디지털통신 Introduction 임 민 중 동국대학교 정보통신공학과 1

Introduction

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

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

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

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)

Basics

Sine and Cosine - 1 Sine and Cosine

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

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

Complex Number - 2 Example: complex numbers X- and Y-coordinates Complex Conjugate = 0.5 - j Polar form Amplitude = 1 Phase = /4 Amplitude = 1 Phase = 0, /4, /2, 3/4, , -3/4, -/2, -/4

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

Vector and Matrix Matrix Vector Identity Matrix Addition Multiplication

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) =

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 1 0 1 1 0 0 0 1 1 0 1 symbol duration

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

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

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

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

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

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

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

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 = [1 2 3 4]; % array index sum = 0; % starts from 1 for i=1:4 % 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