外文翻譯----擴頻通信系統(tǒng)及matlab仿真

1、<p>　　Spread Spectrum Communication System and MATLAB Simulation</p><p><b>　　Abstract</b></p><p>　　This thesis expounds the basic principles of spread spectrum communication , a

2、nd 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 e

3、stablished the direct sequence spread spectrum communications system simulation model which does not have when the disturbance through the analysis error rate simulation curve and theory predicted value</p><p&

4、gt;　　Key words：Spread spectrum；communication；MATLAB</p><p>　　1 Introduction</p><p>　　1.1 Spread Spectrum Communication System</p><p>　　Spread spectrum communication, namely, spread

5、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 spect

6、rum communication 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

7、the same modem</p><p>　　Carrier is an unpredictable, or so-called pseudo-random broadband signal.</p><p>　　Carrier data bandwidth than the modulation bandwidth is much wider.</p><p>

8、;　　Receiving process is generated by local broadband carrier signal and receiving a copy of the signal to the broadband signal to achieve.</p><p>　　The main way of spread spectrum are as follows:Direct Seque

9、nce 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 frequency in a wide

10、r 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 number of ways of hybrid systems are often applied.<

11、/p><p>　　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 performance c

12、haracteristics with a series of advantages.</p><p>　　1.2 The purpose of spread spectrum communication studies and significance </p><p>　　Spread spectrum communication is an important branch of c

13、ommunication 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

14、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 well as the application of

15、som</p><p>　　2 The basic principles of spread spectrum communication</p><p>　　2.1 The definition of spread spectrum communication</p><p>　　The so-called spread spectrum communicatio

16、ns, 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 necessar

17、y 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 synchroni

18、zation code related to </p><p>　　1)The signal spectrum by a broadening.</p><p>　　We know that the transmission of any information needs to a certain bandwidth, as the information bandwidth.For e

19、xample, the human voice information bandwidth of 300Hz --- 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

20、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 use</p><p>　　2)The use of spread-spectrum c

21、ode sequence modulation signal approach to broadening the spectrum.</p><p>　　We know that in time limited signal, its spectrum is infinite.For example, very narrow pulses, the spectrum is very wide.Signal ba

22、ndwidth is 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 gi

23、ve rise to very broad-band signal.As described in the following direct sequence spread spectrum system is the method used to obtain spread spectrum si</p><p>　　This very narrow pulse sequences, the code rate

24、 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 sinusoidal carrier signal, will no

25、t affect the transparency of information transmission.Sequence spread-spectrum code signals only from the expansion of the role of the spectrum.</p><p>　　3)In the receiving end to use of the relevant desprea

26、ding demodulator.</p><p>　　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 rece

27、iver 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 demo

28、dulation role to play.That is, to expand beyond the original signal is restored by the mass of infor</p><p>　　This narrow-band information in the originator to expand into the broadband signal, and in the cl

29、ose-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 mechanism is to understand the nature of spre

30、ad spectrum communication key.</p><p>　　2.2 The theoretical basis for spread spectrum communication</p><p>　　A long period of time, people have the idea of the signal as far as possible the occu

31、pation 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 ch

32、aracteristics of spread spectrum communication is the transmission signal bandwidth occupied by (W) is much larger than the original information to their actual minimum requirements (effective) b</p><p><

33、b>　　(1)</b></p><p>　　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

34、 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 (coaxial cable, microwave and fiber-

35、optic, etc.), and measures such as compression band, at the same time strive to make the transmission o</p><p>　　Due to the current use of the telephone, radio system, whether it is using AM, FM, or pulse co

36、de 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, kno

37、wn 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 Sha</p>&l

38、t;p><b>　　(2)</b></p><p><b>　?。?）Where:</b></p><p>　　C--- Channel capacity (with transmission rate measurement)</p><p>　　W--- Signal bandwidth</p>&

39、lt;p>　　P--- Signal power</p><p>　　N--- White noise power</p><p>　　Type (2) shows that：In a given transmission rate under the same conditions, the bandwidth and the signal-to-noise level ar

40、e interchangeable.By increasing the bandwidth 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 import

41、ant feature of spread spectrum communication, and thus the application of spread spectrum communication for the foundation.</p><p>　　Spread spectrum communication based on the feasibility of another theory f

42、or the transmission of information Baryshnikov error probability formula:</p><p><b>　?。?）</b></p><p><b>　　Where:</b></p><p>　　- Error Probability</p>

43、<p>　　--- Signal energy</p><p>　　--- Noise power spectral density</p><p>　　Signal power (T for the duration of information)</p><p>　　Noise Power (W for the signal band width)

44、</p><p>　　Information bandwidth </p><p>　　The type (3) can be translated into:</p><p><b>　?。?）</b></p><p>　　shows that for a certain bandwidth of the inform

45、ation in terms of , with values greater broadband signal transmission, anti-interference ability can improve communications to ensure that under conditions of strong interference, safe and reliable communications.That i

46、s, (4) and type (2) the same signal to noise ratio and bandwidth that can be interchangeable.</p><p>　　In short, we use the information bandwidth of 100 times, or even 1000 times higher than the broadband si

47、gnal to transmit the message that in order to improve the communication of anti-interference ability, that is in strong interference conditions to ensure safe and reliable communication.This is the spread-spectrum commun

48、ications based on the basic ideas and theories.</p><p>　　2.3 Spread Spectrum Communication's main performance indicators</p><p>　　The processing gain is the tolerance and anti-jamming spread

49、-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 b

50、and and the signal bandwidth W ratio:</p><p><b>　?。?）</b></p><p>　　In spread spectrum communication system. Demodulation for spread-spectrum receiver, the only pseudo-random code ex

51、tract treatment, the bandwidth related to the information DF, and ruled out the external W-wideband interference, noise and its impact to the user's communications.Therefore, the processing gain G reflects the spread

52、 spectrum communication system to improve the level of signal to noise ratio.</p><p>　　2) interference tolerance</p><p>　　Spread spectrum communication system refers to how much interference in

53、the environment's ability to work, is defined as:</p><p><b>　　（6）</b></p><p><b>　　Of which:</b></p><p>　　--- Anti-interference capacity</p><p&

54、gt;　　--- Processing gain</p><p>　　--- Information data is correct and the requirements of the smallest demodulator output signal to noise ratio</p><p>　　--- The work of the receiving system loss

55、</p><p>　　2.4 Spread Spectrum Communication System working principle</p><p>　　Digital Spread Spectrum Communication general working principle as shown in Figure 1.</p><p>　　Figure 1

56、 the number of the basic block diagram of spread spectrum communication system</p><p>　　Shown in Figure 1 for a digital spread spectrum communication system, the basic block diagram.Which channel encoder, ch

57、annel decoder, modulator and demodulator is a traditional digital communication systems constitute the basic unit.Spread spectrum communication system in the removal of these units, should use the same pseudo-random sequ

58、ence generator, sending the front-end, respectively, the role of the modulator and demodulator to receive the front end.The two pseudo-random sequence generator </p><p>　　3 Characteristics of Spread Spectrum

59、 Communication System</p><p>　　Spread spectrum signal is unpredictable pseudo-random broadband signal bandwidth is much larger than its wish to transfer data (information) bandwidth, at the same time, the re

60、ceiver 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:</p><p>　　3.1 The strong an

61、ti-jamming</p><p>　　Due 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 im

62、prove their performance, and can only be fired with the interference of the interference signal does not match the technology, therefore, would not contribute significantly interfere; As the spread spectrum communication

63、 system in the transmission signal bandwidth expansion, so even if the signal to noise ratio </p><p>　　3.2 LPI of</p><p>　　Spread spectrum signal is equivalent to the power being distributed eve

64、nly 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

65、 of interception.</p><p>　　3.3 Anti-interference performance of multi-path</p><p>　　Multi-path interference is due to radio propagation encountered in the course of a variety of non-expected ref

66、lector (such as the ionosphere, 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 ot

67、her.Multi-path interference in radar and communication are severely affected.Since the spread spectrum communication system in an increase of spread-spectrum modulation a</p><p>　　3.4 Good Privacy </p>

68、<p>　　Transmitting power in certain circumstances, due to the distribution of spread-spectrum signals over a wide frequency band, Useful signal channel power spectral density is extremely low, so the signal can be

69、 in strong background noise, or even a useful signal to be the case of noise drowned reliable communications,Intercepted by the outside world it is very difficult to send the information, would like to detect the charact

70、eristic parameters of the signal even harder.Therefore, the spread spectr</p><p>　　4 Spread Spectrum Communication in the MATLAB simulation</p><p>　　4.1 Direct Sequence Spread Spectrum system BE

71、R simulation</p><p>　　According to Shannon theorem, we can see:</p><p><b>　　（7）</b></p><p>　　Where: W for the transmission bandwidth; C for more information. (7) means t

72、hat 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 c

73、an see:</p><p><b>　?。?）</b></p><p>　　Where: For the bit error rate; For the signal frequency; For the signal energy; For the noise power spectral density.The transmission bandwidth

74、 ,Signal power,Noise Power,Signal duration,Information signal bandwidth ,Into the type(8) ,a：</p><p><b>　　(9)</b></p><p>　　Style (9) Description, ByDecision,In other words, a certai

75、n bandwidth</p><p>　　transmission Information,SNRAnd bandwidth can beExchange.</p><p>　　Binary sequences for spread spectrum communication of information, assuming that the information rate of

76、, Symbol interval is ,Effective bandwidth to transmit information to .In the DS system, the use of MatLab toolbox function of the pseudo-random sequence to generate pseudo-random code sequence. There is the PN code is a

77、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, linearly</p><p><b>　　(10)</b>

78、</p><p>　　Type (10): In order to send the signal interference within the frequency bandwidth.</p><p>　　andMultiplied so that cosine form of interference into the broadband interference，Its energ

79、y density spectrum,Where: For the average energy of interference signal.In order to more intuitive analysis of DS-sinusoidal interference signal suppression effects,The establishment of a Monte Carlo simulation model,<

80、;/p><p>　　Figure 2 DS Monte Carlo simulation model system</p><p>　　As can be seen from Figure 2, by the random number generator produce a series of binary (± 1) information and data, Repeat fo

81、r each information</p><p>　　Times, Correspond to the information contained in each of the pseudo-code chip number, a random number generatorSequence Multiplied,And then superimposed on the sequence of varian

82、ce for</p><p>　　Gaussian white noise and the form of Sinusoidal interference signal, which and.In the demodulator, PN sequence with inter-related operations Information and will form the sum of d samples.In

83、formation and will form the sum of samples.Adder output will be sent to decision, and on the signal and threshold 0 to determine the data transmission +1 or -1, Figure 2 in the counter's decision to record the numbe

84、r of wrongful convictions .</p><p>　　4.2 Analysis of simulation results</p><p>　　Adding noise and interference, the access = 10 ,With three different sinusoidal signal interference, the amplitud

85、e of 2, 3, 7. In bit error rate in computing the variance of additive noise is fixed, a total of 10,000 calculations, and each operator, the signal energy values are required to meet the requirements of the signal to noi

86、se ratio, which has been shown in Figure 3 the simulation curve.Can be seen that the amplitude of the sinusoidal interference signal the greater the greater the error </p><p>　　Figure 3 Monte-Carlo simulatio

87、n of the spread spectrum communication system the interference of different amplitude sine BER simulation curves</p><p>　　5 Conclusion</p><p>　　1)The author in this paper, the establishment and

88、optimization of the Monte Carlo simulation model, can be a variety of direct sequence spread spectrum communication system bit error rate simulation analysis, simulation results show that the DS is capable of ruling syst

89、em to the smaller errors the probability of the restoration of the original signal, the verdict has the excellent performance.</p><p>　　2) in the same signal to noise ratio, the greater the processing gain,

90、the smaller the error rate, especially in the large signal to noise ratio, this difference is particularly evident; no change in processing gain, the sinusoidal interference signal amplitude increases, the incidence of f

91、alse rate is increased.</p><p>　　擴頻通信系統(tǒng)及MATLAB仿真</p><p>　　摘 要：本文先闡述了擴頻通信的基本原理、主要性能指標及其工作特點, 然后本文根據香農定理和柯捷爾尼可夫潛在抗干擾理論,借助MatLab工具箱和Monte Carlo 仿真算法,建立了直接序列擴頻通信系統(tǒng)仿真模型. 通過分析無干擾時的誤碼率仿真曲線與理論計算值,證明了所建仿

92、真模型的正確性。</p><p>　　關鍵詞：擴頻；通信；MATLAB。</p><p><b>　　1 引言</b></p><p>　　1.1 擴頻通系統(tǒng)概述</p><p>　　擴頻通信，即擴展頻譜通信(Spread Spectrum Communication)，它與光纖通信、衛(wèi)星通信，一同被譽為進入信息時代的三

93、大高技術通信傳輸方式。擴頻通信是將待傳送的信息數據被偽隨機編碼(擴頻序列：Spread Sequence)調制，實現頻譜擴展后再傳輸；接收端則采用相同的編碼進行解調及相關處理，恢復原始信息數據。擴頻通信系統(tǒng)具備3個主要特征：</p><p>　　載波是一種不可預測的，或稱之為偽隨機的寬帶信號</p><p>　　載波的帶寬比調制數據的帶寬要寬得多</p><p>　

94、　接收過程是通過將本地產生的寬帶載波信號的復制信號與接收到的寬帶信號相關來實現的。</p><p>　　頻譜擴展的方式主要有以下幾種:直序擴頻(DSSS)使用高速偽隨機碼對要傳輸的低速數據進行擴頻調制；跳頻系統(tǒng)則利用偽隨機碼控制載波頻率在一個更寬的頻帶內變化；跳時則是數據的傳輸時隙是偽隨機的；線性調頻系統(tǒng)中的頻率擴展則是一個線性變化的過程。幾種方式組合的混合系統(tǒng)也經常得到應用?！?lt;/p><p

95、>　　衡量擴頻系統(tǒng)最重要的一個指標就是擴頻增益，又稱為處理增益。正是因為擴頻系統(tǒng)本身具有的特征使其性能具有一系列的優(yōu)勢。</p><p>　　1.2 研究擴頻通信的目的和意義</p><p>　　擴頻通信是通信的一個重要分支和信道通信系統(tǒng)的發(fā)展方向。擴頻技術具有抗干擾能力強、保密性好、易于實現多址通信等優(yōu)點，因此該技術越來越受到人們的重視。近年來，隨著超大規(guī)模集成電路技術、微處理器技

96、術的飛速發(fā)展，以及一些新型元器件的應用，擴頻通信在技術上已邁上了一個新的臺階，不僅在軍事通信中占有重要地位，而且正迅速地滲透到了個人通信和計算機通信等民用領域，成為新世紀最有潛力的通信技術之一。因此研究擴頻通信具有很深遠的意義，本人通過畢業(yè)論文設計，進行深入地研究擴頻通信技術及對它進行仿真應用，將所學的知識進行歸納與總結，從而鞏固通信專業(yè)基礎知識，為以后的個人學習和工作打下基礎。</p><p>　　2 擴頻通信

97、的基本原理</p><p>　　2.1 擴頻通信的定義</p><p>　　所謂擴展頻譜通信，可簡單表述如下：“擴頻通信技術是一種信息傳輸方式，其信號所占有的頻帶寬度遠大于所傳信息必需的最小帶寬；頻帶的擴展是通過一個獨立的碼序列來完成，用編碼及調制的方法來實現的，與所傳信息數據無關；在接收端則用同樣的碼進行相關同步接收、解擴及恢復所傳信息數據”。這一定義包含了以下三方面的意思：</p

98、><p>　　1）信號的頻譜被展寬了。</p><p>　　我們知道，傳輸任何信息都需要一定的帶寬，稱為信息帶寬。例如人類的語音的信息帶寬為300Hz --- 3400Hz，電視圖像信息帶寬為數MHz。為了充分利用頻率資源，通常都是盡量采用大體相當的帶寬的信號來傳輸信息。在無線電通信中射頻信號的帶寬與所傳信息的帶寬是相比擬的。如用調幅信號來傳送語音信息，其帶寬為語音信息帶寬的兩倍；電視廣播射頻

99、信號帶寬也只是其視頻信號帶寬的一倍多。這些都屬于窄帶通信。一般的調頻信號，或脈沖編碼調制信號，它們的帶寬與信息帶寬之比也只有幾到十幾。擴展頻譜通信信號帶寬與信息帶寬之比則高達100 --- 1000，屬于寬帶通信。為什么要用這樣寬的頻帶的信號來傳輸信息呢? 這樣豈不太浪費寶貴的頻率資源了嗎?</p><p>　　2）采用擴頻碼序列調制的方式來展寬信號頻譜。</p><p>　　我們知道，在

100、時間上有限的信號，其頻譜是無限的。例如很窄的脈沖信號，其頻譜則很寬。信號的頻帶寬度與其持續(xù)時間近似成反比。1微秒的脈沖的帶寬約為1MHz。因此，如果用限窄的脈沖序列被所傳信息調制，則可產生很寬頻帶的信號。如下面介紹的直接序列擴頻系統(tǒng)就是采用這種方法獲得擴頻信號。這種很窄的脈沖碼序列，其碼速率是很高的，稱為擴頻碼序列。這里需要說明的一點是所采用的擴頻碼序列與所傳信息數據是無關的，也就是說它與一般的正弦載波信號一樣，絲毫不影響信息傳輸的透明

101、性。擴頻碼序列僅僅起擴展信號頻譜的作用。</p><p>　　3）在接收端用相關解調來解擴。</p><p>　　正如在一般的窄帶通信中，已調信號在接收端都要進行解調來恢復所傳的信息。在擴頻通信中接收端則用與發(fā)送端相同的擴頻碼序列與收到的擴頻信號進行相關解調，恢復所傳的信息。換句話說，這種相關解調起到解擴的作用。即把擴展以后的信號又恢復成原來所傳的信息。這種在發(fā)端把窄帶信息擴展成寬帶信號，