南京邮电大学研究生专业英语翻译reading10.doc

南京邮电大学研究生专业英语翻译 刘旭老师 2017年第一学期注：译文仅供参考Reading 10(1) A signal propagating through the wireless channel arrives at the destination along a number of different paths, collectively referred to as multipath. These paths arise from scattering, reflection and diffraction of the radiated energy by objects in the environment or refraction in the medium.信号通过无线信道传播沿着多个不同的路径到达目的地，统称为多径。这些路径是由环境中的物体辐射能量的散射，反射和衍射以及介质中的折射产生的。(2) The different propagation mechanisms influence path loss and fading models differently. However, for convenience we refer to all these distorting mechanisms as “scattering”. Further, throughout the part, we assume a complex baseband representation for the signal and channel unless otherwise specified.不同的传播机制影响路径损耗和衰落模型不同。然而，为了方便起见，我们将所有这些扭曲机制称为“散射”。此外，在整个部分，除非另有说明，否则我们假设用复基带来表示信号和信道。(3) The signal power drops off due to three effects: mean propagation (path) loss, macroscopic fading and microscopic fading. The mean propagation loss in macro-cellular environments comes from inverse square law power loss, absorption by water and foliage and the effect of ground reflection.信号功率由于三个效应而下降：平均传播（路径）损耗，宏观衰落和微观衰落。在宏蜂窝环境中的平均传播损耗来自平方反比功率损耗，水和植被的吸收以及地面反射的影响。(4) Mean propagation loss is range dependent. Macroscopic fading results from a blocking effect by buildings and natural features and is also known as long term fading or shadowing. Microscopic fading results from the constructive and destructive combination of multipath and is also known as short term fading or fast fading.平均传播损耗取决于范围。宏观衰落是由建筑物和自然特征的阻塞效应引起的，也被称为长期衰落或阴影。微观衰落来自多径的建设性和破坏性组合，也称为短期衰落或快速衰落。(5) Multipath propagation results in the spreading of the signal in different dimensions. These are delay spread, Doppler (or frequency) spread (This needs a time-varying multipath channel) and angle spread. 多径传播导致信号在不同维度上的扩展。这些是延迟扩展，多普勒（或频率）扩展（这需要时变多径信道）和角度扩展。(6) These spreads have significant effects on the signal. Mean path loss, macroscopic fading, microscopic fading, delay spread, Doppler spread and angle spread are the main channel effects and are described below.这些扩展对信号有显着的影响。平均路径损耗，宏观衰落，微观衰落，延迟扩展，多普勒扩展和角度扩散是主要的信道效应，如下所述。(7) In ideal free space propagation we have inverse square law power loss and the received signal power is given by (1)where Pt and Pr are the transmitted and received powers respectively. is the wavelength, Gt, Gr are the power gains of the transmit and receive antennas respectively and d is the range separation.在理想的自由空间传播中，我们具有平方反比功率损耗，接收信号功率由下式给出 (1)其中Pt和Pr分别是发射和接收的功率。是波长，Gt，Gr分别是发射和接收天线的功率增益，d是分离范围。(8) Equation (1) is also known as the Friis equation. In cellular environments, the main path is accompanied by a surface reflected path that destructively interferes with the primary path. The received power can now be approximated by （2）where ht, hr are the effective heights of the transmit and received antennas respectively and we have made the assumption that d2ht*hr.方程（1）也称为Friis方程。在蜂窝环境中，对主路径有破坏性干扰的表面反射路径伴随着主路径。接收的功率现在可以近似为 （2）其中ht，hr分别是发射天线和接收天线的有效高度，我们假设d2 ht * hr。(9) The effective path loss follows an inverse fourth power law (the path loss exponent is equal to 4) that results in a loss of 40dB/decade. In real environments the path loss exponent varies from 2.5 to 6 and depends on the terrain and foliage. Several empirically based path loss models have been developed for macro-cellular and micro-cellular environments such as the Okumur