Figure,(a) and (b), shows
the encoding and data modulation process. For digital signal, a data source
g(t), which may be either digital or analog, is encoded into a signal x(t). The
actual form of x(t) depends on the encoding technique and is chosen to optimize
use of the transmission medium.
The basis for analog
signaling is a continuous constant-frequency signal known as the carrier
signal. Data may be modulation. Modulation is the process of encoding source
data onto a carrier signal with frequency fc. All modulation techniques involve
operation on one or more of the three fundamental frequency domain parameters
amplitude, frequency and phase.
The input signal m(t) may
be analog or digital and is called the modulating signal or baseband signal.
The result of modulating the carrier signal is called the modulated signal
s(t).
Figure (b) indicates, s
(t) is a band limited signal. The location of the bandwidth on the spectrum is
related to fc and is often centered as fc. Again the actual form of the encoding
is chosen to optimize some characteristic of the transmission.
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