Modulation and Multiplexing Techniques
Here is the work-script for chapter 6
We found 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 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.
Here is a graphical
between AM and FM.
For the FM spectrum, click here.
For an explanation and for applets for analog modulation
and FM) click here.
27 November 2017
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.
Then we turned to multiplexing. We saw the whole scheme of a
transmitting and receiving end of a typical
FDM stands for frequency-division-multiplexing. We looked
at digital baseband signals and digital modulation and the
bandwidth of a digitally modulated signal. Then we looked at digital baseband
1 December 2017
We looked at digital modulation
and the bandwidth of a digitally modulated signal. For an explanation and for applets for digital
FSK and PSK) click here. We
learned about the bit error rate (BER) and compared it to the
for analogue modulation. We looked at the whole scheme
of a transmitting and receiving end of a typical TDM system. TDM
stands for time-division-multiplexing.