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Types of spread spectrum system
 There are three types of spread spectrum signals:
1. When spectrum spreading is accomplished by phase
modulation of a carrier by a code sequence, the resultant
signal is called a direct-sequence (DS) spread spectrum signal.
2. When the spectrum spreading is accomplished by rapid
changing of the carrier frequency based on the code sequence,
the resultant signal is called a frequency-hop (FH) spread
spectrum signal.
3. When the spectrum spreading is accomplished by very short
pulse modulation, and the code sequence is used to key the
transmitter on the code-controlled duration, the resultant
signal is called a time-hop (TH) spread spectrum signal.
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Wireless Communication Technologies 2.4.1
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