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.
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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