【正文】 料。另一種實現(xiàn)形式的OFDM系統(tǒng)的多樣性是由前向糾錯信道編碼，在這里，每個數(shù)據(jù)位的信息分散在幾個代碼位。移動無線信道建模為不相關(guān)瑞利衰落信道（）。沒有其他的分集技術(shù)被應(yīng)用。CODIT [7]：這些通道模型定義的宏，微，微微蜂窩和室外和室內(nèi)傳播的典型案例。 GHz或24千兆赫。微細胞類型被定義為細胞體積約300米， GHz或5 GHz載波頻率。三種類型的通道模型定義。空間分辨率與已定義的通道模型在造價259。207信道的成本模型是基于一個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量。經(jīng)典的多普勒頻譜與均勻分布的到達角路徑可以用于簡化所有的頻道。在這種傳播環(huán)境的幾個表中的相應(yīng)路徑延遲和電源配置給出。這些頻道功率密度的離散譜的實現(xiàn)都是通過使用多達12個頻道。一種廣泛使用的離散多徑信道模型概述于下。各類離散多與不同的細胞大小的室內(nèi)和室外蜂窩系統(tǒng)的信道模型已經(jīng)被指定。不過，如果多載波系統(tǒng)的設(shè)計選擇了這樣的多普勒展寬在子載波間隔或更高，秩序是在頻率RAKE接收機域名可以使用[22]。為了避免性能降級或因與ICI卜內(nèi)門更復(fù)雜的接收機均衡，子載波間隔財政司司長應(yīng)定為這樣說，由于多普勒效應(yīng)可以忽略不擴散（見第4章）。只要所有子載波只要是一個共同的多普勒頻移金融衍生工具的影響，這可以補償多普勒頻移在接收器和ICI是可以避免的。最大多普勒在移動無線應(yīng)用傳播使用單載波調(diào)制通常比相鄰?fù)ǖ?，這樣，干擾對由于多普勒傳播相鄰?fù)ǖ赖淖饔貌皇且粋€單載波調(diào)制系統(tǒng)的問題距離。這種效果是利用多載波傳輸?shù)牡胤?，每發(fā)送符號的增加與子載波數(shù)控數(shù)目，因此，ISI的金額減少的持續(xù)時間。（ISI）和通道間干擾（ICI）延遲的蔓延引起的符號間干擾（ISI）當相鄰的數(shù)據(jù)符號上的重疊與互相不同的傳播路徑，由于不同的延遲干涉。根據(jù)信道脈沖響應(yīng)的假設(shè)一個復(fù)雜的值高斯過程，其大小通道的傳遞函數(shù)A的水稻分布給出賴斯因素KRice是由占主導地位的路徑權(quán)力的威力比分散的路徑。相均勻分布在區(qū)間[0，2π]。在對視線（LOS）或線的主要組成部分的情況下，這個過程是零的意思。一個簡單而經(jīng)常使用的方法是從假設(shè)有一個通道中的散射，有助于在大量接收端的信號。多徑信道頻率分散性能是最常見的量化發(fā)生的多普勒頻率和多普勒fDmax蔓延fDspread最大。平均延遲τ，均方根（RMS）的時延擴展τRMS和最大延遲τmax都是延遲功率密度譜特征參數(shù)。多普勒頻率取決于終端站，光速c，載波頻率fc的速度和發(fā)病路徑分配給速度v波αp角度頁具有相應(yīng)通道傳輸信道沖激響應(yīng)函數(shù)圖12所示。此外，一個一般概觀的擴頻技術(shù)，尤其dscdma，被給，潛力的例子申請參考正交頻分復(fù)用，DS對1。第一篇：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 in the order of three to of the received power due to shadowing and path loss can be efficiently counteracted by power the following, the mobile radio channel is described with respect to its fast fading Channel Modeling The mobile radio channel can be characterized by the timevariant channel impulse response h(τ , t)or by the timevariant channel transfer function H(f, t), which is the Fourier transform of h(τ , t).The channel impulse response represents the response of the channel at time t due to an impulse applied at time t ? mobile radio channel is assumed to be a widesense stationary random process, ., the channel has a fading statistic that remains constant over short periods of time or small spatial environments with multipath propagation, the channel impulse response is posed of a large number of scattered impulses received over Np different paths，Whereand ap, fD,p, ?p, and τp are the amplitude, the Doppler frequency, the phase, and the propagation delay, respectively, associated with path p, p = 0,..., Np ? assigned channel transfer function isThe delays are measured relative to the first detectable path at the Doppler Frequencydepends on the velocity v of the terminal station, the speed of light c, the carrier frequency fc, and the angle of incidence αp of a wave assigned to path channel impulse response with corresponding channel transfer function is illustrated in Figure delay power density spectrum ρ(τ)that characterizes the frequency selectivity of the mobile radio channel gives the average power of the channel output as a function of the delay mean delay τ , the root mean square(RMS)delay spread τRMS and the maximum delay τmax are characteristic parameters of the delay power density mean delay isWhereFigure 12 Timevariant channel impulse response and channel transfer function with frequencyselect