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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
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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)
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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
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Chapter One
Introduction
Why? Information Age Information Superhighway
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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
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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
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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
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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
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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
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1.2 Digital and Analog source and system 3.Disadvantages of Digital communication
1)More bandwidth is required generally 2)Sychronization is required
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1.2 Digital and Analog source and system
(classification of communication system)
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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
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1.2 Digital and Analog source and system (model of digital communication system)
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1.2 Digital and Analog source and system
2 the advantage of digital system
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1.1 Introduction
What is a communication system? Communication systems is used to transmit information.
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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.