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Basic Concepts „Modulation & Detection”  Zdzisław Papir Definition of modulation Spectra of information source signals Purposes of using modulation Does.

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Presentation on theme: "Basic Concepts „Modulation & Detection”  Zdzisław Papir Definition of modulation Spectra of information source signals Purposes of using modulation Does."— Presentation transcript:

1 Basic Concepts „Modulation & Detection”  Zdzisław Papir 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

2 Definition of modulation „Modulation & Detection”  Zdzisław Papir 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)φ(t) x(t)x(t) c(t)c(t)

3 Amplitude modulation „Modulation & Detection”  Zdzisław Papir MODULATOR

4 Amplitude Modulation „Modulation & Detection”  Zdzisław Papir t

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

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

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

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

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

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

11 The free lunch does not exist „Modulation & Detection”  Zdzisław Papir #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 f m [Hz] or ω m [rad/s] – spectrum of the modulating signal spectrum widening coefficient

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

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

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

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

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

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

18 „Modulation & Detection”  Zdzisław Papir LPFMOD BPF Transmission System BPFDEMOD LPF

19 „Modulation & Detection”  Zdzisław Papir LPFMOD BPF Transmission System Quality BPFDEMOD LPF

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

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


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