Chapter 6: Modulation and Multiplexing Techniques

Here is the work-script for chapter 6 (Slides)

24 November 2021
We learned about the parameters for the quality of an analogue transmission and a digital transmission, S/N and BER, respectively.
Each of the parameters depends on C/N and also on the modulation technique. That gets us into analogue and
digital modulations. There are three types for each of the two kinds of modulation. First we looked at analogue modulation.
We plotted a block diagram with a carrier modulator having two inputs, the carrier and the modulating signal which is
the baseband signal. The output is the modulated carrier. We assumed for the carrier a cos wave and for the baseband signal also a cos wave, however at a much lower frequency. We wrote down the equations for AM, FM and PM.
We plotted the amplitude modulated carrier and imagined how it would change if we changed the modulation index.
We plotted the spectrum of the baseband signal and the AM carrier. For the general case of a continuum of a spectrum, we use the symbolic triangle for the spectrum. We learned about upper side band (USB) and lower side band (LSB). We also learned that AM does not provide an improvement of the S/N in comparison to the C/N. Basically the highest S/N for amplitude modulation cannot be larger than C/N. Then we turned to FM. We plotted the amplitude as a function of time for a simple cases of a FM modulated carrier and looked at the equation for a frequency modulated carrier. Bessel functions were needed.

26 November 2021
We  looked at the FM waveform and thought how the spectrum of the FM carrier would appear. We realized that the theoretical bandwidth of an FM waveform is infinite. However, Carson's rule gives a bandwidth where most of the information is contained. We looked at examples. Then we focussed on the S/N ratio for the FM case and learned that it can indeed be larger than the C/N. 
Although the theoretical bandwidth of an FM waveform is infinite, Carson's rule gives a bandwidth where most of the information is contained. We looked at examples. We looked at the improvement factors.


29 November 2021
We turned to multiplexing. We saw the whole scheme of a transmitting and receiving end of a typical FDM system. FDM stands for frequency-division-multiplexing.


1 December 2021
We looked at digital baseband signals and digital modulation and the bandwidth of a digitally modulated signal. Then we looked at digital baseband signals.
We looked at digital modulation, ASK, FSK and PSK.  We learned about the bit error rate (BER) and compared it to the S/N ratio
for analogue modulation.

3 December 2021
We shortly looked at the whole scheme of a transmitting and receiving end of a typical TDM system. TDM stands for time-division-multiplexing.