Binary Pass-Band Modulation Techniques

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Binary Pass-Band Modulation Techniques

  1. 1. 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
  2. 2. 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
  3. 3. 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
  4. 4. 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
  5. 5. 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
  6. 6. Detection of ASK Coherent Detection with Correlator  Optimum Receiver ASK in t SampleAc 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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
  14. 14. 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
  15. 15. BFSK(Binary Frequency ShiftKeying)• 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 f2s(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
  16. 16. 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
  17. 17. 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

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