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Quadrature Amplitude Modulation
(QAM)
QAM
Date
Transmitting Information … (Analog or
Digital)
Modify a Signal
“Modulate”
Detect the Modifications
“Demodulate”
Any reliably detectable change in signal
characteristics can carry information
QAM
Date
Signal Properties
QAM
Date
Analog Modulation
Amplitude
(AM)Frequency -
FM
θV= A(t) sin[
(t)]
V= A(t) sin[2 f(t) +
(t)]
π φ
Phase - M
QAM
Date
Analog-to-Digital …
Amplitude
Frequency
Phase
Both Amplitude and
Phase
1 0 1 0
ASK
FSK
PSK
Discrete States
QAM
Date
Concept of I-Q …
PhaseMag
0 deg
(ref.)
“Q” - Quadrature
“I” – In PhaseI value
Q value
Polar Notation:
Magnitude &
Phase
I-Q Notation:
In Phase &
Quadrature
QAM
Date
Signal Changes or Modifications
Phase
Mag
0 deg
Magnitude Change
Phase0 deg
Phase Change
Frequency Change
Both Change0 deg
0 deg
QAM
Date
I-Q Modulation
Transmitter
Receiver
QAM
Date
I-Q Modulation Examples
I
Q
01I
Q0001
1011
BPSK
1bit/sym
Symbol rate = bit rate
QPSK
2bits/sym
Symbol rate = ½ bit rate
I
Q00000011
1100111
1 16-QAM
4bits/sym
Symbol rate =1/4 bit rate
Symbol
Constellation Diagrams
QAM
Date
Bit Rate and Symbol Rate
BIT RATE is the frequency of the system bit stream
SYMBOL RATE is the bit rate divided by the number of
bits that can be transmitted with each symbol (also
known as the BAUD RATE)
� Signal Bandwidth depends on the Symbol Rate
� More complicated modulation formats use less
(narrower) spectrum to provide the same
transmission capacity
QAM
Date
Spectral Efficiency
Trade-Off: as the complexity of the modulation increases, the radio becomes more spectrally efficient. However, it also becomes more susceptible to errors caused by noise and distortion.
QAM
Date
256-QAM
QAM
Date
Error Vector Magnitude
{
I
Q Magnitude Error (IQ error mag)
Error Vector
Ideal (Reference) Signal
Phase Error (IQ error phase)
TestSignal
φφφφ
(
)
average error magnitude
peak symbol magnitudeEVM (%) = x 100
EVM is a measure of the quality of modulation.
QAM
Date
Some QAM Applications
WLAN – 16/64 qam
Point-to-Point – 16/32/64/128/256 qam
Digital Video – 16/32/64 qam
Cable TV – 16/64/256 qam
QAM
Date
Lets look at some pre-recorded QAM
signals …
QAM
Date
256-QAM Recorded Signal
