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