通信工程毕业论文外文翻译--数据通信.doc

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1、题 目 差错控制编码解决加性噪声的仿真 英文原文:Data communicationsGildas Avoine and Philippe OechslinEPFL, Lausanne, Switzerlandfgildas.avoine, philippe.oechslingep.chAbstractData communications are communications and computer technology resulting from the combination of a new means of communication. To transfer informat

2、ion 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 transmission channel data link terminals and computers, different locations of implementati

3、on 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 of transmission of original information.Phase II: Letter Post. (An increase means the

4、 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 exception of language information, there are data, images, text and so on.1.1 The hist

5、ory 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. Maxwells electromagnetic theory in 1833. Bell invented the telephone in 1876. Marconi inven

6、ted 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 invention of the 20th century, the semiconductor 50, thereby the development of digital co

7、mmunications. 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 technology 50. Implementation in 1963 first synchronized satellite communications. The inv

8、ention 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 Bell (1847-1922), English, job in London in 1868. In 1871 to work in Boston. In 1873,

9、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, the pilot at his fathers estate. 1896, to London. In 1897, the company set up the radio

10、 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 Prize. Took part in the Fascist Party. 1.3 Classification of Communication Systems Acco

11、rding to type of information: Telephone communication system, Cable television system ,Data communication systems. Modulation by sub: Baseband transmission,Modulation transfer.Characteristics of transmission signals in accordance with sub: Analog Communication System ,Digital communication system. T

12、ransmission 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 coaxial digital base-band transmission technology. Will gradually replace the coaxial fiber

13、. 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 / Channel. Digital microwave using BPSK, QPSK and QAM modulation techniques. The use of

14、 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 fiber communication is the use of lasers in optical fiber transmission characteristics of

15、 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 of fiber-optic communications network users. At present, based on the long-wave lase

16、rs 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 quickly, and there is a variety of applications, access devices, photoelectric conve

17、rsion 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 two parts. Satellite communications: Distance communications, transmission capacity, c

18、overage, 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. Digital satellite communication using digital modulation, time division multiple road

19、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 Systems. 1.4 Five basic types of data communication system: （1）Off-line data transmi

20、ssion 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 make the data available for computer process, that is, the data when sent and / or re

21、ceived 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 and / or output of data from the computer on which they are processed in batch mode. （

22、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 either at predetermined intervals or as required. （4）Enquiry-response systems provide, a

23、s 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, RETRIEVE THE RECORD FOR EMPLOYEE NUMBER 1234 or complex.Such systems may use terminals pr

24、oducing 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 action to be taken to influence events as they occur (for example as in a process control

25、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 signals are encoded, the signal to be included in the data transmission. Signal in time fo

26、r 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 into continuous signals and discrete signals; according to whether the values of the dep

27、endent 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 reflect changing circumstances. Frequency domain characteristics of signals not only

28、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 transmission and receiving equipment on the request channel, Only know the time-domain charac

29、teristics 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 signal energy is concentrated in a relatively narrow band, so most of our energy focused

30、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 higher bandwidth requirements of transmission medium greater. We will introduce the follow

31、ing 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 much narrower bandwidth of the voice can produce an acceptable return, and the stand

32、ard 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 the signal waveform, as well as the order of 0,1. The greater the bandwidth of the sig

33、nal, 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 through the transmission channel to the receiving end, then at the receiving frequency

34、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 to no wear and tear through all the Frequency components. If all the Fourier compone

35、nts 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 different frequency components of the degree of attenuation is differentSome frequency compon

36、ents 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 distortion. Usually are frequency of 0 Hz to fc-wide channel at Chuan harmonic lost

37、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 channel of the amplitude attenuation of a component to the original 0.707(that is, th

38、e 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 properties. Other cases, it is because people interested in Line filter is installed to

39、 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 the cut-off frequency. This difference between the two cut-off frequency f2-f1 is calle

40、d 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 be the output of the output waveform will be true yet. However, if the input signal b

41、andwidth 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 is produced Distortion. In order to ensure the accuracy of data transmission, we mus

42、t 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 by each Reduce the time that the sequence of binary digital pulse will reduce the cyc

43、le 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 distortion, and when must the input signal bandwidth, the smaller channel bandwidth, out

44、put 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 transmission Rate to a certain degree (signal bandwidth increases to a certain extent), i

45、n 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 System of channel data transfer rate. At early 1924, H. Nyquist (Nyquist) to recognize th

46、e 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 expansion of the channel by the random noise interference. Here we do not add on to prove to

47、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 want to output digital signal, it must be the rate of g (t) for interval Sample. 2B samp

48、les 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, the likely outcome of each sample for the V level of a discrete one, The biggest channe

49、l 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 considered 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