通信工程毕业设计（论文）外文翻译扩频通信系统及MATLAB仿真

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1、华科学院HUAKE INSTITUTE OF TAIYUAN UNIVERSITY OFSCIENCE & TECHNOLOGY外文翻译外文翻译题题目：目：扩频扩频通信系通信系统统及及 MATLAB 仿真仿真学学 生生 姓姓 名名 学学 号号 班班 级级 通信通信 072201H072201H 所属院（系）所属院（系） 电子信息工程系电子信息工程系 指指 导导 教教 师师 2011 年 6 月- 1 -Spread Spectrum Communication System and MATLAB SimulationABSTRACTThis thesis expounds the basic

2、principles of spread spectrum communication , and then the article mainly acts according to the Shannon theorem and tan oak Czechoslovakia you Nepal may the husband latent antijamming theory,With the aid of MatLab toolbox and Monte Carlo simulation algorithm,it has established the direct sequence sp

3、read spectrum communications system simulation model which does not have when the disturbance through the analysis error rate simulation curve and theory predicted value,had proven constructs the simulation model the accuracy.Key words：Spread spectrum；communication；MATLAB1 Introduction1.1 Spread Spe

4、ctrum Communication SystemSpread spectrum communication, namely, spread spectrum communications (Spread Spectrum Communication), with fiber-optic communications, satellite communications, with access to the information age as the three major high-tech communications transmission.Spread spectrum comm

5、unication is to send the information to be pseudo-random data is coded (spread spectrum sequence: Spread Sequence) modulation, spread spectrum and then the realization of transmission; the receiving end is using the same modem code and related processing, the restoration of the original data.Spread

6、spectrum communication system has three main characteristics.Carrier is an unpredictable, or so-called pseudo-random broadband signal.Carrier data bandwidth than the modulation bandwidth is much wider.Receiving process is generated by local broadband carrier signal and receiving a copy of the signal

7、 to the broadband signal to achieve.The main way of spread spectrum are as follows:Direct Sequence Spread Spectrum (DSSS) using high-speed pseudo-random code on to the low-speed data transmission spread spectrum modulation;Frequency-hopping system using pseudo-random code to control the carrier freq

8、uency in a wider band of the change;TH is the data transmission time slot is a pseudo-random;Chirp frequency system is a linear extension of the process of change.Combination of a - 2 -number of ways of hybrid systems are often applied.The most important measure of spread-spectrum system is an indic

9、ator of spreading gain, also known as processing gain.It is precisely because of the spread spectrum system itself with its performance characteristics with a series of advantages.1.2 The purpose of spread spectrum communication studies and significance Spread spectrum communication is an important

10、branch of communication and channel the direction of development of communication systems.Spread-spectrum technology, with strong anti-interference ability, confidentiality, and is easy to realize the advantages of multiple-access communications, so the technology is receiving increasing attention.I

11、n recent years, with very large scale integrated circuit technology, the rapid development of microprocessor technology, as well as the application of some new components, spread spectrum communications is technically feasible to enter a new level, not only in an important military communications st

12、atus, and are quickly penetrated into the personal communications and computer communications and other civilian areas, to become the new century, the most potential of communication technologies.The study is spread spectrum communication with far-reaching significance, I through the thesis the desi

13、gn, conduct in-depth study of the spread spectrum communication technology and its applications for simulation, knowledge will be summarized and summed in order to consolidate the basic knowledge of communications for the After the individual to lay a foundation to study and work.2 The basic princip

14、les of spread spectrum communication2.1 The definition of spread spectrum communicationThe so-called spread spectrum communications, can be simply expressed as follows:Spread spectrum communication technology is a means of information transmission,Share some of its signal bandwidth is much larger th

15、an the minimum mass of information necessary bandwidth;The expansion of the band through a separate code sequence to complete, using the method of coding and modulation to achieve, with the mass of information has nothing to do;Receiving end in the same synchronization code related to receiving, des

16、preading and recovery of the mass data. This definition includes the meaning of the following three aspects: 1)The signal spectrum by a broadening.We know that the transmission of any information needs to a certain bandwidth, as the information bandwidth.For example, the human voice information band

17、width of 300Hz - - 3 -3400Hz, television image information bandwidth of MHz.In order to make full use of frequency resources, which are roughly the same as far as possible the signal bandwidth to transmit information.In the radio communication bandwidth RF signals with the mass of information is com

18、parable to the bandwidth.Such as the AM signal used to transmit voice messages, voice messages of their bandwidth for twice the bandwidth;Television broadcasting RF signal bandwidth is only the video signal bandwidth more than doubled.These are among the narrow-band communications.General FM signal,

19、 or pulse code modulation signals, their bandwidth and the information ratio of bandwidth to only a few dozen.Spread spectrum communication signals and information bandwidth than the bandwidth of up to 100 - 1000, belonging to broadband communications.Why use such a wide-band signal to transmit info

20、rmation? Do not waste valuable resources in the frequency of it?2)The use of spread-spectrum code sequence modulation signal approach to broadening the spectrum.We know that in time limited signal, its spectrum is infinite.For example, very narrow pulses, the spectrum is very wide.Signal bandwidth i

21、s inversely proportional to its approximate duration.1 microsecond pulse bandwidth is about 1MHz.Therefore, if the use of limited and narrow pulse sequence has been modulated by the mass of information it may give rise to very broad-band signal.As described in the following direct sequence spread sp

22、ectrum system is the method used to obtain spread spectrum signals.This very narrow pulse sequences, the code rate is very high, as the spreading code sequence.Should be noted here that the spreading codes used by the mass and sequence data is not relevant, that is to say it and in general the same

23、sinusoidal carrier signal, will not affect the transparency of information transmission.Sequence spread-spectrum code signals only from the expansion of the role of the spectrum.3)In the receiving end to use of the relevant despreading demodulator.As the narrow-band communications in general have be

24、en transferred signal demodulation receiver have to be to restore the mass of information.In spread spectrum communications receiver and transmitter used the same spread spectrum code sequence spread spectrum signals received by the relevant demodulation, the restoration of the mass of information.I

25、n other words, this correlation despreading demodulation role to play.That is, to expand beyond the original signal is restored by the mass of information.This narrow-band information in the originator to expand into the broadband signal, and in - 4 -the close-end solution will expand its narrow-ban

26、d information into the process, will bring a number of advantages.Spread-spectrum extended to clarify the process of reconciliation mechanism is to understand the nature of spread spectrum communication key.2.2 The theoretical basis for spread spectrum communicationA long period of time, people have

27、 the idea of the signal as far as possible the occupation of the narrow spectrum in order to take full advantage of very valuable spectrum resources.Why use such a broad-band signal to transmit information? The short answer is mainly to secure communication .The basic characteristics of spread spect

28、rum communication is the transmission signal bandwidth occupied by (W) is much larger than the original information to their actual minimum requirements (effective) bandwidth (DF), the ratio referred to as processing gain Gp: (1)FWGP/ As we all know, any information needed for effective transmission

29、 of the frequency of a certain width, such as the voice for the 1.7 - 3.1kHz, television images were a few MHz wide.In order to make full use of limited frequency resources, increasing the number of channels, it is a wide selection of different modulation methods, the use of broadband channel (coaxi

30、al cable, microwave and fiber-optic, etc.), and measures such as compression band, at the same time strive to make the transmission of the signal transmission media occupy a narrow bandwidth as much as possible.Due to the current use of the telephone, radio system, whether it is using AM, FM, or pul

31、se code modulation format, Gp values are within the scope of more than 10 times, collectively referred to as narrow-band communications.Gp of the spread spectrum communication value, up to hundreds, thousands, known as broadband communications.The feasibility of spread spectrum communication, inform

32、ation theory and anti-jamming from the basic formula of the theory of extension from.Information on the Shannon information capacity (Shannon) formula is: (2)）（NPWLC/1og2 （2）Where:C- Channel capacity (with transmission rate measurement)W- Signal bandwidthP- Signal powerN- White noise powerType (2) s

33、hows that：In a given transmission rate under the same conditions, the Cbandwidth and the signal-to-noise level are interchangeable.By increasing the WNP/- 5 -bandwidth to the method, at a relatively low signal to noise ratio (), the transmission NP/NS /of information.Spread spectrum signal to noise

34、ratio requirements for the reduction is an important feature of spread spectrum communication, and thus the application of spread spectrum communication for the foundation.Spread spectrum communication based on the feasibility of another theory for the transmission of information Baryshnikov error p

35、robability formula: （3）（0j/fowNEPWhere:- Error ProbabilityjPow- Signal energyE- Noise power spectral density0NSignal power (T for the duration of information)TEP/Noise Power (W for the signal band width)0WNN Information bandwidth TDF/1The type (3) can be translated into: （4）)/(/owFWNPfNPTWfP）（(4) sh

36、ows that for a certain bandwidth of the information in terms of , with values DFPGgreater broadband signal transmission, anti-interference ability can improve communications to ensure that under conditions of strong interference, safe and reliable communications.That is, (4) and type (2) the same si

37、gnal to noise ratio and bandwidth that can be interchangeable.In short, we use the information bandwidth of 100 times, or even 1000 times higher than the broadband signal to transmit the message that in order to improve the communication of anti-interference ability, that is in strong interference c

38、onditions to ensure safe and reliable communication.This is the spread-spectrum communications based on the basic ideas and theories.2.3 Spread Spectrum Communications main performance indicators1) The processing gain is the tolerance and anti-jamming spread-spectrum communication systems are two im

39、portant performance indicators., also known as processing gain spread Gspectrum gain (Spreading Gain) it is defined as the information before spread spectrum bandwidth expansion band and the signal bandwidth W ratio:DF （5）FWGP/ In spread spectrum communication system. Demodulation for spread-spectru

40、m receiver, - 6 -the only pseudo-random code extract treatment, the bandwidth related to the information DF, and ruled out the external W-wideband interference, noise and its impact to the users communications.Therefore, the processing gain G reflects the spread spectrum communication system to impr

41、ove the level of signal to noise ratio.2) interference toleranceSpread spectrum communication system refers to how much interference in the environments ability to work, is defined as: （6） s)/(outjLNSGMOf which: - Anti-interference capacityjM- Processing gainG - Information data is correct and the r

42、equirements of the smallest demodulator out)/(NSoutput signal to noise ratio - The work of the receiving system losssL2.4 Spread Spectrum Communication System working principleDigital Spread Spectrum Communication general working principle as shown in Figure 1. Figure 1 the number of the basic block

43、 diagram of spread spectrum communication systemShown in Figure 1 for a digital spread spectrum communication system, the basic block diagram.Which channel encoder, channel decoder, modulator and demodulator is a traditional digital communication systems constitute the basic unit.Spread spectrum com

44、munication system in the removal of these units, should use the same pseudo-random sequence generator, sending the front-end, respectively, the role of the modulator and demodulator to receive the front end.The two pseudo-random sequence generator noise (PN) binary sequence, the client will send the

45、 signal modulation in the frequency domain for the expansion, in the end demodulation despreading the spread spectrum signal.3 Characteristics of Spread Spectrum Communication System- 7 -Spread spectrum signal is unpredictable pseudo-random broadband signal bandwidth is much larger than its wish to

46、transfer data (information) bandwidth, at the same time, the receiver must be synchronized with a copy of broadband carrier .Spread-spectrum signal as a result of these characteristics, spread spectrum system has the following characteristics:3.1 The strong anti-jammingDue to the unpredictability of

47、 spread-spectrum signal, the spread spectrum system has a high anti-interference ability.It difficult because of interference by observing interference to improve their performance, and can only be fired with the interference of the interference signal does not match the technology, therefore, would

48、 not contribute significantly interfere; As the spread spectrum communication system in the transmission signal bandwidth expansion, so even if the signal to noise ratio is very low, even lower than the useful signal power of interference signal power is still the case to high-quality uninterrupted

49、communication, the expansion of the spectrum The more width, the stronger the anti-interference.3.2 LPI ofSpread spectrum signal is equivalent to the power being distributed evenly over a wide frequency band, so that transmission signals are very low power density, so that it is difficult to monitor

50、 to detect the receiver.Therefore, the spread spectrum communication system has a low probability of interception.3.3 Anti-interference performance of multi-pathMulti-path interference is due to radio propagation encountered in the course of a variety of non-expected reflector (such as the ionospher

51、e, the mountains, buildings, etc.) caused by reflection or scattering.Reflection or scattering of these signals with the direct path signal interference in the receiver interfere with each other.Multi-path interference in radar and communication are severely affected.Since the spread spectrum commun

52、ication system in an increase of spread-spectrum modulation and de-spread process,This spread-spectrum sequences using the correlation between the characteristics of,Despreading at the receiving end when the relevant technology from multi-path signals to isolate the most useful signals, or multipath

53、 signals of the same code sequence signal superposition, so that you can effectively eliminate the wireless communications in multi-path interference caused by signals decline and, therefore, spread spectrum communication system has good properties of anti-multipath fading.3.4 Good Privacy Transmitt

54、ing power in certain circumstances, due to the distribution of spread-spectrum - 8 -signals over a wide frequency band, Useful signal channel power spectral density is extremely low, so the signal can be in strong background noise, or even a useful signal to be the case of noise drowned reliable com

55、munications,Intercepted by the outside world it is very difficult to send the information, would like to detect the characteristic parameters of the signal even harder.Therefore, the spread spectrum communication system can be concealed; At the same time, different users use different code, others c

56、an not be tapping their communications, thus spread-spectrum system with high confidentiality.4 Spread Spectrum Communication in the MATLAB simulation4.1 Direct Sequence Spread Spectrum system BER simulationAccording to Shannon theorem, we can see: （7）（NSWLC/1ogWhere: W for the transmission bandwidt

57、h; C for more information. (7) means that in a given signal power S and noise power N of the conditions, using a coding system to a very small bit error rate of close to C transmission of information transfer rate. Baryshnikov in accordance with theory, we can see: （8）)/(0eNEFP Where: For the bit er

58、ror rate; For the signal frequency; For the signal energy; ePFEFor the noise power spectral density.The transmission bandwidth ,Signal 0NWpower,Noise Power,Signal duration,Information signal bandwidth TES/0WNN T,Into the type(8) ,a：TF/1 (9)FWNSNSTWNE0Style (9) Description, ByDecision,In other words,

59、 a certain bandwidthePFWNStransmission Information,SNRAnd bandwidth can beExchange.FNSWBinary sequences for spread spectrum communication of information, assuming that the information rate of , Symbol interval is ,Effective bandwidth to transmit RSRT/1b information to .In the DS system, the use of M

60、atLab toolbox function of the pseudo-)m(RBBCCrandom sequence to generate pseudo-random code sequence. There is the PN code is a bit more than 0,1 code sequences, which undergo a rigorous selection process, and has a good auto-correlation, but similar to each other but are mutually orthogonal, linear

61、ly independent and, in many key type, they can easily identify with their own code the same type, and not easily - 9 -confused with other code-based. The use of PN sequences in the transmitter, the message sequence will be the expansion of narrow-band wideband signal for transmission into the channe

62、l, the receiver will receive the broadband signal synchronized with the transmitter PN sequence multiplied, the narrow-band de-spread the message sequence, and the types of interference signals are multiplied with the PN sequence to the expansion of the form for broadband,Will eventually weaken the

63、energy of interference signal W / R times. In the modulator, the message sequence for the bandwidth expansion,Prevalent as a result of CBW transmission interference, and therefore must be taken into account in the simulation of the interference signal of the decision ruling the impact of device. Ass

64、uming that the process of signal transmission by the cosine form of interference with the role of signal, the signal current of (10)2cos()(tfAtijjType (10): In order to send the signal interference within the frequency bandwidth.jf andMultiplied so that cosine form of interference into the broadband

65、 )(ti)(tcinterference，Its energy density spectrum,Where: For the average energy WPJJ/02/2JJAP of interference signal.In order to more intuitive analysis of DS-sinusoidal interference signal suppression effects,The establishment of a Monte Carlo simulation model,Figure 2 DS Monte Carlo simulation mod

66、el systemAs can be seen from Figure 2, by the random number generator produce a series of binary ( 1) information and data, Repeat for each informationTimes, Correspond to the information contained in each of the pseudo-code chip CLCL- 10 -number, a random number generatorSequence Multiplied,And then superimposed on PN)(ncthe sequence of variance forGaussian white noise and the form of Sinusoidal interference signal, 2/02NnAni0sin)(which and.In the demodulator, PN sequence with inter-related ope