cnu dept. of electronics d. j. kim1 lecture on communication theory 1. introduction 1.1 the...

CNU Dept. of Electronics

D. J. Kim1

Lecture on Communication Theory

1. Introduction

1.1 The communication Process

1. Process of communication1) Generation of a thought pattern or image

2) Description of that image by a set of aural or visual symbols

3) Encoding of these symbols in a form that is suitable for Tx

4) Transmission (Tx)

5) Decoding and reproduction of the original symbols

6) Recreation of the original thought pattern or image

2. 통신의 예전화 , Radio, TV, Computer terminal, Cellular, Beeper,

Cordless telephone, 자동시동장치 , Satellite, Rocket, …….


D. J. Kim2


1.2 Source of information

1. Source of information: Speech, TV, fax, PC

2. Speech Production

Propagation: air, 전화선 ( 300Hz ~ 3100Hz)

Perception

3. TV 30 Frame / sec

2 Field / Frame …. (even, odd) interlaced

525 lines / Frame

262.5 lines / Field. line scanning 15.75KHz. (63.5 sec)

Vertical Blanking

Horizontal Blanking

Video BW = 4.2MHz, Kell factor = 0.7 for NTSC

4. Fax : Still pictures


D. J. Kim3



D. J. Kim4



D. J. Kim5


4) PC 의 연결1. RS - 232 Serial ports

when transmission is idle, a long series of 1s is sent

2. generally one character sent at a time

3. asynchronous

synchronous

4. burst data

continuous video, voice

5. Modem

5. PC : 1) 통신으로 사용 : e-mail, exchange of s/w, sharing of resources2) ASCII : 27 = 128 different characters

American Standard Code for Information Interchange 3) Transmission of ASCII or storing 7bit + 1 bit (parity) byte or octet


D. J. Kim6


1.3 Communication channels

1. Important channels : telephone, optical fibers, mobile

radio channels, satellite channel.

2. Telephone channel (network)1) Circuit switching

2) Microphone, moving- coil receiver (speaker)

3) Linear, band limited channel

4) Minimize the channel bandwidth 300 ~ 3100Hz

3. Optical fiber1)

Core 내에서 빛이 전반사

2) 장점 및 특색1. Enormous potential BW : 2 X 1014 Hz

2. Low Tx Losses ; 0.2 dB / km

cf. Coaxial cable 은 500m 마다 Repeater

3. Immunity to electromagnetic interference

4. Small size & weight

5. Ruggedness & flexibility

6. Potential for low-coat : from sand

Core ( 굴절률 크다 )

Cladding ( 굴절률 작다 )


D. J. Kim7


4. Mobile radio channel1) Mobility

2) Multi-path

3) Linear time-varying channel

5. Satellite channel1) Broad-area coverage

2) To be geo-stationary orbit 1. Geo synchronous = 22,300 miles (35,784km) 상공 , ( 중력 = 원심력)

2. Above the equator

3. 지구 자전과 같은 속도로

3) Geo-stationary satellite 의 장점1. Broad-area coverage

2. Reliable transmission links

3. Wide transmission BW

4) Up link ex) 무궁화 14.5~15.8G

Transponder 내에서 amplified repeater in a sky

Down link ex) 무궁화 11.7~12.0G

40 spacing 4 / 6GHz

30 spacing 12 / 14GHz

5) up-link 로 6G, down-load 로 4G 를 사용 시 장점1. Relatively inexpensive microwave equipment

2. Low attentive due to rainfall

3. Insignificant sky background noise

6) 500MHz Total BW

12 transponders one TV signal

36MHz / transponder 1200 voice

50Mbps


D. J. Kim8


6. Channel 의 분류 1) linear or nonlinear

2) time invariant or time varying

3) bandwidth limited or power limited

전화선 optic, satellite

1.4 Base-band & pass-band signalsAnalog signal

Digital signal ex) binary signal

Baseband Tx

Passband Tx

cos(wct)basebandsignal

passbandsignal

modulation


D. J. Kim9


1.5 Representation of signals and system

1. Periodic g(t) = g(t+to) for all t

non-periodic2. Deterministic signal ; modeled as completely specified

functions of times Random signal

3. Energy signal 0 < E <

power signal 0 < P <

ex) periodic, random

4. Fourier series frequency domain description

Fourier Transform spectrum

1.6 Probabilistic considerations

1. Uncertainty - noise thermal

shot

- interference

2. Random signal

Random process or stochastic process

dttgT

T

2

t)(lim

E

dttgT

T

T

2

t)(

2

1lim

P


D. J. Kim10


1.7 The modulation process

1. Modulation : modification of the message signal into a form suitable for transmission over the channel

Demodulation

2. CW modulationAM (Amplitude Modulation)

Angle modulation

FM (Frequency Modulation)

PM (Phase Modulation)

3. Pulse modulation1) Analog mod

Pulse - amplitude Mod (PAM)

Pulse - duration Mod (PDM)

Pulse - position Mod (PPM)

2) PCM digital

장점 1. Robustness in noisy environment by regenerating

2. Flexible operation

3. Integration of diverse sources of information into a common format

4. Security of information in its Tx from source to destination

4. Multiplexing1) FDM (Frequency Division Multiplexing)

2) TDM (Time Division Multiplexing)

3) SDM (Space Division Multiplexing)


D. J. Kim11


1.8 primary communication resourcesPower limited ex) satellite, space comm link

BW limited ex) Telephone

Noise

1.9 Information Theory and coding1. 디지털 통신 시스템의 블록도

Sourceencoder

Data compression

encoder

Data compaction

encoder

Data encryption

encoder

lossycoding

losslesscoding


D. J. Kim12


2. Information Capacity Theorem Information capacity = channel capacity

where B=BW

To make C B or S/N

1.10 Analog versus Digital communication

1. 송수신기 Design guideline1) produce an “estimate” of the message at the receiver output that satisfies the expectation of the user block

2) cost : channel 특성에 맞게 Design 되어야 한다 .

2. Analog : simple, low cost

Digital : complex, efficient, reliable,

becomes cost down due to VLSI integrity

bps C NSB /1log2


D. J. Kim13


1.11 Networks1. Network

2. Circuit switching1) circuit : dedicated communication path

2) remains uninterrupted for the entire duration of Tx

3) ex) telephone network

3. Packet switching1) sharing is done on a demand basis

2) careful control 이 필요3) ex) data network

4. OSI Reference Model1) Repeater : layer 12) Bridge : layer 1 & 23) Router : layer 34) gate way : layer 5 이상


D. J. Kim14


* TCP/IP 와 OSI 7 layer 의 비교


D. J. Kim15


cnu dept. of electronics d. j. kim1 lecture on communication theory 1. introduction 1.1 the...

Documents