Post on 03-Jun-2018
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Line Coding
Unnikrishnan BSDE RTTC TVM
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Figure 4.1 Line coding and decoding
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Figure 4.1 Line coding
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Line codingis the process of convertingbinary data, a sequence of bits to a digitalsignal.
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Definitions of the components/Keywords:
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1 Binary data can be transmitted using a number of differenttypes of pulses. The choice of a particular pair of pulses torepresent the symbols 1 and 0 is called Line Coding.
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Master Layout
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1 0 1 1 0 1 1 1 0 1 0 1nput!ata
!igital"ignal
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Step 1:1
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unipolar #$% on $eturn to %ero'
Instruction for the animator Text to be displayed in the orkin! area "DT#
( The first fig should appear then thesecond fig should appear.
( In parallel to the figures the textshould be displayed.
( Bit 0 is mapped to amplitude close to zero
( Bit 1 is mapped to a positive amplitude
( D! component is present
$epresentation of 0 $epresentation of 1
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Step 2:1
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)olar #$% on $eturn to %ero'
Instruction for the animator Text to be displayed in the orkin! area "DT#
( The first fig should appear then thesecond fig should appear.
( In parallel to the figures the textshould be displayed.
( Bit 0 is mapped to a negative amplitude
( Bit 1 is mapped to a positive amplitude
( D! component is present
$epresentation of 0 $epresentation of 1
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Step 5:1
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Manchester coding
Instruction for the animator Text to be displayed in the orkin! area "DT#
( The first fig should appear then thesecond fig should appear.
( In parallel to the figures the textshould be displayed.
&it " is sent by having a mid'bit transition from high to low.
(&it $ is sent by having a mid'bit transition from low to high.
$epresentation of 0 $epresentation of 1
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The corresponding *aveforms should be sho*n in the demo part *hen aparticular line code is selected.
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+igh !ensity Bipolar &+!Bn'
modified bipolar codes *hich guaranteetransitions despite runs of eros.
thus substitute runs of more than n eros
an alternative name is Bn%" in this case substitute runs of n or moreeros
+!B- is a popular code
note +!B- is equivalent to B%"
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#eed for line codes Type of Line codes !ifferent Line codes
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Return-to-zero
Return-to-zero (RZ) describes a line codeused in telecommunications sinals in !"ic"t"e sinal drops (returns) to zero bet!eeneac" pulse# T"is ta$es place e%en i& a
number o& consecuti%e 's or 1s occur in t"esinal# T"e sinal is sel&-cloc$in# T"ismeans t"at a separate cloc$ does not need tobe sent alonside t"e sinal but su&&ers &romusin t!ice t"e band!idt" to ac"ie%e t"e
same data-rate as compared to non-return-to-zero &ormat#
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RZ and NRZ
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AMIAMI
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*nipolar encodinis a line code. / positive voltage representsa binary 1, and ero volts indicates a binary 0. t is the simplest linecode, directly encoding the bitstream, and is analogous to onoffeying in modulation.
ts dra*bacs are that it is not selfclocing and it has asignificant !C component, *hich can be halved by using returntoero, *here the signal returns to ero in the middle of the bit period.2ith a 304 duty cycle each rectangular pulse is only at a positivevoltage for half of the bit period. This is ideal if one symbol is sentmuch more often than the other and po*er considerations arenecessary, and also maes the signal selfclocing.
Traditionally, a unipolar scheme *as designed as a nonreturntoero $%' scheme, in *hich the positive voltage defines bit 1 andthe ero voltage defines bit 0. t is called #$% because the signaldoes not return to ero at the middle of the bit.
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coded mar$ in%ersion (+,I)
n telecommunication, coded mar$ in%ersion(+,I)is a nonreturntoero $%' line code. tencodes zerobits as a half bit time of erofollo*ed by a half bit time of one, and *hile onebits are encoded as a full bit time of a constant
level. The level used for onebits alternates eachtime one is coded.
+,Idoubles the bitstream frequency, *hencompared to its simple #$% equivalent, but
allo*s easy and reliable cloc recovery.
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+,I
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Non Return To Zero (NRZ)
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HDB3 substitution rules
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+!B- Coding $ules
)olarity of thepreceding pulse
#umber of Bipolar &ones')ulsessince last substitution
5dd 6ven
000 7007
7 0007 00
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MULTIPLEXIN TE!HNI"UE
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Fi 4 1 Li di
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Figure 4.1 Line coding
Fi 4 2 Si l l l d l l
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Figure 4.2 Signal level versus data level
Fi 4 3 DC
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Figure 4.3 DC component
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Example 1Example 1
A signal has two data levels with a pulse duration of 1
ms. We calculate the pulse rate and bit rate as follows:
Pulse Rate = 1/ 10Pulse Rate = 1/ 10-3-3= 1000 pulses/s= 1000 pulses/s
Bit Rate = Pulse Rate x logBit Rate = Pulse Rate x log22L = 1000 x logL = 1000 x log222 = 1000 bps2 = 1000 bps
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Example 2Example 2
A signal has four data levels with a pulse duration of 1
ms. We calculate the pulse rate and bit rate as follows:
Pulse Rate = = 1000 pulses/sPulse Rate = = 1000 pulses/s
Bit Rate = PulseRate x logBit Rate = PulseRate x log22L = 1000 x logL = 1000 x log224 = 2000 bps4 = 2000 bps
Figure 4 4 L k f h i ti
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Figure 4.4 Lack of synchronization
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Example 3Example 3
In a digital transmission, the receiver clock is 0.1 percent
faster than the sender clock. How many extra bits per
second does the receiver receive if the data rate is 1
Kbps? How many if the data rate is 1 Mbps?
SolutionSolution
At 1 Kbps:
1000 bits sent1001 bits reei!e"1 extra bps
At 1 #bps:1$000$000 bits sent1$001$000 bits reei!e"1000 extra bps
Figure 4 5 Line coding schemes
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Figure 4.5 Line coding schemes
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nipolar encoding uses only one
voltage level!
%ote:%ote:
Figure 4 6 nipolar encoding
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Figure 4.6 nipolar encoding
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Figure 4 7 &ypes of polar encoding
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Figure 4.7 &ypes of polar encoding
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'n ()*+L the level of the signal is'n ()*+L the level of the signal is
dependent upon the state of the ,it!dependent upon the state of the ,it!
%ote:%ote:
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'n ()*+' the signal is inverted if a 1 is'n ()*+' the signal is inverted if a 1 is
encountered!encountered!
%ote:%ote:
Figure 4.8 ()*+L and ()*+' encoding
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Figure 4.8 ()* L and ()* ' encoding
Figure 4.9 )* encoding
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Figure 4.9 )* encoding
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- good encoded digital signal must- good encoded digital signal must
contain a provision forcontain a provision forsynchronization!synchronization!
%ote:%ote:
Figure 4.10 .anchester encoding
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Figure 4.10 .anchester encoding
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'n .anchester encoding/ the'n .anchester encoding/ the
transition at the middle of the ,it istransition at the middle of the ,it isused for ,oth synchronization and ,itused for ,oth synchronization and ,it
representation!representation!
%ote:%ote:
Figure 4.11 Differential .anchester encoding
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g ff g
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Figure 4.12 ipolar -.' encoding
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g p g
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Figure 4.14 .L&+3 signal
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