What is the difference between signal and symbol in wireless communications?
A signal is a sequence of symbols transmitted sequentially over time.

A symbol is any distinct state of the communication channel.

For example, in a binary (two-state) channel, the states could be two voltage levels, two different values of current, or even two different frequencies &mdash; i.e., a simple modem. Such a channel can transmit one bit of information at a time.

Many types of channels can have more than two states, and this gives you the ability to transmit more than one bit at a time. For example, a 64-state channel can transmit 6 bits at a time, because 64 = 26. We say that each symbol represents 6 bits, and the channel capacity is the symbol rate (also sometimes called baud rate) multiplied by the number of bits per symbol.