Principle of Communication Eeng 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 Eeng  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

Principle of Communication Eeng Binary Bandpass Signaling techniques

Principle of Communication Eeng  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

Principle of Communication Eeng T b – bit period ; R – bit rate Message Unipolar Modulation Bipolar Modulation OOK signal m(t)m(t) m(t)m(t) s(t)s(t) On-Off Keying (OOK)

Principle of Communication Eeng  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 On-Off Keying (OOK)

Principle of Communication Eeng OOK in Binary output Envelope Detector LPF OOK in Binary output  Non-Coherent Detection Detection of OOK  Coherent Detection with Low-pass filter

Principle of Communication Eeng 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) Message Unipolar Modulation Bipolar Modulation BPSK output m(t) s(t) Generation:

Principle of Communication Eeng  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 Binary Phase Shift Keying (BPSK)

Principle of Communication Eeng  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 Binary Phase Shift Keying (BPSK)

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

Principle of Communication Eeng 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

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

Principle of Communication Eeng 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)

Principle of Communication Eeng 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 Frequency Shift Keying (FSK)