【正文】 ve quite good personal 。History is created by 。，不要開(kāi)窗。趁熱吃。顧客可能會(huì)失去對(duì)我們產(chǎn)品的興趣。平均延遲τ，均方根（RMS）的時(shí)延擴(kuò)展τRMS和最大延遲τmax都是延遲功率密度譜特征參數(shù)。相均勻分布在區(qū)間[0，2π]。最大多普勒在移動(dòng)無(wú)線應(yīng)用傳播使用單載波調(diào)制通常比相鄰?fù)ǖ?，這樣，干擾對(duì)由于多普勒傳播相鄰?fù)ǖ赖淖饔貌皇且粋€(gè)單載波調(diào)制系統(tǒng)的問(wèn)題距離。各類離散多與不同的細(xì)胞大小的室內(nèi)和室外蜂窩系統(tǒng)的信道模型已經(jīng)被指定。經(jīng)典的多普勒頻譜與均勻分布的到達(dá)角路徑可以用于簡(jiǎn)化所有的頻道。微細(xì)胞類型被定義為細(xì)胞體積約300米， GHz或5 GHz載波頻率。移動(dòng)無(wú)線信道建模為不相關(guān)瑞利衰落信道（）。在某些情況下，傳統(tǒng)加工可能行不通。相比于利用不同刀具進(jìn)行金屬切削和磨削的常規(guī)加工，電火花加工更為吸引人之處在于它利用工件和電極間的一系列重復(fù)產(chǎn)生的（脈沖）離散電火花所產(chǎn)生的熱電作用，從工件表面通過(guò)電腐蝕去除掉多余的材料。每次電火花所蝕除掉的材料量通常在105～106mm3范圍內(nèi)。該工藝采用如下幾種形式：凹坑加工、輪廓加工和整體金屬去除的化學(xué)銑，在薄板上進(jìn)行蝕刻的化學(xué)造型，在微電子領(lǐng)域中利用光敏抗蝕劑完成蝕刻的光化學(xué)加工(PCM)，采用弱化學(xué)試劑進(jìn)行拋光或去毛刺的電化學(xué)拋光，以及利用單一化學(xué)活性噴射的化學(xué)噴射加工等。盡管利用電解作用作為金屬加工手段是近代的事，但其基本原理是法拉第定律。型腔的形狀正好是與工具相匹配的陰模的形狀。由于工具和工件間沒(méi)有接觸，電化學(xué)加工是加工薄壁、易變形零件及表面容易破裂的脆性材料的首選。由于這個(gè)原因，激光切削所產(chǎn)生的切口非常窄。激光加工適用于任何可以很好地吸收激光輻射的材料，而傳統(tǒng)加工工藝必須針對(duì)不同硬度和耐磨性的材料選擇合適的刀具。超聲加工超聲加工為日益增長(zhǎng)的對(duì)脆性材料如單晶體、玻璃、多晶陶瓷材料的加工需求及不斷提高的工件復(fù)雜形狀和輪廓加工提供了解決手段。超聲加工系統(tǒng)包括音極組件、超聲發(fā)生器、磨料供給系統(tǒng)及操作人員的控制。另外，除了提供磨粒進(jìn)行切削外，漿料還可對(duì)音極進(jìn)行冷卻，并將切削區(qū)的磨粒和切屑帶走。 types of nontraditional machining processes have been developed to meet extra required machining these processes are employed properly, they offer many advantages over traditional machining mon nontraditional machining processes are described in the following Discharge Machining(EDM)Electrical discharge machining(EDM)sometimes is colloquially referred to as spark machining, spark eroding, burning, die sinking or wire is one of the most widely used nontraditional machining main attraction of EDM over traditional machining processes such as metal cutting using different tools and grinding is that this technique utilizes thermoelectric process to erode undesired materials from the workpiece by a series of rapidly recurring discrete electrical sparks between workpiece and traditional mac。in some cases traditional machining may not be machining also results in tool wear and loss of quality in the product owing to induced residual stresses during machining processes, also called unconventional machining process or advanced manufacturing processes, are employed where traditional machining processes are not feasible, satisfactory or economical due to special reasons as outlined below: hard fragile materials difficult to clamp for traditional machining。音極/工具組件由換能器、變幅桿和音極組成。因此，超聲加工被廣泛應(yīng)用于傳統(tǒng)加工難以切削的硬脆材料。激光切割的邊緣光滑且潔凈，無(wú)須進(jìn)一步處理。采用這種方法可以節(jié)省材料，這對(duì)于貴重材料或微加工中的精密結(jié)構(gòu)而言非常重要。雖然激光在某些場(chǎng)合可用來(lái)作為放大器，但它的主要用途是光激射振蕩器，或者是作為將電能轉(zhuǎn)換為具有高度準(zhǔn)直性光束的換能器。通過(guò)將工具電極向去除工件表面材料的方向進(jìn)給， mm范圍內(nèi)，～20 mm/min左右。這個(gè)加工過(guò)程一般用于在高強(qiáng)度材料上加工復(fù)雜形腔和形狀，特別是在航空工業(yè)中如渦輪機(jī)葉片、噴氣發(fā)動(dòng)機(jī)零件和噴嘴，以及在汽車業(yè)（發(fā)動(dòng)機(jī)鑄件和齒輪）和醫(yī)療衛(wèi)生業(yè)中。在化學(xué)造型中最典型的公差范圍可保持在材料厚度的177。化學(xué)加工化學(xué)加工是眾所周知的特種加工工藝之一，它將工件浸入化學(xué)溶液通過(guò)腐蝕溶解作用將多余材料從工件上去除掉。因此，材料的硬度不再是電火花加工中的關(guān)鍵因素?；谝韵赂鞣N特殊理由，特種加工工藝或稱為先進(jìn)制造工藝，可以應(yīng)用于采用傳統(tǒng)加工方法不可行，不令人滿意或者不經(jīng)濟(jì)的場(chǎng)合：； ； ；。另一種實(shí)現(xiàn)形式的OFDM系統(tǒng)的多樣性是由前向糾錯(cuò)信道編碼，在這里，每個(gè)數(shù)據(jù)位的信息分散在幾個(gè)代碼位。 GHz或24千兆赫。207信道的成本模型是基于一個(gè)810兆赫的2G，如GSM系統(tǒng)中使用的900兆赫頻段信道帶寬的測(cè)量。一種廣泛使用的離散多徑信道模型概述于下。只要所有子載波只要是一個(gè)共同的多普勒頻移金融衍生工具的影響，這可以補(bǔ)償多普勒頻移在接收器和ICI是可以避免的。根據(jù)信道脈沖響應(yīng)的假設(shè)一個(gè)復(fù)雜的值高斯過(guò)程，其大小通道的傳遞函數(shù)A的水稻分布給出賴斯因素KRice是由占主導(dǎo)地位的路徑權(quán)力的威力比分散的路徑。多徑信道頻率分散性能是最常見(jiàn)的量化發(fā)生的多普勒頻率和多普勒f(shuō)Dmax蔓延fDspread最大。Some parents just buy whatever their children want.第二篇：中英文翻譯Fundamentals This chapter describes the fundamentals of today’s wireless a detailed description of the radio channel and its modeling are presented, followed by the introduction of the principle of OFDM multicarrier addition, a general overview of the spread spectrum technique, especially DSCDMA, is given and examples of potential applications for OFDM and DSCDMA are introduction is essential for a better understanding of the idea behind the bination of OFDM with the spread spectrum technique, which is briefly introduced in the last part of this Radio Channel Characteristics Understanding the characteristics of the munications medium is crucial for the appropriate selection of transmission system architecture, dimensioning of its ponents, and optimizing system parameters, especially since mobile radio channels are considered to be the most difficult channels, since they suffer from many imperfections like multipath fading, interference, Doppler shift, and choice of system ponents is totally different if, for instance, multipath propagation with long echoes dominates the radio , an accurate channel model describing the behavior of radio wave propagation in different environments such as mobile/fixed and indoor/outdoor is may allow one, through simulations, to estimate and validate the performance of a given transmission scheme in its several design Understanding Radio Channels In mobile radio channels(see Figure 11), the transmitted signal suffers from different effects, which are characterized as follows: Multipath propagation occurs as a consequence of reflections, scattering, and diffraction of the transmitted electromagnetic wave at natural and manmade , at the receiver antenna, a multitude of waves arrives from many different directions with different delays, attenuations, and superposition of these waves results in amplitude and phase variations of the posite received spread is caused by moving objects in the mobile radio in the phases and amplitudes of the arriving waves occur which lead to timevariant multipath small movements on the order of the wavelength may result in a totally different wave varying signal strength due to timevariant multipath propagation is referred to as fast is caused by obstruction of the transmitted waves by, ., hills, buildings, walls, and trees, which results in more or less strong attenuation of the signal to fast fading, longer distances have to be covered to significantly change the shadowing varying signal strength due to shadowing is called slow fading and can be described by a lognormal distribution [36].Path loss indicates how the mean signal power decays with distance between transmitter and free space, the mean signal power decreases with the square of the distance between base station(BS)and terminal station(TS).In a mobile radio channel, where often no line of sight(LOS)path exists, signal power decreases with a power higher than two and is typically