1. Chapter 5 Digital Modulation Systems
Binary Bandpass Signalling Techniques
OOK
BPSK
FSK
Huseyin Bilgekul
EEE 461 Communication Systems II
Department of Electrical and Electronic Engineering
Eastern Mediterranean University

2. Pulse Modulation Schemes
Digital Modulation
Pulse Modulation Schemes
Keying Schemes
The basic idea is to use a pulse train as the carrier signal
Either the frequency or phase of a carrier signal is keyed in response to patterns of 1s and 0s.
Passband PAM Modulation
PWM modulation

3. Digital Modulation Carrier signal: Ac cos (2pfct + θ) Modulation: m(t)
Modulated signal: Ac (t) cos (2pfc(t) t + θ(t))
 m(t); discrete
Vary Vary
amplitude frequency & phase
Variations are discrete!!!!!
Binary
OOK
BPSK
DPSK
FSK
Multilevel
QPSK
MPSK
QAM

4. 5-9 Binary Modulated Bandpass signaling:
The most common binary bandpass signaling techniques are:
On –Off keying (OOK),
OOK is also called amplitude shift keying (ASK), which consists of keying (switching) a carrier sinusoid on and off with a uni-polar 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),
BPSK consists of shifting the phase of a sinusoidal carrier 0 or 180 with a unipolar binary signal. BPSK is equivalent to PM signaling with a digital waveform.
Frequency-Shift Keying (FSK),
FSK consists of shifting the frequency of a sinusoidal carrier from a mark frequency to a space frequency, according to the baseband digital signal. FSK is identical to modulating an FM carrier with a binary digital signal.

5. Binary bandpass signaling techniques1 1 1
Change in Phase
Change in Freq
Note:
Digitally modulated bandpass signals are generated by using the complex envelopes for AM,PM,FM or QM
Modulating signal m(t) is a digital signal given by binary or multilevel signals

6. On-Off Keying (OOK) / Amplitude Shift Keying (ASK)
Key/ Switch
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

7. Tb – Bit period ; R – Bit rate
On-Off Keying (OOK)
Message
Unipolar
Modulation
m(t)
Bipolar
Modulation
m(t)
s (t)
OOK signal
Tb – Bit period ; R – Bit rate

8. Spectrum of On-Off Keying (OOK)
PSD of the bandpass waveform is given by
For OOK
Null-to-Null bandwidth is and absolute bandwidth is
The Transmission bandwidth is Where B is the baseband bandwidth
Using Raised cosine pulse shape the bandwidth is:

9. Detection of OOK Non-Coherent Detection Binary output OOK in Envelope
Detector
Coherent Detection with Low-pass filter
OOK in
LPF
Binary output

10. Optimum Detection of OOK
For optimum detection (Lowest Bit Error Rate BER) of OOK product detection with MATCHED Filter processing is required.

11. Binary Phase Shift Keying (BPSK)
The BPSK signal is represented by
To make this problem simple let,
Pilot carrier term
Data term
The level of the pilot carrier term is set by the value of the Peak Deviation Δθ = Dp
The digital modulation index ‘h’ is defined as
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 :
Optimum BPSK signal :

12. 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
m(t)
Bipolar
Modulation
m(t)
s(t)
BPSK output

13. Spectrum of Binary Phase Shift Keying (BPSK)
The complex envelope Optimum 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) :
2R = 2/Tb
Null-to-Null BW
PSD of optimum BPSK

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

15. Frequency Shift Keying (FSK)
Continuous FSK
Discontinuous FSK
Discontinuous Phase FSK: Switching between two different oscillators.
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
This FSK is not used often.

16. Continous Phase (FSK) Continuous FSK : m(t) is discontinuous (Digital)
Frequency
Modulator
Carrier fc
FSK output
Message: m(t)
The Continuous-phase FSK signal is represented by or
Where
for FSK
m(t) is discontinuous (Digital)
θ(t) is continuous ( Integration of m(t))

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

18. Application of FSK – PC MODEM
Computer
FSK modem
(Originate)
Center
(Answer)
Digital
data
PSTN
Dial up
phone line
f1 = 1270Hz
f2 = 1070Hz
f1 = 2225Hz
f2 = 2025Hz
FSK modem with 300 Bps
Historically FSK signalling was for telephone modems.
Fast (28.8 kb/s and 56 kb/s modems use QAM signalling.

19. Bandwidth of FSK
The approximate bandwidth of FSK is given by CARSON’S Rule.
If Raised cosine-rolloff premodulation filter is used then,

20. Detection of FSK
FSK signal can be detected both coherently and incoherently.