Tutorial 3 1 Briefly describe the working principle

Tutorial 3 1. Briefly describe the working principle of Modulation and Demodulation. List the common Modulation schemes in data communication. 2. Why does the ITU-R only regulate ‘lower’ frequencies (up to some hundred GHz) and not higher frequencies (in the THz range)? 3. What are the main problems of signal propagation? Why do radio waves not always follow a straight line? Why is reflection both useful and harmful?

Tutorial 3 Briefly describe the working principle of Modulation and Demodulation. List the common Modulation schemes in data communication. 1. Ø ü ü ü Ø ü ü Modulation: conversion of data into signals for sending Basic schemes Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM) Two steps Digital modulation • Digital data are translated into analog signals • Differences in spectral efficiency, power efficiency, robustness Analog modulation • Shifts center frequency of baseband signals up to the radio carrier

Tutorial 3 2. Why does the ITU-R only regulate ‘lower’ frequencies (up to some hundred GHz) and not higher frequencies (in the THz range)? • Frequencies in the THz range, e. g. , infrared, visible light, are easily blocked by obstacles and, thus, do not interfere with other transmissions. In this case, only the standard safety regulations apply (e. g. , laser emission). Most radio systems stay well beyond 100 GHz as it is not that simple to generate higher frequencies (in the lower THz range). • •

Tutorial 3 3. What are the main problems of signal propagation? Why do radio waves not always follow a straight line? Why is reflection both useful and harmful? • Problems: attenuation, scattering, diffraction, reflection, refraction. Except for attenuation all other effects can divert the waves from a straight line. Only in vacuum and without gravitational effects radio waves follow a straight line. Without reflection radio reception in towns would be almost impossible. A line-of-sight almost never exists. However, reflection is the main reason for multi-path propagation causing ISI. • • •