現(xiàn)代通信原理課件chapterone-wenkub.com
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【正文】 19, 167。 duplex ? Parallel transmitting munication ? Series transmitting munication 21 1. Key conception Digital information source produces a finite set of possible messages. Such as typewriter and keyboard Analog information source produces messages that are defined on continuum. Digital munication system transfers information from a digital source to the intended receiver(sink) Analog munication system transfers information from a analog source to the intended receiver(sink) Digital and Analog source and system 22 1) Deterministic waveform It can be modeled as a pletely specified function of time 2) Random waveform(stochastic waveform) It can not be pletely specified as a function of time and must be modeled probabilistically 1) Example: Deterministic and Random waveforms )c o s ()( 00 ??? ?? tAt23 1)Property of the book a. from easiness to difficulty b. from concept to performance analysis 2) Methods of learning it a. reading it again and again b. grasping the important concept c. understanding the basic munication system by deriving some key formula d. simulation using Matlab The property of the book and methods of learning it 24 1. Information Content If the probabiltiy of transmitting jth message is Pj， the information content sent from a digital source when it was transmitted is given by: Information Measure bi tPPI jjj )(l og)1(l og22 ???25 Information Measure From the definition, we have the following results: 1) The message that are less likely to occur provide more information 2) Information content depends on only the likehood of sending the message and does not depend on possible interpretation of the content as to whether or not it makes sense. 26 2 Unit of information Information Measure b i t sPI jb i t sj )(l o
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