Transcript Digital Modulation Technique

Digital Modulation Technique
Presented By:
Amit Degada.
Teaching Assistant,
SV NIT, Surat.
Goal of Today’s Lecture





Differential Phase Shift keying
Quadrature Phase Shift Keying
Minimum Phase Shift Keying
Introduction To Information Theory
Information Measure
Differential Phase Shift Keying (DPSK)
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Why We Require?
•
•

To Have Non-coherent Detection
That Makes Receiver Design
How can we do?
•
•
0 may be used represent transition
1 indicate No Transition
DPSK Transmitter
bK
Encoder
dK
Product
Modulator
S(t)=AcCos(2Πfct)
dK-1
Delay Tb
What Should We Do to make Encoder?
AcCos(2Πfct)
DPSK Transmitter…………Modified
bK
Ex- NOR
Gate
dK
Product
Modulator
S(t)=±AcCos(2Πfct)
dK-1
Delay Tb
AcCos(2Πfct)
Differentially Encoded Sequence
Binary Data
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
1
Differentially
Encoded Data
1
0
1
1
Phase of DPSK
0
π
0
0
π
0
0
π
0
0
0
Shifted
Differentially
encoded Data
dk-1
1
0
1
1
0
1
1
0
1
1
Phase of
shifted Data
0
π
0
0
π
0
0
π
0
0
Phase
Comparision
Output
-
-
+
-
-
+
-
-
+
+
Detected
Binary Seq.
0
0
0
0
1
0
0
1
1
1
DPSK Receiver
Goal of Today’s Lecture





Differential Phase Shift keying
Quadrature Phase Shift Keying
Minimum Phase Shift Keying
Introduction To Information Theory
Information Measure
Quadrature Phase Shift Keying
(QPSK)
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

Extension of Binary-PSK
Spectrum Efficient Technique
In M-ary Transmission it is Possible to Transmit M Possible
Signal
M = 2n
where,
n= no of Bits that we Combine
signaling Interval T= nTb
In QPSK n=2 === > So M =4
and
signaling Interval T= 2Tb
Quadrature Phase Shift Keying
(QPSK)
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M=4 so we have possible signal are
00,01,10,11
Or In Natural Coded Form 00,10,11,01
s(t )  Ac cos(2 fct 
3
)
4

 Ac cos(2 fct  )
4

 Ac cos(2 fct  )
4
 Ac cos(2 fct 
3
)
4
-135
Binary Dibit 00
-45
Binary Dibit 10
45
Binary Dibit 11
135
Binary Dibit 01
QPSK Waveform
00
11
00
11
10
10
QPSK Signal Phase
Constellation Diagram
Quadrature Phase Shift Keying
(QPSK)
The QPSK Formula
s(t )  Ac cos(2 fct   (t ))
………………(1)
Where, ϕ(t)=135,45,-45,-135
Simplifying Equation 1
S (t )  Ac cos  (t ).cos(2 fct )  Ac sin  (t )sin(2 fct )
This Gives the Idea about Transmitter design
QPSK Transmitter
QPSK Receiver
Synchronization Circuit
Goal of Today’s Lecture





Differential Phase Shift keying
Quadrature Phase Shift Keying
Minimum Phase Shift Keying
Introduction To Information Theory
Information Measure
Minimum Shift Keying (MSK)
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In Binary FSK the Phase Continuity is
maintained at the transition Point. This
type of Modulated wave is referred as
Continuous Phase Frequency Shift Keying
(CPFSK)
In MSK there is phase change equals to
one half Bit Rate when the bit Changes 0
to 1 and 1 to 0.
f 
1
2Tb
Minimum Shift Keying (MSK)
Let’s take fc1 and fc2 represents binary 1 and 0 Respectively
fc1 
fc1  fc 2 fc1  fc 2

2
2
 fc 
f
2
Where
fc1  fc 2
fc 
2
 f  fc1  fc 2
Similarly
fc 2 
fc1  fc 2 fc1  fc 2

2
2
 fc 
f
2
Minimum Shift Keying (MSK)

The MSK Equation
s(t )  Ac cos(2 fct   (t ))
where
 (t )   ft
For Symbol 0
For Symbol 1
 (t )   ft

t
2Tb
 (t )   ft

t
2Tb
Carrier Phase Coding
For dibit 00
Tb
-π/2
-π
Φ(t)
2Tb
t
Carrier Phase Coding
For dibit 10
π
π/2
Tb
2Tb
Carrier Phase Coding
For dibit 11
π
π/2
Tb
2Tb
Carrier Phase Coding
For dibit 01
Tb
-π/2
-π
Φ(t)
2Tb
t
Goal of Today’s Lecture





Differential Phase Shift keying
Quadrature Phase Shift Keying
Minimum Phase Shift Keying
Introduction To Information Theory
Information Measure
Information Theory


It is a study of Communication
Engineering plus Maths
A Communication Engineer has to
Fight with
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
Limited Power
Inevitable Background Noise
Limited Bandwidth
Information Theory deals with
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The Measure of Source
Information
The Information Capacity of
the channel
Coding
If The rate of Information from a source does not exceed the
capacity of the Channel, then there exist a Coding Scheme such that
Information can be transmitted over the Communication Channel with
arbitrary small amount of errors despite the presence of Noise
Equivalent noiseless
Channel
Source
Encoder
Channel
Encoder
Noisy
Channel
Channel
Decoder
Source
Decoder
Goal of Today’s Lecture





Differential Phase Shift keying
Quadrature Phase Shift Keying
Minimum Phase Shift Keying
Introduction To Information Theory
Information Measure
Information Measure

This is utilized to determine the
information rate of discrete Sources
Consider Two Messages
A Dog bites a man
A man bites a dog
Thank You