Amplitude Modulation
Consists of a technique used most commonly for transmitting information via a radio carrier wave.
It consists of multiplying a signal (called "message signal"; i.e. the signal that is going to be transmitted) with a carrier signal, called modulation of the signal, then transmitting the modulated signal and retrieving the message signal, process called demodulation.
AM works by varying the strength (amplitude) of the transmitted signal in relation to the information being sent.
For example,
We have a message signal x(t) which is intended to be transmitted.
We also have a carrier signal c(t) which modulates the message signal.
So,
$ x(t)c(t) = y (t) $
Now, demodulation process can vary depending on what carrier signal is chosen for the modulation process. The two most common signals used for modulation are:
1) Complex exponential
$ c(t) = e^{j(Wct)} $
where y(t) = e^{j(Wct)} x(t)
and the demodulation process consists of simply multiplying y(t) by e^{-j(Wct)}
2) Cosine modulation
in this case, the carrier signal is c(t) = cos(Wct)
where y(t) = cos(Wct x(t).
Many methods can be used to recover the modulated signal being a common one the low pas filter,
