英语翻译As is the case in radio frequency transmission systems,m

英语翻译
As is the case in radio frequency transmission systems,multipath propagation
effects are important for wireless optical networks.The power launched from
the transmitter may take many reflected and refracted paths before arriving at
the receiver.In radio systems,the sum of the transmitted signal and its images
at the receive antenna cause spectral nulls in the transmission characteristic.
These nulls are located at frequencies where the phase shift between the paths
causes destructive interference at the receiver.This effect is known as multipath
fading [19].
Unlike radio systems,multipath fading is not a major impairment in wireless
optical transmission.The “antenna” in a wireless optical system is the light
detector which typically has an active radiation collection area of approximately
The relative size of this antenna with respect to the wavelength of the
infrared light is immense,on the order of The multipath propagation of
light produces fades in the amplitude of the received electromagnetic signal at
spacings on the order of half a wavelength apart.As mentioned earlier,the light
detector is a square law device which integrates the square of the amplitude of
the electromagnetic radiation impinging on it.The large size of the detector
with respect to the wavelength of the light provides a degree of inherent spatial
diversity in the receiver which mitigates the impact of multipath fading [2].
Although multipath fading is not a major impediment to wireless optical
links,temporal dispersion of the received signal due to multipath propagation
remains a problem.This dispersion is often modelled as a linear time invariant
system since the channel properties change slowly over many symbol periods
[ 1,20].The impact of multipath dispersion is most noticeable in diffuse infrared
communication systems,which are described in more detail in Section 2.4.2.In
short distance line-of-sight (LOS) links,presented in Section 2.4.1,multipath
dispersion is seldom an issue.Indeed,channel models proposed for LOS links
assume the LOS path dominates and model the channel as a linear attenuation
and delay [21].

这种事情射频传输系统、多径繁殖
影响无线光网络是很重要的.电力启动,从
发射机可以采取很多反映出的和折射路径到达之前
接受者.在无线电系统,集体的发送信号和其中的偶像
在接收天线的光谱nulls原因传输特性.
这些nulls位于其相位频率之间变换的路径
造成破坏性的干扰接受者.这种作用被称为多路径
逝去的(19).
不像无线电系统、多径衰落不是一个主要障碍的无线网络
光传输.“天线设计”的无线光学系统光
检测器通常有一个很积极辐射收藏面积约
这种天线基于相对大小对波长
红外线是巨大的,以收多径传播的
光产生会褪色了幅度的电磁信号
距订单上半个波长分开.如前面提到的,光
检测平方定律装置相结合的振幅的广场
碰撞的电磁辐射.大检测器
关于光的波长提供了一定程度的内在空间
在电话的另一端道出的多样性的影响,多径衰落上[2].
虽然多径衰落不是一个主要障碍无线光学
链接,时间分散由于多径接收信号传播
仍然是一个问题.这种情况经常是模仿为一个线性时间不变的
系统自频道慢慢地特性改变许多象征的时期
[1]20].多径扩散的影响红外漫射最引人注目
通信系统,更详细地被描述2.4.2节.在
配合LOS导引短的距离,介绍了在部分连接2.4.1、多径
弥散很少一个问题.事实上,频道飞往洛杉机的模型的链接
假设洛杉矶路径者和万能主宰通道模型为一个线性衰减
和延迟(21).