通信系统绪论ppt课件.ppt

东南大学移动通信国家重点实验室1Communication Systems （Fourth Edition） Simon Haykin 东南大学移动通信国家重点实验室2Contents CH0: Background and PreviewCH1: Random ProcessesCH2: Continuous-Wave ModulationCH3: Pulse ModulationCH4: Baseband Pulse TransmissionCH5: Signal-Space AnalysisCH6: Passband Data TransmissionCH7: Spread-Spectrum ModulationCH8: Multiuser Radio CommunicationsCH9: Fundamental Limits in Information TheoryCH10: Error-Control Coding东南大学移动通信国家重点实验室3Ch.0 Background and Preview1.The Communication Process2.Primary Communication Resources3.Sources of Information4.Communication Networks5.Communication Channels6.Modulation Process7.Analog and Digital Types of Communication8.Shannons Information Capacity Theorem9.A Digital Communications Problem10. Historical Notes 东南大学移动通信国家重点实验室40.1 The Communication ProcessFig. 1. Elements of a communication system.东南大学移动通信国家重点实验室5The Communication Process (contd) Three basic elements to every communication system Transmitter: to convert the message signal produced by the source of information into a form suitable for transmission over the channel Channel: introduces distortion and noise Receiver: to reconstruct the original message signal from the received signal东南大学移动通信国家重点实验室6The Communication Process (contd) Two basic modes of communication Broadcasting One-to-many communication Usually one directional flow of signals E.g. radio and television Point-to-point communication One-to-one communication Usually bidirectional flow of signals E.g. telephone and satellite communication One common feature of communication process: Statistical in nature 东南大学移动通信国家重点实验室70.2 Primary Communication Resources Transmitted power: the average power of the transmitted signal Channel bandwidth: the band of frequencies allocated for the transmission of the message signal Two types of communication channels: Power limited: e.g. satellite channel Band limited: e.g. telephone circuit Noise Unwanted and unavoidable The signal-to-noise ratio (SNR) Usually expressed in decibels (dBs), SNRdB = 10log10(SNR)东南大学移动通信国家重点实验室80.3 Sources of Information Four important sources of information: Speech: Using the 300 3100 Hz band Music: up to 15 kHz Pictures Can be dynamic (e.g. television) or static (e.g. facsimile) The scanning process Wideband signals Computer data The American Standard Code for Information Interchange (ASCII) Wideband signals Burstiness Compression (lossless and lossy)东南大学移动通信国家重点实验室90.4 Communication NetworksFig. 4. Communication network.东南大学移动通信国家重点实验室10Communication Networks Switching Mode Circuit switching E.g. the telephone network Suitable to relatively stable and long duration signals, such as voice Packet switching E.g. the Internet “Store and forward” Suitable to computer communication where data is bursty in nature Requires careful control from end users东南大学移动通信国家重点实验室11Communication Networks Layered ArchitectureFig. 5. OSI model.东南大学移动通信国家重点实验室12Communication Networks InternetFig. 6. An interconnected network of subnets. Network of networks Underlying network technology is decoupled from the applications Best effort service东南大学移动通信国家重点实验室13Communication Networks Internet (Contd)Fig. 7. Illustrating the network architecture of the Internet.东南大学移动通信国家重点实验室14Communication Networks Broadband Networks B-ISDN Stands for “broadband integrated services digital networks” Evolves from telephone network whose major service is voice Supports multimedia communications The underlying technology is asynchronous transfer mode (ATM)东南大学移动通信国家重点实验室15 ATM A cell-switching technology Basic transmission unit is cells (small, fixed-size packets) Preserves cell sequencing in transmission Is not synchronous High bandwidth and low delay Provide quality of service (QoS) guarantees QoS is measured in terms of loss ratio, delay, and delay variationCommunication Networks Broadband Networks (Contd)东南大学移动通信国家重点实验室16 SONET Stands for “synchronous optical network” Using time-division multiplexing (TDM) Need synchronization A hierarchy of data rates The basic rate is 51.84 Mb/s Byte-interleaved to generate higher ratesCommunication Networks Broadband Networks (Contd)东南大学移动通信国家重点实验室170.5 Communication ChannelsGuided propagationTelephone channelsCoaxial cablesOptical fibersFree propagationBroadcast channelsMobile radio channelsSatellite channelsDifferent ways of classificationLinear or nonlinearTime invariant or time varyingBand limited or power limited东南大学移动通信国家重点实验室18Communication Channels Telephone ChannelsBandwidth limited (300 3100 Hz)Using twisted pairsSusceptible to electromagnetic interference (EMI)Fig. 8. Characteristics of typical telephone connection: (a) Insertion loss. (b) Envelope delay. (Adapted from Bellamy, 1991.)东南大学移动通信国家重点实验室19Communication Channels Coaxial Cables Better immunity to EMI than twisted pairs Has a characteristic impedance of 50 or 75 ohms Higher bandwidth than twisted pairs (up to 20 Mb/s) Can be used as a multiple-access medium Applications Local area networks (LAN) Cable-television systems东南大学移动通信国家重点实验室20Communication Channels Optical Fibers Dielectric wave guide transporting light signals Enormous potential bandwidth (21013 Hz) Low transmission losses (0.1 dB/km) Immunity to EMI (dielectric) Small size and weight (thinner than a hair) Ruggedness and flexibility Low cost of the materials东南大学移动通信国家重点实验室21Communication Channels Wireless Broadcast Channels Information-bearing signal is usually modulated for transmission Antenna is used to efficiently transmit and receive electromagnetic waves Typically line-of-sight (LOS) propagation The super-heterodyne type receiver东南大学移动通信国家重点实验室22Communication Channels Mobile Radio Channels Typically non-line-of-sight (NLOS) propagation The multipath phenomenon The energy reaches the receiving antenna via more than one path Resulting from scattering of signals during propagation Linear and time-varying东南大学移动通信国家重点实验室23Communication Channels Satellite Channels Communicating through geostationary satellites Broad-area coverage Reliable transmission links Wide transmission bandwidth (6 GHz for the uplink and 4 GHz for the downlink)东南大学移动通信国家重点实验室240.6 Modulation 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.东南大学移动通信国家重点实验室25Modulation Process Classification Continuous-wave modulation The carrier is a sinusoidal wave Amplitude modulation (AM) Angle modulation Frequency modulation (FM) Phase modulation (PM) Pulse modulation The carries is a periodic sequence of pulses Analog pulse modulation (PAM, PDM, and PPM) Digital pulse modulation (PCM)东南大学移动通信国家重点实验室26Modulation Process Multiplexing Multiplexing 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)东南大学移动通信国家重点实验室270.7 Analog and Digital Types of CommunicationFig. 9. Block diagram of digital communication system.东南大学移动通信国家重点实验室28Analog Digital Types of Communication Digital Communication System is complex, including Source encoder-decoder Channel encoder-decoder Modulator-demodulator Easy to build Efficient and reliable With the ever-increasing availability of very-large-scale integrated (VLSI) circuits, digital communications become popular today.东南大学移动通信国家重点实验室29Analog Digital Types of Communication Analog Communication System is simple Difficult to build Stringent requirements on linearity Difficult on system adjustment Very high-speed and very low-power communication systems may dictate the use of an analog approach.东南大学移动通信国家重点实验室300.8 Shannons Information Capacity Theory Bit error rate (BER) reliability metric The information capacity theoryA message signal can be transmitted through the system without error provided that the actual signaling rate is less than the information capacity C,C = B log2 (1+SNR) b/swhere B is the channel bandwidth.东南大学移动通信国家重点实验室310.9 A Digital Communication ProblemFig. 10. Elements of a digital communication system. (a) Block diagram of transmitter. (b) Block diagram of channel. (c) Block diagram of receiver.东南大学移动通信国家重点实验室32A Digital Communication Problem (Contd)cos(2)( )cos(2) for symbol 1 for symbol 0ccccAf ts tAf t( )( )( )x ts tw t0( )cos(2)22 for symbol 1 for symbol 0TTccTcTyx tf t dtAwAw东南大学移动通信国家重点实验室330.10 Historical Notes1837，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)