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, …….
CNU Dept. of Electronics
D. J. Kim2
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim3
Lecture on Communication Theory
CNU Dept. of Electronics
D. J. Kim4
Lecture on Communication Theory
CNU Dept. of Electronics
D. J. Kim5
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim6
Lecture on Communication Theory
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 )
CNU Dept. of Electronics
D. J. Kim7
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim8
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim9
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim10
Lecture on Communication Theory
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)
CNU Dept. of Electronics
D. J. Kim11
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim12
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim13
Lecture on Communication Theory
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
CNU Dept. of Electronics
D. J. Kim14
Lecture on Communication Theory
* TCP/IP 와 OSI 7 layer 의 비교
CNU Dept. of Electronics
D. J. Kim15
Lecture on Communication Theory