Binary Band-Pass Modulation Techniques

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OutlinesASK(Amplitude Shift-Keying)

Detection of ASKBPSK(Binary Phase Shift Keying)

Detection of BPSKFSK(Frequency Shift Keying)

Detection of FSK

Binary Band-Pass Modulation Techniques

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ASK (Amplitude Shift Keying)Also known as OOK (On-Off Keying)

CarrierCos(2fct)

Messagem(t)

ASK outputAcm(t)Cos(2fct)

1 0 1 0 1 0 1Message

UnipolarModulation

BipolarModulation

ASK output

1bT

R

Binary Band-Pass Modulation Techniques

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ASK (Amplitude Shift Keying)ASK signal in time domain

PSD(Power Spectral Density)

Conventional AM type

( ) ( ) cos(2 )c cs t A m t f t

fc

2R = 2/Tb

2

8cA

22sin( ( ) / )

( )8 ( ) /

c c

c

A f f R

R f f R

Binary Band-Pass Modulation Techniques

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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

• Susceptible to noise• Inefficient modulation technique• used for

up to 1200bps on voice grade lines very high speeds over optical fiber

0,0

1),2cos()(

binary

binarytfAts c

Binary Band-Pass Modulation Techniques

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Detection of ASKNon-Coherent Detection

Coherent Detection with Low Pass Filter

EnvelopeDetector

ASK in Binary output

LPFASK in Binary output

cos(2 )cf t

( ) ( ) cos(2 )c cs t A m t f t

2( ) cos (2 )c cA m t f t

1( )

2 cA m t

Binary Band-Pass Modulation Techniques

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Detection of ASKCoherent Detection with Correlator

Optimum Receiver

Sample&

Hold

ASK in

cos(2 )cf t

( ) cos(2 )

( )c cA m t f t

n t

From PLL

0( )

td

ClockFrom Bit sync logic

VT

BinaryOut

VT

Correlator output

Binary output

Comparator input

Binary Band-Pass Modulation Techniques

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Detection of ASKChoosing 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

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BPSK(Binary Phase Shift Keying)Generation

Carrier:Cos(2fct)Message: m(t)

BPSK outputAcCos(2fct+kpm(t))

180 Phase shift

1 0 1 0 1 0 1Message

UnipolarModulation

BipolarModulation

BPSK output

1bT

R

Binary Band-Pass Modulation Techniques

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BPSK(Binary Phase Shift Keying)Signals in time domain

Since m(t) = 1

If kp is small Then little power in data term, most power in pilot

termTo maximized performance (low Pe)

Optimum case : kp = /2

( ) cos(2 ( ))

cos( ( )) cos(2 ) sin( ( ))sin(2 )

cos( ) cos(2 ) sin( ) ( )sin(2 )

c c p

c p c c p c

c p c c p c

s t A f t k m t

A k m t f t A k m t f t

A k f t A k m t f t

Pilot term Data term

( ) ( )sin(2 )c cs t A m t f t

Binary Band-Pass Modulation Techniques

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BPSK(Binary Phase Shift Keying)PSD of optimum BPSK

fc

2R = 2/Tb

22sin( ( ) / )

( )4 ( ) /

c c

c

A f f R

R f f R

If kp /2Pilot exists

Binary Band-Pass Modulation Techniques

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Detection of BPSKCoherent Detector with Low Pass Filter

To remove Half cycle (180 phase) ambiguity DPSK(Differential PSK) is used

LPFBPSK in Binary output

cos(2 )cf t

( ) ( )sin(2 )c cs t A m t f t 1( )

2 cA m t

From PLL if pilot existCostas Loop or Squaring Loop if no pilot exist

Binary Band-Pass Modulation Techniques

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Detection of BPSKOptimum Detector

Sample&

Hold

BPSK in

cos(2 )cf t

( ) cos(2 )

( )c cA m t f t

n t

From PLL,Costas loop

0( )

td

ClockFrom Bit sync logic

VT=0

BinaryOut

VT=0

Correlator output

Binary output

Comparator input

Binary Band-Pass Modulation Techniques

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FSK(Frequency Shift Keying)Generation

Discontinuous FSK

Continuous FSK

Cos(2f1t)Message: m(t)

FSK outputAcCos(2f1t+1) orAcCos(2f2t+2)Osc. f2

Osc. f1

Cos(2f2t)

FrequencyModulator

fc

Message: m(t) FSK output

cos(2 ( ) )t

c c fA f t k m d

Binary Band-Pass Modulation Techniques

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FSK(Frequency Shift Keying)Waveforms in FSK

1 0 1 0 1 0 1MessageUnipolarModulationBipolarModulation

FSK output(Discontinuous)

1bT

R

FSK output(Continuous)

Mark(binary 1) frequency: f1

Space(binary 0) frequency: f2

Binary Band-Pass Modulation Techniques

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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 )

• 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

0),2cos(

1),2cos()(

2

1

binarytfA

binarytfAts

0 0 1 1 0 1 0 0 0 1 0

f2 f2 f1 f1 f2 f1 f2 f2 f2 f1 f2

Binary Band-Pass Modulation Techniques

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Detection of FSKNoncoherent Detector

Coherent Detector with Low Pass Filter

FrequencyDetector

FSK in Binary Output

Cos(2f1t)

Cos(2f2t)

FSK inLPF

LPF

Binary Output

Binary Band-Pass Modulation Techniques

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Detection of FSKOptimum Detector

Cos(2f1t)

Cos(2f2t)

FSK inCorrelator

OrMatched Filter Binary Output

CorrelatorOr

Matched Filter

detector

Binary Band-Pass Modulation Techniques

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