The document outlines various digital modulation techniques including ASK, BPSK, and FSK. It describes how each technique generates and detects modulated signals. ASK encodes data in signal amplitude levels. BPSK uses two phase shift keying to encode bits. FSK encodes data by shifting the carrier frequency between two values. Optimum detection requires coherent demodulation that correlates the received signal with a reference carrier.

2. Outlines
 ASK(Amplitude Shift-Keying)
 Detection of ASK
 BPSK(Binary Phase Shift Keying)
 Detection of BPSK
 FSK(Frequency Shift Keying)
 Detection of FSK
Binary Band-Pass Modulation Techniques 2

3. ASK (Amplitude Shift Keying)
 Also known as OOK (On-Off Keying)
Carrier ASK output
Cos(2fct) Acm(t)Cos(2fct)
Message
m(t) 1
Tb 
R
Message 1 0 1 0 1 0 1
Unipolar
Modulation
Bipolar
Modulation
ASK output
Binary Band-Pass Modulation Techniques 3

4. ASK (Amplitude Shift Keying)
 ASK signal in time domain
 s(t )  Ac m(t ) cos(2 f c t )
 PSD(Power Spectral Density)
 Conventional AM type
Ac2
8
Ac2 sin( ( f  f c ) / R) 2
( )
8R  ( f  f c ) / R
fc
2R = 2/Tb
Binary Band-Pass Modulation Techniques 4

5. ASK (Amplitude Shift Keying)
• The two binary values are represented by two different
amplitudes of the carrier frequency
• The resulting modulated signal for one bit time is
 A cos(2f ct ), binary 1
s(t )  
0, binary 0
• Susceptible to noise
• Inefficient modulation technique
• used for
 up to 1200bps on voice grade lines
 very high speeds over optical fiber
Binary Band-Pass Modulation Techniques 5

6. Detection of ASK
 Non-Coherent Detection
ASK in Envelope Binary output
Detector
 Coherent Detection with Low Pass Filter
Ac m(t ) cos 2 (2 f c t )
ASK in Binary output
s(t )  Ac m(t ) cos(2 f c t )
LPF
1
Ac m(t )
2
cos(2 f c t )
Binary Band-Pass Modulation Techniques 6

7. Detection of ASK
 Coherent Detection with Correlator
 Optimum Receiver
ASK in t
Sample
Ac m(t ) cos(2 f c t )  ( ) d
0
& Binary
Hold Out
 n(t )
cos(2 f c t )
Clock VT
From PLL From Bit sync logic
Correlator output
VT
Comparator input
Binary output
Binary Band-Pass Modulation Techniques 7

8. Detection of ASK
 Choosing the detector
 Optimum coherent detector
 Best noise performance
 More costly
 Non-Coherent detector
 More error rate
 Less costly
 Trade-off between
 Cost / Noise Performance
Binary Band-Pass Modulation Techniques 8

9. BPSK(Binary Phase Shift Keying)
 Generation Message: m(t)
Carrier:Cos(2fct)
BPSK output
AcCos(2fct+kpm(t))
180
Phase shift
1
Tb 
R
Message 1 0 1 0 1 0 1
Unipolar
Modulation
Bipolar
Modulation
BPSK output
Binary Band-Pass Modulation Techniques 9

10. BPSK(Binary Phase Shift Keying)
 Signals in time domain
 Since m(t) = 1
s(t )  Ac cos(2 f c t  k p m(t ))
 Ac cos(k p m(t )) cos(2 f c t )  Ac sin(k p m(t ))sin(2 f c t )
 Ac cos(k p ) cos(2 f c t )  Ac sin(k p )m(t )sin(2 f c t )
Pilot term Data term
 If kp is small
 Then little power in data term, most power in pilot term
 To maximized performance (low Pe)
 Optimum case : kp = /2
 s (t )   Ac m(t )sin(2 f c t )
Binary Band-Pass Modulation Techniques 10

11. BPSK(Binary Phase Shift Keying)
 PSD of optimum BPSK
If kp  /2
Pilot exists Ac2 sin( ( f  f c ) / R) 2
( )
4R  ( f  fc ) / R
fc
2R = 2/Tb
Binary Band-Pass Modulation Techniques 11

12. Detection of BPSK
 Coherent Detector with Low Pass Filter
BPSK in Binary output
s(t )   Ac m(t )sin(2 f c t )
LPF
1
Ac m(t )
2
cos(2 f c t )
From PLL if pilot exist
Costas Loop or Squaring Loop if no pilot exist
 To remove Half cycle (180 phase) ambiguity
 DPSK(Differential PSK) is used
Binary Band-Pass Modulation Techniques 12

13. Detection of BPSK
 Optimum Detector
BPSK in t
Sample
Ac m(t ) cos(2 f c t )  ( ) d
0
& Binary
Hold Out
 n(t )
cos(2 f c t )
Clock VT=0
From PLL, From Bit sync logic
Costas loop
Correlator output
VT=0
Comparator input
Binary output
Binary Band-Pass Modulation Techniques 13

14. FSK(Frequency Shift Keying)
 Generation
 Discontinuous FSK
Message: m(t)
Cos(2f1t)
Osc. f1 FSK output
AcCos(2f1t+1) or
Cos(2f2t) AcCos(2f2t+2)
Osc. f2
 Continuous FSK
Message: m(t) Frequency FSK output
Modulator t
fc Ac cos(2 f c t  k f 

m( ) d )
Binary Band-Pass Modulation Techniques 14

15. FSK(Frequency Shift Keying)
 Waveforms in FSK
1
Tb 
R
Message 1 0 1 0 1 0 1
Unipolar
Modulation
Bipolar
Modulation
FSK output
(Discontinuous)
FSK output
(Continuous)
Mark(binary 1) frequency: f1
Space(binary 0) frequency: f2
Binary Band-Pass Modulation Techniques 15

16. BFSK(Binary Frequency Shift
Keying)
• The most common form of FSK is Binary FSK (BFSK)
• Two binary values represented by two different
frequencies ( f1 and f2 ) 0 0 1 1 0 1 0 0 0 1 0
 A cos(2f1t ), binary 1
f2 f2 f1 f1 f2 f1 f2 f2 f2 f1 f2
s(t )  
 A cos(2f 2t ), binary 0
• less susceptible to noise than ASK
• used for
 up to 1200bps on voice grade lines
 high frequency radio (3 to 30MHz)
 even higher frequency on LANs using coaxial cable
Binary Band-Pass Modulation Techniques 16

17. Detection of FSK
 Noncoherent Detector
FSK in Frequency Binary Output
Detector
 Coherent Detector with Low Pass Filter
FSK in
LPF
Binary Output
Cos(2f1t)
LPF
Cos(2f2t)
Binary Band-Pass Modulation Techniques 17

18. Detection of FSK
 Optimum Detector
Correlator
FSK in
Or
Matched Filter Binary Output
Cos(2f1t) detector
Correlator
Or
Matched Filter
Cos(2f2t)
Binary Band-Pass Modulation Techniques 18