whatno matter , goes around,be you wanna, ive done,so is love, time is it,b..u.wanna, is up, 电信 dian xin 电信（telecommunication）指利用电子技术在不同的地点之间传递信息。电信包括不同种类的远距离通讯方式，例如：无线电，电报，电视，电话，数据通讯以及计算机网络通讯等。 dian xin telecommunication zhi li yong dian zi ji shu zai bu tong de di dian zhi jian chuan di xin xi dian xin bao kuo bu tong zhong lei de yuan ju li tong xun fang shi li ru wu xian dian dian bao dian shi dian hua shu ju tong xun yi ji ji suan ji wang luo tong xun deng 组成通信系统的基本要素包括发信机，通道以及收信机。发信机负责将信息进行编码或转换成适合传输的信号。信号通过信道传输至收信机。在传输过程中, zu cheng tong xin xi tong de ji ben yao su bao kuo fa xin ji tong dao yi ji shou xin ji fa xin ji fu ze jiang xin xi jin hang bian ma huo zhuan huan cheng shi he chuan shu de xin hao xin hao tong guo xin dao chuan shu zhi shou xin ji zai chuan shu guo cheng zhong , 由于噪声的存在，信号不可避免的会受到改变。收信机端试图应用适当的解码手段从劣化的信号中恢复信息的原样。描述信道的的一个重要指标是带宽。 you yu zao sheng de cun zai xin hao bu ke bi mian de hui shou dao gai bian shou xin ji duan shi tu ying yong shi dang de jie ma shou duan cong lie hua de xin hao zhong hui fu xin xi de yuan yang miao shu xin dao de de yi ge zhong yao zhi biao shi dai kuan 通信系统的结构可以是点对点，也可以是一点对多点，广播则是一种特殊的一点对多点的传播形式。 tong xin xi tong de jie gou ke yi shi dian dui dian ye ke yi shi yi dian dui duo dian guang bo ze shi yi zhong te shu de yi dian dui duo dian de chuan bo xing shi 1948年，当时工作于贝尔实验室的香农发表了论文“通信的数学原理”，这一标志性的论文创建了分析通信系统的数学理论方法，也即信息论。信息论使我们可以根据信道的带宽和信噪比特性推算其容量。 1948 nian dang shi gong zuo yu bei er shi yan shi de xiang nong fa biao le lun wen tong xin de shu xue yuan li zhe yi biao zhi xing de lun wen chuang jian le fen xi tong xin xi tong de shu xue li lun fang fa ye ji xin xi lun xin xi lun shi wo men ke yi gen ju xin dao de dai kuan he xin zao bi te xing tui suan qi rong liang 在论文发表的时代，电信系统主要是基于模拟电路系统。此后，随着数字集成电路的大量普及，电信系统的设计可以充分利用信息论的理论指导提升性能。由此，数字信号处理也成为一个新的领域。 zai lun wen fa biao de shi dai dian xin xi tong zhu yao shi ji yu mo ni dian lu xi tong ci hou sui zhe shu zi ji cheng dian lu de da liang pu ji dian xin xi tong de she ji ke yi chong fen li yong xin xi lun de li lun zhi dao ti sheng xing neng you ci shu zi xin hao chu li ye cheng wei yi ge xin de ling yu 实际的通信信道不可避免的存在各种缺陷，其中包括：散弹噪声、热噪声、延迟、非线性传输函数、快速衰落、带宽限制以及信号反射等等。在一些当前的电信系统设计中，这些缺陷可以被利用来改善信道传输的质量。 shi ji de tong xin xin dao bu ke bi mian de cun zai ge zhong que xian qi zhong bao kuo san dan zao sheng re zao sheng yan chi fei xian xing chuan shu han shu kuai su shuai luo dai kuan xian zhi yi ji xin hao fan she deng deng zai yi xie dang qian de dian xin xi tong she ji zhong zhe xie que xian ke yi bei li yong lai gai shan xin dao chuan shu de zhi liang 现代通信系统普遍对于时间同步提出很高的要求。精确定时技术与通讯技术发展之间有着紧密的联系。大多数现代广域通讯系统都以原子钟作为时间基准。 xian dai tong xin xi tong pu bian dui yu shi jian tong bu ti chu hen gao de yao qiu jing que ding shi ji shu yu tong xun ji shu fa zhan zhi jian you zhe jin mi de lian xi da duo shu xian dai guang yu tong xun xi tong dou yi yuan zi zhong zuo wei shi jian ji zhun 调变是指将信息转换成适合远距离传播的模拟信号的处理过程。 diao bian shi zhi jiang xin xi zhuan huan cheng shi he yuan ju li chuan bo de mo ni xin hao de chu li guo cheng 主要数字信道编码方式：汉明码、格雷码、二进制码、turbo码。 zhu yao shu zi xin dao bian ma fang shi han ming ma ge lei ma er jin zhi ma turbo ma telecommunication telecommunication telecommunication refers to telecommunication refers to communication over long distances. in practice, something of the communication over long distances. in practice, something of the message may be lost in the process. telecommunication covers all message may be lost in the process. telecommunication covers all forms of distance and/or conversion of the original communications, forms of distance and/or conversion of the original communications, including radio, telegraphy, television, telephony, data including radio, telegraphy, television, telephony, data communication and computer networking. communication and computer networking. the elements of a the elements of a telecommunication system are a transmitter, a medium (line) and telecommunication system are a transmitter, a medium (line) and possibly a channel imposed upon the medium (see baseband and possibly a channel imposed upon the medium (see baseband and broadband as well as multiplexing), and a receiver. the transmitter broadband as well as multiplexing), and a receiver. the transmitter is a device that transforms or encodes the message into a physical is a device that transforms or encodes the message into a physical phenomenon; the signal. the transmission medium, by its physical phenomenon; the signal. the transmission medium, by its physical nature, is likely to modify or degrade the signal on its path from nature, is likely to modify or degrade the signal on its path from the transmitter to the receiver. the receiver has a decoding the transmitter to the receiver. the receiver has a decoding mechanism capable of recovering the message within certain limits mechanism capable of recovering the message within certain limits of signal degradation. sometimes, the final receiver is the human of signal degradation. sometimes, the final receiver is the human eye and/or ear (or in some extreme cases other sensory organs) and eye and/or ear (or in some extreme cases other sensory organs) and the recovery of the message is done by the brain (see the recovery of the message is done by the brain (see psychoacoustics.) psychoacoustics.) telecommunication can be telecommunication can be point-to-point, point-to-multipoint or broadcasting, which is a point-to-point, point-to-multipoint or broadcasting, which is a particular form of point-to-multipoint that goes only from the whatno matter , goes around,be you wanna, ive done,so is love, time is it,b..u.wanna, is up, particular form of point-to-multipoint that goes only from the whatno matter , goes around,be you wanna, ive done,so is love, time is it,b..u.wanna, is up, transmitter to the receivers. transmitter to the receivers. one of the roles of the one of the roles of the telecommunications engineer is to analyse the physical properties telecommunications engineer is to analyse the physical properties of the line or transmission medium, and the statistical properties of the line or transmission medium, and the statistical properties of the message in order to design the most effective encoding and of the message in order to design the most effective encoding and decoding mechanisms. decoding mechanisms. when systems are designed to when systems are designed to communicate through human sensory organs (mainly those for vision communicate through human sensory organs (mainly those for vision and hearing), physiological and psychological characteristics of and hearing), physiological and psychological characteristics of human perception must be taken into account. this has important human perception must be taken into account. this has important economic implications and engineers must research what defects can economic implications and engineers must research what defects can be tolerated in the signal and not significantly degrade the be tolerated in the signal and not significantly degrade the viewing or hearing experience. viewing or hearing experience. examples of human examples of human (tele)communications (tele)communications in a simplistic example, in a simplistic example, consider a normal conversation between two people. the message is consider a normal conversation between two people. the message is the sentence that the speaker decides to communicate to the the sentence that the speaker decides to communicate to the listener. the transmitter is the language areas in the brain, the listener. the transmitter is the language areas in the brain, the motor cortex, the vocal cords, the larynx, and the mouth that motor cortex, the vocal cords, the larynx, and the mouth that produce those sounds called speech. the signal is the sound waves produce those sounds called speech. the signal is the sound waves (pressure fluctuations in air particles) that can be identified as (pressure fluctuations in air particles) that can be identified as speech. the channel is the air carrying those sound waves, and all speech. the channel is the air carrying those sound waves, and all the acoustic properties of the surrounding space: echoes, ambient the acoustic properties of the surrounding space: echoes, ambient noise, reverberation. between the speaker and the listener, there noise, reverberation. between the speaker and the listener, there might be other devices that do or do not introduce their own might be other devices that do or do not introduce their own distortions of the original vocal signal (for example a telephone, distortions of the original vocal signal (for example a telephone, a ham radio, an ip phone, etc.) the receiver is the listener's ear a ham radio, an ip phone, etc.) the receiver is the listener's ear and auditory system, the auditory nerve, and the language areas in and auditory system, the auditory nerve, and the language areas in the listener's brain that will decode the signal into information the listener's brain that will decode the signal into information and filter out background noise. and filter out background noise. all channels have. another all channels have. another important aspect of the channel is called the bandwidth. a low important aspect of the channel is called the bandwidth. a low bandwidth channel, such as a telephone, cannot carry all of the bandwidth channel, such as a telephone, cannot carry all of the audio information that is transmitted in normal conversation, audio information that is transmitted in normal conversation, causing distortion and irregularities in the speaker's voice, as causing distortion and irregularities in the speaker's voice, as compared to normal, in-person speech. compared to normal, in-person speech. whatno matter , goes around,be you wanna, ive done,so is love, time is it,b..u.wanna, is up,