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Exponential Modulation

Exponential Modulation. Analog and Digital Communications Autumn 2005-2006. Exponential Modulation. Modulation in which information signal is encoded in carrier frequency or phase Amplitude of the transmitted signal is constant This modulation is robust to channel gain variations

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Exponential Modulation

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  1. Exponential Modulation Analog and Digital Communications Autumn 2005-2006 CS477: Analog and Digital Communications

  2. Exponential Modulation • Modulation in which information signal is encoded in carrier frequency or phase • Amplitude of the transmitted signal is constant • This modulation is robust to channel gain variations • The modulation is non-linear • Bandwidth of the transmitted signals depends upon the amplitude of the information signal CS477: Analog and Digital Communications

  3. Exponential Modulation Transmitted/Modulated signal: Total instantaneous angle: To obtain angle or exponential modulation: Make instantaneous phase dependent on the information signal CS477: Analog and Digital Communications

  4. Instantaneous Frequency Instantaneous frequency: For constant phase signals: For signals with time varying phase: CS477: Analog and Digital Communications

  5. is called phase deviation Phase Modulation (PM) Make phase proportional to the information signal: Instantaneous frequency is dependent on the derivative of the information signal CS477: Analog and Digital Communications

  6. is called frequency deviation Frequency Modulation (FM) Make instantaneous frequency dependent on the information signal What is the transmitted signal? CS477: Analog and Digital Communications

  7. PM Modulator Input FM Output PM to FM and Vice Versa (For FM) (For PM) CS477: Analog and Digital Communications

  8. Peak and Average Powers • Peak power is: • Average power is: • Peak to average power ratio is 2 • Compare with DSB and AM • Low peak to average power ratio is good for circuit designers CS477: Analog and Digital Communications

  9. AM, FM, and PM Comparison CS477: Analog and Digital Communications

  10. Spectral Analysis of FM • Exponential modulation is non-linear • Bandwidth of the transmitted signals depends upon the amplitude of the information signal • Hard to analyze with Fourier transforms • Narrowband approximation makes analysis a little easier  NBFM and NBPM • For narrowband approximation to hold: CS477: Analog and Digital Communications

  11. NBFM and NBPM Consider the bandpass transmitted signal: For narrowband approximation: CS477: Analog and Digital Communications

  12. NBFM and NBPM Thus, for NBFM and NBPM: CS477: Analog and Digital Communications

  13. Tone Modulation Thus, for NBFM and NBPM: CS477: Analog and Digital Communications

  14. Tone Modulation with NB CS477: Analog and Digital Communications

  15. Tone Modulation with NB CS477: Analog and Digital Communications

  16. NOTE: and are periodic Tone Modulation with WB CS477: Analog and Digital Communications

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