文档介绍：Chapter 5
AM,FM, and digital modulation systems
1
Introduction (Chapter objectives)
Amplitude modulation and single sideband
Frequency and phase modulation
Digitally modulated signals(OOK, BPSK, FSK, MSK MPSK, QAM, QPSK, π/4QPSK, and OFDM)
Spread sprectrum and CDMA system
2
Introduction (the goal of this chapter)
Study g(t) and s(t) for various types of analog and digital modulations
Evaluate the spectrum for various types of analog and digital modulations
Examine some transmitter and receiver structures
Learn about spread spectrum systems
3
Introduction (the key of this chapter)
Grasping phase modulation and frequency modulation
Grasping Binary modulation and Bandpass signaling
Grasping Multilevel Modulated bandpass signaling
Grasping Minimum-shift keying (MSK)and GMSK
Knowing the principle of FDM, OFDM and Spread Spectrum Systems
4
Introduction (band-pass signal and its spectra)
Communication system constructure
input
signal
processing
carrier
circuits
Transmission
Medium
(channel)
transmitter
g(t)
s(t)
carrier
circuits
signal
processing
r(t)
g(t)
output
Modulation is the process of imparting the source information onto a Band-pass signal with a carrier frequency fc by the introduction of amplitude or phase perturbations or both.
5
Introduction (band-pass signal and its spectra)
Theorem:Any physical band-pass waveform can be representative by
g(t) is called plex envelope of s(t),and fc is carrier frequency (in hertz), ωc=2πfc
Notice: The desired type of modulated signal,s(t),is obtained by selecting the appropriate modulation mapping function g[m(t)],where m(t) is the analog or digital base-band signal.
The voltage (or current)spectrum of the band-pass signal is
and the PSD is
6
Amplitude Modulation
plex envelope of an AM signal is given by
Where Ac specifies the power level and m(t) is the modulating signal. The representation for AM signal is given by:
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7
Amplitude Modulation (modu