ABSTRACT
In digital communications, as we have discussed in Chapter 3, modulation is the process of impressing a bitstream on a carrier wave by varying its amplitude, frequency, or phase relative to a certain point in time. Every state of modulated waveform lasts for a fixed period of time, which is referred to as a symbol. In order to convey K bits of data in one symbol, it needs to have 2K different states. The symbol rate of a communications system is usually fixed. Thus, a sender realizes different transmission rates by adjusting K.
