1、精選優(yōu)質(zhì)文檔-傾情為你奉上Unit 9A.1. According to the Nyquist theorem, a signal with a maximum frequency of W Hz (called a band-limited signal) must be sampled at least 2W samples per second to ensure accurate recording.根據(jù)奈奎斯特采樣定理，為了確保準(zhǔn)確記錄信號(hào)，最高頻率為W Hz的信號(hào)（稱為帶限信號(hào)），每秒內(nèi)必須采集至少2W個(gè)樣本。2. This process begins by convertin

2、g each digital code into an analog voltage that is proportional in size to the number represented by the code.這個(gè)電壓值在零階保持器中保持到下一個(gè)碼字出現(xiàn)，即需要保持一個(gè)采樣間隔。3. Depending on the relationship between the signal frequencies and the sampling rate, spectral inversion may cause the shape of the spectrum in the baseba

3、nd to be inverted from the true spectrum of the signal. 根據(jù)信號(hào)頻率和采樣頻率之間的關(guān)系的不同，可能出現(xiàn)“頻譜反轉(zhuǎn)”現(xiàn)象基帶頻譜的形狀和信號(hào)真實(shí)頻譜的形狀正好相反。4. Field-Programmable Gate Arrays (FPGA) have the capability of being reconfigurable within a system, which can be a big advantage in applications that need multiple trial versions within de

4、velopment, offering reasonably fast time to market. 現(xiàn)場可編程門陣列具有在系統(tǒng)可重新配置的能力，在開發(fā)需要多次試用的應(yīng)用時(shí)，這是一個(gè)巨大的優(yōu)勢(shì)它能提供快速的上市時(shí)間。5. However, for applications in which the end product must process answers in real time, or must do so while powered by consumer batteries, GPPs comparatively poor real time performance and h

5、igh power consumption all but rules them out.然而，在最終產(chǎn)品必須實(shí)時(shí)響應(yīng)的應(yīng)用中，或者必須在電池供電下實(shí)現(xiàn)實(shí)時(shí)響應(yīng)的應(yīng)用中，由于GPP實(shí)時(shí)性能較差、功耗大，因此就被排除在外了。6. More and more, these processors are being seen as the dinosaurs of the industry, too enoumbered with PC compatibility and desktop features to adapt to the changing real time market place

6、.GPP正在越來越多的被視為業(yè)界的龐然大物，為了適應(yīng)不斷變化的實(shí)時(shí)應(yīng)用市場，不斷增加的PC兼容性和臺(tái)式電腦性能使GPP受到了拖累。B.1. While traditional processors follow the Von Neumann architecture model, which assumes a shared single memory to be used for both program instructions and data, DSPs use the Harvard or modified Harvard architecture, which includes

7、multiple program and data memories, along with multiple buses to access them.傳統(tǒng)的處理器遵循馮.諾依曼模型，該模型采用一個(gè)單一的共享存儲(chǔ)器，同時(shí)存儲(chǔ)程序指令和數(shù)據(jù)；而數(shù)字信號(hào)處理器使用的是哈佛結(jié)構(gòu)或改進(jìn)的哈佛結(jié)構(gòu)，該結(jié)構(gòu)包含多個(gè)程序和數(shù)據(jù)存儲(chǔ)器以及訪問這些存儲(chǔ)器的多套總線。2. The specific hardware and software features offered by a particular DSP can make one choice better than another, as can t

8、he amount of on-chip memory available. Sometimes DSPs are chosen because well-matched supporting hardware, particularly A/D and D/A converters, is obtainable. Frequently, the quality and convenience of the software tools, for both low level and high level programming languages, are also major factor

9、s, as is the availability of third party software.當(dāng)片上存儲(chǔ)量足夠時(shí)，特定DSP提供的軟硬件功能使其成為不二之選。有時(shí)選擇一個(gè)DSP是因?yàn)槠淦ヅ湫粤己玫挠布С郑绕涫窃谀?shù)和數(shù)模轉(zhuǎn)換可實(shí)現(xiàn)的情況下。通常軟件工具對(duì)于低級(jí)和高級(jí)編程語言的質(zhì)量和便利性都是主要因素，第三方軟件的可用性也是其一。3. While some of these boards are intended to be used as stand alone computers, most are configured to be plugged into a host, suc

10、h as a personal computer.但有些電路板是作為獨(dú)立電腦使用的，但大多數(shù)電腦是連接到主機(jī)上的，比如個(gè)人電腦。Unit 17A.1. A digital image is made up of many rows and columns of pixels. For gray scale images, each pixel is assigned a number that represents the gray shade assigned to that pixel.一幅數(shù)字圖像是由多行和多列像素組成的。對(duì)灰度圖像而言，每個(gè)像素被賦予一個(gè)代表該像素灰度級(jí)的數(shù)。2. Wh

11、en an image uses only a small portion of the available gray scale levels, histogram equalization can be used to spread out the usage of gray scale levels over the entire available range.當(dāng)一幅圖像只使用了可用灰度級(jí)的一小部分時(shí)，可以使用直方圖均衡的方法將灰度級(jí)的使用擴(kuò)展到整個(gè)可用的范圍。3. The locations and colors of pixels not explicitly marked as

12、control elements are determined by the locations and colors of the control elements that are nearest.那些沒有明確標(biāo)為控制元素的像素的位置，顏色由離其最近的控制元素的位置和顏色來確定。4. One simple compression scheme is run-length encoding, which codes more than three repetitions of a number as three copies of the number followed by a count

13、 of the additional copies needed.行程編碼是一種簡單的壓縮方式，這種編碼方法將一個(gè)數(shù)字超過三次的重復(fù)次數(shù)附加在這個(gè)數(shù)字后面。B.1. Compression rates may be generated by determining the size of the compressed image in terms of number of bits per image pixel for the original image.壓縮比可以通過原始圖像每像素所需壓縮的比特?cái)?shù)來確定。2.In fact, for some Land-sat scenes with u

14、rban areas and many small farms, the factor of 2 bits per pixel may not be able to achieve. The same technique applied to a Land-sat image of the mid-west where large fields occur and few shadows exist in images might produce a much better compression.實(shí)際上，對(duì)于一些郊區(qū)和有許多小農(nóng)場的陸地場景，2比特每像素的系數(shù)可能無法達(dá)到。對(duì)于遼闊的中西部，

15、圖像中陰影極少，相同的技術(shù)在其陸地圖像中生成的壓縮會(huì)好得多。3. In image processing, a procedure called principal components has been designed to identify correlation between image bands and to create a new set of transformed bands that represent a new color space in which the new image bands are uncorrelated.在圖像處理過程中，一個(gè)稱為主分量的過程被

16、設(shè)計(jì)用以確認(rèn)圖像頻譜之間的相關(guān)性，并產(chǎn)生一組新的變換頻譜，其中新圖像頻譜互不相關(guān)地表示一個(gè)新的彩色空間。5.The VQ technique is an example of asymmetric compression in that considerably more time is spent deriving the codebook than in decompressing via a codebook lookup. Since different images may have different characteristics, a robust codebook is ne

17、cessary to successfully code and decode Land-sat and other satellite images. A VQ technique using between channel correlation as well as spatial correlation achieves higher compression rates with lossless than independent band VQ.矢量量化編碼技術(shù)是不對(duì)稱壓縮的例子，其中更多時(shí)間花在推到碼本而不是通過查找碼本解壓上。因?yàn)椴煌膱D像可能有不同特點(diǎn)，要成功滴編碼和解碼陸地和

18、其他衛(wèi)星圖像，穩(wěn)定的碼本必不可少。利用信道相關(guān)和空間相關(guān)的矢量技術(shù)能獲得比獨(dú)立的矢量技術(shù)更高的壓縮率，更低的損失。6. The last type of compression considered is fractal compression. Based on Mandelbrot sets which take advantage of a self similar, scaling independent, statistical feature of nature, fractal compression and decompression involves a clustering

19、 approach to finding regions which exhibit the same characteristics as a sample region without regard to rotation and scale.最后一種可考慮的是分型壓縮。它基于曼德布羅特集，利用自相關(guān)，獨(dú)立規(guī)模，自然的統(tǒng)計(jì)特性。分型壓縮和解壓縮涉及一種聚類方法，這種方法是查找展現(xiàn)相同特點(diǎn)的區(qū)域作為樣本區(qū)而不考慮旋轉(zhuǎn)和規(guī)模。Unit 19 A1. Within a communication system the information transfer is frequently achi

20、eved by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier for the information signal.在通信系統(tǒng)中，信息傳輸是通過把信息疊加在電磁波上或?qū)﹄姶挪ㄟM(jìn)行調(diào)制來實(shí)現(xiàn)的，電磁波起著載送信號(hào)的作用。2. Although often simpler to implement , analog modulation with an optical fiber communication system is less effici

21、ent, requiring a far higher signal to noise ratio at the receiver than digital modulation.雖然光纖系統(tǒng)的模擬調(diào)制易于實(shí)現(xiàn)，但其效率較低，且要求在接收端有比數(shù)字調(diào)制高得多的信噪比。3. The avalanche photodiode (APD) detector is followed by a front-end amplifier and equalizer or filter to provide gain as well linear signal processing and noise ban

22、dwidth reduction.前置放大器與均衡放大器或?yàn)V波器在雪崩二極管檢測(cè)器的后面以獲得增益、線信號(hào)處理及噪聲寬帶的抑制。B.1. At present, the bandwidth available to fiber systems is not fully utilized but modulation at several gigahertz over a hundred kilometers and hundreds of megahertz over three hundred kilometers without intervening electronics (repea

23、ters) is possible.目前，傳輸100km的幾吉赫茲的調(diào)制信號(hào)和傳輸300km的幾百兆赫茲的調(diào)制信號(hào)都是可能的，因此，光纖系統(tǒng)的可用帶寬并沒有得到充分利用。 2.Low transmission loss. The development of optical fibers over the last twenty years has resulted in the production of optical fiber cables which exhibit very low attenuation or transmission loss in comparison wit

24、h the best copper conductors. Fibers have been fabricated with losses as low as 0.2 dB/km and this feature has become a major advantage of optical fiber communications. It facilitates the implementation of communication links with extremely wide repeater spacing (long transmission distances without

25、intermediate electronics), thus reducing both system cost and complexity. Together with the already proven modulation bandwidth capability of fiber cable this property provides a totally compelling case for the adoption of optical fiber communication in the majority of long-haul telecommunication ap

26、plications.傳輸損耗低。過去二十年，光纖的發(fā)展使得光纜的生產(chǎn)表現(xiàn)出相比于最好的銅導(dǎo)線極低的衰減或傳輸損失。光纖以低至0.2 dB/km的損耗生產(chǎn)，這一特點(diǎn)成為了光纖通訊的主要優(yōu)點(diǎn)。這促使有著極寬中繼距離的通訊線路得以實(shí)現(xiàn)（遠(yuǎn)程無中介器件傳輸），因此降低了系統(tǒng)成本和復(fù)雜度。連同已證明的光纜的調(diào)制帶寬容量，這個(gè)性質(zhì)使得光纖通訊在大多數(shù)長途電信中的采用令人信服。3. Potential low cost. The glass which generally provides the optical fiber transmission medium is made from sandnot

27、 a scarce resource. So, in comparison with copper conductors, optical fibers offer the potential for low cost line communication. Although over recent years this potential has largely been realized in the costs of the optical fiber transmission medium which for bulk purchases is now becoming competi

28、tive with copper wires (i.e. twisted pairs), it has not yet been achieved in all the other component areas associated with optical fiber communications. For example, the costs of high performance semiconductor lasers and detector photodiodes are still relatively high, as well as some of those concerned with the connection technology (demountable connectors, couplers, etc).潛在的低成本。通常用作光纖傳輸媒介的玻璃是沙子做成的，不是什么稀缺資源。所以，與銅導(dǎo)線相比，光纖提供了低成本有線通信的潛能。盡管近年來這種潛能在光纖傳輸媒介上已經(jīng)廣泛實(shí)現(xiàn)，這在大量購買的情況下相對(duì)銅導(dǎo)線（即雙絞線）來說是極具競爭力的，但在其他與光纖通信有關(guān)的零件上還沒有達(dá)到。例如，高性能半導(dǎo)體激光器和光電二極管檢測(cè)器的成本仍相對(duì)較高