DIGITAL COMMUNICATION LINK USING PULSE - CODED MODULATION TECHNIQUES

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DIGITAL COMMUNICATION LINK USING PULSE - CODED MODULATION TECHNIQUES

«'ONG KHANG VEONG

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Universiti Malaysia Sarawak

1998

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DIGITAL COMMUNICATION LINK

I SING PULSE-CODED MODULATION TECHNIQUES

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Borang Penyerahan Tesis Universiti Malaysia Sarawak

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BORANG PENYERAHAN TESIS

Judul: DIGITAL COMMUNICATION LINK USING PULSE-CODED MODULATION TECHNIQUES

SESI PENGAJIAN: 1998/1999

Saya WONG KHANG YEONG

(HURUF BESAR)

mcngaku mcmbenarkan tesis im disimpan di Pusat khidmat Maklunuat Akademik. Universiti Malaysia SaraHak dengan s) arat-sýarat kcgunaan scpcrt. z ben kut

I Hakmilik kcxtas projck adalah di haWah nama penulis melainkan penulisan sebagai projek bersama dan dibmai olch UNIMAS, hakmilikma adatah kepumyaan UNIMAS

ý Naskhah ; alinan di dalam bentuk kertas atau mikro hama boleh dibuat dengan kebenaran bertulis danpada penults

Pusat l; htdmat Maklumat Akademtk. UNIMAS dibenarkan membuat saiinan untuk pengajian mereka

t Kertas pro)ek hama boleh diterbitkan dengan kehenaran penulis. Bayaran royalti adalah mengikut kadar ý ang dtpersetujut kelak

ý" Sea atembeeºarken/udak membenarkan Perpustakaan membuat satman kertas projek ini sebagai bahan pcrtukaran di antara institust pengajian ttnggt.

"" Sila tandakan ()

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SULZT (Mengandungi maklumat yang bcrdarjah keselamatan atau kepentingan Malaysia sepcrtJ yang termaktub di dalam AKTA RAHSIA RASMI 1972).

TERHAD (Mengandungi maklumat TERHAD vang telah ditcntukan olch organisasi/

badan di mana pemelidikan dijalankan)

; ýý TIDAK TERHAD

Disahkan oleh

ITANDATANGAN PENULTS) (TANDATAWAN PENYELIA)

Atamat tetap ?? h. JALAN BESAR l6200 fl'MPAT

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T arikh 22 SEP'TE: ME3E: R 1998 _.

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Tarikh

Nama Penmelia

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orpnkasi berkenaan desRan menvertaksn sekaii teetpek kertas projek. lni perir dikeiaskan sebaRsi SULIT atau TERHAD.

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Tesis ini telah dibaca dan disahkan oleh:

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Encik NiViang Yew Tarikh

Penyeha

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To all my loved ones who has been there

when I needed them most - Mom, Dad, CYY

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ACKNOWLEDGEMENT

The author would like to present millions of thanks to Mr Ng Liang Yew, who as the supervisor of this project, has given his full co-operation in the course of the project.

Without his ever present patience and understanding, this project would not have taken off successfully.

Special thanks also to those who has directly of indirectly helped to contribute in the research of the project, especially to the two IKS member, Tan Chong Eng and Lee Kon Keong. Their suggestion and help are very much appreciated and remembered.

A special thanks to one person who is the most important beacon in the author's life in Unimas - Miss Cheong Yen Yee. She had been there for the author whenever he needed help and comfort. Without her assistance and guidance, the author would be able to complete the project in time.

Last but not least, a dedication to the author's parents and family, whose support throughout the years will always be remembered. Their sacrifice is much appreciated,

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ABSTRACT

Pulse-coded modulation (PCM) technique is very popular in the digital communication field. The general purpose of this project is to introduce the basic concept of using PCM technique in digital communication. In this project, PCM will be used to form an error-free high-speed digital or data communication

links, using basic analog to digital converter (ADC) and a digital to analog converter (I)AC) circuits. This project will demonstrate the noise immunity of

PCM technique while the transmission is converted from parallel data to serial data and serial data back to parallel format. The standard being studied and used in the conversion are the RS-232, RS-422 and Transistor-to-Transistor

Logic (TTL). The importance of sampling of the signal according to the Nyquist Sampling Theorem will also be demonstrated.

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ABSTRAK

Ttaknik Pulr+e-('(xied Modulation (PCM) adalah popular dalam bidang komunrkaKr digital. Tujuan projek ini adalah untuk memperkenalkan kaedah rnenggunakan P('M dalarn komunikasi digital. Dalam projek ini, PCM akan digunakan dalarn membina hubungan komunikasi digital atau data dengan

kadar kelajuan yang tinggi dan bebas gangguan, dengan litar ringkas menggunakan penukar analog ke digital (ADC) dan penukar digital ke analog MAC). hekebalan teknik PCM terhadap gangguan juga dapat ditunjukkan

nuelalur penukaran format data dari format sesiri ke format selari, dan tu-balrknya. Pri1H'aran yang dikaji dan diguna dalam projek adalah RS-232, RS- -122 dan T71.. hepentrngan mematuhi Hukum Sample Nyquist juga dapat drtunjukkan.

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1'c«M Khidniat NiAlunnat

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1.3 Coding in Digital Communication

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Z PULSE CODE MODULATION (PCM) 10

2.1 Introduction to PCM

2.1.1 Advantages of PCM System 2.2 Basic PCM System

2.3 Sample-and-Hold Circuit

2.4 Pulse-Amplitude Modulation 2.5 Sampling Rate

2.6 Quantization

2.6.1 Basic Definition

2.6.2 Quantization Technique 2.6.3 Quantization Noise

2.6.4 Resolution of Quantization

2.7 Dynamic Range and Signal-to-Noise Calculation

2.8 Companding

2.8.1 Analog Companding 2.8.1.1 µ-Law Companding 2.8.1.2 A-Law Companding 2.8.2 Digital Companding

2.9 Encoding and Decoding 2.9.1 Encoder or Coder

2.9.2 Principles of Iterative Encoder 2.9.: 3 Decoding

2.9. -1 Encoding

10

11 12 13 16 18

19 19

21

23 24 25

26

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27

28 28

29

29 29

31 31

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2.9.1.1 Parallel Encoding 31

2.9. -1.2 Serial Encoding 33

2.10 Digital Signal Encoding Formats 2.10.1 The NRZ Group

2.10.2 The RZ Group

2.10.: 3 Phase-Encoded and Delay Modulation (Miller) Codes

2.10.. 1 Multilevel Binary Codes

35

36

37 39

40

EXPERIMENTAL CIRCUIT 43

: 3.1 Introduction 43

: 3.2 Basic PC, N1 Data Link using ADC and DAC 43

: 3.2.1 Procedure 1 44

: 3.2.: 3 Procedure :3 45

: 3_'x. 5 Procedure 5 47

: 3. 'ß. E; Procedure 047

3.2.7 Procedure 7 48

Procedure 8 49

3.: 3 Parallel-Serial-Parallel Conversion 49

3.3.1 Procedure S) 50

3.3.2 Procedure 10 51

:3.: 1

.: 1 Procedure 11 51

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3.3.4 Procedure 12 3.3.5 Procedure 13 3.3.6 Procedure 14 3.3.7 Procedure 15 3.3.8 Procedure 16 3.3.9 Procedure 17 3.4 RS-232

- TTL Serial Data Conversion 3.4.1 Procedure 18

: 3.5 RS-422

-TTL Serial Data Conversion 3.5.1 Procedure 19

3.6 Typical Components Used 3.6.1 Integrated Circuits (ICs)

3.6.1.1 SM6103 : 3.6.1.2 AD557 3.6.1.3 74HC04 3.6.1.4 74HC74 3.6.1.5 74HC163 : 3.6.1. (; 74HC164 3.6.1.7 7411(1164 : 3.6.1.8 74110374 : 3.6.1.9 AM26LS31 3.6.1.10 AM26LS32 : 3.6.1.11 MAX232

3.6.2 Transistor : 3.6.: 3 Resistors

52

52 53

53

54 55 56 56

58 58

60 60 60 62 64

65

67 69

71 73

75

76

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79

80

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3.6.4 Capacitors

80

3.6.5 Light-Emitting Diodes (LEDs) 81

4 TRANSMISSION STANDARD 82

4.1 RS-232 Standard 82

4.1.1 Electrical Signal Specification 84

4.1.1.1 Noise Margin and Noise Immunity 86

4.1.2 Mechanical Specification 86

4.1.3 Detailed Mechanical Functional Specification 88

4.1.3.1 Functional Definition 88

4.2 The New Standard

- RS-449, RS-422 and RS-423

4.2.1 Objectives of the New Standard

89

90

5 APPLICATION OF PCM 95

5.1 PCM / TDM Repeaters

5.2 Digital Telephony: T-1 Carrier System 5.3 Radio Telemetry

95

98 98

6 EXPERIMENTAL CIRCUIT OBSERVATIONS 100

6.1 Observation

6.1.1 Resolution of ADC and DAC E3.1.2 Clock Rate

6.1.3 Serial Data Format

6.1.4 Performance of RS-232, RS-422 and TTL

100 100

102 102

103

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7 PROBLEMS AND RECOMMENDATIONS

8 CONCLUSION

104

106

Appendices 107

References 109

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LIST OF TABLES

Page

Table

2.1 NRZ codes 37

2.2 RZ codes 38

2.3 Phase encoded and delay modulation codes 39

2.4 Multilevel binary codes 40

3.1 Results for Procedure 2 45

3.4 Maximum ratings specification for SM6103 62 3.5 Maximum ratings specification for AD557 64 3.6 AC characteristics specifications for 74HC04 65 3.7 AC characteristics specifications for 74HC74 66 : 3.8 AC characteristics specifications for 74HC 163 69 3.9 Maximum ratings specification for 74HC164 71 3.10 Maximum ratings specification for 74HC165 73 3.11 Maximum ratings specification for 74HC374 75

: 3.12 Maximum ratings specification for 76

AM26LS31

3.13 Maximum ratings specification for 77

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AM26LS32

3.14 Maximum ratings specification for MAX232 79 3.15 Maximum ratings specification for 2N3904 80

4.1 Category I circuit 91

4.2 Category II circuits (new circuits) 91

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LIST OF FIGURES

Page

Figure

1.1 Binary code by Bacon for alphabets 2

1.2 M-ary code by Wilkins 3

1.3 Binary code by Leibniz for integers 4

2.1 Block Diagram of PCM system 14

2.2 A sample-and-hold circuit 15

2.3 Flat top sampling 18

2.4 Natural sampling 18

2.5 Basic concepts in quantizing 20

2.7 Example of a PCM encoding process 24

2.8 Companding process 27

2.9 Decision tree for the iterative encoding (for 31 positive values)

2.10 Parallel encoder 33

2.11 Counter-controlled serial encoder 34

2.12 Digital signal encoding formats 36

3.1 Block diagram for basic PCM data link using 43

ADC

3.2 Results for Procedure 1 44

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3.3 Results for Procedure 5 3.4 Results for Procedure 6 3.5 Results for Procedure 7 3.6 Results for Procedure 8

3.7 Parallel-serial-parallel conversion 3.8 Results for Procedure 9

3.9 Results for Procedure 11 3.10 Results for Procedure 12 3.11 Results for Procedure 13 3.12 Results for Procedure 14 3.13 Results for Procedure 16 3.14 Results for Procedure 17 3.15 Serial data conversion

3.16 RS-232 to TTL serial data conversion 3.17 Results for Procedure 18

3.18 RS-422

- TTL serial data conversion 3.19 Results for Procedure 19

3.20 Pin configuration for SM6103 3.21 Pin configuration for AD557 3.22 Pin configuration for 74HC04 3.23 Pin configuration for 74HC74 3.24 Pin configuration for 74HC163 3.25 Pin configuration for 74HC 164 3.26 Pin configuration for 74HC165 3.27 Pin configuration for 74HC374

47 48 48

49

50 50 51 52

52 53 54 55 56 57 58 58 59 60 63 65 66 68

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71 74

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3.28 Pin configuration for AM26LS31 3.29 Pin configuration for AM26LS32 3.30 Pin configuration for MAX232

4.1 RS-232 communications interface 4.2 RS-232 equivalent circuit

4.3 RS-232 logic levels

4.4 RS-232 connector assignment 4.5 DB-25 pin connector

5.1 PCM/TDM repeaters

76 78 79 83 84 86 87 87 97

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LIST OF APPENDICES

APPENDIX Page

A Basic PCM data link using ADC and DAC 107 B PCM data link with added parallel-serial- 108

parallel conversion

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CHAPTER I

INTRODUCTION

1.1. Digital Communication

I. I. I. History

Digital communication is defined as the transfer of information as the transfer of information in digital form. An English philosopher, Francis Bacon, developed the earliest recorded concept of over 400 years ago. In 1605, Francis Bacon (1561 - 1626) developed a two-letter alphabet, where he formed a five- letter "words" using the two basic letters. These words can represent the 24 alphabet that was used in the early English alphabet system then (which excludes the letters j and v).

A=aaaaa B=aaaab C=aaaba Daaabb E=aabaa Faabab

H=aabbb I =abaaa K=abaab L=ababa M=ababb N =abbaa

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G=aabba 0 =abbab

Figure 1.1 Binary code by Bacon for alphabets

The terminology used today for "words" is codewords and the whole system of the codewords is called a code. For the case above, the code suggested by Bacon is actually a form of binary code since only two basic letters are used.

Other scientists who had pioneered the coding system include John Wilkins (1614 - 1672) and Gottfried Wilhelm Leibniz. Wilkins had developed the M-ary codes where M is equal to 2,3 or 5 and the code length used is 5,3 and 2 respectively. Leibniz uses the numbers 0 and 1 to represent the integers, which is also another form of binary code. Thus, the codes by Bacon and Leibniz are basically equivalent.

Integer Codeword

0 0

1 1

2 10

3 11

4 100

5 101

6 110

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7

8

111

1000

Figure 1.2 Binary code by Leibniz for integers

Alphabet Letter Codeword using Basic Letters Indicated

a, b a, b, c a, b, c, d, e

A aaaaa aaa as

B aaaab aab ab

L ababa cbb ca

M ababb cbc cb

Y babba bcb ec

Z babbb bcc ed

Figure 1.3 M-ary code by Wilkins

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1.1.2. Practical Development

The digital codes proposed by the three scientists began to find its practical use in the telegraph links in the 1800s. In 1838, Samuel F. B. Morse demonstrated a telegraph machine for sending messages rapidly over long distances. The codes used in telegraph links includes the Morse code, using a binary code composed of dots and dash to represent different codewords of variable length, and later Baudot code, which uses the digit 1 and 0 instead of the dots and dashes with a fixed number of 5 digits per codeword. Works by James Clerk Maxwell and Heinrich Hertz later lead to transmission of information by radio telegraph by Marconi in 1897. However, despite having the genesis of digital framework, for about the next 100 years, communication still become predominantly analog in forms of the telephone, radio and television.

The work of Nyquist in the 1920s was perhaps the next major conceptual contribution to the development of digital communications. Nyquist was able to establish the relationship between the available channel bandwidth and the maximum pulse transmission rate that would support zero interpulse interference, which is stated in the famous Nyquist sampling theorem. Today, this theorem is used in most modern digital communication systems.

In 1937 Alec Reeves invented the most important digital techniques that it is still used widely today in transmission and storage of speech, music, visual and telemetry signals. This technique is called Pulse Code Modulation (PCM).

PCM basically takes an analog signal, sample it periodically, quantize it to an one of the finite set of discrete amplitude. The amplitudes are technically the same as the codewords encoded by Bacon or Leibniz.

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DIGITAL COMMUNICATION LINK USING PULSE - CODED MODULATION TECHNIQUES