What is a symbol? What is a bit?

A unit of measure for information, the smallest unit of information.

Symbol: "In digital communications, a binary digit is often represented by symbols with the same time interval. The signal within such time interval is called (binary) symbol." This interval is called the symbol length. The unit is "Baud", commonly represented by the symbol "Baud", abbreviated as "B"(difficult to understand, I know T_T).

How to understand better?

A symbol is the smallest pulse unit in the channel. The pulse is the picture with high and low values below (please ignore the picture content, as long as you roughly know what the pulse looks like).

If this signal only has two changes, high and low, then one symbol is one bit.

Example: The binary representation of the number "1" is "01," so how many bits does a symbol carry?

There's this formula that you have to remember:

N: A few bits.

N: several pulse changes

In the example above, if the letter 1 is represented by "01"

n = log2 2

Then n=1, that is, a symbol carries one bit (so binary is one symbol, one bit).

For example, if we send a symbol with eight transitions, then

n = log2 8

The result is n =3, i.e. one symbol carries 3 bits.

For example, a quaternary symbol is represented by two binary digits (n = log2 4 , n = 2), in other words, this quaternary symbol contains 2 bits of information.

Therefore, if the rate and efficiency of data transmission are to be improved, the symbol must be able to carry enough bits of information.