《现代通信原理课件ChapterOne(1)26943.pptx》由会员分享，可在线阅读，更多相关《现代通信原理课件ChapterOne(1)26943.pptx（36页珍藏版）》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、 现代通信原理课件Chapter One1IntroductionChapter OneWhy?Information AgeInformation Superhighway2Application military application;common application;Chapter One3What is a communication system?Communication systems is used to transmit information.1.1 Introduction4Key conceptions or words(1)Information;(2)Mess
2、age;(3)Signal;(4)Waveforms1.1 Introduction51 Jimes C.Maxwell（1864）2 Heinrich Hertz（1887）3 Claude E.Shannon(1948)4.Winner1.1 Introduction6Perspective of communicationWire optic-fiber and networks wireless 1G-2G-3G-B3G WLAN;MIMO and MIMO-OFDM,UWB,optic wireless communication1.1 Introduction7What must
3、be considered when you design a communication system?1.Selection of the information-bearing waveform2.Bandwidth and power of the waveform3.Effect of system noise on the received information4.Cost of the system1.1 Introduction81.2 Digital and Analog source and system The generation of communication s
4、ystem91)signal processor 2)In analog system it may be an analog low-pass filter;In hybrid one,it may be analog-to-digital converter(ADC)3)2)Function of signal-processing block in hybrid one4)Source coding5)Channel coding(adding parity and others)6)3)Function of Carrier Circuits7)modulationFunction o
5、f transmitter 101）Classification:wire and wirelessWire channel including twisted-pair telephone line/Coaxial cables,waveguides and fiber-optic cables Wireless channel having air,vacuum and seawater2)Note:The general principles of digital and analog modulation apply to all types of channels,although
6、channel characteristics may impose constraints that favor a particular type of signalingChannel11The 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 baseband processor estimate
7、 the source information and output the estimation resultReceiver12The 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.
8、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.Summary131.2 Digital and Analog source and system Model of analog communication system141.2 Digital
9、 and Analog source and system(model of digital communication system)151）Relatively inexpensive digital circuits may be used2）Privacy is preserved by using data encryption3）Greater dynamic range is possible4）Data from different sources my be transmitted over a common digital transmission system2 the
10、advantage of digital system1.2 Digital and Analog source and system165）Noise does not accumulate in long-distance systems by repeater6）Error in detected data may be small,even in large amount of noise on the received signal7）Error may often be corrected by the use of coding2 the advantage of digital
11、 system1.2 Digital and Analog source and system171)More bandwidth is required generally2)Sychronization is required3.Disadvantages of Digital communication1.2 Digital and Analog source and system181.2 Digital and Analog source and system(classification of communication system)according to physical p
12、roperties of information:Telephone/data/image and so on according to frequency:baseband transmitting/bandpass transmitting system according to transmitting medium:wire/wireless according to multiplexing patterm:Frequency division multiplexing access(FDMA)Time division multiplexing access(TDMS)Code d
13、ivision multiplexing access(CDMA)191.2 Digital and Analog source and system Classification of communication patterm Peer to peer communication:simplex;half duplex;duplex Parallel transmitting communication Series transmitting communication201.Key conception2.Digital information source produces a fin
14、ite set of possible messages.Such as typewriter and keyboard 3.Analog information source produces messages that are defined on continuum.4.Digital communication system transfers information from a digital source to the intended receiver(sink)5.Analog communication system transfers information from a
15、 analog source to the intended receiver(sink)1.2 Digital and Analog source and system211)Deterministic waveform It can be modeled as a completely specified function of time2)Random waveform(stochastic waveform)3)It can not be completely specified as a function of time and must be modeled probabilist
16、ically4)Example:1.3 Deterministic and Random waveforms 221)Property of the book a.from easiness to difficulty b.from concept to performance analysis2)Methods of learning it a.reading it again and again b.grasping the important concept c.understanding the basic communication system by deriving some k
17、ey formula d.simulation using Matlab1.4 The property of the book and methods of learning it231.Information ContentIf the probabiltiy of transmitting jth message is Pj，the information content sent from a digital source when it was transmitted is given by:1.9 Information Measure241.9 Information Measu
18、reFrom the definition,we have the following results:1)The message that are less likely to occur provide more information2)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.252 Unit
19、 of information1.9 Information Measure1)Bits,Nats and Hartley262 Unit of information1.9 Information Measure2)Relationship between Bit,Nat and Hartley271)Definition2)If there are m possible different source message in a digital source(m is finite),and Pj is the probabiltiy of sending the jth message,
20、the entropy(also called average information)is:1.9 Information Measure3.Entropy for Digital Source284 Example1-1:In a string of 12 symbols,where each symbol consistis of one of four levels,there are 412 different combinations(words),since each levels is equally likely,and all the different words equ
21、ally likely.Thus Pj=(1/4)12,And Ij=log2(1/(1/4)12)=12log2(4)=24bits 1.9 Information Measure295 Source Rate 1.9 Information MeasureSource Rate is defined asExample:A1-2 A telephone touch-tone keypad has the digits 0 to 9 with probability of sending being 0.099 each,plus“*”and“#”with probability of se
22、nding being 0.005 each.If the keys are pressed at a rate of 2keys/pute the data rate for this source.Solution:Using define above,where T=1/2=0.5s/key,then:30For digital systems,the optimum system might be defined as the system that minimizes the BER at the system output subject to constraints on tra
23、nsmitted energy and channel bandwidth.Thus bit error rate and signal bandwidth are of prime importance in this course.1.10 Channel capacityShannon gives channel capacity as311.10 Channel capacityWhere B is the channel bandwidth in hertz,S/N is the signal-to-noise power ratio at the input to the digi
24、tal receiver.And showed that if the rate of information R(bits/s)was less than C,the BER would approach zero.32In analog system,the optimum system might be defined as the one that achieves the largest signal-to-noise ratio at the receiver output,subject to design constraints such as channel bandwidt
25、h and transmitted power.Nyquist showed that if a pulse represents one bit of data,noninterfering pulse could be sent over a channel no faster than 2B pulses/s,where B is the channel bandwidth in hertz.That is now known as the dimensionality theorem.1.10 Channel Capacity33Example SA1-3:A computer use
26、r plans to buy a higher-speed modem for sending data over his or her analog telephone line.The telephone line has a signal-to-noise ratio(SNR)of 25dB and passes audio frequencies over the range,from 300 to 3200Hz,Calculate the maximum data rate that could be sent over the telephone line when there a
27、re on errors at the receiving end.Solution:In the term of a power ratio,the SNR=10(25/10)=316.2,the bandwidth is B=3200-300=2900 Hz，we get:1.10 Channel CapacityProblem:Can a 28.8kbit/s modem work on this telephone line?And a 14.4kbits/s modem?34Problems:1.5,1.7,1.9,1.10,1.12,1.13 1.15Reading:page 1-2,1-2,1-3,1-6 1-9,1-10 Homework35谢谢观看/欢迎下载BY FAITH I MEAN A VISION OF GOOD ONE CHERISHES AND THE ENTHUSIASM THAT PUSHES ONE TO SEEK ITS FULFILLMENT REGARDLESS OF OBSTACLES.BY FAITH I BY FAITH