Basic Concepts Definition of modulation Spectra of information source signals Purposes of using modulation Does the free lunch exist? Definition of demodulation Definition of detection The whole picture – transmission system Classification of modulations „Modulation & Detection” Zdzisław Papir

Definition of modulation Modulation involves three signals: information carrying signal = modulating signal x(t) carrier c(t) modulated signal φ(t) Modulation is mapping of the information signal into one of the parameters of the carrier. The output signal is called the modulated signal. MODULATOR φ(t) x(t) c(t) „Modulation & Detection” Zdzisław Papir

Amplitude modulation MODULATOR „Modulation & Detection” Zdzisław Papir

Amplitude Modulation t „Modulation & Detection” Zdzisław Papir

Baseband modulation (line code, transmission code) + – Transition graph for Miller’s code „Modulation & Detection” Zdzisław Papir

Baseband modulation (line code) + – 1 „Modulation & Detection” Zdzisław Papir

Spectra of information source signals Voice - baseband – up to several kHzs Sound - baseband – up to tens of kHzs Video – baseband up to several MHzs Raw data – baseband up to ...? „Modulation & Detection” Zdzisław Papir

Access to different parts of the electromagnetic spectrum Purposes of using modulation Access to different parts of the electromagnetic spectrum Microwave - MHzs Satellite - GHzs Copper plant – baseband up to 10 MHz Fiber – narrow frequency window at THzs „Modulation & Detection” Zdzisław Papir

Purposes of using modulation Better noise immunity of transmission TRANSMITTER RECEIVER TRANSMISSION CHANNEL noise SNR modulation detection improvment of the Signal to Noise Ratio (SNR) SNR (modulation & detection) > SNR (baseband system) (modulation gain) „Modulation & Detection” Zdzisław Papir

interleaved signal spectra interleaved data blocks Purposes of using modulation Frequency Division Multiplex Time interleaved signal spectra Frequency (FDM) Time (TDM) interleaved data blocks „Modulation & Detection” Zdzisław Papir

spectrum widening coefficient The free lunch does not exist #1 Access to different parts of the electromagnetic spectrum #2 Better noise immunity of transmission #3 Frequency or Time Division Multiplex of transmission channels #4 SPECTRUM WIDENING B [Hz] or W [rad/s] – spectrum of the modulated signal fm [Hz] or ωm [rad/s] – spectrum of the modulating signal spectrum widening coefficient „Modulation & Detection” Zdzisław Papir

Definition of Demodulation Modulation is MAPPING the information signal onto the carrier. MODULATOR φ(t) x(t) c(t) Demodulation is STRIPPING the information signal from the modulated carrier. φ(t) x(t) DEMODULATOR c(t) „Modulation & Detection” Zdzisław Papir

Definition of Detection Detection is STRIPPING the information signal from the carrier in a noisy environment. φ(t) + noise x(t) + noise DETECTION c(t) „Modulation & Detection” Zdzisław Papir

The Whole Picture TRANSMITTER RECEIVER noise modulation detection TRANSMISSION CHANNEL noise modulation detection „Modulation & Detection” Zdzisław Papir

Transmitter LPF MOD BPF Carrier LPF – Lowpass Filter Modulated signal Information signal Carrier LPF – Lowpass Filter BPF – Bandpass Filter MOD – Modulator „Modulation & Detection” Zdzisław Papir

Receiver BPF DEMOD LPF Carrier LPF – Lowpass Filter Modulated signal Information signal Carrier LPF – Lowpass Filter BPF – Bandpass Filter DEMOD – Demodulator „Modulation & Detection” Zdzisław Papir

Transmission Channel AWGN – Additive White Gaussian Noise The common assumption is that the transmission channel disturbes the signal being transmitted with the Additive White Gaussian Noise. AWGN – Additive White Gaussian Noise „Modulation & Detection” Zdzisław Papir

Transmission System LPF MOD BPF BPF DEMOD LPF „Modulation & Detection” Zdzisław Papir

Transmission System Quality LPF MOD BPF BPF DEMOD LPF „Modulation & Detection” Zdzisław Papir

Classification of Modulations MODULATOR φ(t) x(t) c(t) Digital - Analog Digital - Analog Analog waveform – sin or cos waveform (A) Digital waveform – sequence of pulses (D) „Modulation & Detection” Zdzisław Papir

Classification of Modulations carrier A Keying ASK PSK FSK MSK GMSK AM FM SSB QAM Classics DSB A D Line codes NRZ Miller HDB PRS Sampling theorem PAM PFM PDM information signal D „Modulation & Detection” Zdzisław Papir