现代通信原理课件(英文版)(ppt 35页)
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通信原理(英文版)1ppt课件
t
t
Analog signals
s(t) s(t)
Symbol
t
t
Digital signals
.
7
Two kinds of communication systems
• Analog communication system Requirement － High fidelity Criterion － Signal to noise ratio Basic issue － parameter estimation
• Digital communication system Requirement － correct decision Criterion － Error probability Basic issur － statistical decision theory
.
8
1.3.2 Advantages of Digital Communication
Fig. 1.3.2 Distortion and restoration of digital signal waveforms
.
9
Error correcting techniques can be used.
Digital encryption can be used.
Different kinds of analog & digital message can be integrated to transmit
# For an equal probability binary symbol:
I = log2 [1/P(x)] = log2 [1/(1/2)] = 1 bit
.
t
Analog signals
s(t) s(t)
Symbol
t
t
Digital signals
.
7
Two kinds of communication systems
• Analog communication system Requirement － High fidelity Criterion － Signal to noise ratio Basic issue － parameter estimation
• Digital communication system Requirement － correct decision Criterion － Error probability Basic issur － statistical decision theory
.
8
1.3.2 Advantages of Digital Communication
Fig. 1.3.2 Distortion and restoration of digital signal waveforms
.
9
Error correcting techniques can be used.
Digital encryption can be used.
Different kinds of analog & digital message can be integrated to transmit
# For an equal probability binary symbol:
I = log2 [1/P(x)] = log2 [1/(1/2)] = 1 bit
.
现代通信原理
标准正态随机变量
2018/9/12
f x
x2 1 exp 2 2
14
信息与通信工程系
3.2.1随机过程的分布函数和概率密度函数 对随机过程 X t 1. 一维概率分布函数 t t1 时，X t1 为随机变量。
F1 x1, t1 P{X t1 x1}
现代通信原理
Modern Communication Principles
第三章 随机信号和噪声分析
2018/9/12
信息与通信工程系
2
本章安排
随机信号和噪声分析
• 随机过程的基本概念 • 随机过程的统计描述
• 平稳随机过程
• 平稳随机过程的自相关函数与功率谱密度的关系 • 两个随机过程之间的统计联系
（1） F x 为不 减函数 （2） 0 F x 1
b.概率密度函数 f x
F x f ( x)dx
2018/9/12 信息与通信工程系 13
3.2.1随机过程的分布函数和概率密度函数
f x 的性质：
（1） f x 为非负 函数；
2018/9/12 信息与通信工程系 21
3.2.2 随机过程的数字特征
2 2 J进一步分析， 2 t E X t E X t 2 2 当 E 时，有 t E X X t 0 t （平均功率）
2.一维概率密度函数 如果
F1 x1 , t1 x1 f1 x1, t1 存在，则称 f1 x1 , t1 为随机的
一维概率密度函数。
2018/9/12 信息与通信工程系 15
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
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
现代通信原理
1
f x dx 1 ；
x2
（4）若 f x 在 x 处连续，则 f x
dF x 。 dx
正态随机变量
f x
x a 2 1 exp 2 2 2
标准正态随机变量
2019/4/3
f x
x2 1 exp 2 2
b.概率密度函数 f x
F x f ( x)dx
2019/4/3 信息与通信工程系 13
3.2.1随机过程的分布函数和概率密度函数
f x 的性质：
（1） f x 为非负 函数；
（2） （3） x2 x1 时， F ( x2 ) F ( x1 ) x f x dx ；
2019/4/3 信息与通信工程系 5
3.1 随机过程的基本概念 数学上可用随机实验和样本空间的概念定义随机 过程：设进行某一随机实验 E，S {e} 是它的样本空 间。如果对每一个样本 e(e S ) 来说，总可以按某一规 则确定一个时间函数 X (e, t )与之对应，那么，对所有 的样本，就得到一簇时间函数，并称此簇时间函数为 随机过程，其中每个时间函数称为该随机过程的样本 函数。
典型随机过程---接收机噪声
2019/4/3 信息与通信工程系 6
3.1 随机过程的基本概念
典型随机过程---噪声
2019/4/3 信息与通信工程系 7
3.1 随机过程的基本概念 归纳起来，随机过程具有如下特性：
（1）取值的随机性；
X t1 是一个随机变量（在t1时刻观察随机过程的值）
（2）样本的确定性。
2019/4/3
信息与通信工程系
f x dx 1 ；
x2
（4）若 f x 在 x 处连续，则 f x
dF x 。 dx
正态随机变量
f x
x a 2 1 exp 2 2 2
标准正态随机变量
2019/4/3
f x
x2 1 exp 2 2
b.概率密度函数 f x
F x f ( x)dx
2019/4/3 信息与通信工程系 13
3.2.1随机过程的分布函数和概率密度函数
f x 的性质：
（1） f x 为非负 函数；
（2） （3） x2 x1 时， F ( x2 ) F ( x1 ) x f x dx ；
2019/4/3 信息与通信工程系 5
3.1 随机过程的基本概念 数学上可用随机实验和样本空间的概念定义随机 过程：设进行某一随机实验 E，S {e} 是它的样本空 间。如果对每一个样本 e(e S ) 来说，总可以按某一规 则确定一个时间函数 X (e, t )与之对应，那么，对所有 的样本，就得到一簇时间函数，并称此簇时间函数为 随机过程，其中每个时间函数称为该随机过程的样本 函数。
典型随机过程---接收机噪声
2019/4/3 信息与通信工程系 6
3.1 随机过程的基本概念
典型随机过程---噪声
2019/4/3 信息与通信工程系 7
3.1 随机过程的基本概念 归纳起来，随机过程具有如下特性：
（1）取值的随机性；
X t1 是一个随机变量（在t1时刻观察随机过程的值）
（2）样本的确定性。
2019/4/3
信息与通信工程系
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
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
-
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)
-
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
-
西南交通大学 Southwest Jiaotong University
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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
waveform
2. Bandwidth and power of the
waveform
3. Effect of system noise on the received
information
4. Cost of the system
22
1.4 The property of the book and methods of learning it
20
1.2 Digital and Analog source and system
1. Key conception 2. Digital information source produces a finite set of
possible messages. Such as typewriter and keyboard 3. Analog information source produces messages that
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.
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
10
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 proຫໍສະໝຸດ essingCarrier circuits
Receiver
9
Function of transmitter
1) signal processor 2) In analog system it may be an analog low-
pass filter; In hybrid one, it may be analogto-digital converter(ADC) 3) 2)Function of signal-processing block in hybrid one 4) Source coding 5) Channel coding(adding parity and others) 6) 3) Function of Carrier Circuits 7) modulation
18
1.2 Digital and Analog source and system
(classification of communication system)
according to physical properties of information : Telephone /data /image and so on according to frequency : baseband transmitting/ bandpass transmitting system
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;
D e m o d u la to r
S in k O r (a c c e p ta n t)
R e c e iv in g e n d
14
1.2 Digital and Analog source and system (model of digital communication system)
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
19
1.2 Digital and Analog source and system
• Classification of communication patterm • Peer to peer communication :
simplex; half duplex; duplex • Parallel transmitting communication • Series transmitting communication
13
1.2 Digital and Analog source and system
• Model of analog communication system
In fo r m a tio n so u r c e
m o d u la to r
T r a n sm ittin g e n d
c h a n n e l n o ise
7）Error may often be corrected by the use of coding
17
1.2 Digital and Analog source and system 3.Disadvantages of Digital communication
1)More bandwidth is required generally 2)Sychronization is required
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
3） Greater dynamic range is possible 4） Data from different sources my be
transmitted over a common digital transmission system
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
waveform
2. Bandwidth and power of the
waveform
3. Effect of system noise on the received
information
4. Cost of the system
22
1.4 The property of the book and methods of learning it
20
1.2 Digital and Analog source and system
1. Key conception 2. Digital information source produces a finite set of
possible messages. Such as typewriter and keyboard 3. Analog information source produces messages that
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.
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
10
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 proຫໍສະໝຸດ essingCarrier circuits
Receiver
9
Function of transmitter
1) signal processor 2) In analog system it may be an analog low-
pass filter; In hybrid one, it may be analogto-digital converter(ADC) 3) 2)Function of signal-processing block in hybrid one 4) Source coding 5) Channel coding(adding parity and others) 6) 3) Function of Carrier Circuits 7) modulation
18
1.2 Digital and Analog source and system
(classification of communication system)
according to physical properties of information : Telephone /data /image and so on according to frequency : baseband transmitting/ bandpass transmitting system
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;
D e m o d u la to r
S in k O r (a c c e p ta n t)
R e c e iv in g e n d
14
1.2 Digital and Analog source and system (model of digital communication system)
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
19
1.2 Digital and Analog source and system
• Classification of communication patterm • Peer to peer communication :
simplex; half duplex; duplex • Parallel transmitting communication • Series transmitting communication
13
1.2 Digital and Analog source and system
• Model of analog communication system
In fo r m a tio n so u r c e
m o d u la to r
T r a n sm ittin g e n d
c h a n n e l n o ise
7）Error may often be corrected by the use of coding
17
1.2 Digital and Analog source and system 3.Disadvantages of Digital communication
1)More bandwidth is required generally 2)Sychronization is required
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
3） Greater dynamic range is possible 4） Data from different sources my be
transmitted over a common digital transmission system