop

Received DBPSK Signal (Input):
 The received DBPSK-modulated signal, denoted as r(t), is the input to the demodulator.

Bandpass Filter (BPF):
 The received signal is passed through a bandpass filter (BPF) to filter out unwanted
frequency components and shape the signal.

Encoder or Logic Circuit (XNOR):
 The filtered signal is processed by an encoder or logic circuit, typically an XNOR gate.
 The output of the encoder, denoted as sk, represents the XOR of the current bit and the
delayed version of the current bit: ( ) ( )
kb
s r t r t T  

Delay (Tb):
 The received signal is delayed by one-bit period (Tb), creating a delayed version ()
br t T

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Correlator (Balanced Modulator + Integrator):
 The output of the encoder is used to modulate the delayed signal using a balanced
modulator.
 The balanced modulator output is integrated over a period of Tb, typically using a low-
pass filter or integrator.
 The correlator output is given by: ()()
k
b
t
tT
s r t dtyt




Decision Device:
 The decision device compares the correlator output y(t) with a threshold. ()
0, (
1,
)
()
if y t T
if y t T
yt








Detected Output:
 The detected output is the binary data sequence, denoted as b^k, based on the decision
made by the decision device.

DBPSK Transmitter and Receiver Operation

Example:1
A binary data sequence 0 0 1 0 0 1 1 is to be transmitted using DBPSK. Show the step-by-step
procedure of generating and detecting DBPSK signal. Assume arbitrary starting reference bit
as 0.

Example:2
A binary data sequence 0 0 1 0 0 1 1 is to be transmitted using DBPSK. Show the step-by-step
procedure of generating and detecting DBPSK signal. Assume arbitrary starting reference bit
as 1.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Performance Measure of DBPSK
1. Bit Rate (Rb) and Baud Rate (Rbaud) Rbaud
1
Rb = =
Tb

2.Bandwidth(BW) and Power Spectral Density (PSD)
 Bandwidth is the range of frequencies required to transmit the signal without
significant loss.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

ccbbDBPSKBW = (f +f )-(f -f )
bDBPSKBW = 2f
s b b
DBPSK
2 2 1
==
T 2T T
BW =
bDBPSK
BW =f

3.Probability of Error (Pe) or Bit Error Rate (BER)
b
0
-E
N
e(DBSK)
1
P = e
2

Advantages of DBPSK:
1. Resilience to Phase Ambiguity: DBPSK is less susceptible to phase ambiguities, as it
relies on changes in phase rather than absolute phase values.
2. Simplicity: Like BPSK, DBPSK is relatively simple to implement, making it suitable
for practical applications.
3. Suitable for Noisy Environments: It performs better than BPSK in environments with
phase noise, making it suitable for certain communication scenarios.

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Disadvantages of DBPSK:
1. Lower Data Rate: Compared to more complex modulation schemes, DBPSK may
have a lower data rate.
2. Limited Spectral Efficiency: The spectral efficiency of DBPSK may not be as high as
more advanced modulation techniques.
3. Not Ideal for High-Speed Applications: DBPSK might not be the best choice for
high-speed data transmission due to its inherent limitations.

Applications of DBPSK:
1. Wireless Communication Systems: DBPSK is used in wireless communication
systems, particularly in scenarios where phase changes are more reliable than absolute
phase values.
2. Power-Line Communication: It finds applications in power-line communication
systems where simplicity and robustness are essential.
3. Satellite Communication: DBPSK can be employed in satellite communication
systems where noise and phase distortions are common.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Comparison of BASK, BFSK, BPSK and DBPSK

Parameter BASK BFSK BPSK DBPSK

Definition
The carrier signal's amplitude is
switched between two levels to
encode the digital information.
The carrier signal's frequency is
switched between two
predetermined values to convey
digital data.
The phase of the carrier is shifted by
180 degrees to indicate a change in
the binary state.
DBPSK is a variation of BPSK where the
phase changes are relative to the previous bit
rather than an absolute phase reference.

Modulated
Signals 1
)s t = A×cos 2π)( fct(
And 2
s(t)=0
11
)s t = cos 2(πf( t)

And 22
)s t = cos 2(πf( t)
11
)s t = cos 2(πf( t)

And 
2
( ) ( )s t = cos 2πfct +


1
)s)t = os((c

And 
2
( ) ( )s t = cos

() nnDBPSK t
()s = Acos 2πfct+ - -1

Bandwidth bBASK
BW =2f

bBFSK
BW =4f

bBPSK
BW =2f

bDBPSK
BW =f

Pe or BER 



b
e(BASK)
o
E1
erfc
2 4N
P=




b
e(BFSK)
o
E1
erfc
2 2N
P= 



b
e(BPSK)
o
E1
erfc
2N
P= b
0
-E
N
e(DBSK)
1
e
2
P=
Sensitivity to
Noise and
Efficiency
Susceptible to amplitude
variations
Susceptible to frequency
variations
Susceptible to phase variations Improved due to differential encoding

Demodulation

Both Coherent and Non-Coherent

Both Coherent and Non-Coherent

Coherent Only

Non-Coherent Only
Complexity of
Receiver
Simple Simple More complex than BASK and
BFSK
More complex than BPSK
Application Limited (used in optical fiber
communication)
Used in wireless communication,
RFID, Bluetooth
Used in digital communication,
PSK31
Used in wireless communication, RFID,
Bluetooth, Zigbee

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Probability Error (Pe) Comparison of BASK, BFSK, BPSK and DBPSK

M-ary Modulation Techniques
1. Quadrature Phase Shift Keying (QPSK)/4-PSK/M-ary PSK
 M-ary Quadrature Phase Shift Keying (QPSK), often referred to as 4-PSK, is a
modulation scheme used in digital communication systems.
 In QPSK, each symbol represents multiple bits, and the term "m-ary" indicates the
number of different phase shifts used to encode these bits.
 In the case of 4-PSK (QPSK), there are four possible phase shifts, and each phase shift
corresponds to a unique combination of two bits known as dibits.
 QPSK has four different phase shifts, separated by multiples of 90°or π (360/4=90) of
the carrier signal, vc(t) = Vc cos (2pfct).
 Four output phases are possible for a single carrier frequency, corresponding to 00, 01,
11, and 10 dibits.
 Each dibit code generates one of the four possible output phases (0°, + 90°, 180°, 270°).
 A single change in output phase occurs for each two-bit (dibit).
 The rate of change at the output (baud) is equal to one-half the input bit rate.

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Mathematically, the QPSK signal for one symbol duration, consisting of two bits each,
can be expressed as:
 
 





  







cc
cc
cc
cc
QPSK
V cos 2pf t
π
V cos 2pf t +
2
3π
V
V
cos 2pf

for 00
for 01
(t) =
for 1
2
1
f
t+
V cos 2 + or 10pf tπ

The relationship between symbols, bits, and phase shifts in QPSK carrier signal

Symbol In-phase (I) Quadrature (Q) Phase Shift
S1 0 (-1v) 0 (-1v) 0° (0 radians)
S2
0(-1v) 1 (+1v) 90° 2



radians
S3
1 (+1v) 1 (+1v) 180° radians
S4
1 (+1v) 0 (-1v) 270° 3
2



radians

 Note: The choice of how to assign phase shifts to binary values (bits) in QPSK is
somewhat arbitrary, and different standards or implementations may use different
mappings.

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QPSK Waveforms
For the input binary data sequence 1 0 1 0 0 0 1 1, draw the step-by-step QPSK signal
waveforms.

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QPSK Modulator
 Quadrature Phase Shift Keying (QPSK) is a digital modulation scheme that transmits
two bits of data per symbol by changing the phase of the carrier signal.
 QPSK modulator involves two balanced modulators and an adder.

Binary Input Data Stream
 The input is a binary data stream b1,b2,b3,… with a data rate of fb bits per second.
 Each pair of bits is mapped to a complex symbol. QPSK uses four possible symbols,
each representing two bits: 00,01,10,11.

Bipolar NRZ Encode and 2-bit Serial-to-Parallel Converter
 The binary data is first encoded using Bipolar Non-Return-to-Zero (NRZ) encoding.
 In this encoding scheme, binary '0's are represented by negative voltage level, and
binary '1's are represented by positive voltage levels.
 The encoded data stream is then converted from a serial format to a parallel format by
grouping every 2 bits together.
 This is done to create separate streams for the in-phase (I) and quadrature (Q)
components.

Balance Modulator 1 (in-phase (I) I(t)):
 The in-phase (I) component is modulated using a balance modulator with a carrier
signal cos(2πft), where 'f' is the carrier frequency.
 The equation for the modulated signal is given by 1
( ) ( ) ( )v t = I t cos 2πft

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Balance Modulator 2 (quadrature (Q) Q(t)):
 The quadrature (Q) component is modulated using another balance modulator, but
with a carrier signal sin(2πft).
 The equation for the modulated signal is given by 2
( ) ( ) ( )v t = Q t sin 2πft

The angle θ determines the phase relationship between I and Q components

Adder for QPSK:
 The outputs of the two balance modulators are added together to obtain the final
QPSK signal. The equation for the QPSK signal is given by 12
)v t = v t) ( )v(( +t (QPSK)t
1
v ]= I t cos 2πfct -Q t sin 2πfct
2
[ ( ) ( ) ( ) ( )

Where,
 vQPSK(t) is the QPSK modulated signal.
 I(t) is the in-phase component.
 Q(t) is the quadrature component.
 fc is the carrier frequency.
 1
2 is a normalization factor, which is common in QPSK to ensure that the average
power of the signal is constant.

Bandpass Filter (BPF):
A Bandpass Filter is often used to filter out unwanted frequency components and shape the
spectrum of the QPSK signal.

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Coherent QPSK Demodulator
A coherent QPSK (Quadrature Phase Shift Keying) demodulator is designed to recover the
original binary data from the received QPSK modulated signal while maintaining phase
coherence with the carrier signal.

Let the received QPSK signal be denoted as r(t).

Power Splitter:
he received signal r(t) is split into two branches: one for the in-phase (I) component and the
other for the quadrature (Q) component.

Correlator 1(Balance Modulator M1+ Integrator 1):
 Multiplies the I branch by a coherent in-phase carrier signal cos(ωct), where ωc is the
carrier frequency.
 Integrates the product over a bit period Tb 
b
T

0
Correlator 1 Output = M1 I ×cosωct)t( ) ( d

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Correlator 2(Balance Modulator M2+ Integrator 2):
 Multiplies the Q branch by a coherent quadrature carrier signal sin(ωct).
 Integrates the product over a bit period Tb 
b
T

0
Correlator 2 Output = M2 I ×sinωct)t( ) ( d

MUX (Multiplexer)
Combines the outputs of Correlator 1 and Correlator 2. MUX Output = Correlator 1 Output +Correlator 2 Output

The detected signal is typically passed through a thresholding or decision-making process to
obtain the demodulated binary data

Carrier Recovery Circuit
The purpose of the carrier recovery circuit is to synchronize with the carrier frequency of the
incoming signal, which might have phase variations due to channel effects. 4
)
1
Recovered Carrier = ×BPF Detected Output
4
(

 Raised to 4 Power: This operation is often employed in QPSK demodulation to
accentuate phase changes associated with the carrier frequency.

 Bandpass Filter (BPF): A Bandpass Filter is applied to pass frequency components
around four times the carrier frequency (4fc). This is done to isolate the carrier
frequency and its multiples from other unwanted frequency components.

 Divide by 4: The filtered signal is then divided by 4. This division is necessary to
normalize the recovered carrier signal.

The recovered carrier signal is now synchronized with the carrier frequency of the incoming
signal. It is then used to demodulate the in-phase and quadrature components of the QPSK
signal.

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Performance Measures of QPSK

1. Bit Rate (Rb)
For QPSK, each symbol represents 2 bits because QPSK can transmit 2 bits per symbol.
Therefore, the bit rate (Rb) for QPSK b
R = 2×Baud rate
i.e. 2 bits per second

2.Baud Rate (Rbaud)
For QPSK, each symbol represents 2 bits, so the baud rate (Rb) is half of the bit rate baud
Bit rate
R=
2

3.Bandwidth(BW) and Power Spectral Density (PSD)

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4.Probability of Error (Pe) or Bit Error Rate (BER) 



b
e(QPSK)
bo
2E1
erfc
2 R N
P=

Advantages of QPSK:

1. Spectral Efficiency: QPSK provides higher spectral efficiency compared to binary
modulation schemes like Binary Phase Shift Keying (BPSK) because it can transmit
two bits per symbol.
2. Error Performance: QPSK exhibits good error performance, especially in the
presence of noise and interference, making it suitable for communication systems
where reliability is crucial.
3. Bandwidth Efficiency: QPSK allows for more efficient use of available bandwidth,
making it suitable for applications where bandwidth is limited.
4. Robustness to Fading: QPSK is more robust to multipath fading compared to simpler
modulation schemes. This makes it suitable for wireless communication systems where
signals may encounter varying channel conditions.

Disadvantages of QPSK:

1. Complexity: Implementing QPSK requires more complex hardware and software
compared to simpler modulation schemes. This complexity can translate to higher costs
and power consumption.
2. Higher Symbol Rate: QPSK typically has a higher symbol rate than simpler
modulation schemes, which may pose challenges in some communication scenarios,
especially when there are restrictions on the symbol rate.
3. Vulnerability to Phase Noise: QPSK is sensitive to phase noise, which can degrade
its performance in some communication environments.

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Applications of QPSK:

1. Wireless LANs: QPSK is used in some wireless LAN (Local Area Network) standards,
providing a balance between data rate and robustness.
2. Satellite Communication: QPSK is commonly employed in satellite communication
systems due to its ability to handle the challenges posed by the satellite channel, such
as noise and fading.
3. Digital Audio Broadcasting (DAB): QPSK is used in DAB systems to efficiently
transmit digital audio signals.
4. Digital Video Broadcasting (DVB): QPSK is used in some DVB standards for the
transmission of digital television signals.

2. Offset Quadrature Phase Shift Keying (OQPSK)
 In QPSK, two bits are represented by each symbol, and the phase of the carrier signal
symbol can allow the phase of the signal to jump by as much as 180° at a time.
 When the signal is low-pass filtered (as is typical in a receiver), these phase-shifts result
in large amplitude fluctuations, an undesirable quality in communication systems.
 OQPSK introduces an offset in the timing of the quadrature components (I and Q) to
reduce the abrupt changes in the signal, which can help in minimizing problems like
spectral splatter and bandwidth efficiency.
 The "offset" in OQPSK refers to the fact that the transitions between symbols occur at
the midpoint of the bit period, rather than at the edges. This helps to avoid sudden
changes in the signal, making it more suitable for communication systems where
minimizing bandwidth and power usage is important.

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 OQPSK is obtained by introducing a shift or offset equal to one bit delay (Tb) in the
Quadrature signal Q(t).
 Mathematically, the OQPSK signal can be expressed as:

 In the constellation diagram shown on the right, it can be seen that this will limit the
phase-shift to no more than 90° at a time. There is never more than a 90° phase shift in
the output phase.

 This yields much lower amplitude fluctuations than non-offset QPSK and is sometimes
preferred in practice.

Performance Measures of OQPSK: Same as QPSK

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3.Differential Quadrature Phase Shift Keying Demodulator(DQPSK)
Differential Quadrature Phase Shift Keying (DQPSK) is a variant of QPSK that encodes data
by modulating the phase difference between successive symbols rather than the absolute phase
of each symbol.

DQPSK Modulator

Non-Coherent DQPSK Demodulator

Probability of Error (Pe) or Bit Error Rate (BER) of DQPSK




b
e(DQPSK)
o
2E1
erfc
2N
P=

For DQPSK, Es is related to Eb (energy per bit) : Es= Eb×Rb





bb
e(DQPSK)
o
2E ×R1
erfc
2N
P=

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Parameter QPSK OQPSK DQPSK
Encoding N/A (Absolute phase
modulation)
Uses offset to encode
information
Modulates phase difference
between symbols
Max Phase
Shift π
2
π
π

BER
Equation 



b
e(QPSK)
bo
2E1
erfc
2 R N
P=




b
e(QPSK)
bo
2E1
erfc
2 R N
P= 



bb
e(DQPSK)
o
2E ×R1
erfc
2N
P=
Demodulation Coherent Coherent Non-coherent
Receiver
Complexity
Moderate Moderate Lower (due to non-coherent
detection)

4. Quadrature Amplitude Modulation/Quadrature Amplitude Shift Keying
(QAM/QASK) (M-ary ASK+PSK)

Quadrature amplitude modulation (QAM), also called Quadrature amplitude shiftkeying
(QASK), is a form of digital modulation similar to PSK except the digital information is
contained in both the amplitude and the phase of the modulated signal.

 QAM can either be considered a logical extension of QPSK or a combination of ASK
and PSK.

 QAM is an efficient way to achieve high data rates with a narrowband channel by
increasing the number of bits per symbol, and uses a combination of amplitude and
phase modulation.
 It conveys data by modulating the amplitude of two signal waves, known as the in-
phase (I) and quadrature (Q) components.

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 The term "quadrature" refers to the use of two orthogonal (perpendicular) signal
components. By varying the amplitude of these components independently, multiple
bits of information can be encoded in each symbol.
 The higher the number of amplitude levels (constellations), the more bits can be
transmitted per symbol, allowing for increased data rates.

 For example, a common QAM constellation is 8-QAM, where each symbol represents
three bits (2^3 = 8 possible combinations). More advanced constellations like 16-
QAM,64-QAM and 256-QAM are also used in high-speed communication systems but
may be more susceptible to noise and interference.

 The modulation equations for QAM can be expressed as follows: )st( ) ( )t = Icos 2πfc +Qsin 2(πfct

Waveform: 8-QAM

Constellation Diagram

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8-QAM Modulator

Input Data (fb):
This is the incoming data with a symbol rate (data rate) of 'fb.'

Bit Splitter (QIC):
The incoming data is split into three-bit groups (tribits) named I, Q, and C. Each with a bit rate
equal to one-third of the incoming data rate.

I Channel
 2-to-4 Level Converter 1 (I Channel): This block converts the incoming I bits from 2
levels to 4 levels. This conversion process is often done using a mapping that represents
2 bits as one symbol (level) in the 4-level system. Converts the binary I-channel input
into a 4-level PAM (Pulse Amplitude Modulation) signal. 1
, 0 / 2()
PAM
I t A for t T   

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 PAM (Pulse Amplitude Modulator) 1 (I Channel): The output from the 2-to-4 Level
Converter 1 modulates the amplitude of the pulse. The amplitude is determined by the
logic condition of the I bits. 11
( ) ( ) ( )2
mod PAM
I t I t sin fct

Q Channel:
 2-to-4 Level Converter 2 (Q Channel): Similar to the I channel, this block converts
the incoming Q bits from 2 levels to 4 levels. Similar to the I channel, it converts the
binary Q-channel input into a 4-level PAM signal. 2
, 0 / 2()
PAM
Q t A for t T   

 PAM 2 (Q Channel): The output from the 2-to-4 Level Converter 2 modulates the
amplitude of the pulse in the Q channel. 22
( ) ( ) ( )2
mod PAM
Q t Q t cos fct

Linear Summer:
The PAM signals from the I and Q channels are combined in the linear summer. The linear
summer takes care of the addition or subtraction of the signals based on the logic conditions of
the I and Q bits. 12
( ) ( ) ( )
mod mod
S t I t Q t

Bandpass Filter (BPF):
The combined signal from the linear summer is passed through a bandpass filter. The purpose
of the bandpass filter is to filter out unwanted frequency components and retain only the desired
frequency band. ()
{ ( )}
BPF t
S BPF S t

8-QAM Output:
The filtered signal is the 8-QAM modulated signal, where each symbol represents a
combination of three bits. 8
( ) ( )
QAM BPF
S t S t
QAM
= Icos 2πf )Vct +Qs(t) ( ) in 2πfct(

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8-QAM Coherent Demodulator

8-QAM Input:
The incoming signal consists of symbols modulated using 8-QAM. = Icos 2πfct )R+Qsi( n2) π(t ( fct)

Power Splitter:
The incoming signal is split into two paths, I (In-phase) and Q (Quadrature).

Carrier Recovery:
The carrier recovery block is responsible for extracting the carrier frequency information from
the received signal. This is essential for coherent demodulation.

I Channel: ()
)sin 2(
I t i i
R A fct

 Product Modulator 1: Multiplies the incoming signal with the in-phase carrier signal. s( ) ( ) ( )in 2
I
I t R t fct

 4-level PAM (Pulse Amplitude Modulation): Converts the analog signal into a 4-
level PAM signal, where each symbol represents 2 bits.

 A to D Converter 1: The output of the 4-level PAM is a quantized version of the analog
signal, and the A to D conversion provides a digital representation.

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Q Channel: ()
(2 )
Q t q q
R A cos fct

 Product Modulator 2: Multiplies the incoming signal with the quadrature carrier
signal. c( ) ( ) ( )os 2
Q
Q t R t fct

 4-level PAM: Similar to the I channel, it converts the analog signal into a 4-level PAM
signal.
 A to D Converter 2: The output of the 4-level PAM is a quantized version of the analog
signal, and the A to D conversion provides a digital representation.

QIC (Quadrature to In-phase Conversion) Parallel to Serial Converter: Converts the
parallel streams of digital data from the I and Q channels into a serial data stream.

Clock Recovery: Recovers the clock signal from the received serial data to synchronize the
demodulator with the incoming data.

QIC Output Data Bits: The final output of the demodulator is the recovered data bits from
both I and Q channels.

Performance Measures of 8-QAM

1. Bit Rate (Rb) b
R = 3×Baud rate
i.e. 3 bits per second

2.Baud Rate (Rbaud) baud
Bit rate
R=
2

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3.Bandwidth(BW) and Power Spectral Density (PSD)

The bandwidth of M-ary QAM signal is given by M-aryQAM b
2
BW = ×R
m

Where m is the number of bits and fb is the input bit rate.

 For M = 8 or m = 3, 8-QAM b
2
BW = ×R
3
 For M = 16 or m = 4, 16-QAM b
1
BW = ×R
2

4.Probability of Error (Pe) or Bit Error Rate (BER)




b
0
3×E1
Pe = erfc
2 2×k×N

Where:
 Pe is the probability of error.
 Eb is the energy per bit.
 k is the number of bits per symbol (for QAM, this is the log2 of the modulation order,
e.g., 3 bits for 8-QAM).
 N0 is the one-sided power spectral density of the noise.

Note: The factor of 3 in the numerator of the square root is specific to QAM.

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5. M-ary FSK (Multiple frequency-shift keying (MFSK))

Multiple frequency-shift keying (MFSK) is higher level version of FSK modulation technique, in
which more than two frequencies are used.

 Unlike Binary Frequency Shift Keying (BFSK), which uses only two frequencies to represent
binary data, MFSK employs more than two frequencies, making it suitable for transmitting
multiple bits per symbol.
 The general expression for the transmitted MFSK signal for one signal element duration is
given by ()
(2 1)
ciMFSK t
v V cos f t for i M  

 The frequency fi for each signal element is given by the formula i c i d
f = f + 2 -1( M)-f

where:
 Vc is the amplitude of the carrier signal,
 fi is the frequency of the i-th signal element,
 fc is the carrier signal frequency,
 fd is the frequency difference between consecutive signal elements,
 M is the number of different signal elements (m
M = 2 , where m is the number
of bits per signal element).
Example:
Now, let's consider an example with 4-FSK (M = 4), where fc=250 kHz, fd=25 kHz, and
m=log2(M)=log2(4)=2 (since M=2
m
) i c i d
f = f + 2 -1( M)-f

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This table illustrates how each pair of binary bits is mapped to a specific frequency in the 4-
FSK modulation scheme.

MFSK Modulator
In MFSK, multiple discrete frequencies are used to represent different symbols or bits. The
modulator takes in a digital input sequence and maps each symbol to a specific frequency.

Input Sequence (b(t)):
 The input sequence b(t) is a digital signal that typically represents binary data.
 Each symbol in the sequence represents a group of bits, and the entire sequence is to be
transmitted over a communication channel.

Serial to Parallel Converter:
 The serial to parallel converter takes the input bitstream b(t) and converts it into parallel
streams b0, b1, b2, ..., bn-1.
 Each of these parallel streams corresponds to a specific bit in the input sequence.

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N-bit Digital-to-Analog Converter (DAC):
 The N-bit digital-to-analog converter converts each of the parallel streams (b0, b1, b2,
..., bn-1) into an analog signal.
 The output of the DAC represents the amplitude or voltage level associated with each
bit.

Clock at Every Ts:
 The clock signal is used to synchronize the operations of the modulator.
 It ensures that each bit is processed at the correct time and helps in maintaining the
timing and synchronization of the transmitted signal.

Modulation Signal (sm(t)):
 The modulation signal sm(t) is generated based on the output of the digital-to-analog
converter.
 For MFSK, this signal will have multiple frequencies, each corresponding to a different
symbol or bit.
 The modulation signal represents the information to be transmitted and is used to
modulate the carrier signal.

Frequency Modulator:
 The frequency modulator takes the modulation signal sm(t) and modulates it onto a
carrier signal.
 In MFSK, each frequency corresponds to a different symbol or bit.
 The carrier frequency is shifted based on the frequency of the modulation signal at each
symbol time.

Output Signal (s(t)):
The final output signal s(t) is the modulated signal that carries the information from the input
sequence. It is the result of the carrier signal being modulated by the MFSK modulation
technique. 
N-1
kk
k =0
()f ×m t )s t = A×cos 2πfct+)( π( 2

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Where:
 A is the amplitude of the carrier signal.
 fc is the carrier frequency.
 N is the number of frequency levels (MFSK modulation order).
 fk is the frequency associated with the k-th symbol.
 mk(t) is the baseband modulation signal corresponding to the k-th symbol.

MFSK Demodulator

Received Signal (s(t)):
The received signal s(t) is the modulated signal that has passed through the communication
channel and is now received at the demodulator.

Bandpass Filters at ,f1,…,fm−1:
 The received signal s(t) is passed through m bandpass filters, each centered at a specific
frequency corresponding to the frequencies used in the MFSK modulation.
 These bandpass filters isolate the individual frequency components in the received
signal.
Envelope Detectors (Envelop Detectors 1, 2, 3, ..., m):
 Each bandpass-filtered signal is then fed into an envelope detector.
 The envelope detector extracts the envelope or magnitude of the filtered signal,
effectively demodulating it and producing a baseband signal.

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I
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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

kk
K=argmax Envelope Detector∣∣

Where:
 k^ is the estimated transmitted symbol.
 Envelope Detector k represents the output of the k-th envelope detector.

Decision Device (Selecting Largest Output):
 The outputs from the envelope detectors represent the demodulated signals
corresponding to different frequencies.
 The decision device compares these outputs and selects the one with the highest
amplitude, as it corresponds to the transmitted frequency.
 This is typically done by choosing the maximum output among the m envelope detector
outputs.

N-bit Analog-to-Digital Converter (ADC):
 The output of the decision device, which represents the demodulated symbol, is then
converted from analog to digital using an N-bit analog-to-digital converter.
 This process quantizes the analog signal into a digital representation.

Parallel to Serial Converter:
 The digital outputs from the ADC are in parallel form, with each bit corresponding to
a specific frequency or symbol.
 The parallel-to-serial converter combines these bits into a serial bitstream.

Output Binary Data Sequence (b(t)):
 The final output is the binary data sequence b(t), which represents the demodulated
information.
 This binary data sequence is a digital representation of the original data that was
modulated and transmitted.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Performance Measures of MFSK
1. Bit Rate (Rb)
For MFSK, where each symbol represents multiple bits, the bit rate is given by the product of
the baud rate and the number of bits per symbol. b baud 2
)R = R log(×M

Where, M is the number of frequencies used in MFSK.
2.Baud Rate (Rbaud) baud
R = M

where M is the number of frequencies.
3.Bandwidth(BW) and Power Spectral Density (PSD)

4.Probability of Error (Pe) or Bit Error Rate (BER)

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Effect of Inter Symbol Interference(ISI)
 Intersymbol Interference (ISI) is a phenomenon that occurs in communication systems,
 ISI happens when the symbols transmitted in a digital signal spread and overlap with
each other in time, making it challenging to distinguish one symbol from another at the
receiver.

Causes of ISI:
1. Channel Dispersion: This is a major cause of ISI. Dispersion occurs when different
frequency components of a signal travel at different speeds through a communication
medium. As a result, the symbols spread out in time and overlap, leading to
interference.
2. Bandwidth Limitations: Limited bandwidth of the communication channel can also
cause ISI. If the channel cannot support the entire bandwidth of the transmitted signal,
the symbols may overlap during transmission.
3. Multipath Propagation: In wireless communication, signals may take multiple paths
to reach the receiver due to reflections, refractions, or diffractions. The delayed versions
of the signal may interfere with the original signal at the receiver.

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Consequences of ISI:

1. Reduced Signal Quality: ISI can make it challenging to correctly decode the symbols
at the receiver, leading to errors in the received data.
2. Increased Error Rates: The interference caused by ISI can lead to errors in the
received data. This is particularly crucial in digital communication systems where
accurate decoding of symbols is essential for proper information retrieval.
3. Reduced Bit Rate: The presence of ISI may necessitate the use of additional resources,
such as error correction coding, which can reduce the effective bit rate of the
communication system.

Mitigation Techniques:

1. Equalization: Equalization techniques are used to compensate for the effects of ISI.
This involves adjusting the amplitude and phase of the received signal to mitigate the
distortion caused by channel dispersion.

2. Guard Intervals: Inserting guard intervals between symbols can help reduce the
impact of ISI. These intervals provide a buffer between symbols, allowing them to be
more easily distinguished at the receiver.

3. Adaptive Techniques: Adaptive equalization algorithms can dynamically adjust the
equalization parameters based on the changing characteristics of the communication
channel.

4. Frequency-Division Multiplexing (FDM): FDM can be employed to avoid
overlapping in the frequency domain, reducing the likelihood of ISI.

5. Channel Coding: The use of error correction codes can help mitigate the impact of
errors caused by ISI, improving the overall reliability of the communication system.

6. Synchronization: ISI can be mitigated by proper timing synchronization. Ensuring that
the receiver's sampling instants are aligned with the symbol boundaries helps in
minimizing the interference between symbols

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Notes by Mr. Chandrakantha T S, Dept.t of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri, Shankaraghatta,2023-24

Applications:

1. Digital Communication Systems: ISI is a critical consideration in various digital
communication systems, including wired and wireless communication, where symbols
are used to represent data.

2. Broadband Communication: High-speed communication systems, such as broadband
internet and digital subscriber lines (DSL), often encounter ISI due to channel
dispersion. Mitigating ISI is crucial for maintaining high data rates.

3. Optical Communication: In optical fiber communication, ISI can be caused by
dispersion in the fiber. Techniques like dispersion compensation and adaptive
equalization are employed to address ISI issues.

4. Wireless Communication: Multipath propagation in wireless channels can introduce
ISI. Techniques like equalization and diversity are used to combat the effects of ISI in
wireless communication.
********

ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I Digital modulation techniques

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ELH – 3.1: ADVANCED DIGITAL COMMUNICATION UNIT – I Digital modulation techniques

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