3. 1-Modulation
is the process of varying one or more
properties of a periodic waveform, called
the carrier signal, with a modulating signal
that typically contains information to be
transmitted .
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5. Analog Modulation
.
Amplitude Modulation: In this type of modulation the
amplitude of the carrier signal is varied with the modulating
signal.
Frequency Modulation: In this type of modulation the
frequency of the carrier signal is varied with the modulating
signal.
Phase Modulation: In this type of modulation the phase of the
carrier signal is varied with the modulating signal.
-
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6. Digital Modulation
. The most fundamental digital modulation
techniques are based on keying:
PSK (phase-shift keying): a finite number of phases
are used.
FSK (frequency-shift keying): a finite number of
frequencies are used.
ASK (amplitude-shift keying): a finite number of
amplitudes are used.
QAM (quadrature amplitude modulation): a finite
number of at least two phases and at least two
amplitudes are used.
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7. Pulse Modulation
The Pulse wave modulation are of four
types namely:
Pulse amplitude Modulation
Pulse position Modulation
Pulse width Modulation
Pulse code Modulation.
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9. 3-QAM
1-QAM mean :Quadrature amplitude
modulation
2- is both an analog and a digital modulation
scheme. It conveys two analog message
signals, or two digital bit streams, by changing
(modulating) the amplitudes of two carrier
waves, using the amplitude-shift keying (ASK)
digital modulation scheme or amplitude
modulation (AM) analog modulation scheme
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10. QAM
3-The two carrier waves of the same
frequency, usually sinusoids, are out of
phase with each other by 90° and are thus
called quadrature carriers or quadrature
components — hence the name of the
scheme.
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12. QAM
4- The modulated waves are summed, and
the final waveform is a combination of
both phase-shift keying (PSK) and
amplitude-shift keying (ASK), or, in the
analog case, of phase modulation (PM)
and amplitude modulation
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13. QAM
5-At the receiver the signal is split and
sent to the sine and cosine demodulators .
After demodulation a low pass filter is
.
used to remove noise
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15. 4-QAM application
1- QAM is in many radio communications
and data delivery applications.
2-. For broadcast applications for example,
64 QAM and 256 QAM are often used in
digital cable television and cable modem
applications
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17. 5-Advantage of QAM
the Basic advantage of QAM is that:
Quadrature modulation is an efficient
method of transmitting two message
signals with the same bandwidth .
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18. 6-Disadvantage of QAM
1- Basic disadvantage of QAM is that While it is
possible to transmit more bits per symbol, if the
energy of the constellation is to remain the same,
the points on the constellation must be closer
together and the transmission becomes more
susceptible to noise. This results in a higher bit
error rate than for the lower order QAM variants. In
this way there is a balance between obtaining the
higher data rates and maintaining an acceptable bit
error rate for any radio communications system.
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