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Basic Concepts

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.

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Basic Concepts

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  1. 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

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

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

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

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

  6. – + 1 0 1 1 0 0 0 0 0 1 1 0 1 Baseband modulation(line code) „Modulation & Detection” Zdzisław Papir

  7. Spectra of informationsource 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

  8. Purposes of usingmodulation 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

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

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

  11. 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 wideningcoefficient „Modulation & Detection” Zdzisław Papir

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

  13. 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

  14. TRANSMISSIONCHANNEL TRANSMITTER RECEIVER noise modulation detection The Whole Picture „Modulation & Detection” Zdzisław Papir

  15. Transmitter LPF MOD BPF Modulatedsignal Informationsignal Carrier LPF – Lowpass Filter BPF – Bandpass Filter MOD – Modulator „Modulation & Detection” Zdzisław Papir

  16. Receiver BPF DEMOD LPF Modulatedsignal Informationsignal Carrier LPF – Lowpass Filter BPF – Bandpass Filter DEMOD – Demodulator „Modulation & Detection” Zdzisław Papir

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

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

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

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

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

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