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1、1,Communication Systems （Fourth Edition） Simon Haykin,2,Contents,CH0: Background and PreviewCH1: Random ProcessesCH2: Continuous-Wave ModulationCH3: Pulse ModulationCH4: Baseband Pulse TransmissionCH5: Signal-Space AnalysisCH6: Passband Data TransmissionCH7: Spread-Spectrum ModulationCH8: Multiuser
2、Radio CommunicationsCH9: Fundamental Limits in Information TheoryCH10: Error-Control Coding,3,Ch.0 Background and Preview,The Communication ProcessPrimary Communication ResourcesSources of InformationCommunication NetworksCommunication ChannelsModulation ProcessAnalog and Digital Types of Communicat
3、ionShannons Information Capacity TheoremA Digital Communications ProblemHistorical Notes,4,0.1 The Communication Process,Fig. 1. Elements of a communication system.,5,The Communication Process (contd),Three basic elements to every communication systemTransmitter: to convert the message signal produc
4、ed by the source of information into a form suitable for transmission over the channelChannel: introduces distortion and noiseReceiver: to reconstruct the original message signal from the received signal,6,The Communication Process (contd),Two basic modes of communicationBroadcastingOne-to-many comm
5、unicationUsually one directional flow of signalsE.g. radio and televisionPoint-to-point communicationOne-to-one communicationUsually bidirectional flow of signalsE.g. telephone and satellite communicationOne common feature of communication process:Statistical in nature,7,0.2 Primary Communication Re
6、sources,Transmitted power: the average power of the transmitted signalChannel bandwidth: the band of frequencies allocated for the transmission of the message signalTwo types of communication channels:Power limited: e.g. satellite channelBand limited: e.g. telephone circuitNoiseUnwanted and unavoida
7、bleThe signal-to-noise ratio (SNR)Usually expressed in decibels (dBs), SNRdB = 10log10(SNR),8,0.3 Sources of Information,Four important sources of information: Speech: Using the 300 3100 Hz bandMusic: up to 15 kHzPicturesCan be dynamic (e.g. television) or static (e.g. facsimile)The scanning process
8、Wideband signalsComputer dataThe American Standard Code for Information Interchange (ASCII)Wideband signalsBurstinessCompression (lossless and lossy),9,0.4 Communication Networks,Fig. 4. Communication network.,10,Communication Networks Switching Mode,Circuit switchingE.g. the telephone networkSuitab
9、le to relatively stable and long duration signals, such as voicePacket switchingE.g. the Internet“Store and forward”Suitable to computer communication where data is bursty in natureRequires careful control from end users,11,Communication Networks Layered Architecture,Fig. 5. OSI model.,12,Communicat
10、ion Networks Internet,Fig. 6. An interconnected network of subnets.,Network of networksUnderlying network technology is decoupled from the applicationsBest effort service,13,Communication Networks Internet (Contd),Fig. 7. Illustrating the network architecture of the Internet.,14,Communication Networ
11、ks Broadband Networks,B-ISDNStands for “broadband integrated services digital networks”Evolves from telephone network whose major service is voiceSupports multimedia communicationsThe underlying technology is asynchronous transfer mode (ATM),15,ATMA cell-switching technologyBasic transmission unit i
12、s cells (small, fixed-size packets)Preserves cell sequencing in transmissionIs not synchronousHigh bandwidth and low delayProvide quality of service (QoS) guaranteesQoS is measured in terms of loss ratio, delay, and delay variation,Communication Networks Broadband Networks (Contd),16,SONETStands for
13、 “synchronous optical network”Using time-division multiplexing (TDM)Need synchronizationA hierarchy of data ratesThe basic rate is 51.84 Mb/sByte-interleaved to generate higher rates,Communication Networks Broadband Networks (Contd),17,0.5 Communication Channels,Guided propagationTelephone channelsC
14、oaxial cablesOptical fibersFree propagationBroadcast channelsMobile radio channelsSatellite channelsDifferent ways of classificationLinear or nonlinearTime invariant or time varyingBand limited or power limited,18,Communication Channels Telephone Channels,Bandwidth limited (300 3100 Hz)Using twisted
15、 pairsSusceptible to electromagnetic interference (EMI),Fig. 8. Characteristics of typical telephone connection: (a) Insertion loss. (b) Envelope delay. (Adapted from Bellamy, 1991.),19,Communication Channels Coaxial Cables,Better immunity to EMI than twisted pairsHas a characteristic impedance of 5
16、0 or 75 ohmsHigher bandwidth than twisted pairs (up to 20 Mb/s)Can be used as a multiple-access mediumApplicationsLocal area networks (LAN)Cable-television systems,20,Communication Channels Optical Fibers,Dielectric wave guide transporting light signalsEnormous potential bandwidth (21013 Hz)Low tran
17、smission losses (0.1 dB/km)Immunity to EMI (dielectric)Small size and weight (thinner than a hair)Ruggedness and flexibilityLow cost of the materials,21,Communication Channels Wireless Broadcast Channels,Information-bearing signal is usually modulated for transmissionAntenna is used to efficiently t
18、ransmit and receive electromagnetic wavesTypically line-of-sight (LOS) propagationThe super-heterodyne type receiver,22,Communication Channels Mobile Radio Channels,Typically non-line-of-sight (NLOS) propagationThe multipath phenomenonThe energy reaches the receiving antenna via more than one pathRe
19、sulting from scattering of signals during propagationLinear and time-varying,23,Communication Channels Satellite Channels,Communicating through geostationary satellitesBroad-area coverageReliable transmission linksWide transmission bandwidth (6 GHz for the uplink and 4 GHz for the downlink),24,0.6 M
20、odulation Process,The modulation process varies some parameter of a carrier wave in accordance with the message signal, so that the resulting signal is suitable for transmission over the channel.Demodulation is the reverse of modulation.,25,Modulation Process Classification,Continuous-wave modulatio
21、nThe carrier is a sinusoidal waveAmplitude modulation (AM)Angle modulationFrequency modulation (FM)Phase modulation (PM)Pulse modulationThe carries is a periodic sequence of pulsesAnalog pulse modulation (PAM, PDM, and PPM)Digital pulse modulation (PCM),26,Modulation Process Multiplexing,Multiplexin
22、g is the process of combining several message signals for their simultaneous transmission over the same channel.Frequency-division multiplexing (FDM)Time-division multiplexing (TDM)Code-division multiplexing (CDM)Wavelength-division multiplexing (WDM) (a form of FDM),27,0.7 Analog and Digital Types
23、of Communication,Fig. 9. Block diagram of digital communication system.,28,Analog Digital Types of Communication Digital Communication,System is complex, includingSource encoder-decoderChannel encoder-decoderModulator-demodulatorEasy to buildEfficient and reliableWith the ever-increasing availabilit
24、y of very-large-scale integrated (VLSI) circuits, digital communications become popular today.,29,Analog Digital Types of Communication Analog Communication,System is simpleDifficult to buildStringent requirements on linearityDifficult on system adjustmentVery high-speed and very low-power communica
25、tion systems may dictate the use of an analog approach.,30,0.8 Shannons Information Capacity Theory,Bit error rate (BER) reliability metricThe information capacity theoryA message signal can be transmitted through the system without error provided that the actual signaling rate is less than the info
26、rmation capacity C,C = B log2 (1+SNR) b/swhere B is the channel bandwidth.,31,0.9 A Digital Communication Problem,Fig. 10. Elements of a digital communication system. (a) Block diagram of transmitter. (b) Block diagram of channel. (c) Block diagram of receiver.,32,A Digital Communication Problem (Co
27、ntd),33,0.10 Historical Notes,1837，Telegraph-Samuel Morse1864，Electromagnetic theory-James Clerk Maxwell1875，Telephone-Alexander Graham Bell1904，Vacuum-tube diode-John Ambrose Fleming1918，Superheterodyne radio receiver-Edwin H. Armstrong1928，All-electronic television-Philo T. Farnsworth1937，PCM for speech-Alec Reeves1943，Matched filter-D. O. North1947，Geometric representation of signals-V. A. Kotelnikov1948，Information Theory-Claude Shannon1948，Transistor-Bell Laboratories1943-6，Electronic digital computer-University of Pennsylvania1950-70，Computer Networks-ARPANET (1985Internet, 1990-WWW),
