15979_Digital Transmission and Line Coding Techs

7/31/2019 15979_Digital Transmission and Line Coding Techs.

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DigitalTransmission


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Line Coding

Line Coding Schemes

Some Other Schemes


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Line coding


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Signal level versus data level


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DC component


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Example 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/ 10-3= 1000 pulses/s

Bit Rate = Pulse Rate x log2 L = 1000 x log2 2 = 1000 bps


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Example 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/s

Bit Rate = PulseRate x log2 L = 1000 x log2 4 = 2000 bps


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Lack of synchronization


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Example 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?

Solution

At 1 Kbps:

1000 bits sent1001 bits received1 extra bps

At 1 Mbps:

1,000,000 bits sent1,001,000 bits received1000 extra bps


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Line coding schemes


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Unipolar encoding uses only one

voltage level.

Note:


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Unipolar encoding


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Polar encoding uses two voltage levels

(positive and negative).

Note:


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Types of polar encoding


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In NRZ-L the level of the signal is

dependent upon the state of the bit.

Note:


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In NRZ-I the signal is inverted if a 1 is

encountered.

Note:


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NRZ-L and NRZ-I encoding


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RZ encoding

ZERO is ONE is

Reference level


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A good encoded digital signal must

contain a provision forsynchronization.

Note:


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Manchester encoding


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In Manchester encoding, the

transition at the middle of the bit isused for both synchronization and bit

representation.

Note:


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Differential Manchester encoding


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In differential Manchester encoding,

the transition at the middle of the bit isused only for synchronization.

The bit representation is defined by the

inversion or noninversion at thebeginning of the bit.

Note:


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In bipolar encoding, we use three

levels: positive, zero,and negative.

Note:


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Bipolar AMI encoding


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Block Coding

Steps in Transformation

Some Common Block Codes

Bl k di


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Block coding


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S b tit ti i bl k di


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Substitution in block coding


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Table : 4B/5B encoding

Data Code Data Code

0000 11110 1000 10010

0001 01001 1001 10011

0010 10100 1010 10110

0011 10101 1011 10111

0100 01010 1100 11010

0101 01011 1101 11011

0110 01110 1110 11100

0111 01111 1111 11101


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Table : 4B/5B encoding (Continued)

Data Code

Q (Quiet) 00000

I (Idle) 11111

H (Halt)00100

J (start delimiter) 11000

K (start delimiter) 10001

T (end delimiter) 01101

S (Set) 11001

R (Reset) 00111

Data t a i i


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Data transmission

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15979_Digital Transmission and Line Coding Techs