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Transcript
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
Midterm 45% Final 45% Homework 10%
http://cc.ee.ntu.edu.tw/~wujsh/
1
Contents
Background and Preview
· Communication Process (Sender, receiver, pointto-point, 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
( x(t )  Am(t )cos(2 ft   )  n(t ) )
· Historical Notes
2
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
3
Chapter 2
Continuous-Wave ( CW )
Modulation
· Amplitude Modulation (AM)
· Linear Modulation Schemes( s(t )  sI (t )cos(2 fct )  sQ (t )sin(2 f ct ) )
(DSB-SC, SSB, VSB)
· Frequency–Division Multiplexing ( FDM )
· Angle Modulation s(t )  Ac cos[i (t )]
· 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 )
4
Chapter 3 Pulse Modulation
· Sampling Process (sampling theorem, f s  2 fb )
· 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)
5
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

P( f  nRb )  Tb 沒有noise時)
(No ISI 

· Correlative-Level Coding ( Partial-Response)
(N bits/symbol)
· Adaptive Equalization
6
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)
7
Chapter 6 Passband Transmission
· Passband Transmission Model( mi  si (t )  Am(t )cos(2 ft   )
 x(t )  si (t )  n(t )  m)
· 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
8
Background And Preview
0.1 The Communication Process (Statistical)
- Communication anywhere , anytime , involving
transmission of information from one point to
other places, (Broadcasting , Point-to-point)
generation and description of signals, encoding,
transmission, decoding and recovering.
9
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)
10
0.3 Sources of Information
- Speech
production , propagation , perception
- Music
melodic structure
旋律
harmonic structure 音調和諧
- Picture
11
0.4 Communication Networks
12
- Open Systems Interconnection (OSI)
Reference Model
13
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
14
Broadband Networks
Driving forces : demand for new services(video ,
multimedia ) and enabling technologies (optical
fibers, packet digital switches )
ATM, SONET, SDH, PDH (Plesiochronous
Digital Hierarchy )
15
0.5 Communication Channels
- Guided Propagation
a. Telephone Channels
(twisted pair of wires)
16
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
17
18
19
20
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)
21
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 )
22
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 )
23
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
24
c. The digital communication system
- Source encoder-decoder
(remove redundant information)
- Channel encoder-decoder
(controlled redundancy, FEC, Error detection)
- Modulator-demodulator
25
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
26
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
27
0.10 A Digital Communication Problem (band pass)




28
The random signal m(t) consists of symbols 1 and 0 with duration T.
For PSK,
s(t)= -Ac cos(2fct+m(t) )
(2)
k
where 0  t  T , the carrier frequency fc=
k=integer, Ac is the amplitude.
T ,
Assume the channel is distortionless but noising , the received
signal x(t) is
x(t)=s(t)+w(t)
where w(t) is the additive channel noise (e.g., AWGN).
The output of the correlator is
T
yT   s(t ) cos( 2fct )dt  wT
(3)
(4)
0

= 


Ac
 wT
2
Ac
 wT
2
Decision rule :
If yT  0 output symbol=1
yT  0 output symbol=0
for m (t) =1
(5)
for m (t) = 0
29
T
T
0
0
yT   s(t )cos(2 fct )dt   w(t )cos(2 fct )dt
T
   Ac cos(2 fct  m(t ) )cos(2 fct )dt  WT
0
T
   Ac cos(2 fct )cos(2 fct )dt  WT
for m(t )  0
0
Ac
   WT
2
T
yT    Ac cos(2 fct   )cos(2 fct )  WT
0
for m(t )  1
 cos(2 fct )
Ac

 WT
2
30
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
1
B
T (Fourier Transform)
b. frequency shifting (Fourier Transform)
( m(t )cos(2 ft ) shifts spectral to ± f )
c. signal rate on b  1
s
T
d. justification of the receiver structure
e. relation between wT and w(t)
T
( wT  0 w(t )cos(2 ft )dt )
f. BER(modulation,channel,noise,demodulation)
g. choice of modulation schemes, coding,
synchronization
31
0.11 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
32
1918 Armstrong ,Superheterdyne radio receiver
1936 Armstrong, Frequency modulation
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
1976 ARPA, Computer networks (Packet switching)
1955 Pierce, Satellite communication
1966 K.C. Kao and Hockham, Fibers
33