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现代通信原理课件(英文版)

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通信原理(英文版)1ppt课件

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
.
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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
.

通信原理(英文版)

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)

演示文稿通信原理英文版

演示文稿通信原理英文版
• Digital communication system Requirement － correct decision Criterion － Error probability Basic issur － statistical decision theory
1.3.2 Advantages of Digital Communication
1.2 Message, information & signal
Message：speech, letters, figures, images…
Information：effective content of message. Different types of messages may contain the same information
Finite number of possible values of signals Correct decision may be achieved
(a) Waveforms of distored digital signal
(b) Waveforms of digital signal after shaping
Signal：the carrier of message
What transmitted in a communication system is signal.
Measurement of information：
# “quantity of message” information content
1.3 Digital Communication
1.3.1 Basic concept
Two categories of signals • Analog signal：Its voltage or current

现代通信原理课件(英文版)(ppt 35页)

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

通信原理(英文版)

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

通信原理(英文版)

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)

通信原理(英文版)
# For an equal probability binary symbol:
I = log2 [1/P(x)] = log2 [1/(1/2)] = 1 bit
4
# For an equal probability M-ary symbol:
I = log2 [1/P(x)] = log2 [1/(1/M)] = log2 M bit If M = 2k ，then I = k bit
Out put S/N increases with bandwidth according to exponential law.
10
Digital communication system model 11
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
5
1.3 Digital Communication
1.3.1 Basic concept
Two categories of signals • Analog signal：Its voltage or current
can be expressed by a continuous function of time. For example, speech signal.
# Ex: “Rainfall will be 1 mm tomorrow” – information content small

通信原理(英文版)课件

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.
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1.2 Digital and Analog source and system
• The generation of communication system
Information input m(t)
Signal processing
Carrier circuits
Transmitter
channel noise
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
information from a analog source to the intended receiver(sink)
21
1.3 Deterministic and Random waveforms
1) Deterministic waveform It can be modeled as a completely specified function of time
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;
according to physical properties of information : Telephone /data /image and so on according to frequency : baseband transmitting/ bandpass transmitting system
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
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
transmitted over a common digital transmission system
16
1.2 Digital and Analog source and system
2 the advantage of digital system
5）Noise does not accumulate in long- distance systems by repeater
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
13
1.2 Digital and Analog source and system
• Model of analog communication system
Information source
modulator
Transmitting end
channel noise
Demodulator
Sink Or(acceptant)
6） Error in detected data may be small, even in large amount of noise on the received signal
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
18
1.2 Digital and Analog source and system
(classification of communication system)
22
1.4 The property of the book and methods of learning it
1)Property of the book a. from easiness to difficulty b. from concept to performance analysis
Receiving end
14
1.2 Digital and Analog source and system (model of digital communication system)
15
1.2 Digital and Analog source and system
2 the advantage of digital system
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
according to transmitting medium : wire /wireless
according to multiplexing patterm: Frequency division multiplexing access(FDMA) Time division multiplexing access(TDMS) Code division multiplexing access(CDMA)
are defined on continuum. 4. Digital communication system transfers information
from a digital source to the intended receiver(sink) 5. Analog communication system transfers
1）Relatively inexpensive digital circuits may be used
2） Privacy is preserved by using data encryption
3） Greater dynamic range is possible 4） Data from different sources my be
Information output
Signal processing
Carrier circuits
Receiver
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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
baseband processor estimate the source information and output the estimation result
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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.