communication system chapter 5
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Communication System Communication System Ass. Prof. Ibrar Ullah
BSc (Electrical Engineering)
UET Peshawar
MSc (Communication & Electronics Engineering)
UET Peshawar
PhD (In Progress) Electronics Engineering
(Specialization in Wireless Communication)
MAJU Islamabad
E-Mail: ibrar@cecos.edu.pk
Ph: 03339051548 (0830 to 1300 hrs)
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Chapter-5 Angle Modulation
• What is Angle modulation
• What is the difference between frequency and phase modulation
• What is direct and indirect modulation
• Deviation sensitivity, phase deviation, modulation index
• Bandwidth of angle-modulated wave
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Angle Modulation
• Idea: The angle (t) of the carrier A Cos (Wc + (t))is modulated according to the modulating signal m(t):
• The amplitude A remains constant.
• This modulation type is called Angle modulation
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Angle Modulation
)(cos)( tAt
Generalized sinusoidal function is given by:
(t) = instantaneous phase (radians)
Question:
What is the instantaneous frequency?
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Angle Modulation
)(cos)( tAt
dt
dtwi
)(
dttwtt
ii )()(0
= angle modulated wave (Volt) A = peak carrier amplitude (Volt)
= instantaneous angular frequency (rad/sec) = instantaneous phase (radians)
)(t
iiw
A carrier can be represented as:
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Phase Modulation (PM)
The instantaneous phase of a harmonic carrier signal is varied in such a way that the instantaneous phase deviation i.e. the difference between the instantaneous phase and that of the carrier signal is linearly related to the size of the modulating signal at a given instant of time.
In PM the angle varies linearly with m(t))(t
)(ti
PM
)(twi
)(tmktw pc
)(cos tmktwA pc
dt
tdmkwc
dt
tmktwd
dt
tdp
pci )()()(
Kp is the phase deviation sensitivity (rad/Volt)
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Frequency Modulation (PM)
The frequency of a harmonic carrier signal is varied in such a way that the instantaneous frequency deviation i.e. the difference between the instantaneous frequency and the carrier frequency is linearly related to the size of the modulating signal at a given instant of time.
If wi is varied linearly with the modulating signal we have FM and instantaneous frequency wi is given by:
)(ti
FM
)(twi)(tmkw fc
dttmktwdttwt
fc
t
i )()(00
t
fc tmktwA0
)(cosKf is the frequency deviation sensitivity
/rad s
Volt
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Frequency Modulation (PM)
)(ti
PM
)(twi
)(tmktw pc
)(cos tmktwA pc
dt
tdmkwc
dt
tmktwd
dt
tdp
pci )()()(
PM
)(ti
FM
)(twi)(tmkw fc
dttmktwdttwt
fc
t
i )()(00
t
fc tmktwA0
)(cos
FM
TASK: Make block diagrams of PM and FM modulators
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PM Modulator )(ti
PM
)(twi
)(tmktw pc
)(cos tmktwA pc
dt
tdmkwc
dt
tmktwd
dt
tdp
pci )()()(
PM
DirectPhase
modulator PM waveModulating
signal source
twA ccos
IndirectModulating
signal source
Differentiator
Frequency modulator PM wave
twA ccos
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FM Modulator
)(ti
FM
)(twi)(tmkw fc
dttmktwdttwt
fc
t
i )()(00
t
fc tmktwA0
)(cos
FM
Direct
Indirect
Modulating signal source
Frequency modulator FM wave
twA ccos
IntegratorPhase
modulatorFM wave
Modulating signal source
twA ccos
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Frequency modulation of single frequency signal
PM:
FM:
)cos()( twAtm mm
))cos(cos()( twAktwAt mmpcPM
)cos()( twAtm mm
)sin(cos
)cos(cos)(0
tww
AktwA
dttwAktwAt
mm
mfc
mm
t
fcFM
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Example 5.1 p-212
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Example 5.1 p-212
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Transmission Bandwidth of FM Signal
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Transmission Bandwidth of FM Signal
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Transmission Bandwidth of FM Signal
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Transmission Bandwidth of FM Signal
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Transmission Bandwidth of FM Signal
Summary of bandwidth relations
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Example-1
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Example-1
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Phase Modulation
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Phase Modulation
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Problem-5.3-2
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Problem:
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Solution:
Input Signal m(t)
Signal at point “b”
Signal at point “c”
Signal at point “e”
Signal at point “d”
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