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Binary Modulated Bandpass Signaling. OOK(On-Off Keying) Or ASK(Amplitude Shift Keying) BPSK(Binary Phase Shift Keying) FSK(Frequency Shift Keying). Carrier Cos(2 f c t). OOK output A c m(t)Cos(2 f c t). Message m(t). Message. 1 0 1 0 1 0 1. Unipolar Modulation.

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Binary modulated bandpass signaling

Binary Modulated Bandpass Signaling

OOK(On-Off Keying)

Or ASK(Amplitude Shift Keying)

BPSK(Binary Phase Shift Keying)

FSK(Frequency Shift Keying)


Ook on off keying

Carrier

Cos(2fct)

OOK output

Acm(t)Cos(2fct)

Message

m(t)

Message

1 0 1 0 1 0 1

Unipolar

Modulation

Bipolar

Modulation

OOK output

OOK(On-Off Keying)

  • Also known as ASK(Amplitude Shift Keying)


Ook on off keying1

fc

2R = 2/Tb

OOK(On-Off Keying)

  • OOK signal in time domain

  • PSD(Power Spectral Density)

    • Conventional AM type


Detection of ook

Binary output

OOK in

Envelope

Detector

Binary output

OOK in

LPF

Detection of OOK

  • Noncoherent Detection

  • Coherent Detection with Low Pass Filter


Detection of ook1

Sample

&

Hold

OOK in

Binary

Out

VT

Clock

From Bit sync logic

From PLL

Correlator output

VT

Comparator input

Binary output

Detection of OOK

  • Coherent Detection with Correlator

    • Optimum Receiver


Detection of ook2
Detection of OOK

  • Choosing the detector

    • Optimum coherent detector

      • Best noise performance

      • More costly

    • Noncoherent detector

      • More error rate

      • Less costly

    • Trade-off between

      • Cost / Noise Performance


Bpsk binary phase shift keying

Message: m(t)

Carrier:Cos(2fct)

BPSK output

AcCos(2fct+kpm(t))

-90

Phase shift

Message

1 0 1 0 1 0 1

Unipolar

Modulation

Bipolar

Modulation

BPSK output

BPSK(Binary Phase Shift Keying)

  • Generation


Pilot term Data term

BPSK

  • Signals in time domain

    • Since m(t) = 1

    • If kp is small

      • Then little power in data term, most power in pilot term

    • To maximized performance (low Pe)

      • Optimum case : kp = /2


If kp  /2

Pilot exists

fc

2R = 2/Tb

BPSK

  • PSD of optimum BPSK

    • Equivalent to DSB


Detection of bpsk

Binary output

BPSK in

LPF

From PLL if pilot exist

Costas Loop or Squaring Loop if no pilot exist

Detection of BPSK

  • Coherent Detector with Low Pass Filter

    • To remove Half cycle (180 phase) ambiguity

      • DPSK(Differential PSK) is used


Detection of bpsk1

Correlator output

VT=0

Comparator input

Binary output

Detection of BPSK

  • Optimum Detector

Sample

&

Hold

BPSK in

Binary

Out

Clock

From Bit sync logic

VT=0

From PLL,

Costas loop


Dpsk differential psk
DPSK(Differential PSK)

  • DPSK = Differential Coding + BPSK

  • DPSK is often used instead of BPSK because it does not require carrier synchronizer circuits

  • Differential Coding

    • Differential Encoding :

    • Differential Decoding :


Differential coding

Data in

Delay

Tb

Line Encoder

Channel

Line Decoder

Differential Encoder

Data out

Delay

Tb

Differential Decoder

Differential Coding

  • Differential Encoding/Decoding


Example of differential coding

Encoding

Input sequence dn 1 1 0 1 0 0 1

Encoding sequence en 1 0 1 1 0 0 0 1

Reference digit

Decoding (with correct channel polarity)

received sequence en 1 0 1 1 0 0 0 1

Encoding sequence dn 1 1 0 1 0 0 1

Decoding (with inverted channel polarity)

received sequence en0 1 0 0 1 1 1 0

Encoding sequence dn 1 1 0 1 0 0 1

Example of Differential Coding


Detection of dpsk

BPSK in

LPF

Binary Out

Delay

Tb

BPSK in

Correlator

Or

Matched filter

Binary Out

Delay

Tb

Detection of DPSK

  • Not requires carrier synchronizer circuits

    • Partially Coherent Detector

    • Optimum Detector


Fsk frequency shift keying

Message: m(t)

Cos(2f1t)

FSK output

AcCos(2f1t+1) or

AcCos(2f2t+2)

Osc. f1

Cos(2f2t)

Osc. f2

Frequency

Modulator

fc

FSK output

Message: m(t)

FSK(Frequency Shift Keying)

  • Generation

    • Discontinuous FSK

    • Continuous FSK


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

FSK

  • Waveforms in FSK


Detection of fsk

FSK in

Frequency

Detector

Binary Output

FSK in

LPF

Binary Output

Cos(2f1t)

LPF

Cos(2f2t)

Detection of FSK

  • Noncoherent Detector

  • Coherent Detector with Low Pass Filter


Detection of fsk1

detector

Correlator

Or

Matched Filter

FSK in

Binary Output

Cos(2f1t)

Correlator

Or

Matched Filter

Cos(2f2t)

Detection of FSK

  • Optimum Detector


Bell type 103 fsk modem

Digital

data

Dial up

phone line

Computer

FSK modem

(Originate)

f1 = 2225Hz

f2 = 2025Hz

PSTN

Computer

Center

FSK modem

(Answer)

f1 = 1270Hz

f2 = 1070Hz

Bell-Type 103 FSK Modem

  • FSK with speed of 300 bps

    • QAM is used for higher data rate


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