31
Digital Modulation Technique Presented By: Amit Degada. Teaching Assistant, SV NIT, Surat.
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)
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
dK
dK-1
bK
AcCos(2Πfct)
S(t)=AcCos(2Πfct)Encoder
Delay Tb
Product Modulator
What Should We Do to make Encoder?
DPSK Transmitter…………Modified
dK
dK-1
bK
AcCos(2Πfct)
S(t)=±AcCos(2Πfct)
Delay Tb
Product Modulator
Ex- NOR Gate
Differentially Encoded Sequence
Binary Data 0 0 1 0 0 1 0 0 1 1
Differentially Encoded Data
1 0 1 1 0 1 1 0 1 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 1 0 0 1 0 0 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)
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)
M=4 so we have possible signal are 00,01,10,11
Or In Natural Coded Form 00,10,11,01
3( ) cos(2 )
4c cs t A f t
cos(2 )4
c cA f t
cos(2 )4
c cA f t
3cos(2 )
4c cA f t
-135
-45
45
135
Binary Dibit 00
Binary Dibit 10
Binary Dibit 11
Binary Dibit 01
QPSK Waveform
00 11 00 11 10 10
QPSK Signal Phase
Constellation Diagram
Quadrature Phase Shift Keying (QPSK)
( ) cos(2 ( ))c cs t A f t t
The QPSK Formula
Where, ϕ(t)=135,45,-45,-135
( ) cos ( ).cos(2 ) sin ( )sin(2 )c c c cS t A t f t A t f t
………………(1)
Simplifying Equation 1
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)
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.
1
2 bf
T
Minimum Shift Keying (MSK)
1 2 1 21
2 2
c c c cc
f f f ff
2c
ff
1 2
1 2
2
c c
c c
f ffc
f f f
1 2 1 22
2 2
c c c cc
f f f ff
2c
ff
Let’s take fc1 and fc2 represents binary 1 and 0 Respectively
Where
Similarly
Minimum Shift Keying (MSK)
The MSK Equation
where
( ) cos(2 ( ))s t Ac fct t
( )t ft
For Symbol 1
( )t ft
2 b
t
T
For Symbol 0
( )t ft
2 b
t
T
Carrier Phase Coding
For dibit 00
Φ(t)
tTb 2Tb
-π/2
-π
Carrier Phase Coding
For dibit 10
Tb2Tb
π/2
π
Carrier Phase Coding
Tb2Tb
π/2
π
For dibit 11
Carrier Phase Coding
For dibit 01
Φ(t)
tTb 2Tb
-π/2
-π
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
Limited Power Inevitable Background Noise Limited Bandwidth
Information Theory deals with
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
Source Encoder
Channel Encoder
Noisy Channel
Channel Decoder
Source Decoder
Equivalent noiseless Channel
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
