外文翻譯--通信系統(tǒng)簡介

1、<p>　　Introduction to Communication System</p><p>　　It is often said that we are living in the information age. Communication technology is absolutely vital to the generation, storage, and transmission

2、of this information.</p><p>　　Any communication system moves information from a source to a destination through a channel. Figure 1 illustrates this very simple idea. The information from the source will gen

3、erally not be in a form that can travel through the channel, so a device called a transmitter will be employed at one end and a receiver at the other.</p><p>　　Figure 1 simple communication system</p>

4、<p>　　The source or information signal can be analog or digital. Common examples are analog audio, video signals and digital data. Sources are often described in terms of the frequency range that they occupy. Telep

5、hone-quality analog voice signals, for instance, contain frequencies from 300Hz to 3kHz, while analog high-fidelity music needs a frequency range of approximately 20Hz to 20kHz.</p><p>　　Digital sources can

6、be derived from audio or video signals can have almost any bandwidth depending on the number of bits transmitted per second, and the method used to convert binary ones and zeros into electrical signals.</p><p&

7、gt;　　A communication channel can be almost anything: a pair of conductors, an optical fiber or a free space that we live. Sometimes a channel can carry the information signal directly. For example, an audio signal can be

8、 carried directly by a twisted-pair telephone cable. On the other hand, a radio link through free space cannot be used directly for voice signals. Such situation require the use of a carrier wave will be altered, or modu

9、lated m, by the information signals in such a way that the inform</p><p>　　Technology is at the core of many new and emerging digital information products and applications that support the information societ

10、y. Such products and applications often require the collection, sometimes in real time. The ability of technology to handle real world signals digitally has made it possible to create affordable, innovative; and high qua

11、lity products and applications for large consumer market for example: digital cellular mobile phone, digital television and video games. The impact </p><p>　　Most of the major cities in the domestic bus stop

12、 artificial voice. Every one of the key points from the driver or attendant to stop by voice. But sometimes due to various factors such as weather, vehicle congestion, flight attendants are feeling the effects of the cha

13、nges. There being given the station's reporting stations, especially for passengers not familiar with the topography of the city, causing a lot of unnecessary trouble. Well thus affect the image of a city constructio

14、n window, then </p><p>　　Using radians per second in the mathematics dealing with modulation makes the equation simpler. Of course, frequency is usually given in hertz, rather than in radians per second, whe

15、n practical devices are being discussed. It is easy to convert between the two systems per second, when practical devices are being discussed. It is easy to convert between the two systems by recalling from basic AC theo

16、ry, ω=2πf.</p><p>　　In modulation, the parameters that can be changed are amplitude E, frequency ω, and phase θ. Combinations are also possible. For example, many schemes for transmitting digital information

17、 use both amplitude and phase modulation.</p><p>　　Multiplexing is the term used in communications to refer to the combining of two or more information signals. When the available frequency range is divided

18、among the signals, the process is known as frequency-division multiplexing (FDM).</p><p>　　Radio and television broadcasting, in which the available spectrum is divided among many signals, are everyday examp

19、les of FDM. There are limitations to the number of signals that can be crowded into a given frequency range because each requires a certain bandwidth, For example, a television channel only occupies s given bandwidth of

20、6MHz in 6~8MHz bandwidth of VHF.</p><p>　　Parallel DSP chip to enhance the performance of a traditional improved through the use of multiply-add units and the Harvard structure, it goes far beyond the comput

21、ational capabilities of the traditional microprocessor. A reasonable inference is: chip operations by increasing the number of modules and the corresponding number of bus linking computational modules. The chip can be do

22、ubled to enhance the overall operational capacity. Of course, such an inference two preconditions must be met : Fir</p><p>　　An alternative method for using a single communication channel to send many signal

23、s is to use time-division multiplexing (TDM). Instead of dividing the available bandwidth of the channel among many signals, the entire bandwidth is used for each signal, but only for a small part of the time. A nonelect

24、ronic example is the division of the total available time on a television channel among the various programs transmitted. Each program uses the whole bandwidth of the channel, but only for part of t</p><p>　

25、　It is certainly possible to combine FDM and TDM, For example, the available bandwidth of a communication satellite is divided among a number of transmitter-receiver combinations called transponders. This is an example o

26、f FDM. A single transponder can be used to carry a large number of digital signals using TDM.</p><p>　　This course presents a top-down approach to communications system design. The course will cover communic

27、ation theory, algorithms and implementation architectures for essential blocks in modern physical-layer communication systems (coders and decoders, filters, multi-tone modulation, synchronization sub-systems). The course

28、 is hands-on, with a project component serving as a vehicle for study of different communication techniques, architectures and implementations. This year, the project is focuse</p><p><b>　　通信系統(tǒng)簡介</b

29、></p><p>　　人們常說我們正生活在一個信息時代，通信技術(shù)對信息的產(chǎn)生，存儲與轉(zhuǎn)換有著至關(guān)重要的作用。</p><p>　　任何通信系統(tǒng)的都是通過信道將信息從信源傳送到目的地，圖1所示為一個簡單的系統(tǒng)。來自信源的信息一般是不能通過信道直接傳輸?shù)?，因此在一端要用到被稱為是發(fā)射機的裝置，另一端要用到被稱為是接收機的裝置。</p><p><b>

30、;　　圖1 簡單通信系統(tǒng)</b></p><p>　　信號源或信息信號 可以是模擬的或數(shù)字的。常見的例子是模擬音頻信號、視頻信號及數(shù)據(jù)。信息源常被描述為信號所占用的頻率范圍，例如，電話質(zhì)量的語音信號，包含著300 Hz~3kHz的頻率范圍，而模擬高保真音樂信號大概需要20 Hz~20kHz的頻率范圍。</p><p>　　數(shù)字信號源于音頻或視頻信號，或由數(shù)據(jù)組成（如文字和字符）

31、。數(shù)字信號可以有任意帶寬，這要取決于每秒鐘傳送的比特數(shù)和所采用的將二進(jìn)制1和0轉(zhuǎn)換成電信號的方法。</p><p>　　通信信道可以是任何媒介：一對導(dǎo)體、一條光纖或者是我們生活的自由空間。有時信道可以直接承載信息。例如，語音信號可以直接有一對雙絞線電話電纜來承載。另一方面，自由空間無線鏈路不能直接用于承載語音信號，這就需要使用一個載波信號，它的頻率能夠使語音信號通過信道傳輸或傳播。載波有信息信號改變或調(diào)制，這樣信

32、息才能夠在接受端被恢復(fù)。當(dāng)使用載波時信息信號被稱為調(diào)制信號。</p><p>　　通信技術(shù)是許多新的和正在涌現(xiàn)的支撐信息社會的數(shù)字信息產(chǎn)品和應(yīng)用的核心，這些產(chǎn)品和應(yīng)用要求收集，分析，傳輸，顯示和存儲現(xiàn)實世界的信息，有時候則需要實時實現(xiàn)。通信技術(shù)數(shù)字化地處理現(xiàn)實世界信息的能力，使得廣大的消費市場如：數(shù)字蜂窩移動電話，數(shù)字電視和視頻游戲等等。創(chuàng)造可生產(chǎn)的，新的，高指令的產(chǎn)品和應(yīng)用成為可能，DSP在其它領(lǐng)域的影響力也十

33、分明顯的，例如：醫(yī)學(xué)，健康監(jiān)護，病人監(jiān)護，數(shù)字X光機，先進(jìn)的心臟和腦電圖系統(tǒng)等等，以及數(shù)字音頻，例如：CD播放器，音頻混頻器和電子音樂和個人計算機系統(tǒng)，例如：有效數(shù)據(jù)存儲的磁盤，誤差校正，調(diào)制解調(diào)器，聲卡和視頻會議等等。</p><p>　　當(dāng)前國內(nèi)主要大城市的公交車大都采用人工語音報站，即每到一站由司機或者乘務(wù)員按語音鍵來進(jìn)行報站。但有時由于受到各種因素如雨雪天路滑、車上擁擠、乘務(wù)員心情的變化等的影響，會出現(xiàn)報

34、錯車站，漏報車站的情況，給乘客特別是不熟悉本市地形的乘客帶來了不必要的麻煩，進(jìn)而會影響到一個城市的窗口形象工程建設(shè)，于是開發(fā)研制自動報站系統(tǒng)成為必然。系統(tǒng)中由于要求對接收到的公交車GPS定位信息（經(jīng)緯度信息等）進(jìn)行處理，由經(jīng)緯度信息生成站牌與公交車之間的距離信息，這之間會經(jīng)歷繁瑣的計算，用一般的微控制器難于實現(xiàn)，而當(dāng)采用處理芯片時，這一問題就很好解決了。</p><p>　　調(diào)制在數(shù)學(xué)上采用弧度單位，能釋放流程變

35、得簡單。當(dāng)然，在討論實際裝置時，頻率通常用赫茲來表示，而不是用弧度每秒來表示，運用交流基本理論ω=2πf，兩者之間很容易轉(zhuǎn)換。</p><p>　　調(diào)制時，能夠改變的參數(shù)是幅度E頻率ω和相位θ。復(fù)合調(diào)制是可能的，例如，發(fā)送數(shù)字信息的電路既可以采用幅度調(diào)制又可以采用相位調(diào)制。</p><p>　　多路復(fù)用是通信的一個術(shù)語，它是指將兩個或更多的信息復(fù)合在一起調(diào)制，當(dāng)在信號中劃分可用頻率范圍時，

36、這個過程被稱為頻率復(fù)用。</p><p>　　無線電和電視廣播是我們每天都能夠感受到的FDM例子，在許多信號中劃分它們的頻率，由于每種信號都需要占用一定的帶寬，因此，對于有些擁擠在給定頻率范圍內(nèi)的信號來說，就要受到限制。例如，一個電視信道在6~8MHz VHF 帶寬內(nèi)，只給定占用6MHz帶寬。</p><p>　　數(shù)字化技術(shù)正在極大地改變著我們的生活和體驗。作為數(shù)字化技術(shù)的基石，數(shù)字信號處

37、理技術(shù)已經(jīng)、正在、并且還將在其中扮演一個不可或缺的角色。核心是算法與實現(xiàn)，越來越多的人正在認(rèn)識、熟悉和使用它。因此，理性地評價通信器件的優(yōu)缺點，及時了解通信的現(xiàn)狀以及發(fā)展趨勢，正確使用芯片，才有可能真正發(fā)揮出DSP的作用。現(xiàn)代數(shù)字信號處理器的特點和發(fā)展趨勢是：通信的發(fā)展，必須兼顧3P的因素，即性能 、功耗和價格?？偟膩碚f，隨著VLSI技術(shù)的高速發(fā)展，現(xiàn)代通信器件在價格顯著下降的同時，仍然保持著性能的不斷提升和單位運算量的功耗不斷降低。&

38、lt;/p><p>　　選擇單一通信信道發(fā)送多個信號的方法是采用時分復(fù)用，為取代多信號信道對可用帶寬的分割，時分復(fù)用的每一路信號占用了整個帶寬，但卻只占用了很少一部分時間。以一個電視節(jié)目為例子，時分復(fù)用相當(dāng)于所發(fā)送多個節(jié)目對一個電視頻道總的占用時間的分割。盡管每個節(jié)目占用了信道的整個帶寬，但只占用了時間的一部分。</p><p>　　將FDM與TDM結(jié)合在一起使用是當(dāng)然可以的，例如。在一些被稱

39、為是發(fā)送與接收一體化的轉(zhuǎn)發(fā)器中劃分出可用帶寬，就是一個FDM的應(yīng)用例子，即可以用單一轉(zhuǎn)發(fā)器攜帶大量的TDM數(shù)字信號。</p><p>　　這當(dāng)然是一種由上而下的方法，以通信系統(tǒng)的設(shè)計This course presents a top-down approach to communications system design.The course will cover communication theory,

40、algorithms and implementation architectures for essential blocks in modern physical-layer communication systems (coders and decoders, filters, multi-tone modulation, synchronization sub-systems).課程將涵蓋通信理論，算法和執(zhí)行架構(gòu)至關(guān)重要的大廈在