现代通信原理课件(英文版)
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通信原理(英文版)
Chapter 2 Signals
2.1 Classification of Signals
2.1.1 Deterministic signals and random signals
• What is deterministic signal? • What is random signal?
2.1.2 Energy signals and power signals
f (t) f (t T) t
Its frequency spectrum is
/2
C( jn0 )
1 T
/ 2 Ve j n0t dt
/ 2
1 T
V
jn 0
e
j n0 t
/ 2
V e j n0 / 2 e j n0 / 2
f (t) sin(t) Its frequency spefct(rtu)m: f (t 1)
0 t 1 t
C(
jn 0 )
1 T0
T0 / 2 s(t )e jn0t dt
T0 / 2
1 sin(t )e j 2nt dt
Solution: Let the expression of the rectangular pulse be
Then its frequency spectral density is
its
Fourier
tragns(fto)rm:
1
0
t /2 t /2
G() / 2 e jt dt 1 (e j / 2 e j / 2 ) sin( / 2)
2.1 Classification of Signals
2.1.1 Deterministic signals and random signals
• What is deterministic signal? • What is random signal?
2.1.2 Energy signals and power signals
f (t) f (t T) t
Its frequency spectrum is
/2
C( jn0 )
1 T
/ 2 Ve j n0t dt
/ 2
1 T
V
jn 0
e
j n0 t
/ 2
V e j n0 / 2 e j n0 / 2
f (t) sin(t) Its frequency spefct(rtu)m: f (t 1)
0 t 1 t
C(
jn 0 )
1 T0
T0 / 2 s(t )e jn0t dt
T0 / 2
1 sin(t )e j 2nt dt
Solution: Let the expression of the rectangular pulse be
Then its frequency spectral density is
its
Fourier
tragns(fto)rm:
1
0
t /2 t /2
G() / 2 e jt dt 1 (e j / 2 e j / 2 ) sin( / 2)
通信原理(英文版)课件
36
l 4-ary coding channel model
0
0
1
Transmitting end
2
1
Receiving end
2
3
3
Figure 1.4.12 4-ary coding channel model
37
1.4.4 Influence of channel characteristics on signal transmission
2
1.2 Message, information & signal
lMessage：speech, letters, figures, images…
lInformation：effective content of message. Different types of messages may contain the same information
# Information content I = I [ P(x) ]，P(x) – Occurrence probability
# Definition：I = loga [1/P(x)] = -logaP(x) # Usually, set a = 2, the unit of the information content will be called a bit.
0
ω
0
Ideal characteristic
Ideal characteristic: phase --- () = k ;
group delay --- () = d()/d = k
Influence of distortion: waveform distortion, inter-symbol interference
现代通信原理课件(英文版)(ppt 35页)
are defined on continuum. 4. Digital communication system transfers information
from a digital source to the intended receiver(sink) 5. Analog communication system transfers
2) Note: The general principles of digital and analog modulation apply to all types of channels, although channel characteristics may impose constraints that favor a particular type of signaling
15
1.2 Digital and Analog source and system
2 the advantage of digital system
1）Relatively inexpensive digital circuits may be used
2） Privacy is preserved by using data encryption
8
1.2 Digital and Analog source and system
• The generation of communication system
Information input m(t)
Signal processing
Carrier circuits
Transmitter
channel noise
1. Selection of the information-bearing
from a digital source to the intended receiver(sink) 5. Analog communication system transfers
2) Note: The general principles of digital and analog modulation apply to all types of channels, although channel characteristics may impose constraints that favor a particular type of signaling
15
1.2 Digital and Analog source and system
2 the advantage of digital system
1）Relatively inexpensive digital circuits may be used
2） Privacy is preserved by using data encryption
8
1.2 Digital and Analog source and system
• The generation of communication system
Information input m(t)
Signal processing
Carrier circuits
Transmitter
channel noise
1. Selection of the information-bearing
通信原理(英文版)
6
【Example 2.4】Find the waveform and the frequency spectral density of a sample function. Solution: The definition of the sample function is
sin t Sa ( t ) t
d(t)
1
(f)
0
t
0
f
meaning of d function: It is a pulse with infinite height, infinitesimal width, and unit area. Sa(t) has the following property:
Physical
F ( ) lim
/2 / 2
cos 0 te
jt
sin[( 0 ) / 2] sin[( 0 ) / 2] dt lim 2 ( ) / 2 ( ) / 2 0 0
The frequency spectral density of d(t):
( f ) d (t )e
jt
d (t ) 0
t 0
dt 1 d (t )dt 1
7
d(t)
and its frequency spectral density:
f (t ) f (t 1) t
1
Its frequency spectrum:
1 C ( jn 0 ) T0
T0 / 2
T0 / 2
s(t )e
【Example 2.4】Find the waveform and the frequency spectral density of a sample function. Solution: The definition of the sample function is
sin t Sa ( t ) t
d(t)
1
(f)
0
t
0
f
meaning of d function: It is a pulse with infinite height, infinitesimal width, and unit area. Sa(t) has the following property:
Physical
F ( ) lim
/2 / 2
cos 0 te
jt
sin[( 0 ) / 2] sin[( 0 ) / 2] dt lim 2 ( ) / 2 ( ) / 2 0 0
The frequency spectral density of d(t):
( f ) d (t )e
jt
d (t ) 0
t 0
dt 1 d (t )dt 1
7
d(t)
and its frequency spectral density:
f (t ) f (t 1) t
1
Its frequency spectrum:
1 C ( jn 0 ) T0
T0 / 2
T0 / 2
s(t )e
通信原理(英文版)
can be generalized to power signal.
10
Energy spectral density
Let the energy of an energy signal s(t) be E, then the energy
of
the
signal
is
decided
byE
s2 (t)dt
is
S() s(t)e jt dt
The inverse Fourier transform of S() is the original signal:
s(t) S ()e jtd
【Example 2.3】Find the frequency spectral density of a rectangular pulse.
0, 当t 0,
u(t)
1,
当t 0
1
u(t) = d(t)
0
Fig. 2.2.6 Unit step function
t
➢ Difference between frequency spectral density S(f) of
energy signal and frequency spectrum of periodic power
Chapter 2 Signals
2.1 Classification of Signals
2.1.1 Deterministic signals and random signals
➢ What is deterministic signal? ➢ What is random signal?
通信原理(英文版)1
大家好
2
1.2 Message, information & signal
Message：speech, letters, figures, images…
Information：effective content of message. Different types of messages may contain the same information
Demodulation
Channel
Modulation
Informitter
1.3.4 Specifications of Digital
Communication Systems
Relationship between efficiency & reliability (rate ~ accuracy)
Two categories of signals
• Analog signal：Its voltage or current can be expressed by a continuous function of time. For example, speech signal.
• Digital signal： Its voltage or current can only take finite number of discrete values. For example, digital computer data signal.
(MF)
direction-finding, distress
calling, coast guard
大家好
17
Division of frequency band
通信原理(数字通信)PCM(41页英文ppt)
6/41
A First Course in Digital Communications
Chapter 4: Sampling and Quantization
Sampling Theorem
Theorem A signal having no frequency components above W Hertz is completely described by specifying the values of the signal at periodic time instants that are separated by at most 1/2W seconds. fs ≥ 2W is known as the Nyquist criterion, the sampling rate fs = 2W is called the Nyquist rate and its reciprocal called the Nyquist interval. Ideal sampling is not practical ⇒ Need practical sampling methods.
Sampling: How many samples per second are needed to exactly represent the signal and how to reconstruct the analog message from the samples? Quantization: To represent the sample value by a digital symbol chosen from a finite set. What is the choice of a discrete set of amplitudes to represent the continuous range of possible amplitudes and how to measure the distortion due to quantization? Encoding: Map the quantized signal sample into a string of digital, typically binary, symbols.
A First Course in Digital Communications
Chapter 4: Sampling and Quantization
Sampling Theorem
Theorem A signal having no frequency components above W Hertz is completely described by specifying the values of the signal at periodic time instants that are separated by at most 1/2W seconds. fs ≥ 2W is known as the Nyquist criterion, the sampling rate fs = 2W is called the Nyquist rate and its reciprocal called the Nyquist interval. Ideal sampling is not practical ⇒ Need practical sampling methods.
Sampling: How many samples per second are needed to exactly represent the signal and how to reconstruct the analog message from the samples? Quantization: To represent the sample value by a digital symbol chosen from a finite set. What is the choice of a discrete set of amplitudes to represent the continuous range of possible amplitudes and how to measure the distortion due to quantization? Encoding: Map the quantized signal sample into a string of digital, typically binary, symbols.
现代通信原理-第9章PPT课件
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西南交通大学 Southwest Jiaotong University
-2-
m(t)
现代通信原理 Principle of Modern Communications
(a)
T(t)
-3T -2T -T 0 T 2T 3T
(c) ms(t)
(e)
模拟信号的数字化过程：抽样
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西南交通大学 Southwest Jiaotong University
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西南交通大学 Southwest Jiaotong University
-11-
现代通信原理 Principle of Modern Communications
• 模拟带通信号的抽样定理
【模拟带通信号的抽样定理】：若模拟带通信号的频率介 于 f L 和 f H 之间，则此模拟带通信号的最小抽样频率为
第九章 模拟信号的数字化传输
• 模拟信号的抽样 • 模拟脉冲调制 • 抽样信号的量化 • 脉冲编码调制 (PCM)
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西南交通大学 Southwest Jiaotong University
-5-
现代通信原理 Principle of Modern Communications
• 模拟低通信号的抽样定理
-
西南交通大学 Southwest Jiaotong University
-20-
现代通信原理 Principle of Modern Communications
ms(t)
t
m(t) ms(t) 保持 mH(t) 电路 MH(f) mH(t)
H (f)
s(t)
T
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西南交通大学 Southwest Jiaotong University
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5
1.1 Introduction
1 Jimes C.Maxwell（1864） 2 Heinrich Hertz （1887） 3 Claude E.Shannon (1948) 4.Winner
6
1.1 Introduction
Perspective of communication Wire
3
1.1 Introduction
What is a communication system? Communication systems is used to transmit information.
4
1.1 Introduction
Key conceptions or words (1) Information; (2) Message; (3) Signal; (4) Waveforms
11
Receiver
The receiver takes the corrupted signal at the channel output and converts it to a baseband
signal that can be handled by the receiver baseband processor, and then the receiver
现代通信原理课件Chapter One
1
Chapter One
Introduction
Why? Information Age Information Superhighway
2
Chapter One Application
military application; common application;
2)Function of signal-processing block in hybrid one Source coding Channel coding(adding parity and others)
3) Function of Carrier Circuits modulation
10
1. Selection of the information-bearing
waveform
2. Bandwidth and power of the
waveform
3. Effect of system noise on the received
information
4. Cost of the system
2) Note: The general principles of digital and analog modulation apply to all types of channels, although channel characteristics may impose constraints that favor a particular type of signaling
optic-fiber and networks wireless
1G->2G->3G->B3G WLAN; MIMO and MIMO-OFDM, UWB, optic –wireless communication
7
1.1 Introduction
What must be considered when you design a communication system?
8
1.2 Digital and Analog source and system
• The generation of communication system
Information input m(t)
Signal processing
Carrier circuits
Transmitter
channel noise
baseband processor estimate the source information and output the estimation result
12
Summary
The goal is to design communication system that transmit information to the receiver with as little deterioration as possible while satisfying design constrains such as allowable transmitted energy,allowable signal bandwidth and cost. In digital system measure of deterioration is taken to be bit error rate(BER),while in analog system the performance measure is usually taken to be the signal-to-noise ratio(SNR) at the receiver output.
13
1.2 Digital and Analog source and system
Channel
1） Classification: wire and wireless
Wire channel including twisted-pair telephone line/Coaxial cables,waveguides and fiber-optic cables
Wireless channel having air,vacuum and seawater
Information output
Signal processing
Carrier circuits
Receiver
9
Function of transmitter
1) signal processor In analog system it may be an analog lowpass filter; In hybrid one, it may be analogto-digital converter(ADC)
1.1 Introduction
1 Jimes C.Maxwell（1864） 2 Heinrich Hertz （1887） 3 Claude E.Shannon (1948) 4.Winner
6
1.1 Introduction
Perspective of communication Wire
3
1.1 Introduction
What is a communication system? Communication systems is used to transmit information.
4
1.1 Introduction
Key conceptions or words (1) Information; (2) Message; (3) Signal; (4) Waveforms
11
Receiver
The receiver takes the corrupted signal at the channel output and converts it to a baseband
signal that can be handled by the receiver baseband processor, and then the receiver
现代通信原理课件Chapter One
1
Chapter One
Introduction
Why? Information Age Information Superhighway
2
Chapter One Application
military application; common application;
2)Function of signal-processing block in hybrid one Source coding Channel coding(adding parity and others)
3) Function of Carrier Circuits modulation
10
1. Selection of the information-bearing
waveform
2. Bandwidth and power of the
waveform
3. Effect of system noise on the received
information
4. Cost of the system
2) Note: The general principles of digital and analog modulation apply to all types of channels, although channel characteristics may impose constraints that favor a particular type of signaling
optic-fiber and networks wireless
1G->2G->3G->B3G WLAN; MIMO and MIMO-OFDM, UWB, optic –wireless communication
7
1.1 Introduction
What must be considered when you design a communication system?
8
1.2 Digital and Analog source and system
• The generation of communication system
Information input m(t)
Signal processing
Carrier circuits
Transmitter
channel noise
baseband processor estimate the source information and output the estimation result
12
Summary
The goal is to design communication system that transmit information to the receiver with as little deterioration as possible while satisfying design constrains such as allowable transmitted energy,allowable signal bandwidth and cost. In digital system measure of deterioration is taken to be bit error rate(BER),while in analog system the performance measure is usually taken to be the signal-to-noise ratio(SNR) at the receiver output.
13
1.2 Digital and Analog source and system
Channel
1） Classification: wire and wireless
Wire channel including twisted-pair telephone line/Coaxial cables,waveguides and fiber-optic cables
Wireless channel having air,vacuum and seawater
Information output
Signal processing
Carrier circuits
Receiver
9
Function of transmitter
1) signal processor In analog system it may be an analog lowpass filter; In hybrid one, it may be analogto-digital converter(ADC)