Understanding Digital Modulation in Data Transmission

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igit
a
l Modul
a
tion B
a
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)
Data Transmission And Digital  Communication
 
Lecture 3– 2019/1440
 
By: Elham Sunbu
 
OUTLINE
 
Digital Introduction to digital modulation
Relevant modulation schemes
Geometric representations
Coherent & Non-Coherent Detection
Modulation spectra
 
 
Digital-to-analog
 conversion is the process of changing one of the
characteristics of an analog signal based on the information in
digital data.
 
Topics discussed in this section:
1.
Aspects of Digital-to-Analog Conversion
2.
 Amplitude Shift 
Keying
3.
 Frequency Shift 
Keying
4.
 Phase Shift Keying
5.
 Quadrature Amplitude Modulation
Digital To Analog Conversion
Digital-to-analog conversion
 
Digital-to-analog conversion is the process of changing one of the characteristics of an
analog signal (
carrier signal
) based on the information in digital data.
 
Digital /Analog converter
 
Analog /Digital converter
Why we need digital modulation
 
-
Digital modulation is required if digital data has to be
transmitted over a medium that only 
allows
 analog
transmission.
-
Modems
 in wired networks.
-
Wireless
 must use analogue sine waves.
 
5
Types of digital-to-analog conversion
Modulation
 
& Demodulation
Ba
s
eband
Mod
ulation
 
Ca
rr
i
e
r
Radio
Channel
Syn
c
hron
izati
o
n/
Detection/
 
D
eci
s
ion
 
Ca
rr
i
e
r
 
7
Data out
Data in
Modulation
 
Modulation
 
:
process 
(or 
result 
of 
the process) 
of  
translation
 
the baseband message
signal to  bandpass (modulated carrier) signal at frequencies  that are
very high compared to the baseband  frequencies.
Demodulation
 
is the process 
of 
extracting the  baseband message
back the modulated
 
carrier.
An 
information-bearing signal 
is non-  deterministic, i.e. it changes
in an unpredictable  manner.
Why
 
Carrier?
 
Effective 
radiation 
of 
EM
 
waves 
requires
antenna dimensions comparable with 
the
wavelength
:
Antenna 
for 3 kHz 
would 
be 
~100 
km
 
long
Antenna 
for 3 GHz 
carrier is 
10 
cm
 
long
Sharing the 
access 
to the telecommunication
channel
 
resources
 
Bit rate, 
N
, is the number of bits per second (bps).
Baud rate is the number of signal
elements per second (
bauds
).
In the analog transmission of digital data, the signal or baud rate is 
less than
or 
equal
 to the bit rate.
S=Nx1/r 
bauds
Where 
r
 is the number of data bits per signal element.
NOTE:
 
An analog signal carries 4 bits per signal element. If 1000 signal elements are sent per
second, find the bit rate.
 
Solution:
In this case, r = 4, S = 1000, and N is unknown. We can find the value of N from
Example 1:
Example 2:
 
An analog signal has a bit rate of 8000 bps and a baud rate of 1000 baud.
How many data elements are carried by each signal element? How many
signal elements do we need?
 
Solution:
 
In this example, S = 1000, N = 8000, and r and L are unknown. We find first the value
of r and then the value of L.
Modulation
 
Process
 
f
 
 
f
 
a
1
 
,
 
a
2
 
,
 
a
3
 
,
.
.
.
a
n
 
,
 
t
 
 
(= 
c
a
rr
i
e
r
)
a
1
 
,
 
a
2
 
,
 
a
3
 
,...
a
n
 
(= 
modulation
 
parameters
)
t 
(=
 
time
)
Modulation implies 
varying 
one or more  
characteristics
(modulation parameters a
1
, a
2
, 
a
n
) 
of  a 
carrier 
f 
in accordance
with the information-bearing  (modulating) baseband
 
signal.
Sinusoidal waves
, pulse train, square wave, 
etc. can 
be  
used as
carriers
Amplitude Shift Keying
 
(ASK)
 
Pulse shaping can 
be 
employed to remove spectral spreading
ASK 
demonstrates 
poor 
performance, as it is heavily 
affected 
by 
noise,
fading, and
 
interference
 
Ba
s
e
b
a
nd
Data
 
ASK
m
odu
late
d
signal
 
1
 
1
 
0
 
0
 
Acos(
t)
 
Acos(
t)
 
In 
ASK
 the amplitude of the carrier signal is varied to represent
binary 1 or 0.
Carrier signal is a high frequency signal that acts as a basis for the information
signal.
Both frequency and phase remain constant while the amplitude changes.
The peak amplitude of the signal during each bit duration is constant, and its
value depends on the  bit (0 or 1)
.
Amplitude Shift Keying  (ASK)
 
15
 
- Although we can have several levels of signal elements,
each with a different amplitude, ASK is normally
implemented using 
only two levels
. 
This is referred to as
binary amplitude shift keying.
- In ON OFF Keying: bit 
0
 is represented by the absence of a
carrier and bit 
1
 is represented by the presence of a carrier .
Binary ASK (BASK)  or On Off Keying (OOK)
 
16
 
- 
Pros
:
ASK transmitter and receiver are simple to design.
ASK needs less bandwidth than FSK.
 
- 
Cons
:
ASK transmission can be easily corrupted by noise.
 
- 
Application
:
Early telephone modem (AFSK).
ASK is used to transmit digital data over optical fiber.
Pros and Cons
 
17
Frequency
 
Shift Keying
 
(FSK)
 
Baseband
Data
 
BFSK
m
odu
late
d
signal
 
1
 
1
 
0
 
0
 
f
1
 
f
0
 
f
0
 
f
1
where 
f
0 
=Acos(
c
-

)t and 
f
1
 
=Acos(
c
+

)t
Example
: 
The 
ITU-T 
V.21 
modem standard uses
 
FSK
FSK 
can 
be 
expanded to 
a 
M-ary scheme, employing 
multiple
frequencies as 
different
 
states
 
19
FSK (Frequency Shift Keying)
 
The frequency of the carrier signal is varied to represent binary
1
 or 
0
.
Both peak amplitude and phase remain constant while the
frequency changes.
The frequency of the signal during each bit duration is constant,
and its value depends on the  bit (0 or 1).
 
20
FSK Modulator
 
- 
One way to think about binary FSK (or BFSK) is to consider two
carrier frequencies
 
Switch between two oscillators accordingly
ASK and FSK
Phase Shift Keyin
g 
(PSK)
 
Baseband
Data
 
BPSK
m
odu
late
d
signal
 
1
 
1
 
0
 
0
 
where 
s
0 
=-Acos(
c
t) and 
s
1
 
=Acos(
c
t)
Major 
drawback – 
rapid amplitude 
change 
between symbols 
due 
to phase  
discontinuity, 
which requires 
infinite
bandwidth
. 
Binary Phase Shift Keying  
(BPSK) demonstrates better performance than 
ASK
 
and
 
BFSK
BPSK 
can be expanded 
to 
a M-ary 
scheme, employing multiple phases 
and  
amplitudes 
as 
different
 
states
 
s
1
 
s
0
 
s
0
 
s
1
Phase Shift Keying
 
In phase shift keying, the phase of the carrier is varied to
represent two or more different signal elements (Both
peak amplitude and frequency remain constant).
In binary PSK, we have only two signal elements: one
with a phase of 0°, and the other with a phase of 180°
.
 
23
Bandwidth  of Binary PSK
 
PSK is less susceptible to noise than ASK.
 PSK is superior to FSK because we do not need two carrier signals.
The implementation of BPSK :
the signal element with phase 180° can be seen as the complement of the signal
element with phase 0°.
 
24
Digital Modulation Summary
 
25
Digital Modulation Summary
 
26
 
27
 
Thank You
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Delve into the world of digital modulation for data transmission, exploring various modulation schemes, digital-to-analog conversion processes, the importance of digital modulation in mixed networks, and the fundamentals of modulation and demodulation.


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  1. (Digital Modulation Basics) Data Transmission And Digital Communication Lecture 3 2019/1440 By: Elham Sunbu

  2. OUTLINE Digital Introduction to digital modulation Relevant modulation schemes Geometric representations Coherent & Non-Coherent Detection Modulation spectra

  3. Digital To Analog Conversion Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data. Topics discussed in this section: 1. Aspects of Digital-to-Analog Conversion 2. Amplitude Shift Keying 3. Frequency Shift Keying 4. Phase Shift Keying 5. Quadrature Amplitude Modulation

  4. Digital-to-analog conversion Digital-to-analog conversion is the process of changing one of the characteristics of an analog signal (carrier signal) based on the information in digital data. Analog /Digital converter Digital /Analog converter

  5. Why we need digital modulation - Digital modulation is required if digital data has to be transmitted over a medium that only allows analog transmission. - Modems in wired networks. - Wireless must use analogue sine waves. 5

  6. Types of digital-to-analog conversion

  7. 7 Modulation & Demodulation Radio Channel Carrier Carrier Baseband Modulation Synchronization/ Detection/ Decision Data in Data out

  8. Modulation Modulation : process (or result of the process) of translation the baseband message signal to bandpass (modulated carrier) signal at frequencies that are very high compared to the baseband frequencies. Demodulation is the process of extracting the baseband message back the modulated carrier. An information-bearing signal is non- deterministic, i.e. it changes in an unpredictable manner.

  9. Why Carrier? Effective radiation of EM waves requires antenna dimensions comparable with the wavelength: Antenna for 3 kHz would be ~100 km long Antenna for 3 GHz carrier is 10 cm long Sharing the access to the telecommunication channel resources

  10. NOTE: Bit rate, N, is the number of bits per second (bps). Baud rate is the number of signal elements per second (bauds). In the analog transmission of digital data, the signal or baud rate is less than or equal to the bit rate. S=Nx1/r bauds Where r is the number of data bits per signal element.

  11. Example 1: An analog signal carries 4 bits per signal element. If 1000 signal elements are sent per second, find the bit rate. Solution: In this case, r = 4, S = 1000, and N is unknown. We can find the value of N from

  12. Example 2: An analog signal has a bit rate of 8000 bps and a baud rate of 1000 baud. How many data elements are carried by each signal element? How many signal elements do we need? Solution: In this example, S = 1000, N = 8000, and r and L are unknown. We find first the value of r and then the value of L.

  13. Modulation Process f = f (a1,a2,a3,...an,t) (= carrier) a1,a2,a3,...an(= modulation parameters) t (=time) Modulation implies varying one or more characteristics (modulation parameters a1, a2, an) of a carrier f in accordance with the information-bearing (modulating) baseband signal. Sinusoidal waves, pulse train, square wave, etc. can be used as carriers

  14. Amplitude Shift Keying (ASK) Baseband Data 1 0 0 1 ASK modulated signal Acos( t) Acos( t) Pulse shaping can be employed to remove spectral spreading ASK demonstrates poor performance, as it is heavily affected by noise, fading, and interference

  15. Amplitude Shift Keying (ASK) In ASK the amplitude of the carrier signal is varied to represent binary 1 or 0. Carrier signal is a high frequency signal that acts as a basis for the information signal. Both frequency and phase remain constant while the amplitude changes. The peak amplitude of the signal during each bit duration is constant, and its value depends on the bit (0 or 1). 15

  16. Binary ASK (BASK) or On Off Keying (OOK) - Although we can have several levels of signal elements, each with a different amplitude, ASK is normally implemented using only two levels. This is referred to as binary amplitude shift keying. - In ON OFF Keying: bit 0 is represented by the absence of a carrier and bit 1 is represented by the presence of a carrier . 16

  17. Pros and Cons - Pros: ASK transmitter and receiver are simple to design. ASK needs less bandwidth than FSK. - Cons: ASK transmission can be easily corrupted by noise. - Application: Early telephone modem (AFSK). ASK is used to transmit digital data over optical fiber. 17

  18. Frequency Shift Keying (FSK) Baseband Data 1 0 0 1 BFSK modulated signal f0 f0 f1 f1 where f0 =Acos( c- )t and f1=Acos( c+ )t Example: The ITU-T V.21 modem standard uses FSK FSK can be expanded to a M-ary scheme, employing multiple frequencies as different states

  19. FSK (Frequency Shift Keying) The frequency of the carrier signal is varied to represent binary 1 or 0. Both peak amplitude and phase remain constant while the frequency changes. The frequency of the signal during each bit duration is constant, and its value depends on the bit (0 or 1). 19

  20. FSK Modulator - One way to think about binary FSK (or BFSK) is to consider two carrier frequencies Switch between two oscillators accordingly 20

  21. ASK and FSK Amplitude Shift Keying (ASK) Very simple. Frequency Shift Keying (FSK) Needs larger bandwidth. Low bandwidth requirements. More error resilience than AM. Very susceptible to interference

  22. Phase Shift Keying (PSK) Baseband Data 1 0 0 1 BPSK modulated signal s0 s0 s1 s1 where s0 =-Acos( ct) and s1=Acos( ct) Major drawback rapid amplitude change between symbols due to phase discontinuity, which requires infinite bandwidth. Binary Phase Shift Keying (BPSK) demonstrates better performance than ASK and BFSK BPSK can be expanded to a M-ary scheme, employing multiple phases and amplitudes as different states

  23. Phase Shift Keying In phase shift keying, the phase of the carrier is varied to represent two or more different signal elements (Both peak amplitude and frequency remain constant). In binary PSK, we have only two signal elements: one with a phase of 0 , and the other with a phase of 180 . 23

  24. Bandwidth of Binary PSK PSK is less susceptible to noise than ASK. PSK is superior to FSK because we do not need two carrier signals. The implementation of BPSK : the signal element with phase 180 can be seen as the complement of the signal element with phase 0 . 24

  25. Digital Modulation Summary Amplitude Shift Keying (ASK) Frequency Shift Keying (FSK) Phase Shift Keying (PSK) Very simple. Needs larger bandwidth. More error resilience than AM. More complex. Low bandwidth requirements Robust against interference. Very susceptible to interference 25

  26. Digital Modulation Summary 26

  27. Thank You 27

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