Digital Modulation

A digital source produces a sequence of bits in the form of $0$s and $1$s. The question is how to send these bits from point A to point B. For this purpose, an electromagnetic wave acts as a carrier of information.

Remember that the signal produced by an unmodulated electromagnetic wave is a sinusoid given as:

$$x(t) = A \cos \left(2\pi ft + \theta\right)$$

There are three tunable parameters, which are listed below:

• Amplitude $A$
• Frequency $f$
• Phase $\theta$

Information can be conveyed by altering any of these parameters.

Let’s explore them below.

Amplitude shift keying

The process starts with converting the bits of $0$s and $1$s into voltage levels known as symbols, for example:

$$\begin{align*} 0 \quad &\longrightarrow \quad 1 \\ 1 \quad &\longrightarrow \quad 2 \end{align*}$$ ...