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Chapter 14
Compressive Modulation
14.1 Introduction
In digital communications, as we have discussed in Chapter 3, modulation is the pro-
cess 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 2
K
different states. The symbol rate of a com-
munications system is usually fixed. Thus, a sender realizes different transmission
rates by adjusting K.
A symbol can also be conveniently represented as a point on a complex plane,
called constellation diagram. So, there are 2
K
possible points on the sender’s con-
stellation ...