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Bandpass Signaling: Understanding Modulation and Functional Blocks in Communication Systems

Explore the world of bandpass signaling by learning about modulation, spectra, distortions, and functional blocks in communication systems. Discover the process of translating baseband waveforms to bandpass signals and the importance of carrier frequencies in communication.

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Bandpass Signaling: Understanding Modulation and Functional Blocks in Communication Systems

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  1. Chapter 4 Bandpass Signaling

  2. In this chapter, we consider the situations where the information from a source is transmitted at its non-natural frequency (i.e., shifted frequency). This process is called the modulation. • Representation of modulated signals • Spectra • Distortions (linear and non-linear) • Functional blocks in bandpass communication systems

  3. Basic Model for Bandpass Communication Source Destination Source can be analog or digital. The use of channel is restricted around certain frequency, fc (>> 0). For example, a radio station may be given this frequency range for commercial broadcasting. The goal is to recover the original information, m, exactly or in the minimum, as closely as possible.

  4. Definition. A baseband waveform has a spectral magnitude (and thus its power) concentrated around f=0 and zero elsewhere.Definition. A bandpass waveform has a spectral magnitude concentrated around f=±fc (fc >> 0) and zero elsewhere. (fc: carrier frequency)Definition. Modulation translates the baseband waveform from a source to a bandpass waveform with carrier frequency, fc. baseband waveform: modulating signal bandpass waveform: modulated signal

  5. Examples of Frequency Spectrum 300 Hz – 20K Hz human voice / sound 50 kHz navigation (ships, submarines, etc) 1 MHz AM radio (20 k Hz channels) 10 MHz CB, short wave 100 MHz FM radio, TV 1 GHz UHF TV, mobile telephony 10 GHz amateur satellite 100 GHz upper microwave 10 T Hz Infrared 1015 Hz Visible light 1018 Hz X-rays

  6. Bandpass Signals over Bandpass Channel Channel Out of Transmitter Into Receiver Can we translate this into a baseband model? YES!

  7. Equivalent Baseband Model for Bandpass Signals Channel Out of Transmitter Into Receiver Equivalent baseband impulse response We can now decouple the complexity of shifted frequency.

  8. Distortionless Bandpass Channel

  9. Types of (Analog) Filter

  10. analog x(t) analog y(t) Digital Filter A/D D/A manipulate digital data

  11. Example of Non-Linear Distortion by Output Saturation

  12. Harmonic Distortion

  13. Intermodulation Distortion (IMD)

  14. IMD Analysis for Filter Output

  15. Cross Modulation (Distortion)

  16. Limiter

  17. Mixer input1(t) output(t) = input1(t) x input2(t) input2(t)

  18. The nonlinear device generates “undesired” effects of product term between vin(t) and vLO(t).

  19. Mixer Implementation through Switching

  20. Double-Balanced Mixer

  21. More on Frequency Multiplier

  22. Detector Circuits Source Destination

  23. Envelop Detector low pass filter

  24. Product Detector

  25. Frequency Modulation Detector

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