碼分多址通信系統(tǒng)、擴頻通信外文翻譯

1、<p><b>　　中文2800字</b></p><p><b>　　畢業(yè)設(shè)計英文翻譯</b></p><p>　　專 業(yè) 電子信息工程 </p><p>　　班 級 2010級 <

2、/p><p>　　學(xué)生姓名 </p><p>　　學(xué) 號 </p><p>　　課 題 碼分多址通信系統(tǒng)的建模、仿真和設(shè)計 </p><p>　　——初始化模塊、基站接收模塊

3、 </p><p>　　指導(dǎo)教師 </p><p>　　2014 年 06 月 10 日</p><p><b>　　譯文原文</b></p><p>　　1.1 The basi

4、c concept of spread-spectrum communication</p><p>　　Spread spectrum communication’s basic characteristics, is used to transmit information to the signal bandwidth(W) is far greater than practical required mi

5、nimum(effective) bandwidth (),as the radio of processing gain .</p><p>　　As we well know,the ordinary AM,FM,or pulse code modulation,GP value in the area more than 10 times,collectively,the “narrow-band comm

6、unication”,and spread-spectrum communication GP values as hundred or even thousands of times, can be called “broadband communication”.</p><p>　　Due to the spread-spectrum signal,it is very low power transmit

7、ters,transmission space mostly drowned in the noise,it is difficult to intercepted by the other receiver ,only spreading codes with the same (or random PN code) receiver, Gain can be dealt with ,and despreading resume th

8、e original signal.</p><p>　　1.2 The technology superiority of spread-spectrum communication.</p><p>　　Strong anti-interference, bit error rate is low. As noted above, the spread spectrum communi

9、cation system due to the expansion of the transmitter signal spectrum, the receiver despreading reduction signal produced spreading gain, thereby greatly enhancing its interference tolerance. Under the spreading gain, or

10、 even negative in the signal-to-noise ratio conditions, can also signal from the noise drowned out Extraction, in the current business communications systems, spread spectrum communication</p><p>　　Anti-mult

11、i-path interference capability, increase the reliability of system. Spread-spectrum systems as used in the PN has a good correlation, correlation is very weak. Different paths to the transmission signal can easily be sep

12、arated and may in time and re-alignment phase, formation of several superimposed signal power, thereby improving the system’s performance to receive increased reliability of the system.</p><p>　　Easy to use

13、the same frequency, improving the wireless spectrum utilization. Wireless spectrum is very valuable,although long-wave microwave have to be exploited, and still can not meet the needs of community. To this end, countries

14、 around the world are designed spectrum management, users can only use the frequency applications,rely on the channel to prevent the division between the channel interference.</p><p>　　Due to the use of spre

15、ad-spectrum communication related receive this high-tech,low signal output power(“a W,as a general-100mW),and will work in the channel noise and thermal noise in the background,easy to duplicate in the same area using th

16、e same frequency,can now all share the same narrow-band frequency communication resources.</p><p>　　Spread-spectrum communication is digital communication,particularly for digital voice and data transmission

17、 with their own encryption, only in the same PN code communication between users, is good for hiding and confidential in nature, facilitating communication business. Easy to use spread-spectrum CDMA communications, voice

18、 compression and many other new technologies, more applicable to computer networks and digitization of voice,image information transmission.</p><p>　　Communication in the most digital circuits, equipment, hi

19、ghly integrated, easy installation, easy maintenance, but also very compact and reliable. The average failure rate no time was very long.</p><p>　　1.3 Spread spectrum communication system</p><p>

20、;　　Spread 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

21、-tech communications transmission. Spread spectrum communication is to send the information to be pseudo-random data is coded(Spread spectrum sequence: spread sequence) modulation, spread spectrum and then the realizatio

22、n of transmission; the receiving end is using the same modem co</p><p>　　(1) Carrier is an unpredictable, or so-called pseudo-random broadband signal.</p><p>　　(2) Carrier data bandwidth than th

23、e modulation bandwidth is much wilder.</p><p>　　(3) Receiving process is generated by local broadband carrier signal and receiving a copy of the signal to the broadband signal to achieve.</p><p>

24、;　　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 usin

25、g 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 linear extension of the process of change. Combin

26、ation of a number of ways of hybrid systems are often applied.</p><p>　　The most important measure pf spread-spectrum system is an indicator of spreading gain, also known as processing gain. It is precisely

27、because of the spread spectrum system itself with its performance characteristics with a series of advantages.</p><p>　　1.4 Code division multiple access</p><p>　　Code division multiple access (

28、CDMA) is a channel access method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne, CDMA2000(the 3G evolution of cdmaOne) and WCDMA (the 3Gstandard

29、 used by GSM carrier), which are often referred to as simply CDMA, and use CDMA as an underlying channel access method.</p><p>　　One of the concepts in data communication is the idea of allowing several tran

30、smitters to send information simultaneously over a signal communication channel. This allows several users to share a band of frequencies (see bandwidth). This concept is called multiple access. CDMA employs spread-spect

31、rum technology and a special coding scheme( where each transmitter is assigned a code) to allow multiple user to be multiplexed over the same physical channel. By contrast, time division multiple access</p><p&

32、gt;　　1.5 Spread-spectrum characteristic of CDMA</p><p>　　Most modulation schemes try to minimize the bandwidth of this signal since bandwidth is a limited resource. However, spread spectrum use a transmissio

33、n bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth. One of the initial reasons for doing this was military applications including guidance and communication systems. These

34、system were designed using spread spectrum because if its security and resistance to jamming. Asynchronous CDMA has some level of </p><p>　　CDMA can also effectively reject narrow band interference. Since na

35、rrow band interference affects only a small portion of the spread spectrum signal, it can easily be removed through notch filtering without much loss of information. Convolution encoding and interleaving can be used to a

36、ssist in recovering this lost data. CDMA signal are also resistant to multipath fading. Since the spread spectrum signal occupies a large bandwidth only a small portion of this will undergo fading due to multipath</p&

37、gt;<p>　　Another reason CDMA is resistant to multipath interference is because the delayed versions of the transmitted pseudo-random code, and will thus appear as another user, which is ignored at the receiver. In

38、 other words, as long as the multipath channel induces at least one chip of delay, 天the multipath channel induces at least one chip of delay,the multipath signals will arrive at the receiver.in other words, as long as th

39、e multipath channel induces at least one chip of delay, the multipath signal</p><p>　　Some CDMA devices use a rake receiver, which exploits multipath delay components to improve the performance of the system

40、. A rake receiver combines the information from several correlators, each one tuned to a different path delay, producing a stronger version of the signal than a simple receiver with a signal correlation tuned to the path

41、 delay of the strongest signal.</p><p>　　Frequency reuse is the ability to reuse the same radio channel frequency at other cell sites within a cellular system. In the FDMA and TDMA systems frequency planning

42、 is and important consideration. The frequencies used in different cells must be planned carefully to ensure signals from different cells do not interfere with each other. In a CDMA system, the same frequency can be used

43、 in every cell, because channelization is done using the pseudo-random codes. Reusing the same frequency in every </p><p>　　Since adjacent cell use the same frequencies, CDMA systems have the ability to perf

44、orm soft handoffs. Soft handoffs allow the mobile telephone to communication simultaneously with two or more cells. The best signal quality in selected until the handoff is complete. This is different from hard handoffs

45、utilized in other cellular systems. In a hard handoff situation, as the mobile telephone approaches a handoff, signal strength may vary abruptly. In contrast, CDMA systems use the soft handoff, whi</p><p>　　

46、Concluding remarks</p><p>　　spread-spectrum technology in the initial stages of development, it has become a theory and a major technological breakthrough. Later in the development process is the improvement

47、 and hardware performance improved. Development to the present,spread-spectrum technology and the theory has been almost perfect,mainly from the point of view of overall performance, and the other new technology applicat

48、ions. Therefore, the application has been driven by the development of spread-spectrum technology is</p><p><b>　　譯文正文</b></p><p>　　1.擴頻通信系統(tǒng)概述</p><p>　　擴頻通信，即擴展頻譜通信（Spre

49、ad spectrum communication)，它與光纖通信、衛(wèi)星通信，一同譽為進入信息時代的三大高技術(shù)通信傳輸方式，擴頻通信是將待傳送的信息數(shù)據(jù)被偽隨機碼調(diào)制，實現(xiàn)頻譜擴展后再傳輸；接收端則采用相同的編碼進行解調(diào)及相關(guān)處理，恢復(fù)原始信息數(shù)據(jù)。擴頻通信系統(tǒng)具有3個主要特征：</p><p>　　（1）載波是不可預(yù)測的，或者稱為偽隨機的寬帶信號</p><p>　?。?）載波的帶寬比調(diào)

50、制數(shù)據(jù)的帶寬要寬得多</p><p>　?。?）接收過程是通過本地將本地產(chǎn)生的寬帶載波信號的復(fù)制信號與接收到的寬帶信號相關(guān)來實現(xiàn)的。</p><p>　　擴展頻譜的方式主要有一下幾種：直接序列擴頻（DSSS）使用高速偽隨機碼對要傳輸?shù)牡退俾蕯?shù)據(jù)進行擴頻調(diào)制；跳頻系統(tǒng)則采用偽隨機碼控制載波頻率在一個更寬的頻帶內(nèi)變化；跳時則是數(shù)據(jù)傳輸時隙是偽隨機的；線性調(diào)頻系統(tǒng)中的頻率擴展則是一個線性變化的過

51、程。幾種方式組合的混合系統(tǒng)也經(jīng)常得到應(yīng)用。</p><p>　　衡量擴頻系統(tǒng)最重要的一個指標是擴頻增益，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擴頻通信技術(shù)的基本概念</p><p>　　擴頻通信的基本特點：其傳輸信息所用信號的帶寬（W）遠大于信息本身實際所需的最?。ㄓ行В挘ǎ浔戎捣Q為處理增益<

52、;/p><p>　　眾所周知，在普通的調(diào)幅、調(diào)頻或者脈沖編碼調(diào)制通信中，值一般都在十多倍范圍內(nèi)，稱為“窄帶通信”，而擴頻通信的值高達幾百甚至幾千倍，可以稱為“寬帶通信”。</p><p>　　由于擴頻后的信號，它的發(fā)射功率很低，傳輸時大多數(shù)淹沒在空間的噪聲中，因此很難被其他接收機截獲，只有具有相同的擴頻碼（或稱PN碼）的接收機，才能獲得處理增益，解擴并恢復(fù)出原發(fā)的信號。</p>

53、<p>　　1.3擴頻技術(shù)的優(yōu)越性</p><p>　　抗干擾能力強，誤碼率低，如上所述，擴頻通信系統(tǒng)由于在發(fā)送端擴展信號頻譜，在接收端解擴還原信號，產(chǎn)生擴頻增益，從而大大提高了抗干擾容限。根據(jù)擴頻增益的不同，甚至在負的信噪比條件下，也可以將信號從噪聲的淹沒中提取出來，在目前商用的通信系統(tǒng)中，擴頻通信是唯一能夠工作于負信噪比條件下的通信方式。</p><p>　　抗多徑干擾能力強

54、，增加了系統(tǒng)的可靠性。由于擴頻系統(tǒng)中采用的PN碼具有很好的自相關(guān)性，互相關(guān)性很弱，不同路徑傳來的信號很容易被分開，并可在時間相位上重新對齊，形成幾路信號功率的疊加，從而改善了接收系統(tǒng)的性能增加了系統(tǒng)的可靠性，易于同頻使用，提高了無線頻譜利用率。無線頻譜十分寶貴，雖然從長波、微波都已得到開發(fā)利用，仍然滿足不了社會的需求。為此，世界各地都設(shè)立了頻譜管理機構(gòu)，用戶只能使用申請獲得的頻率，依靠頻率劃分來防止信道之間的干擾。</p>

55、<p>　　由于擴頻通信又采取了相關(guān)接收這一技術(shù)，信號發(fā)送功率極低（＜1W，一般為1~100mW），且可工作在信道噪聲和熱噪聲背景中，易于在同一地區(qū)重復(fù)使用同一頻率，也可以在現(xiàn)今各種窄帶通信共享同一頻率資源。</p><p>　　擴頻通信是數(shù)字通信，特別適合數(shù)字語音和數(shù)據(jù)同時傳輸，擴頻通信自身具有加密功能，只能在PN碼相同的用戶之間進行通信，隱蔽性好，保密性強，便于開展各種通信業(yè)務(wù)。擴頻通信容易采用碼

56、分多址、語音壓縮等多項新技術(shù)，更加適用于計算機網(wǎng)絡(luò)以及數(shù)字化的語音、圖像信息傳輸。</p><p>　　擴頻通信絕大多數(shù)是數(shù)字電路，設(shè)備高度集成，安裝便捷，易于維護，也十分小巧可靠，平均無故障時間也很長。</p><p><b>　　1.4碼分多址</b></p><p>　　碼分多址（CDMA）是一種用于各種無線通信技術(shù)的信道接入方法。它不應(yīng)

57、該與被用在移動電話標準的要求的cdmaOne，CDMA2000（cdmaOne的的3G演進）和WCDMA相混淆（用于GSM的載波3G標準），它往往被簡稱為CDMA，并且作為一個潛在的信道接入方法。</p><p>　　在數(shù)據(jù)通信中有一種想法是允許多個發(fā)射機同時發(fā)送的信息通過信號通信信道。這允許多個用戶共享一個頻帶（見帶寬）。這個概念被稱為多址接入。CDMA采用擴頻技術(shù)和特殊編碼方案（其中每個發(fā)射機分配一個碼），以

58、允許多個用戶被復(fù)用在同一物理信道。相比之下，頻分多址（FDMA）由頻率劃分。 CDMA是擴展頻譜信號的一種形式，由于調(diào)制的編碼信號具有比被傳送的數(shù)據(jù)更高的數(shù)據(jù)帶寬。</p><p>　　1.5擴頻CDMA的特點</p><p>　　大多數(shù)調(diào)制方案都盡量減少信號的帶寬，因為帶寬是有限的資源。然而，擴頻技術(shù)用比所需的最小信號帶寬大幾個數(shù)量級的傳輸帶寬。這樣做的最初原因之一是軍事上的應(yīng)用，包括指

59、導(dǎo)和通信系統(tǒng)。這些系統(tǒng)的設(shè)計使用，因為其安全性和抗干擾擴頻。異步CDMA有一些內(nèi)置的隱私級別，因為信號傳播使用偽隨機碼，這個代碼使擴頻信號出現(xiàn)隨機或有噪聲性能。不能接收解調(diào)不用于編碼數(shù)據(jù)的偽隨機序列的信號傳輸。CDMA還耐干擾。一個干擾信號只有有限的能量去干擾信號。干擾信號可以傳播其能量在信號的整個帶寬或者信號的整個帶寬的一部分。</p><p>　　CDMA還可以有效抑制窄帶干擾。由于窄帶干擾只影響擴頻信號的一

60、小部分，它可以很容易地通過陷波濾波，沒有多少信息損失就可以將它除去。卷積編碼和交織可以用來協(xié)助回收這丟失的數(shù)據(jù)。 CDMA信號也耐多徑衰落。由于擴展頻譜信號占有相當(dāng)大的帶寬，只一小部分信號將經(jīng)受衰落由于多路徑。像窄帶干擾，這將導(dǎo)致只有一小數(shù)據(jù)丟失，并且可以被克服。</p><p>　　CDMA抗多徑干擾的另一個原因是由于所發(fā)射的偽隨機碼的延遲，并且將顯示為另一個用戶，這樣在接收機就會被忽略。換句話說，只要在多徑信

61、道產(chǎn)生的至少一個芯片的延遲，多徑信號將到達接收機。換句話說，只要在多徑信道引起至少一個芯片的延遲，多徑信號將到達接收機，這樣，它們比預(yù)定信號中在時間上移位一個芯片延遲。</p><p>　　偽隨機碼的相關(guān)特性是這樣的，這稍微的延遲會導(dǎo)致多路徑出現(xiàn)與預(yù)期不相關(guān)的信號，因此，它會被忽略。</p><p>　　一些CDMA設(shè)備使用RAKE接收器，它利用多徑時延組件來提高系統(tǒng)的性能。RAKE接收器

62、整合多個相關(guān)器的信息，每一個調(diào)諧到不同的路徑延遲，產(chǎn)生一個比相關(guān)的簡單調(diào)整，以最強的信號路徑延遲接收的信號更強的信號版本。</p><p>　　頻率復(fù)用是在蜂窩系統(tǒng)內(nèi)的其他小區(qū)站點重復(fù)使用相同的無線電頻率的能力。在FDMA和TDMA系統(tǒng)中頻率規(guī)劃是重要的考慮因素。在不同小區(qū)中使用的頻率必須仔細規(guī)劃，以確保來自不同小區(qū)的信號不會相互干擾。在CDMA系統(tǒng)中，在相同的頻率可以在每個小區(qū)中使用的，因為所使用的偽隨機碼會進

63、行信道化。在每一個小區(qū)內(nèi)可以重復(fù)使用相同的頻率，所以在CDMA系統(tǒng)中不需要頻率規(guī)劃;然而，必須得對不同的偽隨機序列進行規(guī)劃，以確保從一個小區(qū)接收到的信號不與來自相鄰小區(qū)的信號相關(guān)。</p><p>　　由于相鄰小區(qū)使用相同的頻率，CDMA系統(tǒng)必須有進行軟切換的能力。軟切換允許移動電話同時與兩個或更多個用戶通信。選擇最佳的信號品質(zhì)，直到軟切換完成。這與其他蜂窩系統(tǒng)的硬切換不同。在硬切換的情況下，當(dāng)移動電話進行切換，

64、信號強度可能會突然發(fā)生變化。相比之下，CDMA系統(tǒng)中使用的軟切換，這是不可檢測的，并提供了更可靠和更高質(zhì)量的信號。</p><p><b>　　結(jié)束語</b></p><p>　　擴頻通信在發(fā)展的初始階段，就已經(jīng)實現(xiàn)了理論與技術(shù)上的重大突破，在此之后的發(fā)展過程中主要是硬件的改善和性能的提高。發(fā)展到現(xiàn)在，擴頻技術(shù)和理論已經(jīng)趨于完善，主要應(yīng)從系統(tǒng)的角度考慮總體性能，且與其