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Binary Modulated Bandpass SignalingPowerPoint Presentation

Binary Modulated Bandpass Signaling

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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)

Cos(2fct)

OOK output

Acm(t)Cos(2fct)

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)

fc

2R = 2/Tb

OOK(On-Off Keying)- OOK signal in time domain
- PSD(Power Spectral Density)
- Conventional AM type

OOK in

Envelope

Detector

Binary output

OOK in

LPF

Detection of OOK- Noncoherent Detection
- Coherent Detection with Low Pass Filter

&

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 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

- Optimum coherent detector

Carrier:Cos(2fct)

BPSK output

AcCos(2fct+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

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

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

- To remove Half cycle (180 phase) ambiguity

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 Coding + BPSK
- DPSK is often used instead of BPSK because it does not require carrier synchronizer circuits
- Differential Coding
- Differential Encoding :
- Differential Decoding :

Delay

Tb

Line Encoder

Channel

Line Decoder

Differential Encoder

Data out

Delay

Tb

Differential Decoder

Differential Coding- Differential Encoding/Decoding

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 CodingLPF

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

Cos(2f1t)

FSK output

AcCos(2f1t+1) or

AcCos(2f2t+2)

Osc. f1

Cos(2f2t)

Osc. f2

Frequency

Modulator

fc

FSK output

Message: m(t)

FSK(Frequency Shift Keying)- Generation
- Discontinuous FSK
- Continuous FSK

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

Frequency

Detector

Binary Output

FSK in

LPF

Binary Output

Cos(2f1t)

LPF

Cos(2f2t)

Detection of FSK- Noncoherent Detector
- Coherent Detector with Low Pass Filter

Correlator

Or

Matched Filter

FSK in

Binary Output

Cos(2f1t)

Correlator

Or

Matched Filter

Cos(2f2t)

Detection of FSK- Optimum Detector

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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