1. 디지털통신
Introduction
임 민 중
동국대학교 정보통신공학과 1

2. Introduction

3. Communication Communication Applications
The activity of conveying information.
Requires a sender, a message, and an intended recipient. Thus communication can occur across vast distances in time and space.
Applications
AM and FM radio, television, wireless communications, satellite communications, deep-space communications, telephony, data storage, Internet, and quite a few others

4. Course Outline - 1 Typical Digital Communication Systems
Source
Coding
Encryption
Channel
Coding
Multiplexing
Modulation
Multiple
Access
Source
Decoding
Decryption
Channel
Decoding
Demultiplexing
Demodulation
Multiple
Access
Source encoding removes redundant information
Encryption prevents unauthorized users from understanding messages and injecting false messages into the system
Channel coding reduces the probability of error, or reduces the signal-to-noise ratio requirement at the expense of bandwidth or decoder complexity
Multiplexing and multiple access combine signals that might have different characteristics or might originate from different sources, so that they can share a portion of the communications resource
Modulation is the process by which the symbols are converted to waveforms that are compatible with the transmission channel

5. Course Outline - 2 Introduction Basics and Backgrounds
Signals and Random Variables
Baseband Modulation
Baseband Modulation
Baseband Demodulation
Inter-Symbol Interference
Bandpass Modulation
Linear Modulation
Constant Envelope Modulation
Channel Coding
Channel Coding Basics, Block Coding
Convolutional Coding

6. Digital Communication Wireless Communication
Course Outline - 3
Prerequisites
Basic mathematics
Programming
Signals and Systems
Random Processes
Communication Theory
References
B. Sklar, Digital Communications: Fundamentals and Applications, Prentice Hall, 2001.
S. Haykin, M. Moher, Introduction to Analog & Digital Communications, John Wiley & Sons, 2007.
Communication Theory
Digital Communication
Wireless Communication
Basic Theory
(Fundamental
Theory)
Basic Theory
(System
Understanding)
Application
(System
Examples)

7. Basics

8. Sine and Cosine - 1
Sine and Cosine

9. Sine and Cosine - 2 Example: sine, cosine sin(x) period = 2
max = 1
min = -1
odd function
sin(0) = 0
period = 2
max = 1
min = -1
even function
cos(0) = 1
period = 1
period = 1
max = 1
min = 0
cos2(0) = 1

10. Complex Number - 1
Complex Number
(- <   )
Complex Conjugate

11. Complex Number - 2 Example: complex numbers X- and Y-coordinates
Complex Conjugate
= j
Polar form
Amplitude = 1
Phase = /4
Amplitude = 1
Phase = 0, /4, /2,
3/4, , -3/4,
-/2, -/4

12. Complex Number - 3 Example: complex exponentials real = cos(x)
imaginary = sin(x) 
Amplitude = 1
Phase = x -

13. Vector and Matrix Matrix Vector Identity Matrix Addition
Multiplication

14. Log Log Example: Log log1010 = 1 log102  0.3
log104 = log10(22) = log102 + log102 = 0.6
log1040 = log10(2210) = log102 + log102 + log1010 = 1.6
log10800 = log10(2221010) =
log10(1/8) = log10 (1/21/21/2) =

15. Metric Prefixes - 1 Kilo, Mega, Giga Example: symbol rate
symbol duration = 50 nsec  symbol rate = 20 Msymbol/sec
symbol rate = 250 Ksymbol/sec  symbol duration = 4 sec
1012 Tera
109 Giga
106 Mega
103 Kilo
10-3 Milli
10-6 Micro
10-9 Nano
10-12 Pico
240 Tera
230 Giga
220 Mega
210 Kilo
1024 Giga
1024 Mega
1024 Kilo
1024
symbol duration = 1 sec → 1 symbol/sec
symbol duration = 1 msec → 1 Ksymbol/sec
symbol duration = 1 sec → 1 Msymbol/sec
symbol duration = 1 nsec → 1 Gsymbol/sec
symbol duration

16. Metric Prefixes - 2  = c / f0 Example : wave length
c: speed of light (= 3108m/s)
f0: frequency
Example
f0 = 1MHz   = 300m
f0 = 1GHz   = 0.3m
f0 = 2GHz   = ?
f0 = 10GHz   = ?
3108m 
f0 = 1Hz  1 cycle/sec
f0 = 1KHz  1,000 cycle/sec
f0 = 1MHz  1,000,000 cycle/sec
f0 = 1GHz  1,000,000,000 cycle/sec

17. Shift Register - 1 Shift Register
a cascade of flip-flops, sharing the same clock
the output of each flip-flop is connected to the input of the next flip-flop
register D D D
input
output 1 1 1 1 1 1 1 1 1 1

18. Shift Register - 2 Example: FIR Filter Finite Impulse Response 2 1 2 12 1 + 2 1 2 1 1 1 2 1 2 1 2 1 2 1 2 1 + + + + +

19. Exclusive OR - 1 Exclusive OR (XOR) Example 0  0 = 0 0  1 = 1
1  0  1  1  0  1 = 0
XOR = 0 if # of 1's is even
= 1 if # of 1's is odd
0  0 = 0
0  1 = 1
1  0 = 1
1  1 = 0

20. Exclusive OR - 2 Example Register Contents Output 1 0 0 1 1 1 0 0 1 1
Initial values of registers = {0, 0}
Input values = {1, 1, 0, 0}
Output values = {1, 0, 0, 1}
Output values = {1, 1, 1, 1}
1 bit register
Register Contents
1 0 0
1 1 0
0 1 1
0 0 1
Output 1 D D
Register Contents
1 0 0
1 1 0
0 1 1
0 0 1
Output 1 D D

21. State Diagram - 1 Register Contents 0 0 1 0 1 1 0 1 1 Input Output D
1 bit register
exclusive OR
0 0
1 0
1 1
0 1 1
Input
Output D
exclusive OR
0  0 = 0
0  1 = 1
1  0 = 1
1  1 = 0
0/0
1/0
input/output
next state
1/1
State Transition Diagram 1
state
Mealy Machine
0/1
0/0
0/0
0/0
0/0
state
1/1
1/1
1/1
1/1
Trellis Diagram
0/1
0/1
0/1
0/1 1 1 1 1 1
1/0
1/0
1/0
1/0

22. State Diagram - 2 Example Register Contents 0 0 0 1 0 0 0 1 0 1 0 1
0 0 0
1 0 0
0 1 0
1 0 1
1 1 0
1 1 1
0 1 1
0 0 1 1
Input
Output
1 bit register D D
State Transition Diagram
0/1 00 01
0/0
1/0
0/0
1/1
0/1 10 11
1/1
1/0

23. MATLAB Programming Programming MATLAB C
a[4] = {1, 2, 3, 4}; // array index
sum = 0; // starts from 0
for (i = 0; i < 4; i ++) {
sum += a[i]; }
a = [ ]; % array index
sum = 0; % starts from 1
for i=1: % for i=1:1:4
sum = sum + a(i);
end
Type ‘sum’ to check the result
binary = 1;
if (binary == 1) {
t = 1;
} else {
t = -1; }
binary = 1;
if (binary == 1)
t = 1;
else
t = -1;
end
Type ‘t’ to check the result
quarternary = 2;
switch (quaternary) {
case 0: t = -3; break;
case 1: t = -1; break;
case 2: t = 1; break;
case 3: t = 3; }
quarternary = 2;
switch (quaternary)
case 0, t = -3;
case 1, t = -1;
case 2, t = 1;
case 3, t = 3;
end