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2 Fundamentals of Information, Signal and System Theory

Information Signal

Carrier Signal

time t/s

Fig. 2.3: Principle of the basic analogue and digital modulation methods for a given information and

carrier signal carrier signal: amplitude modulation (AM), frequency modulation (FM), the frequency

modulation (FM), pulse amplitude modulation (PAM), pulse position modulation (PPM) and the pulse

width modulation (PWM) in relation to the analogue information signal (top).

by interference. In other words, the information of digital signals is also transmitted

analogue in the form of harmonics, i.e. not only the carrier frequency fT is transmitted,

but a whole spectrum in the adjacent frequency ranges. The harmonics of a signal (cf.

Figure 2.4) can be described mathematically with the help of the Fourier series:

f(t) = ^a0

2 ⁺

∞

∑

k=1

(ak cos(kt) + bk sin(kt)) .

(2.9)