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
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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
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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
通信原理(英文版)课件
A protocol used to establish a direct connection between two points, often used for dial-up internet access.
Network Security
• Firewalls: Devices that filter incoming and outgoing traffic based on security policies to protect against unauthorized access or malicious attacks.
Modulation and Demodulation
Modulation
The process of varying a property of a carrier wave, such as its amplitude, frequency, or phase, in accordance with the information to be transmitted. This allows information to be carried over long distances through various media.
Channel Capacity and Data Rate
Channel Capacity
The maximum amount of information that can be transmitted over a communication channel without loss of data or degradation in signal quality. It is typically limited by the physical properties of the channel and the noise level present.
Network Security
• Firewalls: Devices that filter incoming and outgoing traffic based on security policies to protect against unauthorized access or malicious attacks.
Modulation and Demodulation
Modulation
The process of varying a property of a carrier wave, such as its amplitude, frequency, or phase, in accordance with the information to be transmitted. This allows information to be carried over long distances through various media.
Channel Capacity and Data Rate
Channel Capacity
The maximum amount of information that can be transmitted over a communication channel without loss of data or degradation in signal quality. It is typically limited by the physical properties of the channel and the noise level present.
通信原理英文版教学课件：class six-2ASK
式中， Ps(f) － pPosw( fe)r sp14ecPtAra( lf denf0s)ityPoAf(sf(t) f0 )
PA(f) － power spectral density of A(t)
∴If PA(f) has been found, then Ps(f) can be calculated by substituting PA(f) int the above equation.
Therefore the mean power of the output noise of the bandpass filter is:
Hence its output signal to nno2 isen0rBati1o.9i2s: 10 8 W
∴（1）the
r symbol
A2
106
1
1
erf
4
ha
2 n
1
1
erf
4
h
2
n
When h equals the optimum threshold h*,
p1(x*) p0 (x*)
Pe
1 erfc 2
r /2
When r>>1,
Pe
1 er / 4
r
13
Envelope detection
∵ The output is the envelope of its input voltage y(t), we have
∴When 1 is transmitted, the probability of x(t) is
p1(x)
1
2
n
exp
(x
A) 2
PA(f) － power spectral density of A(t)
∴If PA(f) has been found, then Ps(f) can be calculated by substituting PA(f) int the above equation.
Therefore the mean power of the output noise of the bandpass filter is:
Hence its output signal to nno2 isen0rBati1o.9i2s: 10 8 W
∴（1）the
r symbol
A2
106
1
1
erf
4
ha
2 n
1
1
erf
4
h
2
n
When h equals the optimum threshold h*,
p1(x*) p0 (x*)
Pe
1 erfc 2
r /2
When r>>1,
Pe
1 er / 4
r
13
Envelope detection
∵ The output is the envelope of its input voltage y(t), we have
∴When 1 is transmitted, the probability of x(t) is
p1(x)
1
2
n
exp
(x
A) 2
通信原理课件
လܹᆓ 6RXWKZHVW -LDRWRQJ 8QLYHUVLW\ -4-
ɴҷỞֵॳˊ ciple of Modern Communications
ഀຬ(Twisted Pair)
A twisted pair consists of two insulated copper wires, typically about 1 mm thick. The wires are twisted together in a helical form, just like a DNA molecule. Twisting is done because two parallel wires constitute a fine antenna. When the wires are twisted, the waves from different twists cancel out, so the wire radiates less effectively.
လܹᆓ 6RXWKZHVW -LDRWRQJ 8QLYHUVLW\ -5-
ɴҷỞֵॳˊ Principle of Modern Communications
ઝఘඔྑ
0 1 2 3 4 5 6 7 8 9 10 11 12
༝ࢻ௲഻੦੦੦੦ჾჾৢёᄉݯԁથથથથᆓᆓຟຟؠူԸԸݮݮၻၻ೭ۜۜႎᄥᄥۜۜӛӛϏϏۤಒຂຂԅԅҎҎࢻහහᆓᆓёᆓᆓຂ((ຂԸԸ12))ྑҎҎහහᄥᄥௐ((ຂຂ12))((හහ12))((12))
ԛసჃ ԁူႎಒ
Chapter 3 Channel and Noise
3.1 3.2 3.3 3.4 3.5 3.6
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ɴҷỞֵॳˊ ciple of Modern Communications
ഀຬ(Twisted Pair)
A twisted pair consists of two insulated copper wires, typically about 1 mm thick. The wires are twisted together in a helical form, just like a DNA molecule. Twisting is done because two parallel wires constitute a fine antenna. When the wires are twisted, the waves from different twists cancel out, so the wire radiates less effectively.
လܹᆓ 6RXWKZHVW -LDRWRQJ 8QLYHUVLW\ -5-
ɴҷỞֵॳˊ Principle of Modern Communications
ઝఘඔྑ
0 1 2 3 4 5 6 7 8 9 10 11 12
༝ࢻ௲഻੦੦੦੦ჾჾৢёᄉݯԁથથથથᆓᆓຟຟؠူԸԸݮݮၻၻ೭ۜۜႎᄥᄥۜۜӛӛϏϏۤಒຂຂԅԅҎҎࢻහහᆓᆓёᆓᆓຂ((ຂԸԸ12))ྑҎҎහහᄥᄥௐ((ຂຂ12))((හහ12))((12))
ԛసჃ ԁူႎಒ
Chapter 3 Channel and Noise
3.1 3.2 3.3 3.4 3.5 3.6
ۺ഻ϵԁԁϵԁԁԅԅԅԅԁՇԁަఘඋ࿌༰උ२ۤ੦ႎדރރಒୣफୣճճۜۜҎҎԅԅູູ
文元美现代通信原理课件1现代通信系统原理绪论
数字基带传输通信系统
图 1-7 数字基带传输通信系统模型
图 1-8 模拟信号数字化传输通信系统模型
模拟信号数字化传输通信系统
1.2.3 数字通信的主要优缺点
数字通信的主要优点 抗干扰、 抗噪声性能好。 差错可控。 易加密。 易于与现代技术相结合。
两类通信方式抗干扰性能比较 模拟信号；(b)数字信号
信息及其量度
消息出现的概率愈小， 它所含信息量愈大； 反之信息量愈小。 且
消息中所含信息量I是消息出现的概率P(x)的函数，即
可以看出I与P(x)间应满足以上三点， 则它们有如下关系式：
(3) 若干个互相独立事件构成的消息， 所含信息量等于各独立事件信息量的和， 即
信息量I的单位与对数的底数a有关： a=2 单位为比特(bit，简写为b)； a=e单位为奈特(nat，简写为n)； a=10单位为笛特(Det)或称为十进制单位； a=r单位称为r进制单位。 通常使用的单位为比特。
3.移动通信
移动通信是现代通信中发展最为迅速的一种通信手段，它是随着汽车、飞机、轮船、火车等交通工具的发展而同步发展起来的。 近10年来， 在微电子技术和计算机技术的推动下，移动通信从过去简单的无线对讲或广播方式发Байду номын сангаас成为一个把有线、 无线融为一体，固定、移动相互连通的全国规模，甚至全球范围的通信系统。
数字微波、 空间通信
脉冲波调制
脉冲模拟调制
脉幅调制PAM
中间调制方式、 遥测
脉宽调制PDM(PWM)
中间调制方式
脉位调制PPM
遥测、 光纤传输
脉冲数字调制
脉码调制PCM
市话、 卫星、 空间通信
增量调制DM
文元美现代通信原理课件1.现代通信系统原理绪论
第1章
绪 论
1.1 通信的基本概念
1.1.1 通信的定义
1、通信的目的是传递消息。 消息的表达形式：语言、文字、图像、数据等。 2、通信的一般概念（定义）
@ 指由一地向另一地进行消息的有效传递。
实现通信的方式很多。目前使用最广泛的是电通信方式， 即用“电”来传递消息的通信方法，称为“电信” （telecommunication)。即用电信号携带所要传递的消息，然 后经过各种电信道进行传输，达到通信的目的。（广泛意义 上来讲，光通信也属于电通信，因为光也是一种电磁波）。
1. 按传输媒质分
按消息由一地向另一地传递时传输媒质的不同，通信可分
为两大类：一类称为有线通信，另一类称为无线通信。
2. 按信道中所传信号的不同分（按信号特征分） 信道是个抽象的概念。这里我们可理解成传输信号的通路。 通常信道中传送的信号可分为数字信号和模拟信号，由此通信 亦可分为数字通信和模拟通信。
第1章
绪 论
二、通信方式 前述通信系统是单向通信系统，但在多数场合下， 信源兼为信宿，需要双向通信，电话就是一个最好的 例子，这时通信双方都要有发送和接收设备，并需要 各自的传输媒质，如果通信双方共用一个信道，就必 须用频率或时间分割的方法来共享信道。因此，通信 过程中涉及通信方式与信道共享问题。 下面介绍通信 方式。 1． 按消息传递的方向与时间关系分 对于点与点之间的通信，按消息传递的方向与时 间关系， 通信方式可分为单工、半双工及全双工通信 三种。 单工通信， 是指消息只能单方向传输的工作方式， 因此只占用一个信道， 如图 (a)所示。广播、遥测、遥 控、无线寻呼等就是单工通信方式的例子。
第1章
绪 论
6. 按收信者是否运动分 通信还可按收信者是否运动分为移动通信和固定通信。移 动通信是指通信双方至少有一方在运动中进行信息交换。移 动通信已被列为现代通信中的三大新兴通信方式之一。 另外，通信还有其它一些分类方法，如按多地址方式可 分为频分多址(FDMA)通信、时分多址(TDMA)通信、码分多 址(CDMA)通信等。按用户类型可分为公用通信和专用通信等。
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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