1. AM, FM, and Digital Modulated Systems
Chapter 5
AM, FM, and Digital Modulated Systems
Binary Bandpass Signalling Techniques
OOK
BPSK
FSK
Huseyin Bilgekul
Eeng360 Communication Systems I
Department of Electrical and Electronic Engineering
Eastern Mediterranean University
Principle of Communication

2. Binary bandpass signaling techniques
On–Off keying (OOK) [amplitude shift keying (ASK)] - Consists of keying (switching) a carrier sinusoid on and off with a unipolar binary signal.
- Morse code radio transmission is an example of this technique.
- OOK was one of the first modulation techniques to be used and precedes analog communication systems.
Binary Phase-Shift Keying (BPSK) - Consists of shifting the phase of a sinusoidal carrier 0o or 180o with a unipolar binary signal.
- BPSK is equivalent to PM signaling with a digital waveform.
Frequency-Shift Keying (FSK) - Consists of shifting the frequency of a sinusoidal carrier from a mark frequency (binary 1) to a space frequency (binary 0), according to the baseband digital signal.
- FSK is identical to modulating an FM carrier with a binary digital signal.
Principle of Communication

3. Binary bandpass signaling techniques
Principle of Communication

4. Principle of Communication
On-Off Keying (OOK)
Also known as Amplitude Shift Keying (ASK)
Carrier
Cos(2fct)
Message
m(t)
OOK output
Acm(t)Cos(2fct)
The complex envelope is
The OOK signal is represented by
The PSD of this complex envelope is given by
where m(t) has a peak value of
So that s(t) has an average normalized power of
Principle of Communication

5. On-Off Keying (OOK) 1 0 1 0 1 0 1 m(t) s(t)
Message
Unipolar
Modulation
Bipolar
OOK signal
m(t)
s(t)
Tb – bit period ; R – bit rate
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6. Principle of Communication
On-Off Keying (OOK)
PSD of the bandpass waveform is given by
Null-to-Null bandwidth is and absolute bandwidth is
The Transmission bandwidth is
Where B is the baseband bandwidth
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7. Principle of Communication
Detection of OOK
Non-Coherent Detection
OOK in
Binary output
Envelope
Detector
Coherent Detection with Low-pass filter
OOK in
LPF
Binary output
Principle of Communication

8. Binary Phase Shift Keying (BPSK)
Generation:
Carrier:Cos(2fct)
Message: m(t)
BPSK output
AcCos(2fct+Dpm(t))
-90
Phase shift
Message
Unipolar
Modulation
Bipolar
BPSK output
m(t)
s(t)
Principle of Communication

9. Binary Phase Shift Keying (BPSK)
The BPSK signal is represented by
let
pilot carrier term
data term
The level of the pilot carrier term is set by the value of the peak deviation
The digital modulation index ‘h’ is given by
2∆θ – maximum peak-to-peak deviation during time Ts
If Dp is small, then there is little power in data term & more in pilot term
To maximize performance (minimum probability of error)
Optimum case :
BPSK signal :
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10. Binary Phase Shift Keying (BPSK)
The complex envelope for this BPSK is given by
The PSD for this complex envelope is given by
PSD of the bandpass waveform is given by
Average normalized power of s(t) :
Null-to-Null BW
Principle of Communication
PSD of optimum BPSK

11. Binary Phase Shift Keying (BPSK)
Power Spectral Density (PSD) of BPSK: fc
2R = 2/Tb
If Dp  /2
Pilot exists
Principle of Communication

12. Frequency Shift Keying (FSK)
Discontinuous FSK :
Cos(2f1t)
Message: m(t)
FSK output
AcCos(2f1t+1) or
AcCos(2f2t+2)
Osc. f2
Osc. f1
Cos(2f2t)
The discontinuous-phase FSK signal is represented by
for t during a binary ‘1’ signal
for t during a binary ‘0’ signal
Principle of Communication

13. Frequency Shift Keying (FSK)
Continuous FSK :
Frequency
Modulator fc
FSK output
Message: m(t)
The Continuous-phase FSK signal is represented by or
where
for FSK
Principle of Communication

14. Frequency Shift Keying (FSK)
Message
Unipolar
Modulation
Bipolar
FSK output
(Discontinuous)
(Continuous)
Mark(binary 1) frequency: f1
Space(binary 0) frequency: f2
m(t)
s(t)
Principle of Communication

15. Frequency Shift Keying (FSK)
Computer
FSK modem
(Originate)
Center
(Answer)
Digital
data
PSTN
Dial up
phone line
f1 = 1270Hz
f2 = 1070Hz
f1 = 2225Hz
f2 = 2025Hz
FSK modem with 300bps
Principle of Communication