数据通信毕业论文外文文献英文翻译.doc

1、郑州轻工业学院本科毕业设计（论文）英文翻译题 目 差错控制编码解决加性噪声的仿真 学生姓名 专业班级 通信工程05-2 学 号 12 院 （系） 计算机与通信工程学院 指导教师 完成时间 2009年4月26日 英文原文:data communicationsgildas avoine and philippe oechslinepfl, lausanne, switzerlandfgildas.avoine, philippe.oechslingep.chabstractdata communications are communications and computer technology

2、 resulting from the combination of a new means of communication. to transfer information between the two places must have transmission channel, according to the different transmission media, there is wired data communications and wireless data communications division. but they are through the transm

3、ission channel data link terminals and computers, different locations of implementation of the data terminal software and hardware and the sharing of information resources. 1 the development of data communicationsthe first phase: the main language, through the human, horsepower, war and other means

4、of transmission of original information.phase ii: letter post. (an increase means the dissemination of information)the third stage: printing. (expand the scope of information dissemination)phase iv: telegraph, telephone, radio. (electric to enter the time)fifth stage: the information age, with the e

5、xception of language information, there are data, images, text and so on.1.1 the history of modern data communicationscommunication as a telecommunications are from the 19th century, the beginning year 30. faraday discovered electromagnetic induction in 1831. morse invented telegraph in 1837. maxwel

6、ls electromagnetic theory in 1833. bell invented the telephone in 1876. marconi invented radio in 1895. telecom has opened up in the new era. tube invented in 1906 in order to simulate the development of communications.sampling theorem of nyquist criteria in 1928. shannong theorem in 1948. the inven

7、tion of the 20th century, the semiconductor 50, thereby the development of digital communications. during the 20th century, the invention of integrated circuits 60. made during the 20th century, 40 the concept of geostationary satellites, but can not be achieved. during the 20th century, space techn

8、ology 50. implementation in 1963 first synchronized satellite communications. the invention of the 20th century, 60 laser, intended to be used for communications, was not successful. 70 the invention of the 20th century, optical fiber, optical fiber communications can be developed. 1.2 key figures b

9、ell (1847-1922), english, job in london in 1868. in 1871 to work in boston. in 1873, he was appointed professor at boston university. in 1875, invented many telegram rd. in 1876, invented the telephone. lot of patents have been life. yes, a deaf wife. marconi (1874-1937), italian people, in 1894, th

10、e pilot at his fathers estate. 1896, to london. in 1897, the company set up the radio reported. in 1899, the first time the british and french wireless communications. 1916, implementation of short-wave radio communications. 1929, set up a global wireless communications network. kim won the nobel pr

11、ize. took part in the fascist party. 1.3 classification of communication systems according to type of information: telephone communication system, cable television system ,data communication systems. modulation by sub: baseband transmission,modulation transfer.characteristics of transmission signals

12、 in accordance with sub: analog communication system ,digital communication system. transmission means of communication system: cable communications,twisted pair, coaxial cable and so on. and long-distance telephone communication. modulation: ssb / fdm. based on the pcm time division multiple coaxia

13、l digital base-band transmission technology. will gradually replace the coaxial fiber. microwave relay communications:comparison of coaxial and easy to set up, low investment, short-cycle. analog phone microwave communications mainly ssb / fm / fdm modulation, communication capacity of 6,000 road /

14、channel. digital microwave using bpsk, qpsk and qam modulation techniques. the use of 64qam, 256qam such as multi-level modulation technique enhance the capacity of microwave communications can be transmitted at 40m channel 1920 7680 telephone rd pcm figure. optical fiber communication: optical fibe

15、r communication is the use of lasers in optical fiber transmission characteristics of long-distance with a large communication capacity, communication, long distance and strong anti-interference characteristics. currently used for local, long distance, trunk transmission, and progressive development

16、 of fiber-optic communications network users. at present, based on the long-wave lasers and single-mode optical fiber, each fiber road approach more than 10,000 calls, optical fiber communication itself is very strong force. over the past decades, optical fiber communication technology develops very

17、 quickly, and there is a variety of applications, access devices, photoelectric conversion equipment, transmission equipment, switching equipment, network equipment and so on. fiber-optic communications equipment has photoelectric conversion module and digital signal processing unit is composed of t

18、wo parts. satellite communications: distance communications, transmission capacity, coverage, and not subject to geographical constraints and high reliability. at present, the use of sophisticated techniques analog modulation, frequency division multiplexing and frequency division multiple access. d

19、igital satellite communication using digital modulation, time division multiple road in time division multiple access. mobile communications: gsm, cdma. number of key technologies for mobile communications: modulation techniques, error correction coding and digital voice encoding. data communication

20、 systems. 1.4 five basic types of data communication system: （1）off-line data transmission is simply the use of a telephone or similar link to transmit data without involving a computer system.the equipment used at both ends of such a link is not part of a computer, or at least does not immediately

21、make the data available for computer process, that is, the data when sent and / or received are off-line. this type of data communication is relatively cheap and simple. （2）remote batch is the term used for the way in which data communication technology is used geographically to separate the input a

22、nd / or output of data from the computer on which they are processed in batch mode. （3）on-line data collection is the method of using communications technology to provide input data to a computer as such input arises-the data are then stored in the computer (say on a magnetic disk) and processed eit

23、her at predetermined intervals or as required. （4）enquiry-response systems provide, as the term suggests, the facility for a user to extract information from a computer.the enquiry facility is passive, that is, does not modify the information stored.the interrogation may be simple, for example, retr

24、ieve the record for employee number 1234 or complex.such systems may use terminals producing hard copy and / or visual displays. （5）real-time systems are those in which information is made available to and processed by a computer system in a dynamic manner so that either the computer may cause actio

25、n to be taken to influence events as they occur (for example as in a process control application) or human operators may be influenced by the accurate and up-to-date information stored in the computer, for example as in reservation systems. 2 signal spectrum with bandwidth electromagnetic data signa

26、ls are encoded, the signal to be included in the data transmission. signal in time for the general argument to show the message (or data) as a parameter (amplitude, frequency or phase) as the dependent variable. signal of their value since the time variables are or not continuous, can be divided int

27、o continuous signals and discrete signals; according to whether the values of the dependent variable continuous, can be divided into analog signals and digital signal. signals with time-domain and frequency domain performance of the two most basic forms and features. time-domain signal over time to

28、reflect changing circumstances. frequency domain characteristics of signals not only contain the same information domain, and the spectrum of signal analysis, can also be a clear understanding of the distribution of the signal spectrum and share the bandwidth. in order to receive the signal transmis

29、sion and receiving equipment on the request channel, only know the time-domain characteristics of the signal is not enough, it is also necessary to know the distribution of the signal spectrum. time-domain characteristics of signals to show the letter .its changes over time. because most of the sign

30、al energy is concentrated in a relatively narrow band, so most of our energy focused on the signal that paragraph referred to as the effective band bandwidth, or bandwidth. have any signal bandwidth. in general, the greater the bandwidth of the signal using this signal to send data rate on the highe

31、r bandwidth requirements of transmission medium greater. we will introduce the following simple common signal and bandwidth of the spectrum. more or less the voice signal spectrum at 20 hz 2000 khz range (below 20 hz infrasound signals for higher than 2000 khz. for the ultrasonic signal), but with a

32、 much narrower bandwidth of the voice can produce an acceptable return, and the standard voice-frequency signal gnal 0 4 mhz, so the bandwidth of 4 mhz. as a special example of the monostable pulse infinite bandwidth. as for the binary signal, the bandwidth depends on the generalthe exact shape of t

33、he signal waveform, as well as the order of 0,1. the greater the bandwidth of the signal, it more faithfully express the number of sequences. 3 the cut-off frequency channel with bandwidth according to fourier series we know that if a signal for all frequency components can be completely the same th

34、rough the transmission channel to the receiving end, then at the receiving frequency components of these formed by stacking up the signal and send the signal side are exactly the same, that is fully recovered from the receiving end of the send-side signals. but on the real world, there is no channel

35、 to no wear and tear through all the frequency components. if all the fourier components are equivalent attenuation, then the signal reception while receive termination at an amplitude up attenuation, but the distortion did not happen. however, all the transmission channel and equipment for differen

36、t frequency components of the degree of attenuation is differentsome frequency components almost no attenuation, and attenuation of some frequency components by a number, that is to say, channel also has a certain amount of vibration increase the frequency characteristics, resulting in output signal

37、 distortion. usually are frequency of 0 hz to fc-wide channel at chuan harmonic lost during the attenuation does not occur (or are a very small attenuation constant), whereas in the fc frequency harmonics at all above the transmission cross decay process a lot, we put the signal in the transmission

38、channel of the amplitude attenuation of a component to the original 0.707(that is, the output signal reduce by half the power) when the frequency of the corresponding channel known as the cut-off frequency (cut - off frequency). cut-off frequency transmission medium reflects the inherent physical pr

39、operties. other cases, it is because people interested in line filter is installed to limit the bandwidth used by each user. in some cases, because of the add channel two-pass filter, which corresponds to two-channel cut-off frequency f1 and f2, they were called up under the cut-off frequency and th

40、e cut-off frequency. this difference between the two cut-off frequency f2-f1 is called the channel bandwidth. if the input signal bandwidth is less than the bandwidth of channel, then the entire input signal frequency components can be adopted by the department of channels, which the letter road to

41、be the output of the output waveform will be true yet. however, if the input signal bandwidth greater than the channel bandwidth, the signal of a frequency components can not be more on the channel, so that the signal output will be sent with the sending end of the signal is somewhat different, that

42、 is produced distortion. in order to ensure the accuracy of data transmission, we must limit the signal bandwidth.4 data transfer ratechannel maximum data transfer rate unit time to be able to transfer binary data transfer rate as the median. improve data transfer rate means that the space occupied

43、by each reduce the time that the sequence of binary digital pulse will reduce the cycle time, of course, will also reduce the pulse width. the previous section we already know, even if the binary digital pulse signal through a limited bandwidth channel will also be the ideal generated wave shape dis

44、tortion, and when must the input signal bandwidth, the smaller channel bandwidth, output waveform distortion will be greater. another angle degree that when a certain channel bandwidth, the greater the bandwidth of the input signal, the output signal the greater the distortion, so when the data tran

45、smission rate to a certain degree (signal bandwidth increases to a certain extent), in the on-channel output signal from the receiver could not have been distortion of the output signal sent to recover a number of sequences. that is to say, even for an ideal channel, the limited bandwidth limit syst

46、em of channel data transfer rate. at early 1924, h. nyquist (nyquist) to recognize the basic limitations of this existence, and deduced that the noise-free limited bandwidth channel maximum data transfer rate formula. in 1948, c. shannon (shannon) put into the work of nyquist 1 step-by-step expansio

47、n of the channel by the random noise interference. here we do not add on to prove to those now seen as the result of a classic. nyquist proved that any continuous signal f (t) through a noise-free bandwidth for channel b, its output signal as a time bandwidth of b continuous signal g (t). if you wan

48、t to output digital signal, it must be the rate of g (t) for interval sample. 2b samples per second times faster than are meaningless, because the signal bandwidth b is higher than the high-frequency component other than a letter has been road decay away. if g (t) by v of discrete levels, namely, th

49、e likely outcome of each sample for the v level of a discrete one, the biggest channel data rate rm ax as follows: rmax = 2blog 2 v (bit / s)for example, a 3000 hz noise bandwidth of the channel should not transmit rate of more than 6,000 bits / second binary digital signal. in front of us considere

50、d only the ideal noise-free channel. there is noise in the channel, the situation will rapidly deteriorate. channel thermal noise with signal power and noise power ratio to measure the signal power and noise power as the signal-to-noise ratio (s ignal - to - noise ratio). if we express the signal po

51、wer s, and n express the noise power, while signal to noise ratio should be expressed as s / n. however, people usually do not use the absolute value of signal to noise ratio, but the use of 10 lo g1 0s / n to indicate the units are decibels (d b). for the s / n equal 10 channel, said its signal to

52、noise ratio for the 1 0 d b; the same token, if the channel s / n equal to one hundred, then the signal to noise ratio for the 2 0 d b; and so on. s hannon noise channel has about the maximum data rate of the conclusions are: the bandwidth for the bh z, signal to noise ratio for the s / n channel, t

53、he maximum data rate rm ax as follows: rmax = blog 2 (1 + s / n) (bits / second)for example, for a bandwidth of 3 khz, signal to noise ratio of 30 db for the channel, regardless of their use to quantify the number of levels, nor fast sampling rate control, the data transfer rate can not be greater t

54、han 30,000 bits / second. s h a n n o n the conclusions are derived based on information theory out for a very wide scope, in order to go beyond this conclusion, like you want to invent perpetual motion machine, as it is almost impossible. it is worth noting that, s hannon conclusions give only a th

55、eoretical limit, and in fact, we should be pretty near the limit difficult. summarymessage signals are (or data) of a magnetic encoder, the signal contains the message to be transmitted. signal according to the dependent variable whether or not a row of values, can be classified into analog signals

56、and digital signals, the corresponding communication can be divided into analog communication and digital communication. fourier has proven: any signal (either analog or digital signal) are different types of harmonic frequencies composed of any signal has a corresponding bandwidth. and any transmis

57、sion channel signal attenuation signals will, therefore, channel transmission of any signal at all, there is a data transfer rate limitations, and this is chengkui n yquist (nyquist) theorem and s hannon (shannon) theorem tells us to conclusions. transmission medium of computer networks and communic

58、ation are the most basic part of it at the cost of the entire computer network in a very large proportion. in order to improve the utilization of transmission medium, we can use multiplexing. frequency division multiplexing technology has many road multiplexing, wave division multiplexing and tdm three that they use on different occasions. data exchange technologies such as circuit switching, packet switching and packet switching three have their respective advantages and disadvantages. m odem