Di Digital Transm smissi ssion on 01204325 Data Communications - - PowerPoint PPT Presentation

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Di Digital Transm smissi ssion on 01204325 Data Communications - - PowerPoint PPT Presentation

Jan 05, 2024 273 likes •604 views

Di Digital Transm smissi ssion on 01204325 Data Communications and Computer Networks Chaipo Chaiporn J n Jaik aikae aeo Department of De f Computer Engineering Kasetsart Unive versity Based on lecture materials from Data

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Di Digital Transm smissi ssion

  • n

Chaipo Chaiporn J n Jaik aikae aeo De Department of f Computer Engineering Kasetsart Unive versity

01204325 Data Communications and Computer Networks

Based on lecture materials from Data Communications and Networking, 5th ed., Behrouz A. Forouzan, McGraw Hill, 2012.

Revised 2019-08-12

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Out Outline line

  • Line coding
  • Encoding considerations
  • DC components in signals
  • Synchronization
  • Various line coding methods
  • Analog to digital conversion
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3

Li Line Cod Coding

  • Process of converting binary data to digital signal
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4

Si Signa gnal v

  • vs. D

. Data E Eleme ments

1 data element = 1 symbol

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En Encod

  • ding Con

Consi siderati tion

  • ns
  • Signal spectrum
  • Lack of DC components
  • Lack of high frequency components
  • Clocking/synchronization
  • Error detection
  • Noise immunity
  • Cost and complexity
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SLIDE 6

6

DC DC Com Compon

  • nents

ts

  • DC components in signals are not desirable
  • Cannot pass thru certain devices
  • Leave extra (useless) energy on the line
  • Voltage built up due to stray capacitance in long cables

t Signal with DC component v t Signal without DC component v

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7

t

1 1 1 1 1

Sy Synchronization

  • To correctly decode a signal, receiver and sender must

agree on bit interval

t

1 1 1 1

Sender sends: 01001101 Receiver sees: 0100011011 v v

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Pr Providing Synchronizat ation

  • Separate clock wire
  • Self-synchronization

Sender Receiver

data clock t

1 1 1 1

v

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Li Line Cod Coding Me Meth thod

  • ds
  • Unipolar
  • Uses only one voltage level (one side of time axis)
  • Polar
  • Uses two voltage levels (negative and positive)
  • E.g., NRZ, RZ, Manchester, Differential Manchester
  • Bipolar
  • Uses three voltage levels (+, 0, and –) for data bits
  • Multilevel
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10

Uni Unipo polar

  • Simplest form of line coding
  • Only one polarity of voltage is used
  • E.g., polarity assigned to 1 (TTL)

t

1 1 1

5V

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11

Po Polar Encoding

  • Two voltage levels (+,-) represent data bits
  • Most popular four
  • Nonreturn-to-Zero (NRZ)
  • Return-to-Zero (RZ)
  • Manchester
  • Differential Manchester
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NR NRZ E Enc ncoding ding

  • Nonreturn to Zero
  • NRZ-L (NRZ-Level): Signal level depends on bit value
  • NRZ-I (NRZ-Invert): Signal is inverted if 1 is encountered

t

1 1 1 1

t

? 1 1 1 1

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RZ RZ Encoding

  • Return to Zero
  • Uses three voltage levels: +, - and 0, but only + and - represent

data bits

  • Half way thru each bit, signal returns to zero

t

1 1 1

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Ma Manchester r En Encod

  • ding
  • Uses an inversion at the middle of each bit
  • For bit representation
  • For synchronization

t

1 1 1 1

= 0 = 1

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Di Differential Manchester Encod

  • ding
  • The inversion on the middle of each bit is only for

synchronization

  • Transition at the beginning of each bit tells the value

t

1 1 1 1

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Bi Bipol

  • lar

r En Encod

  • ding
  • Bipolar encoding uses three voltage levels: +, - and 0
  • Each of all three levels represents a bit
  • E.g., Bipolar AMI (Alternate Mark Inversion)
  • 0V always represents binary 0
  • Binary 1s are represented by alternating + and -

t

1 1 1 1

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BnZS ZS Schemes

  • BnZS – Bipolar n-zero substitution
  • Based on Bipolar AMI
  • n consecutive zeros are substituted with some +/- levels
  • provides synchronization during long sequence of 0s
  • E.g., B8ZS

t

1 1 1 1 1

Bipolar AMI B8ZS

V B V B

V – Bipolar violation B – Valid bipolar signal

t

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mBnL Sche Scheme mes

  • m data elements are substituted with n signal elements
  • 2B1Q (two binary, 1 quaternary)
  • 8B6T (eight binary, six ternary)

t

00 11 01 10 01 10 11 00

  • 3
  • 1

+1 +3

Bit sequence Voltage level 00

  • 3

01

  • 1

10 +3 11 +1

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Bl Bloc

  • ck Cod

Coding

  • Improves the performance of line coding
  • Provides
  • Synchronization
  • Error detection

Division Substitution Line Coding

: 0010 1101 0001 : …01011010001… : 10110 01011 01010 :

t

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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

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

4B/ 4B/5B 5B Encod

  • ding Table
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An Analog to Digital Conversion

  • Pulse Amplitude Modulation (PAM)
  • Converts an analog signal into a series of pulses by sampling

PAM Analog signal PAM signal (Sampled analog data)

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Pu Pulse Code Modulat ation (PCM)

  • Converts an analog signal into a digital signal
  • PAM
  • Quantization
  • Binary encoding
  • Line coding
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PC PCM: Q : Quan uantiz izatio ion

1 2 3 4 5 6 7 Input 2 4 6 Output

  • Converts continuous values of data to a finite number of

discrete values

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PC PCM: Q : Quan uantiz izatio ion

Quantization

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Qua Quantization E n Error

  • Assume sine-wave input and uniform quantization
  • nb is the number of bits per sample
  • Known as the 6 dB/bit approximation

See also: http://en.wikipedia.org/wiki/Quantization_error#Quantization_noise_model

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Solution We can calculate the number of bits as Telephone companies usually assign 7 or 8 bits per sample.

Ex Example: Quanti tizati tion

  • n Err

Error

  • r
  • A telephone subscriber line must have an SNRdB above 40.

What is the minimum number of bits per sample?

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PC PCM: B : Binar inary E y Enc ncoding ding

  • Maps discrete values to binary digits
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PC PCM: T : The Who he Whole P le Proces cess

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Mi Minimum Sampling Rate

Sa Samp mpling ra rate mu must b t be g gre reater th r than tw twice th the highe highest fr frequency

  • Nyquist Theorem:

t sampling interval

  • Ex. Find the maximum sampling

interval for recording human voice (freq. range 300Hz – 3000Hz)

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Ny Nyquis quist’s Sampling The Sampling Theorem

See also: Wagon-wheel effect

Sampling demonstration

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Ex Example: Sa Sampling and Bit Rate

  • Calculate the minimum bit rate for recording human voice,

if each sample requires 60 levels of precision

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Summa Summary

  • Line coding and block coding
  • Digital signal consideration
  • Bit rate
  • Symbol rate
  • DC component
  • Synchronization
  • Analog-to-digital conversion
  • Pulse-Code Modulation
  • Minimum sampling frequency