Digital Transmission over Passband Channels2.72001/06/012002/05/20RoyHarha@rice.eduMohammadJaberBorranmohammad@ece.rice.eduDineshRajandinesh@ece.rice.eduRoyHarha@rice.eduMohammadJaberBorranmohammad@ece.rice.eduDineshRajandinesh@ece.rice.eduamplitude modulationamplitude shift keyingASKcarrier frequencychannelmodulationpassband(Blank Abstract)
For several reasons, including multiplexing many streams of data
on a single broadband channel, and FCC (Federal Communications
Commission) regulations, in most of the practical cases, the
digitally modulated baseband signal has to be translated in
frequency domain to have nonzero energy only in a designated
band. Simple cosines can help translate well designed signals
in baseband to passband, around the frequency of interest. This
center frequency is usually referred to as carrier frequency,
and the cosine signal used for the translation is known as the
carrier signal.
Carrier Amplitude Modulation (Amplitude Shift Keying,
ASK)
Multiplying the baseband PAM signal waveforms by a carrier
signal, shifts their spectrum by the carrier frequency and,
thus, places the signal into the passband of the channel.
This is called amplitude modulation.
mm12…MumtAmgTt2fct
Recall that the Fourier transform of the carrier is
δffcδffc2.
Since multiplication in the time domain corresponds to the
convolution in the frequency domain, the spectrum of the
amplitude-modulated signal in is
UmfAm2GTffcGTffc.
Signal spectra
When the transmitted pulse shape is rectangular, the
amplitude-modulated carrier signal is usually called
amplitude-shift keying (ASK). Note that
impressing the baseband signals onto the amplitude of the
carrier signal does not change the basic geometric
representation of the digital PAM signal waveforms. The
signal space spanned by the signal set is still of dimension
one.
ψ1ts1tEs2EggTt2fctCarrier Phase Modulation (Phase Shift Keying, PSK)
Hello, World 2
Carrier Frequency Modulation(Frequency Shift Keying, FSK)
Hello, World 3
Quadrature Amplitude Modulation (QAM)
Hello, World 4