Principles of Communications

通訊原理

Textbook : Communication Systems , 4th Edition

by Simon Haykin

John Wiley & Sons , Inc

歐亞書局代理

http://cc.ee.ntu.edu.tw/~wujsh

課程助教：林紀亨 電信所通訊組(博理504)E-Mail：b96901025@ntu.edu.tw

1

Grading Rule

Midterm 45%

Final 45%

Homework 10%

Some of the problems in the homework will appear

on the Midterm and the Final Exams.

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ContentsBackground and Preview

· Communication Process (Sender, receiver, point-

to-point, multicast, broadcasting)

· Communication Networks (packet switching, circuit

switching) (layer architecture)

·Channels (AWGN, fading channel)

·Modulation Process (C.W. modulation, PCM, Passband

digital Trans.)

·Analog and Digital Communications

·A Digital Communication Problem

( )

·Historical Notes

( ) ( )cos(2 ) ( )x t Am t ft n t

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Chapter 1 Random Process

·Mathematical Definition of a Random Process

· Stationary Processes

· Mean , Correlation , and Covariance Functions

· Ergodic Processes

· Linear Time-Invariant Filter ( System )

· Power Spectral Density ( PSD )

· Gaussian Process

· Noise

· Narrowband Noise

· Representation of Narrowband Noise

(I,Q, Envelope and phase )

· Sinusoidal Wave Plus Narrowband Noise 26

Chapter 2

Continuous-Wave ( CW )

Modulation · Amplitude Modulation (AM)

· Linear Modulation Schemes( )

(DSB-SC, SSB, VSB)

· Frequency–Division Multiplexing ( FDM )

· Angle Modulation

· Frequency Modulation ( FM )

· Nonlinear Effects in FM Systems

· Superheterodyne Receiver (RF, Mixer, IF, detection, estimation)

· Noise in CW Systems

( Coherent Detection and Envelope Detection in AM , Filtering in FM )

( ) ( )cos(2 ) ( )sin(2 )I c Q c

s t s t f t s t f t

( ) cos[ ( )]c i

s t A t

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Chapter 3 Pulse Modulation

· Sampling Process (sampling theorem, )

· Pulse-Amplitude Modulation (PAM)

· Other Forms of Pulse Modulation (PPM,PDM)

· Bandwidth-Noise Trade-off

· Quantization (preparation for digitization)

· Pulse-Code Modulation (PCM)

· Noise in PCM System (Channel noise, Quantization noise)

· Time-Division Multiplexing (TDM)

· Virtues , Limitations , and Modifications of PCM

· Delta Modulation (±Δ)

· Linear Prediction

· Differential PCM (DPCM) , Adaptive DPCM (ADPCM)

2s b

f f

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Chapter 4

Baseband Pulse Transmission· Matched Filter (matched to the signal)

· Bit Error Rate ( BER ) Due to Noise

· Intersymbol Interference ( ISI )

· Nyquist’s Criterion for Distortionless Baseband Binary Transmission

(No ISI 沒有noise時)

· Correlative-Level Coding ( Partial-Response)

(N bits/symbol)

· Adaptive Equalization

( )b b

P f nR T

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Chapter 5 Signal-Space Analysis

· Geometric Representation of Signals

(Vector representation)

· Conversion of the Continuous AWGN Channel into a Vector Channel

· Likelihood Functions

· Coherent Detection of Signal in Noise:

Maximum Likelihood Decoding

· Correlation Receiver

· Probability of Error (BER)

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Chapter 6 Passband Transmission

· Passband Transmission Model(

· Coherent Phase-Shift Keying (PSK)

· Quadrature-Amplitude Modulation (QAM)

· Coherent Frequency-Shift Keying (FSK)

· Detection of Signals with Unknown Phase

(Non-coherent detection)

· Noncoherent Orthogonal Modulation

(Orthogonal Frequency Carriers)

· Noncoherent Binary FSK

· Comparison of Digital Modulation Schemes Using a Single Carrier

( ) ( )cos(2 )i i

m s t Am t ft

ix t s t n t m ( ) ( ) ( )

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Background And Preview

0.1 The Communication Process (Statistical)

- Communication anywhere , anytime , involving

transmission of information from one point to other

places, (Broadcasting , multicast, Point-to-point)

generation and description of signals, encoding,

transmission, decoding and recovering.

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Fig.1 Elements of a Communication System

0.2 Primary Communication Resources

- transmitted power (power limited)

- channel bandwidth (bandwidth limited)

Due to noise , the ratio of the average signal

power to the average noise power (SNR) is an

important system parameter (in terms dB) , but

not the only one (ISI, jitter) (error free second)

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0.3 Sources of Information

- Speech

production , propagation , perception

- Music

melodic structure 旋律

harmonic structure 音調和諧

- Picture

- Text, Data

- Video34

0.4 Communication Networks

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Fig.4 Communication Network

- Open Systems Interconnection (OSI)

Reference Model

36Fig.5 OSI model, DLC: Data Link Control

Internet

A specific worldwide internet.

A machine is on the Internet if it runs the TCP/IP protocol stack , has an IP address, and has the ability to send and receive IP packets to all the other machines on the Internet.

The network technology is decoupled from

the applications.

· The applications are carried out independently

of the technology

· The network technology is capable of evolving

without affecting the applications 37

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TELNET: (for virtual terminal)

FTP: File Transfer Protocol

SMTP: Simple Mail Transfer Protocol (e-mail)

DNS: Domain Name System39

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0.5 Communication Channels

- Guided Propagation

a. Telephone Channels

(twisted pair of wires)

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b.Coaxial Channel ( 50Ω ,75Ω )

c.Optical Fiber (single mode, multimode)

125 μm

cladding

8 μm

core

·Enormous potential bandwidth (70 x 1012 Hz )

·Low transmission losses (0.158 db/km at 1.55μm )

·Immunity to electromagnetic interference

·Small size and weight

· Ruggedness and flexibility 44

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d. Wireless broadcast channels (AM,FM,TV)

superheterodyne receivers

e. Mobile radio channels

multipath fading , dispersive

f. Satellite channels (geosynchronous , low orbit)

Broad-area coverage, reliable transmission

lines,wide transmission bandwidth

Classification of channels

a. Linear, nonlinear (e.g. satellite) (Power Amplifier)

b. Time invariant, time variant

c. Bandwidth limited (e.g. telephone channel)

Power limited (e.g. satellite)49

0.6 Modulation and Demodulation Processes

a. Continuous-Wave (CW) modulation

- amplitude modulation ( AM )

- frequency modulation ( FM )

- phase modulation ( PM )

b. Pulse modulation

- pulse-amplitude modulation ( PAM )

- pulse-duration modulation ( PDM )

- pulse-positive modulation ( PPM )

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c. Pulse-code modulation ( PCM,digital )

- Sampling , quantization , coding

- Properties of PCM

· Robustness in noisy environments

· Flexible operation

· Integration of diverse sources into a

common format (0.1)

· Security of information

0.7 Multiplexing

a. Frequency-division multiplexing ( FDM )

b. Time-division multiplexing ( TDM )

c. Code-division multiplexing ( CDM )

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0.8 Analog and Digital Types of Communications

a. Guidelines of designing the transmitter

and the receiver

- Encode/modulate the signal,transmit it over the

channel and produce an ’’estimate” of the

original signal at the receiver output that

satisfies the requirements

- Do all of this at an affordable cost

b. The design of an analog communication system

is conceptually simple but difficult to implement

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c. The digital communication system

- Source encoder-decoder

(remove redundant information)

- Channel encoder-decoder

(controlled redundancy, FEC, Error detection)

- Modulator-demodulator

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Fig. 9 Block diagram of digital communication system.

0.9 Shannon’s Information Capacity Theorem

C = B · log2(1+SNR) b/s (1)

C : Channel capacity

B : Channel bandwidth

SNR : Signal-to-noise ratio

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Efficiency of a digital communication system

= R/C

R: actual signaling rate

Equation 1 provides a basis for the trade-off

between B and SNR and an idealized framework

for comparing modulation schemes

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0.10 A Digital Communication Problem (band pass)

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Fig. 10 Elements of a digital communication system.

The random signal m(t) consists of symbols 1 and 0 with duration T.

For PSK,

s(t)= -Ac cos(2fct+m(t) )

where 0 t T , the carrier frequency fc= , k=integer, Ac is the amplitude.

Assume the channel is distortionless but noising , the received

signal x(t) is

x(t)=s(t)+w(t) (3)

where w(t) is the additive channel noise (e.g., AWGN).

The output of the correlator is

Decision rule :

If yT 0 output symbol=1

yT 0 output symbol=0

T

k

TwA

wA

c

c

2

2 T

(5)=for m (t) =1

for m (t) = 0

TwdttftsyT

cT 0 )2cos()( (4)

(2)

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0

0

cos(2 ( ) )cos(2 )

cos(2 )cos(2 )

2

T

c cc T

T

c cc T

cT

A f t m t f t dt W

A f t f t dt W

AW

0 0

0

( )cos(2 ) ( )cos(2 )

cos(2 )cos(2 )

T T

c cT

T

c cT c T

y s t f t dt w t f t dt

y A f t f t W

2c

T

AW

cos(2 )cf t

for ( ) 0m t

for ( ) 1m t

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Important Issues

a. time-bandwidth product of a pulse signal is

constant, e.g., the bandwidth of a rectangular

pulse of duration T is inversely proportional to T

(Fourier Transform)

b. frequency shifting (Fourier Transform)

( shifts spectral to ± )

c. signal rate on

d. justification of the receiver structure

e. relation between wT and w(t)

( )

f. BER(modulation,channel,noise,demodulation)

g. choice of modulation schemes, coding,

synchronization

TB

1

Tsb 1

( )cos(2 )m t ft f

0( )cos(2 )

T

Tw w t ft dt

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0.11

A. Gain and Attenuation

Power gain

G(dB) = 10 log10 Po/ Pi

Voltage gain

G(dB) = 20 log10Vo/ Vi (P=V2/R)

If Po < Pi then G < 1, it is a loss (attenuation).

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B. Power Units

mW vs. dBm

P(dBm) = 10 log10 P(mW)/1 mW

= 10 log10 P(mW)

Examples:

1mW = 0 dBm

0.1 mW = -10 dBm

100mW = 20dBm

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C. Why dBm?

Examples:

PT=100mW

Loss=50dB Loss=40dB Loss=33dB

G=40dB G=39dB PR=?

TX RXA A

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D. Other Units

Practical communication channel

– Attenuation

– Distortion :

• amplitude distortion

• phase distortion

• Inter-modulation distortion

– Interference

– Multipath fading (very severe in wireless communications)

– Noise

• internal noise : amplitude noise, phase noise

• external noise (added noise)

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E. Noise Figure

– NF : a parameter to judge the noise property of a circuit or a

system.

– Define the signal-to-noise ratio (S/N)

– Define NF for a circuit or a system

s

N

Psignal powerSN noise power P

systemi

i

SN

o

o

SN

10log ( )

i

i

o

o

SN

NF dBS

N

0.12 Historical Notes

1837 Morse, Telegraph , Morse Code

1875 Baudot, Fixed length code (five elements)

1864 Maxwell, EM theory

1887 Hertz, Radio wave

1894 Lodge, Wireless communication

1901 Marconi, Long distance radio communication

1875 Bell, Telephone

1897 Stowger, Step-by-step switch

1904 Fleming, Vacuum tube diode

1906 Lee de Forest, Vacuum tube triode

1918 Armstrong ,Superheterdyne radio receiver

1936 Armstrong, Frequency modulation65

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1928 Nyquist, Nyquist’s criteria (No ISI)

1937 Reeves, Pulse-code modulation ( PCM )

1947 Kotel’nikov, Representation of signals

1948 Shannon, Information Theory

1949 Golay, Error-correcting codes

1950 Hamming, Hamming codes

1948 Brattain, Bardeen, and Schockley,Transistor

1958 Noyce, IC

1962 Bell Labs, TI carrier system

1946 Univ. of Penn, Computer

1971 ARPA, Computer networks (Packet switching)

1955 Pierce, Satellite communication

1966 K.C. Kao and Hockham, Fibers

1970 Ethernet

1980 Cellular Phone (AT&T)

1989~1993 (W.W.W) 70