The document discusses modulation techniques, focusing on how modulation encodes information in transmitted signals by varying the characteristics of a high-frequency carrier wave. It explains the importance of modulation for efficient long-distance transmission, multiple channel use, and improved signal quality, as well as detailing categories and techniques of digital modulation, including Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK). Overall, it highlights the process by which digital or analog data is transformed for suitable transmission across various mediums.

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Lecture# 03
Modulation Techniques
Dr. Shahzad Ashraf
Associate Professor
About Modulation
 A process of encoding information in a transmitted signal
 It involves varying one or more characteristics of a high-frequency carrier wave in
accordance with the information signal, which is typically a lower frequency signal
containing the data or message to be transmitted
 Modulation takes two inputs, a carrier and a signal
Why is modulation needed?
o Efficient transmission over long distances
--Higher frequency carrier waves can travel longer distances with less
attenuation compared to lower frequency signals.
o Multiple channel transmission
--Modulation allows multiple signals to be transmitted simultaneously over a
single medium using techniques like frequency-division multiplexing (FDM)
o Improved signal quality
--Modulation can reduce noise and interference, improving the quality of the
received signal

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Digital modulation
• The process of suppressing low frequency information signal on a high
frequency carrier signal is called DM. OR a method of altering the
properties of a high frequency carrier (amplitude, frequency, phase) in
accordance with a low frequency information signal.
• The modulation is always depends on two signals that is high frequency
carrier and low frequency information. Thus, resultant wave achieved
known as modulated signal.
• It can be stated as
Information (modulating signal) + carrier = modulated signal
Digital modulation
• Why does the modulation is indispensable?
because the carrier wave usually appears as a sine wave and the information signal may be
of any type (either analog or digital)
• Converting digital or analog information to a waveform suitable for
transmission over given medium.
• The modulation can be expressed as
• When working with digital data, altering parameters is referred to as keying
such as ASK, PSK, FSK.

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Digital modulation
Categories of the modulation
In either type of modulation (analog or digital), carrier is of analog format.
Digital modulation
Categories of the modulation
• Why not digital carrier?
The only difference between both categories is type of information (modulating) signal.
i.e. analog modulation = analog information signal
digital modulation = digital information signal
Therefore. outcome of a modulated wave is a change in the high frequency carrier's properties.
Analog modulation: If the variation in the parameter of the carrier is
continuous in accordance to the input analog signal the modulation technique is
termed as analog modulation scheme.
Digital modulation: If the variation in the parameter of the carrier is discrete
then it is termed as digital modulation technique. In digital modulation , an
analog carrier signal is modulated by a discrete signal. The modulating wave
consists of binary data and the carrier is sinusoidal wave.
Digital modulation techniques: Three main digital modulation techniques are
discussed as.
a. Amplitude Shift Keying (ASK) b. Frequency Shift Keying (FSK)
c. Phase Shift Keying (PSK)

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Digital modulation techniques
a. Amplitude Shift Keying (ASK)
o It is a simplest digital modulation technique where digital data is converted into analog signal.
o The amplitude of carrier signal varies with respect to amplitude of message signal.
o Bit 1 is transmitted by a signal of one particular amplitude, to transmit 0,only change the amplitude
while keeping the frequency constant.
Digital modulation techniques
a. Amplitude Shift Keying (ASK)
The outcome:
o The information signal carries the discrete bit, only two voltage levels occur at input (either +1V or -1V)
o Thus, only two voltage levels at output are available (either [Ac cos(ωct)] or OV)
o because of these two output voltage levels, the carrier is either in ON or OFF state.
o Therefore, ASK is also known as ON-OFF Keying (OOK)
Applications
o Broadcasting of signal
o Lazer intensity modulation in optical fiber communication

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Digital modulation techniques
b. Frequency Shift Keying (FSK)
o Only change in frequency is occurred in response to the information, a binary information signal
directly modulates frequency of an analog carrier.
o The modulated signal 1, comes up with high frequency while 0 with low frequency
Digital modulation techniques
b. Frequency Shift Keying (FSK)
o Only change in frequency is occurred in response to the information, a binary information signal

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Digital modulation techniques
b. Frequency Shift Keying (FSK)
The outcome:
o The carrier wave continuously shifted by an amount specified as Δf.
o when logic 1 input is applied, the carrier wave modulated itself to a frequency known as mark
frequency (fm).
o when logic 0 input is applied, the carrier wave modulated itself to a frequency known as space
frequency (fc).
o The overall spectrum of FSK will be observed as
Digital modulation techniques
c. Phase Shift Keying (PSK)
o In this technique, the phase of the sinusoidal carrier to indicated information is being changed. Phase
in this context is the starting angle at which the sinusoidal starts.
o One phase change encodes 0 while another phase change encodes 1.To transmit 0,we shift the phase
of the sinusoid by 180. Thus, as the input digital signal changes state (i.e. from 1 to 0 or 0 to 1), the
phase of the output carrier shifts between two phases (that are separated by 180o).
o It is one of a simplest form of Binary phase shift keying (BPSK)

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The End