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Quadrature-Amplitude Modulation (QUAM or Qam) : A Report By: Nikho M. Cubillas

Quadrature-Amplitude Modulation (QAM) is a digital modulation technique that uses both the amplitude and phase of a carrier wave to transmit information. It combines amplitude-shift keying and phase-shift keying, allowing for higher bandwidth efficiency. Specific variants of QAM such as 64 QAM and 256 QAM are commonly used in digital cable and broadcast television. Lower order variants like 8-QAM and 16-QAM divide incoming data into groups of bits that are each mapped to distinct amplitude-phase combinations. Higher order variants can transmit more data per symbol but require a larger signal constellation and greater bandwidth.

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197 views18 pages

Quadrature-Amplitude Modulation (QUAM or Qam) : A Report By: Nikho M. Cubillas

Quadrature-Amplitude Modulation (QAM) is a digital modulation technique that uses both the amplitude and phase of a carrier wave to transmit information. It combines amplitude-shift keying and phase-shift keying, allowing for higher bandwidth efficiency. Specific variants of QAM such as 64 QAM and 256 QAM are commonly used in digital cable and broadcast television. Lower order variants like 8-QAM and 16-QAM divide incoming data into groups of bits that are each mapped to distinct amplitude-phase combinations. Higher order variants can transmit more data per symbol but require a larger signal constellation and greater bandwidth.

Uploaded by

Mark Jason Casil
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Quadrature-Amplitude

Modulation (QUAM or
QAM)

A report by: Nikho M. Cubillas


Quadrature-Amplitude Modulation

• Is a form of digital modulation similar to PSK


except the digital information is contained in
both the amplitude and phase of the
transmitted carrier.
• Amplitude and phase-shift keying are
combined.
• This reduces the likelihood or the similarity of
errors occurring.
Quadrature-Amplitude Modulation Applications

• QAM is in many radio communications and


data delivery applications. However some
specific variants of QAM are used in some
specific applications and standards.
• For domestic broadcast applications for
example, 64 QAM and 256 QAM are often used
in digital cable television and cable modem
applications.
Quadrature-Amplitude Modulation Applications

• In the UK, 16 QAM and 64 QAM are currently


used for digital terrestrial television using DVB
- Digital Video Broadcasting.
• variants of QAM are also used for many
wireless and cellular technology applications
8-QAM
8-QAM

 The incoming data are


divided into groups of
three bits (tribits):
• I
• Q
• C

Each bit has a bit rate


equal to the one-
third( of the total
incoming data rate.
8-QAM
Ex: (000) I = 0, Q= 0, C = 0
Determine the output amplitude and phase for the 8-
QAM modulator shown in the figure:

I/Q C Output
0 0 -0.531 V
0 1 -1.307 V
1 0 +0.541 V
1 1 +1.307 V
8-QAM
Note:
Q:
1 – (+) phase
0 – (-) phase

I:
1 – (45º) phase
0 – (135º) phase

C:
1 – 1.848 V
0 – 0.765 V
8-QAM
8-QAM
8-QAM
Bandwidth Consideration:
• The bit rate in the I and Q channels is
one-third of the input binary rate, same
as 8-PSK.
• The highest fundamental modulating
frequency and fastest output rate of
change are the same as with 8-PSK.
• Minimum bandwidth required: fb/3
16-QAM
16-QAM

The incoming data are


divided into groups of
three bits (tribits):
• Q
• Q’
• I
• I’
As with 8-QAM, both the
phase and the amplitude
of the transmit carrier
are varied.
16-QAM
Ex: (0000) I = 0, I’ = 0, Q= 0, Q’ = 0
Determine the output amplitude and phase for the 16-
QAM modulator shown in the figure:
16-QAM
16-QAM
Bandwidth Consideration:
• The bit rate in the I, I’, Q and Q’ channels
is one-fourth of the input binary rate.
• The highest fundamental modulating
frequency and fastest output rate of
change are the same as with 16-PSK.
• Minimum bandwidth required: fb/4
• Video
‘M’-QAM Comparison

(a) QPSK, (b) 8PSK, (c) 16QAM, (d) 32QAM, (e) 64QAM, and (f)
128QAM
Human na jud.
Daghang Salamat.

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