外文翻譯--直接序列擴(kuò)頻通信系統(tǒng)的混亂

1、<p>　　畢 業(yè) 設(shè) 計(jì)（譯文）</p><p>　　論文題目： 短擴(kuò)頻信號(hào)的相關(guān)性分析 </p><p>　　院 （系）： 通信與信息工程學(xué)院 </p><p>　　專 業(yè)： 電子信息科學(xué)與技術(shù) </p><p>　　班 級(jí)：

2、 </p><p>　　學(xué)生姓名： </p><p>　　導(dǎo)師姓名： 職稱： 副教授 </p><p>　　A Chaotic Direct-Sequence Spread-Spectrum Communicat

3、ion System</p><p>　　Abstract--The use of chaotic sequences as spectral spreading sequences in direct-sequence spread-spectrum (DS/SS) communication systems is proposed. The error probabilities of such system

4、s are investigated and shown to be, for all practical purposes, identical to the conventional DS/SS systems which use binary signature sequences. Among the advantages of the use of chaotic sequences in DS/SS

5、are the availability of a great number of them, the ease of their generation, as well </p><p>　　I. INTRODUCTION </p><p>　　In the past thirty years, there has been a great deal of in

6、terest in the study of non-linear dynamical systems . The introduction of chaos into communication systems offers several opportunities for improvement. This is partly because of the random nature of chaotic syste

7、ms. Since a chaotic dynamical system is a deterministic system, its random-like behavior can be very helpful in disguising modulations as noise. Moreover, through the sensitive dependence of chaotic systems on<

8、/p><p>　　where, is called the state, and f maps the state to the next state Starting with an initial condition , repeated applications of the map f give rise to the sequence of points called

9、 an orbit of the discrete-time system. Chaotic maps do not have to be very complicated. For example, a widely studied dynamical system capable of exhibiting chaos arises in connection with population biology, a

10、nd is called the logistic map : </p><p>　　Paper approved by Gordon L. Stuber, the Editor for Spread Spectrum of IEEE Communications Society. Manuscript received February 24, 1993; revised Septembe

11、r 9, 1993. This work was supported by the National Science Foundation under grant CDR8803017 to the Research Center for Intelligent Manufacturing Systems, Purdue University. </p><p>　　This paper wa

12、s presented in part at the proceedings of 1992 IEEE international Conference on Selected Topics in Wireless Communications, Vancouver, B.C., Canada, June 25-26,. 1992. </p><p>　　Ghobad Heidar-Bateni i

13、s with LCC, 2300 Clarendon Blvd., Suite 800, Arlington, VA 22201, and Clare McGillem is with the School. of Electrical Engineering, Purdue University, W. Lafayette, IN 47907. </p><p>　　where, and

14、 r is called the bifurcation parameter. Depending on the value of r, the dynamics of this system can change dramatically, exhibiting periodicity or chaos. the sequence is for all practical purposes, non-per

15、iodic and non-converging. </p><p>　　Chaotic systems have a very sensitive dependence on their initial conditions. This sensitive dependence can be demonstrated by giving two very close initial poi

16、nts to the iterative map. After a few iterations, the two resulting sequences will look completely uncorrelated. (Fig. 1 illustrates this point for the logistic map.) Hence, an abundant source of almost uncorrel

17、ated signals has been discovered: a slight change in the initial condition will produce a completely di</p><p>　　Section II will propose the use of chaotic signals as spreading sequences in direct

18、-sequence spread-spectrum （DS/SS) communication systems, while section II will discuss the advantages of such systems over the conventional DS/SS systems.</p><p>　　II. CHAOTIC DS/SS SYSTEM </p>

19、<p>　　In order to spread the bandwidth of the transmitting signals, pseudo-noise (PN) sequences have been used extensively in spread-spectrum communication systems. The maximal-length linear code sequenc

20、es (m-sequences) have very desirable auto-correlation functions. However, large spikes can be found in their cross-correlation functions, especially when partially correlated, as in the case of multipath environme

21、nts. Another limiting property of m-sequences is that they are re</p><p>　　Fig. 1 Two sets of iterates of the chaotic logistic map (r = 4) with very closely located initial points (0.10000 a

22、nd 0.10001). The points of the orbits are connected for visual ease.</p><p>　　In what follows, it is proposed to use chaotic sequences as spreading sequences in DS/SS systems. The main adva

23、ntages of such usage are increased security of the transmission and ease of generation of a great number of distinct sequences. </p><p>　　One major difference between chaotic sequences and the ab

24、ove described PN sequences is that chaotic sequences are not binary. Their correlation properties, however, can be shown to be very similar to those of the random binary sequences. This has been done analyti

25、cally for the case of chaotic logistic sequences [S]. The auto-correlation of these sequences is a delta-function and their cross-correlation is identically zero. Furthermore, the estimates of the auto-co

26、</p><p>　　One simple method of generating the chaotic spreading sequences for the BPSK (Binary Phase Shift Keying) DS/SS system is as follows. After assigning a different initial condition to ea

27、ch user, start the chaotic map with the initial condition of the intended receiver and repeatedly generate points of the orbit. Let N be the length of the spreading sequence needed for each bit of inf

28、ormation. Every N consecutive points generated by the chaotic map can then be ta</p><p>　　One problem with the above method of generating chaotic spreading sequences is the occurrence of periodicit

29、ies in the generated sequences, which is due to the limited precision of the finite arithmetic machine. Depending on the application, the </p><p>　　period of the above generated orbit may

30、be short. In order to increase the period of the orbits, a different scheme is proposed which will be described shortly. </p><p>　　Another problem occurs in connection with the CSK (Code Shift K

31、eying) modulation. Recall that in a CSK DS/SS system, a message symbol must have a code sequence nearly orthogonal to those of the other symbols. This can be accomplished, for example, by assigning a dif

32、ferent bifurcation parameter to each symbol. Then, depending on the symbol being transmitted, the code sequence to be used changes from one symbol to the next. The receiver locally generates these sequences. T</p

33、><p>　　In order to overcome these problems, a different scheme is proposed for the generator. (See Fig. 2.) This scheme increases the period of the generated orbits, and prevents error propagatio

34、n in the generated code sequences. Furthermore, this scheme has </p><p>　　the advantage of offering more degrees of freedom for making the generated orbits more secure from unfriendly detection. &

35、lt;/p><p>　　It is assumed that the transmitter and the intended receiver have agreed upon a starting point, , and two chaotic maps, and with their corresponding bifurcation parameters, and .

36、 The chaotic maps and their bifurcation parameters may or may not be the same and their uniqueness among the different pairs of transmitters and receivers is not necessary. As long as x00 is unique for

37、each pair, the resultant sequences will be different. </p><p>　　As illustrated in Fig. 3, , initiates a chaotic sequence through the chaotic map . The elements of this sequence are then used to

38、generate the sequences , through the chaotic map . The sequences S, so obtained are the spreading sequences to be used for each data bit Note that the spreading sequence changes from one bit to another.

39、The receiver regenerates the sequences S,, in exactly the same manner as the transmitter does. Every receivers will be assigned distin</p><p>　　The modulation and detection of the data sequence is o

40、therwise the same as the conventional DS/SS systems. Fig. 4 shows the block diagram of such a system. The detection will be based on correlating the received signal with the chaotic sequence of the receiver.

41、The transmitter-receiver synchronization may be attained in a number of ways, ranging from absolute time measurement, to the periodic transmission of predefined synchronizing sequences. These synchronizing

42、se</p><p>　　Fig. 2 The proposed method of generating the chaotic spreading sequences for </p><p>　　spread-spectrum applications. </p><p>　　Fig. 3 Illustration of the prop

43、osed method of generating the chaotic spreading </p><p>　　sequences as shown in the block diagram of Fig. 2. </p><p>　　For a CSK DS/SS system, either or will have to be changed ever

44、y time a different symbol is to be transmitted. Obviously, an error in detection of one symbol will have no effect on the code sequence generated for the next symbol. Consequently, there will be no propagation

45、 of the error. </p><p>　　A question that arises in replacing the binary PN sequences with chaotic ones in DS/SS systems is what effect, if any, this replacement would have on the error perform

46、ance of the system. Recall that the correlation properties of the chaotic sequences are identical to those of random binary sequences. Since the detection process is dependent solely on the correlation prop

47、erties of the spreading sequences, we can intuitively expect no difference in the error perform</p><p>　　III. ADVANTAGES OF CHAOTIC DS/SS </p><p>　　Why should chaos be used in DS/SS. There

48、 are many answers to this question. Chaotic sequences are easy to generate and store. Only a chaotic map and an initial condition are needed for their generation, which means there is no need for storage of

49、long sequences. Moreover, a large number of different sequences can be generated by simply changing the initial condition. </p><p>　　More importantly, chaotic sequences can be the basis for very secure

50、 communication. The secrecy of the transmission is important in many applications. The chaotic sequences help achieve security from unwanted receptions in several ways. 1)The chaotic sequences make the transmi

51、tted signal look like noise, and therefore, it does not attract the attention of an unfriendly receiver. 2)The sequences are no longer binary. That is, an eavesdropper would have a much larger s</p>

52、<p>　　Fig. 4 Block diagram of a DS/SS multiple-access communication system. </p><p>　　From a security point of view, the incorporation of the chaotic sequences into the DS/SS system has a dr

53、amatic effect on the enhancement of the LPI (low probability of intercept) performance of these systems. Spread-spectrum signals are the most suitable waveforms for LPI applications . Not only does spectral spr

54、eading force the interceptor to monitor a very wide frequency band, it also reduces the power spectral density of the transmitted signal, causing a lower probabilit</p><p>　　However, the DS/SS system

55、 using binary spreading sequences (Binary DS/SS) does not provide much protection against two particular interception methods: the carrier regeneration and the code clock regeneration detectors. This is due to

56、 the binary nature of the spreading sequences used in Binary DS/SS waveforms.</p><p>　　Carrier Regeneration Detector </p><p>　　The carrier regeneration technique is used for the detect

57、ion of signals that suppress the carrier, such as DS/SS systems with BPSK (Binary Phased Shift Keyed), QPSK (Quadrature Phase Shift Keyed), and SQPSK (Staggered Quadrature Phase Shift Keyed) modulation. As show

58、n in Fig. 5, it consists of squaring the received signal in order to wipe out the modulation, and using the resultant double frequency term to detect the signal. In the case of QPSK or SQPSK, the receiv&

59、lt;/p><p>　　Fig. 5 Block diagram of a carrier regenerating detector for BPSK Binary DS/SS </p><p><b>　　systems. </b></p><p>　　Fig. 6 Block diagram of a carrier rege

60、nerating detector for QPSK Binary DS/SS </p><p><b>　　system. </b></p><p>　　Fig. 7 Block diagram of a code clock regenerating detector.</p><p>　　Since the spreading

61、sequence in a Chaotic DS/SS system is no longer binary, (taking on any value in the range [-1, 1],) squaring the received signal would not get rid of the high bandwidth spreading sequence. Hence, no narr

62、owband detection can be made. </p><p>　　B. Code Clock Extraction Detector </p><p>　　A code clock extractor is depicted in Fig. 7. The technique used for the extraction of the chip rate

63、 is called “Delay and Mix“ or “Delay and Multiply” . The idea is to delay the spreading sequence by a fraction of a chip duration and multiply it by the undelayed sequence. Once again, this detection

64、method is effective on the Binary DS/SS systems because of the binary nature of their spreading sequences. However, since chaotic spreading sequences are not b</p><p>　　IV. CONCLUSIONS </p&

65、gt;<p>　　The use of chaotic sequences for spectral spreading in a direct-sequence spread-spectrum system has been shown to provide several advantages over conventional methods while still preservin

66、g the same error performance. One advantage is the availability of an enormous number of different sequences of a given length as compared to the maximal length and Gold code sequences. Regeneration and reg

67、eneration of chaotic sequences is very simple and involves the storage </p><p>　　With the age of the third generation personal communication systems approaching, the privacy of transmission is bec

68、oming an even more important issue. Chaotic spreading sequences provide the DS/SS system with significatly more security features than the conventional binary sequences. Non-repetitiveness, sensitivity on initial

69、 conditions and parameters, non-binary values, random-like behavior, and ease of systematically increasing the complexity of the generators are amon</p><p>　　REFFERENCE </p>

70、<p>　　1] R.M. May, “Special Mathematical Models with Very Complicated Dynamics,” Nature, June 1976. </p><p>　　2] Proc. IEEE, Special Issue on Chaotic Systems, 1987. </p><p>　　

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74、uction, D-6940 Weinheim, </p><p>　　Federal republic of Germany, Physick-Verlag GmnH, 1984. </p><p>　　7] P. M. Gade, R.E. Amritkar, “Characterizing Loss of Memory in a Dynamical System,”

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76、ette, IN, Dec. 1992. </p><p>　　9] G. Heidari-Bateni, C.D. McGillem, “Chaotic sequences for Spread Spectrum: An Alternative to PN-Sequences,” Proceedings of 1992 IEEE International Conference on Sele

77、cted Topics in Wireless Communications, Vancouver, B.C., Canada, June 25-26, 1992, pp. 437-440. </p><p>　　10] R.A. Dillard, “Detectability of Spread--Spectrum Signals,” IEEE Transactions on Aerospace

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81、l-Rate Detector and Radiometer Intercept Receiver Performances in a Nonstationary Environment,” Proceedings of 1989 IEEE Military Communications Conference, vol. 1, Boston, Massachusetts, October 1989, pp. 19.5

82、.1-19.5.5.</p><p><b>　　翻譯</b></p><p>　　直接序列擴(kuò)頻通信系統(tǒng)的混亂</p><p>　　摘要——把混亂序列在直序列擴(kuò)頻通信中作為頻譜擴(kuò)展序列使用已經(jīng)被提出。系統(tǒng)出錯(cuò)的原因已經(jīng)被調(diào)查并且展示,是出于實(shí)用目的,與傳統(tǒng)的DS / SS系統(tǒng)相比的優(yōu)勢(shì)之一就是使用二進(jìn)制標(biāo)志序列，在直序列擴(kuò)頻通信中使用混亂序列的

83、優(yōu)勢(shì)是：它們很多數(shù)量的可獲得性，緩解他們的生成,以及他們?cè)诎踩珎鬏斨泄逃械奶岣摺?lt;/p><p><b>　　I 介紹</b></p><p>　　在過(guò)去的三十年,在研究非線性動(dòng)力系統(tǒng)中一直有很大的興趣?；靵y的引入為通信系統(tǒng)提供了幾種改善的機(jī)會(huì)。這部分是由于隨機(jī)混亂系統(tǒng)的性質(zhì)。因?yàn)橐粋€(gè)混亂系統(tǒng)是一個(gè)確定性系統(tǒng),其隨機(jī)像行為在偽裝噪聲調(diào)節(jié)中是非常有用的。此外,通過(guò)混亂系

84、統(tǒng)對(duì)它們初始環(huán)境、大量的不相關(guān)、隨機(jī)樣等敏感的依賴性,然而確定性和可再生的信號(hào)是可以生成的。這些信號(hào)是只在有限的運(yùn)算機(jī)器中可再生。量化不會(huì)破壞所需的序列屬性,仍然會(huì)有一個(gè)龐大的混亂序列,從中進(jìn)行選擇。這工作集中在一個(gè)應(yīng)用程序的理論混亂的數(shù)字通信。其他應(yīng)用程序的這個(gè)理論也被研究。本文只關(guān)注離散動(dòng)力系統(tǒng)在混亂的狀態(tài)下的操作,用狀態(tài)方程去定義一個(gè)離散時(shí)間動(dòng)態(tài)系統(tǒng)</p><p>　　其中,被稱為狀態(tài),f是從狀態(tài)到下一個(gè)

85、狀態(tài)的映射,從一個(gè)初始條件,重復(fù)的應(yīng)用映射f產(chǎn)生的序列點(diǎn)，該序列稱為軌道的離散時(shí)間系統(tǒng)?；靵y映射不需要很復(fù)雜。例如,一個(gè)廣泛研究的能夠表現(xiàn)出混亂的動(dòng)力系統(tǒng)出現(xiàn)在人口生物學(xué)中,并且被稱為物流地圖:</p><p>　　論文通過(guò)戈登·L·Stuber,他是IEEE通信協(xié)會(huì)關(guān)于擴(kuò)頻通信的編輯家。手稿于1993年2月24日被收到,修訂于1993年9月9日。這項(xiàng)工作是在美國(guó)國(guó)家科學(xué)基金會(huì)資助CDR880

86、3017的條件下，在普渡大學(xué)的智能制造系統(tǒng)中心進(jìn)行研究的。</p><p>　　本文在1992年IEEE國(guó)際會(huì)議中呈現(xiàn)了程序的一部分，該會(huì)議關(guān)于無(wú)線通信主題的選定，地點(diǎn)在英屬哥倫比亞的溫哥華、加拿大，召開(kāi)時(shí)間于1992年6月25日至26日。</p><p>　　其中,并且r稱為分岔參數(shù)。根據(jù)r的值,看出這個(gè)系統(tǒng)顯著的動(dòng)態(tài)變化,表現(xiàn)出周期性或混亂。序列被用于所有實(shí)用目的,非周期和非收斂。&l

87、t;/p><p>　　混亂系統(tǒng)對(duì)它們的初始條件有著非常敏感的依賴性。這個(gè)敏感的依賴可以演示給兩個(gè)非常接近初始點(diǎn)的迭代映射。經(jīng)過(guò)幾次迭代,這兩個(gè)產(chǎn)生的序列將會(huì)看起來(lái)是完全不相關(guān)的。(圖1說(shuō)明了這個(gè)點(diǎn)物流圖。)因此,不相關(guān)的信號(hào)的廣泛來(lái)源已經(jīng)被發(fā)現(xiàn):輕微改變初始條件將會(huì)產(chǎn)生一個(gè)完全不同的信號(hào)。此外,在大多數(shù)情況下,初始條件的系統(tǒng)可能不是推導(dǎo)出有限長(zhǎng)度的序列。</p><p>　　第二部分將提出利用

88、混亂信號(hào)在直接序列、擴(kuò)頻通信系統(tǒng)中傳播,然而第二部分將討論這樣的系統(tǒng)在傳統(tǒng)的DS / SS系統(tǒng)的優(yōu)勢(shì)。</p><p>　　II 混亂的DS / SS系統(tǒng)</p><p>　　為了傳播傳輸信號(hào)的帶寬,偽噪聲序列(PN)被廣泛應(yīng)用于擴(kuò)頻通信系統(tǒng)。最大長(zhǎng)度的線性碼序列(m序列)有非常理想的自相關(guān)函數(shù)。然而,大型峰值可以在它們的互相關(guān)函數(shù),特別是當(dāng)部分相關(guān)、及多路徑環(huán)境中被發(fā)現(xiàn)。另一個(gè)限制m序列

89、特性的就是他們?cè)跀?shù)量相對(duì)較小。取得足夠數(shù)量的不同PN序列、隨機(jī)二進(jìn)制序列已經(jīng)被采取。他們的相關(guān)性屬性類似于隨機(jī)噪聲信號(hào)，并且它們相當(dāng)大數(shù)量是可用的。</p><p>　　圖1 兩套迭代的混亂邏輯圖(r = 4)和非常密切定位初始點(diǎn)(0.10000和0.10001)。軌道點(diǎn)的連接為視覺(jué)緩解。</p><p>　　接下來(lái),提出用混亂序列作為在DS / SS系統(tǒng)中的傳播序列。這種用法的主要優(yōu)

90、點(diǎn)是增加傳輸?shù)陌踩?，并且易于生成大量不同的序列?lt;/p><p>　　一個(gè)主要的混沌序列和上面描述的PN序列的區(qū)別,就是混亂序列不是二進(jìn)制。它們的相關(guān)屬性可以證明是非常類似于隨機(jī)二進(jìn)制序列。這是已經(jīng)完成了對(duì)混亂的邏輯序列的分析。這些序列的自相關(guān)是一個(gè)互相關(guān)函數(shù)，并且它們的相關(guān)值為0。此外,對(duì)函數(shù)自相關(guān)和互相關(guān)的估計(jì)的方法是正確的，在估計(jì)中考慮到序列大量的點(diǎn)。點(diǎn)的標(biāo)準(zhǔn)偏差在估計(jì)函數(shù)中減少為1 / N。</p

91、><p>　　一個(gè)簡(jiǎn)單的產(chǎn)生混沌序列的BPSK(二進(jìn)制相移鍵控)在DS / SS系統(tǒng)中傳播的方法如下。對(duì)每個(gè)用戶分配一個(gè)不同的初始條件后,以接收者的初始條件開(kāi)始畫圖，并且使軌跡點(diǎn)反復(fù)產(chǎn)生。讓N作為傳播序列每一比特的信息的長(zhǎng)度。由混亂圖連續(xù)產(chǎn)生的序列N，可以被一個(gè)標(biāo)志序列作為一個(gè)比特的信息碼。注意,每個(gè)位可以得到不同序列的碼片。</p><p>　　上面產(chǎn)生混亂傳播序列的方法存在一個(gè)問(wèn)題，就是在

92、生成序列周期性的出現(xiàn),這是由于有限運(yùn)算機(jī)有限的精度。根據(jù)不同的應(yīng)用,段以上生成的軌道可能是短的。為了增加軌道周期,一個(gè)不同的方案已經(jīng)被提出,將對(duì)其進(jìn)行簡(jiǎn)要描述。</p><p>　　另一個(gè)問(wèn)題發(fā)生在CSK(代碼移鍵控)調(diào)制器的連接中?；叵胍幌?在CSK DS / SS系統(tǒng)中，一個(gè)信息符號(hào)必須有一個(gè)幾乎正交于其他符號(hào)的代碼序列。這可以被實(shí)現(xiàn),例如,通過(guò)指定一個(gè)不同的分岔參數(shù)給每個(gè)符號(hào)。然后,根據(jù)不同的被傳播符號(hào),代

93、碼序列用于從一個(gè)符號(hào)到下一個(gè)的更改。接收方在本地生成這些序列。接收到的信號(hào)經(jīng)過(guò)并聯(lián)過(guò)濾器對(duì)代碼序列的每一個(gè)符號(hào)進(jìn)行匹配。決策機(jī)制然后選擇符號(hào)與最大輸出，從而決定了傳播符號(hào),因此,相應(yīng)的分岔參數(shù),生成的混亂序列繼續(xù)伴隨著決定代碼序列中最后的碼片。這最后的碼片在代碼序列的任何一位，作為接下來(lái)的代碼序列的初始點(diǎn)。那就是說(shuō),序列對(duì)應(yīng)的每一位依賴于前一個(gè)的。因此,檢測(cè)一個(gè)符號(hào)的錯(cuò)誤將導(dǎo)致接下來(lái)所有代碼序列的錯(cuò)誤產(chǎn)生。</p><

94、;p>　　為了克服這些問(wèn)題,一個(gè)關(guān)于發(fā)生器的不同計(jì)劃已被提出(見(jiàn)圖2)。該方案增加了段生成的軌道,并防止在生成的代碼序列誤差的傳播。此外,該方案的優(yōu)點(diǎn)是提供更多的自由度,使生成的軌道面對(duì)那些惡意的檢測(cè)更安全。</p><p>　　它假定了發(fā)射機(jī)和接收者都同意一個(gè)起點(diǎn),,和兩個(gè)混亂的地圖,和，與它們對(duì)應(yīng)的分岔參數(shù),和。混亂的地圖和它們的分岔參數(shù)可能會(huì)或可能不會(huì)相同，他們的獨(dú)特性在雙不同的發(fā)射器和接收器是沒(méi)有必

95、要的。只要每一對(duì)是獨(dú)一無(wú)二的,合成序列將是不同的。</p><p>　　見(jiàn)圖3,,啟動(dòng)一個(gè)混沌序列通過(guò)混沌映射到。這個(gè)序列的元素被用來(lái)生成序列,,通過(guò)混沌映射到。這個(gè)序列S,所獲得的傳播序列用于每個(gè)數(shù)據(jù)位,傳播序列從一位到另一個(gè)發(fā)生變化。接收方重新生成序列S,與發(fā)射機(jī)的工作方式完全相同。每一個(gè)接收器將分配不同的,,,和/或,因此,產(chǎn)生的傳播序列對(duì)于每個(gè)接收機(jī)在多址通信系統(tǒng)將是完全不同的,而且是幾乎不相關(guān)的。因?yàn)橛?/p>

96、大量的初始條件、分岔和混亂映射的參數(shù)可以去選擇,出于所有實(shí)用目的,在用戶數(shù)量上是沒(méi)有限制的,而且用戶可以安排這些傳播序列。</p><p>　　調(diào)制和檢測(cè)的數(shù)據(jù)序列在傳統(tǒng)DS / SS系統(tǒng)中是否是一樣的。圖4顯示了這樣一個(gè)系統(tǒng)的框圖。檢測(cè)將基于關(guān)聯(lián)的接收信號(hào)與混沌序列的接收機(jī)。收發(fā)同步還可以通過(guò)多種方式,從絕對(duì)時(shí)間測(cè)量,周期傳輸?shù)念A(yù)定義的同步序列。這些同步序列甚至可能是二進(jìn)制而不是混亂的。</p>

97、<p>　　圖2 這個(gè)提出產(chǎn)生的混亂序列的方法是擴(kuò)頻通信的應(yīng)用程序</p><p>　　圖3 說(shuō)明了產(chǎn)生混亂傳播序列的方法如圖2所示。</p><p>　　對(duì)于一個(gè)CSK DS / SS系統(tǒng),要么或?qū)⒈仨毭看胃淖儾煌姆?hào)去傳播。顯然,檢測(cè)一個(gè)符號(hào)的錯(cuò)誤將不會(huì)影響代碼序列下一個(gè)符號(hào)的生成。因此,將沒(méi)有傳播的錯(cuò)誤。</p><p>　　在DS / SS系統(tǒng)中

98、，用PN序列代替二進(jìn)制的混沌問(wèn)題會(huì)產(chǎn)生什么樣的影響,如果有的話,這個(gè)替換會(huì)使系統(tǒng)的性能出現(xiàn)錯(cuò)誤?；叵胍幌?混亂序列的相關(guān)性和隨機(jī)二進(jìn)制序列是相同的。自檢測(cè)過(guò)程是僅僅依賴傳播序列的相關(guān)性,我們可以直觀地期望沒(méi)有誤差性能區(qū)別的混亂的DS / SS系統(tǒng)與二進(jìn)制系統(tǒng)。為了證明這個(gè)結(jié)論的有效性,幾個(gè)計(jì)算機(jī)模擬已經(jīng)執(zhí)行,其結(jié)果與我們的認(rèn)知一致。</p><p>　　III.混亂的DS / SS優(yōu)勢(shì)</p>&l

99、t;p>　　為什么混亂被用于DS / SS系統(tǒng)中？有很多的答案?；煦缧蛄惺侨菀桩a(chǎn)生和存儲(chǔ)的。只有一個(gè)混沌映射和一個(gè)初始條件都需要他們的產(chǎn)生,這意味著沒(méi)有必要存儲(chǔ)長(zhǎng)序列。此外,大量的不同的序列可以通過(guò)簡(jiǎn)單地改變初始條件來(lái)生成。</p><p>　　更重要的是,混沌序列是非常安全通信的基礎(chǔ)。在許多應(yīng)用程序中保密的傳輸是重要的?；煦缧蛄袔椭踩貙?shí)現(xiàn)接收，通過(guò)以下幾種方式。1)混沌序列使傳輸信號(hào)看起來(lái)像噪聲,因此

100、,它不會(huì)吸引不友好接收機(jī)的注意。2)序列不再是二進(jìn)制。這就是說(shuō),一個(gè)偷聽(tīng)者會(huì)面對(duì)一個(gè)更大可能搜索組才能獲得代碼序列。此外,由于代碼序列的每一個(gè)比特的信息不重復(fù),即使代碼序列的一位被成功地發(fā)現(xiàn),另一位依然保持無(wú)解碼的狀態(tài)。3)雖然混亂序列的生成對(duì)于知道其參數(shù)和功能參數(shù)的發(fā)射機(jī)和預(yù)接收機(jī)是簡(jiǎn)單的,但對(duì)于一個(gè)接收器確切的再生是非常困難的,必須對(duì)它們進(jìn)行估計(jì)。一個(gè)輕微的誤差估計(jì)將導(dǎo)致成倍增加的錯(cuò)誤。這是由于對(duì)初始條件，及它們的參數(shù)的混沌系統(tǒng)的敏