QAM Modulation

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Quadrature Amplitude Modulation (QAM)

Transmitting Information (Analog or Digital)Modify a Signal Modulate

Detect the Modifications Demodulate Any reliably detectable change in signal characteristics can carry informationQAM Date

Signal Properties

QAM Date

Analog Modulation

V= A(t) sin[2 f(t) + (t)]Amplitude (AM) Frequency FM Phase - M

QAM Date

V= A(t) sin[ (t)]

Analog-to-Digital

Discrete States 0 0 1 1 ASK FSK PSK

Amplitude Frequency Phase Both Amplitude and PhaseQAM Date

Concept of I-Q

Q - Quadrature

Q value

M

ag

Phase

0 deg (ref.)

I value

I In Phase

Polar Notation: Magnitude & PhaseQAM Date

I-Q Notation: In Phase & Quadrature

Signal Changes or Modificationsag M

Phase 0 deg Phase 0 deg

Magnitude Change

Phase Change

0 deg 0 deg

Both Change Frequency Change

QAM Date

I-Q Modulation

Receiver Transmitter

QAM Date

I-Q Modulation ExamplesQ 1 0 ISymbol

01

Q

00

0011

Q

0000

I

I

11

10

BPSK QPSK 1bit/sym 4bits/sym 2bits/sym Symbol rate = bit rate Symbol rate = bit rate Symbol rate =1/4 bit rate

1100 111 1 16-QAM

Constellation DiagramsQAM Date

Bit Rate and Symbol RateBIT 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 capacityQAM 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 MagnitudeEVM (%) = average error magnitude peak symbol magnitude

Q

Magnitude Error (IQ error mag)

( )

x 100

{

Error Vector Test Signal

EVM is a measure of the quality of Ideal (Reference) Signal modulation.Phase Error (IQ error phase)

I

QAM Date

Some QAM ApplicationsWLAN 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

QAM Date