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ISI- Inter-symbol InterferenceNyquist filters
EELE445-14Lecture 22
Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–24 Baseband pulse-transmission system.
•HT(f) shapes the rectangular pulses to the desired pulse shape transmitted to control the Bandwidth
•Hc(f) is the channel response modeled as a filter
•HR(f) is the receiver filter designed to remove the pulse distortioncaused by the channel and maximize the S/N
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Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Examples of ISI on received pulses in a binary communication system.
Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
System Transfer Functions
)()()()()()()()()()(
)()()(
)()(
fHfHfHfHfHththththth
thnTtatw
nTthatw
rCTe
rCTe
esn
nout
sn
nin
=⊗⊗⊗=
⊗⎥⎦
⎤⎢⎣
⎡−=
−=
∑
∑
δ
System TransferFunction
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Receive Equalization Filter
)()()(1)()(
fHfHfHfHfH
CT
er
==
• Hr is designed to minimize ISI• it may be fixed or adaptive• Adaptive Filter
• trained by using known symbol sequencescalled preambles
Raised Cosine-Rolloff Nyquist Filter
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Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–25 Raised cosine-rolloff Nyquist filter characteristics.
Raised Cosine-Rolloff Nyquist Filter
Raised Cosine-Rolloff Nyquist Filter
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Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–26 Frequency and time response for different rolloff factors.
Raised Cosine-Rolloff Nyquist Filter
Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–26 Frequency and time response for different rolloff factors.
Raised Cosine-Rolloff Nyquist Filter
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Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–27 Nyquist filter characteristic.
Raised Cosine-Rolloff Nyquist Filter
)743(12
−+
=r
BD
Where D is the Supported Data rate without ISI
Look over example in the txt
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Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–28 Transversal filter.
14
Exam 1solution in class
ELE445-14Lecture 23
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DPCM and single bit A/D
EELE445-14Lecture 23
Differential Pulse code Modulation: DPCM
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Differential Pulse code Modulation: DPCM
SpeechDPCMfor
nNS
dB
153
02.6
<<−
+=⎟⎠⎞
⎜⎝⎛
α
α
Used For Speech - up to a 25 dB S/N improvementover μ-law 255
See pp92 in text
Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Delta Modulation –DM is single bit DPCM
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Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–32 DM system waveforms.
Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–33 Signal-to-noise ratio out of a DM system as a function of step size.
ADM- Adaptive Delta Modulation•variable step size
•small step for slow variation •reduce granular noise
•larger step for fast variation•reduce slope overload
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Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0
Figure 3–34 ADM - Adaptive Delta Modulation
Delta Modulation
overloadslopepreventtof
Af
AtAtAdtd
fT
SlopeMaximum
Bs
a
aslope
aaa
ss
2
max
2
cossin
:
πδ
ωωωω
δδ
>
⎯⎯⎯ →⎯=
=
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Delta Modulation
Bff
NS
APSf
BfAN
fBdffPnNNoiseGranular
a
s
out
xs
a
s
B
Bn
2
3
2
2
3
222
22
83
234
3)(,
π
π
δ
=⎟⎠⎞
⎜⎝⎛
===
=== ∫−
( )
2max
2max2
43
/43
:/
xPSQNR
DAPxq
hadweDAtheFor
xn
nqn
×=
=×
=
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TDM Time-Division Multiplexingfor
PAM, PCM, DM
EELE445-14Lecture 24
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Time-Division Multiplexing
Definition: Time-division multiplexing (TDM) is the time
interlieaving of samples from several sources so that the information from these sources can be transmitted serially over a single communication channel.
Figure 3–35 Three-channel TDM PCM system.
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Time-Division Multiplexing
Figure 3–36 TDM frame sync format.
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Figure 3–37 Frame synchronizer with TDM receiver front end.
Figure 3–38 Two-channel bit-interleaved TDM with pulse stuffing.
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Figure 3–39 TDM with analog and digital inputs as described in Example 3–17.
Figure 3–40 North American digital TDM hierarchy.
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TABLE 3–8 TDM STANDARDS FOR NORTH AMERICA
TABLE 3–9 SPECIFICATIONS FOR T-CARRIER BASEBAND DIGITAL TRANSMISSION SYSTEMS
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Figure 3–41 CCITT digital TDM hierarchy.
TABLE 3–10 SONET SIGNAL HIERARCHY
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Figure 3–42 T1 TDM format for one frame.On every sixth frame this VF PCM bit is replaced by a
signaling bit for this channel.
Figure 3–43 Pulse time modulation signaling.
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Figure 3–44 Technique for generating instantaneously sampled PTM signals.
Figure 3–45 Technique for generating naturally sampled PTM signals.
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Figure 3–46 Detection of PWM and PPM signals.
Figure 3–47 Solution for SA3-1. (See SA3_1.m.)
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Figure 3–48 PSD of an RS-232 signal with a data rate of 38,400 bits/s. (See SA3_4.m.)
Figure P3–3