通信工程毕业设计外文翻译-扩频通信系统及MATLAB仿真.doc

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1、HUAKE INSTITUTE OF TAIYUAN UNIVERSITY OFSCIENCE & TECHNOLOGY外文翻译题目：扩频通信系统及MATLAB仿真Spread Spectrum Communication System and MATLAB SimulationABSTRACTThis thesis expounds the basic principles of spread spectrum communication , and then the article mainly acts according to the Shannon theorem and tan o

2、ak 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 spread spectrum communications system simulation model which does not have when the disturbance through the analysis error

3、rate simulation curve and theory predicted value,had proven constructs the simulation model the accuracy.Key words：Spread spectrum；communication；MATLAB1 Introduction1.1 Spread Spectrum Communication SystemSpread spectrum communication, namely, spread spectrum communications (Spread Spectrum Communic

4、ation), with fiber-optic communications, satellite communications, with access to the information age as the three major high-tech communications transmission.Spread spectrum communication is to send the information to be pseudo-random data is coded (spread spectrum sequence: Spread Sequence) modula

5、tion, 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 spectrum communication system has three main characteristics.Carrier is an unpredictable, or so-called pseudo-random broa

6、dband 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 to the broadband signal to achieve.The main way of spread spectrum are as follows:Direct Sequence Spread Spectrum (DSSS)

7、 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 frequency in a wider band of the change;TH is the data transmission time slot is a pseudo-random;Chirp frequency system is a

8、linear extension of the process of change.Combination of a number of ways of hybrid systems are often applied.The most important measure of spread-spectrum system is an indicator of spreading gain, also known as processing gain.It is precisely because of the spread spectrum system itself with its pe

9、rformance characteristics with a series of advantages.1.2 The purpose of spread spectrum communication studies and significance Spread spectrum communication is an important branch of communication and channel the direction of development of communication systems.Spread-spectrum technology, with str

10、ong anti-interference ability, confidentiality, and is easy to realize the advantages of multiple-access communications, so the technology is receiving increasing attention.In recent years, with very large scale integrated circuit technology, the rapid development of microprocessor technology, as we

11、ll 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 status, and are quickly penetrated into the personal communications and computer communications and other civilian areas, to bec

12、ome the new century, the most potential of communication technologies.The study is spread spectrum communication with far-reaching significance, I through the thesis the design, conduct in-depth study of the spread spectrum communication technology and its applications for simulation, knowledge will

13、 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 principles of spread spectrum communication2.1 The definition of spread spectrum communicationThe so-called spread spectrum communica

14、tions, 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 than the minimum mass of information necessary bandwidth;The expansion of the band through a separate code sequence to complete,

15、 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, despreading and recovery of the mass data. This definition includes the meaning of the following three aspects: 1)The signal spec

16、trum 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 bandwidth of 300Hz - 3400Hz, television image information bandwidth of MHz.In order to make full use of frequency resources, which

17、 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 comparable to the bandwidth.Such as the AM signal used to transmit voice messages, voice messages of their bandwidth for twice the ban

18、dwidth;Television broadcasting RF signal bandwidth is only the video signal bandwidth more than doubled.These are among the narrow-band communications.General FM signal, or pulse code modulation signals, their bandwidth and the information ratio of bandwidth to only a few dozen.Spread spectrum commu

19、nication 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 information? Do not waste valuable resources in the frequency of it?2)The use of spread-spectrum code sequence modulation signal approa

20、ch 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 is inversely proportional to its approximate duration.1 microsecond pulse bandwidth is about 1MHz.Therefore, if the use of limited a

21、nd 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 spectrum system is the method used to obtain spread spectrum signals.This very narrow pulse sequences, the code rate is very high, as

22、 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 sinusoidal carrier signal, will not affect the transparency of information transmission.Sequence spread-spectrum code signals only

23、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 been transferred signal demodulation receiver have to be to restore the mass of information.In spread spectrum communications receive

24、r and transmitter used the same spread spectrum code sequence spread spectrum signals received by the relevant demodulation, the restoration of the mass of information.In other words, this correlation despreading demodulation role to play.That is, to expand beyond the original signal is restored by

25、the mass of information.This narrow-band information in the originator to expand into the broadband signal, and in the close-end solution will expand its narrow-band information into the process, will bring a number of advantages.Spread-spectrum extended to clarify the process of reconciliation mech

26、anism 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 the idea of the signal as far as possible the occupation of the narrow spectrum in order to take full advantage of very valuable spectr

27、um resources.Why use such a broad-band signal to transmit information? The short answer is mainly to secure communication .The basic characteristics of spread spectrum communication is the transmission signal bandwidth occupied by (W) is much larger than the original information to their actual mini

28、mum requirements (effective) bandwidth (DF), the ratio referred to as processing gain Gp: (1) As we all know, any information needed for effective transmission 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

29、 of limited frequency resources, increasing the number of channels, it is a wide selection of different modulation methods, the use of broadband channel (coaxial cable, microwave and fiber-optic, etc.), and measures such as compression band, at the same time strive to make the transmission of the si

30、gnal 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 pulse code modulation format, Gp values are within the scope of more than 10 times, collectively referred to as narrow-band communications.Gp of

31、 the spread spectrum communication value, up to hundreds, thousands, known as broadband communications.The feasibility of spread spectrum communication, information theory and anti-jamming from the basic formula of the theory of extension from.Information on the Shannon information capacity (Shannon

32、) formula is: (2) （2）Where:C- Channel capacity (with transmission rate measurement)W- Signal bandwidthP- Signal powerN- White noise powerType (2) shows that：In a given transmission rate under the same conditions, the bandwidth and the signal-to-noise level are interchangeable.By increasing the bandw

33、idth to the method, at a relatively low signal to noise ratio (), the transmission of information.Spread spectrum signal to noise ratio requirements for the reduction is an important feature of spread spectrum communication, and thus the application of spread spectrum communication for the foundatio

34、n.Spread spectrum communication based on the feasibility of another theory for the transmission of information Baryshnikov error probability formula: （3）Where:- Error Probability- Signal energy- Noise power spectral densitySignal power (T for the duration of information)Noise Power (W for the signal

35、 band width)Information bandwidth The type (3) can be translated into: （4）(4) shows that for a certain bandwidth of the information in terms of , with values greater broadband signal transmission, anti-interference ability can improve communications to ensure that under conditions of strong interfer

36、ence, safe and reliable communications.That is, (4) and type (2) the same signal 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

37、communication of anti-interference ability, that is in strong interference conditions 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

38、 tolerance and anti-jamming spread-spectrum communication systems are two important performance indicators., also known as processing gain spread spectrum gain (Spreading Gain) it is defined as the information before spread spectrum bandwidth expansion band and the signal bandwidth W ratio: （5） In s

39、pread spectrum communication system. Demodulation for spread-spectrum receiver, 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 g

40、ain G reflects the spread spectrum communication system to improve 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）Of which: - Anti-interference capacity- Processin

41、g gain - Information data is correct and the requirements of the smallest demodulator output signal to noise ratio - The work of the receiving system loss2.4 Spread Spectrum Communication System working principleDigital Spread Spectrum Communication general working principle as shown in Figure 1. Fi

42、gure 1 the number of the basic block 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 constitut

43、e the basic unit.Spread spectrum communication 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) binar

44、y sequence, the client will send the signal modulation in the frequency domain for the expansion, in the end demodulation despreading the spread spectrum signal.3 Characteristics of Spread Spectrum Communication SystemSpread spectrum signal is unpredictable pseudo-random broadband signal bandwidth i

45、s much larger than its wish to 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-jammin

46、gDue to the unpredictability of 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 t

47、he technology, therefore, would 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

48、 to high-quality uninterrupted 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 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 i