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: 管挺貴 電子所ICS組
E-Mail: [email protected]
藍邦嘗 電信所通信組碩2
E-Mail: [email protected]
Grading Rule
Midterm 45%
Final 45%
Homework 10%
Some of the problems in the homework will appear
on the Midterm and the Final Exams.
At the end of the semester, I may modify the score.( linear
translation )
However for a student with many absences (5 times or
more), his score may
not be adjusted. 2
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
3
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 4
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
5
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
6
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
7
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)
8
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 ( ) ( ) ( )
9
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.
10
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)
11
0.3 Sources of Information
- Speech
production , propagation , perception
- Music
melodic structure 旋律
harmonic structure 音調和諧
- Picture
- Test, Data
- Video12
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 15
TELNET: (for virtual terminal)
FTP: File Transfer Protocol
SMTP: Simple Mail Transfer Protocol (e-mail)
DNS: Domain Name System17
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 22
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)27
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 )
28
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 )
29
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
30
c. The digital communication system
- Source encoder-decoder
(remove redundant information)
- Channel encoder-decoder
(controlled redundancy, FEC, Error detection)
- Modulator-demodulator
31
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
32
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
33
0.10 A Digital Communication Problem (band pass)
34
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)
35
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
36
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
37
38
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).
39
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
41
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)
42
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 modulation43
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) 48