1. Principle of Communication EEE 360 1 Chapter 5 AM, FM, and Digital Modulated Systems  Binary Bandpass Signalling Techniques  OOK  BPSK  FSK

2. Principle of Communication EEE 360 2  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 0 o or 180 o 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. Binary bandpass signaling techniques

3. Principle of Communication EEE 360 3 Binary bandpass signaling techniques

4. Principle of Communication EEE 360 4  The complex envelope is Carrier Cos(2  f c t) Message m(t) OOK output A c m(t)Cos(2  f c t)  The OOK signal is represented by On-Off Keying (OOK)  Also known as Amplitude Shift Keying (ASK)  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

5. Principle of Communication EEE 360 5 On-Off Keying (OOK) T b – bit period ; R – bit rate 1 0 1 0 1 0 1 Message Unipolar Modulation Bipolar Modulation OOK signal m(t)m(t) m(t)m(t) s(t)s(t)

6. Principle of Communication EEE 360 6 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

7. Principle of Communication EEE 360 7 OOK in Binary output Envelope Detector LPF OOK in Binary output  Non-Coherent Detection Detection of OOK  Coherent Detection with Low-pass filter

8. Principle of Communication EEE 360 8 Carrier:Cos(2  f c t) Message: m(t) BPSK output A c Cos(2  f c t+D p m(t)) -90  Phase shift Binary Phase Shift Keying (BPSK) 1 0 1 0 1 0 1 Message Unipolar Modulation Bipolar Modulation BPSK output m(t) s(t) Generation:

9. Principle of Communication EEE 360 9 Binary Phase Shift Keying (BPSK)  The BPSK signal is represented by pilot carrier termdata 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  If D p 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 : 2∆θ – maximum peak-to-peak deviation during time T s let

10. Principle of Communication EEE 360 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 PSD of optimum BPSK

11. Principle of Communication EEE 360 11 fcfc 2R = 2/T b If D p   /2 Pilot exists Binary Phase Shift Keying (BPSK) Power Spectral Density (PSD) of BPSK:

12. Principle of Communication EEE 360 12 Frequency Shift Keying (FSK) Cos(2  f 1 t) Message: m(t) FSK output A c Cos(2  f 1 t+  1 ) or A c Cos(2  f 2 t+  2 ) Osc. f2 Osc. f1 Cos(2  f 2 t)  Discontinuous FSK :  The discontinuous-phase FSK signal is represented by for t during a binary ‘1’ signal for t during a binary ‘0’ signal

13. Principle of Communication EEE 360 13 Frequency Shift Keying (FSK)  The Continuous-phase FSK signal is represented by Frequency Modulator f c Message: m(t) FSK output  Continuous FSK : or where for FSK

14. Principle of Communication EEE 360 14 1 0 1 0 1 0 1 Message Unipolar Modulation Bipolar Modulation FSK output (Discontinuous) FSK output (Continuous) Mark(binary 1) frequency: f 1 Space(binary 0) frequency: f 2 m(t)m(t) m(t)m(t) s(t)s(t) s(t)s(t) Frequency Shift Keying (FSK)

15. Principle of Communication EEE 360 15 Frequency Shift Keying (FSK) Computer FSK modem (Originate) Computer Center FSK modem (Answer) Digital data PSTN Dial up phone line f 1 = 1270Hz f 2 = 1070Hz f 1 = 2225Hz f 2 = 2025Hz FSK modem with 300bps