digital communication- student version
DESCRIPTION
Digital communication- student version. Dr. Uri Mahlab. General overview. Digital Radio Theory and Implementation -How a Digital Radio Works. Digital Radio Block Diagram. CODER. MOD. UPCONVERTER. DEMOD. DECODER. DOWNCONVERTER. Analog vs. Digital Modulation. AM. FM. PM. DIGITAL. - PowerPoint PPT PresentationTRANSCRIPT
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Digital communication- Digital communication- student versionstudent version
Dr. Uri Mahlab
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General overviewGeneral overview
Digital Radio Theoryand Implementation
-How a Digital Radio Works
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Digital Radio Block DiagramDigital Radio Block Diagram
CO
DER MOD
UPCONVERTER
DOWNCONVERTER
DEMOD
DE C
OD
E R
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Analog vs. Digital ModulationAnalog vs. Digital Modulation
AM
FM
PM
DIGITAL
With digital modulation information is in the phase and
amplitude of the signal
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The IQ DiagramThe IQ Diagram
Vq
Vi
magnitude
phase
Q
I
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Analog Modulation on the IQ diagramAnalog Modulation on the IQ diagram
Q
I
B
A
C
D
FM
PM
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BPSK Timing and State DiagramBPSK Timing and State Diagram
Reference
State 1 State 0
= 0 deg. = 180 deg.
0 State 1 State
BPSK
Constellation
Diagram
Q
I
t
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QPSK ModulationQPSK Modulation
Q
I
00
1011
01
Vi
Vq
4 Possible States
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16 QAM State Diagram16 QAM State Diagram
Q
I
0000 00110001
01010100 0111
1100
0010
1101
0110
10011000 1010
1110
1011
1111
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Symbol Rate:Symbol Rate:
“The rate at which the carrier
moves between points in the
constellation”
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Example:Example:
16 Mb/s4 Bits
A 16 QAM radio has 4 bit per state (or symbol).
If the radio operates at 16 Mb/s, then the
carrier must change states
or
4 million times per second (4 MBaud)
SYMBOL RATE = 4MHz
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Some Typical Modulation FormatsSome Typical Modulation Formats
BPSK QPSK 8PSK
16QAM 64QAM
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QPSK ModulatorQPSK Modulator
SERIAL TOPARALLEL
CONVERTERCARRIER PHASE
SHIFT BPFCOMBINER
00
11 10
01
COMBINED VECTOR
STATE DIAGRAM
BALANCED
MODULATION
BALANCED
MODULATION
QUADRATURE DATA STREAM
IN-PHASE DATA STREAM
fs = fb/2
BINARY
NRZ
INPUT
SIGNAL
fb
SYMBOL RATE:fs = fb/2
I
Q
I.F0°
90°
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I, Q, Eye diagram and ConstellationI, Q, Eye diagram and Constellation
EYE
I
Q
+1
-1
+1
-1
CONSTELLATION :
I
Q
1,4
5 3
2
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QPSK DemodulatorQPSK Demodulator
BPF PowerSplitter
CarRec.
PhaseSplitter
Symboltiming
rec.(STR)
Parallelto serial
converter
LPF.
LPF.
ThreshComp.
ThreshComp.
IF
Input
Phase
Demodulation
Phase
Demodulation
Binary
NRZfb
fb/2
fb/2
I
Q
I
Q
0°
90°
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16 QAM Modulator16 QAM Modulator
Data
2-to-4level
convert
2-to-4level
convert
Premod.LPF
Premod.LPF
Phasesplit BPFLO
L.F.
16 QAM
Output
0°
90°
Q
I
4bf
4bfI
Q
2bf
2bf
Binary
NRZ
Data
bf
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16 QAM Demodulator16 QAM Demodulator
BPF CR STR
X2datacon
blner
LPF
LOGIC
1thV
2thV
3thV
4-to-2 level converterof Q channel. Samedesign as I channel.
IF Input
I
Q
0°
90°
4-LevelSignal
4-LevelSignal
4bf
4bf
Regeneration
DataOutfb
2bf
2bf
LPF
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Which waveform requires more bandwidth?Which waveform requires more bandwidth?
A
B
time
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Bandwidth ConsiderationsBandwidth Considerations
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Two random data sequenceTwo random data sequence
timefrequency
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Unfiltered Digital Radio SpectrumUnfiltered Digital Radio Spectrum
0f SFf 0 SFf 20 SFf 30 SFf 40 SFf 0SFf 20 SFf 30 SFf 30 SFf 50
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An UNFILTERD RadioAn UNFILTERD Radio
CO
DER MOD U/C
D/C DEMOD
DEC
OD
ERtime
time
frequency
Data is easier to
recover but signal
requires a lot of
bandwidth
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A FILTERED RadioA FILTERED Radio
CO
DER MOD U/C
D/C DEMOD
time
time
frequency
Signal requires less
bandwidth but data
is filtered
DEC
OD
E R
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Intersymbol InterferenceIntersymbol Interference
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Nyquist FilteringNyquist Filtering
Raised Cosine
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Filter Coefficient & Determines Required B.W.Filter Coefficient & Determines Required B.W.
15.0
3.00
SF2SFRateSymbolFS _
Amplitude
Response
Linear Phase
(Flat Group Delay)
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The Filtering is Distributed in the RadioThe Filtering is Distributed in the Radio
CO
DER MOD
UPCONVERTER
DOWNCONVERTER
DEMOD
DE C
OD
E R
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SUMMARYSUMMARY
As the modulation complexity increases,the radio becomes more spectrally efficient.However, it also become more susceptibleto errors caused by noise and distortions.
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TOTAL PROBABILITYOF NOISE AMPLITUDE
EXCEEDING THISTHRESHOLD
THRESHOLDP(x)
X10 20 30-10-20-30
0.1
0.2
0.3
0.4
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How Error OccurHow Error OccurVOLTAGE
PROBReceived signal withsuperimposed noise
1 ERROR
0 ERROR0
1
THRESHOLDDECISION
NORMAL1 VALUE
NORMAL0 VALUE
BINARY SIGNAL + AMPLTUDENOISE FDP
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Gaussian DistributionGaussian Distribution
0.1
0.2
0.3
0.4
P(x)
X10 20 30-10-20-30
NEVER RECHSZEBO
PROBABILITYDENSITY
FUNCTION
0=RMS VALUE AFTERSUBTRACTING
DC COMPONENT
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Meaning of Eye diagramMeaning of Eye diagram
Threshold