衰落是一个针对功率的概念，或者说是信号强度。衰落就是说信号功率减小的问题，从字面理解就是信号功率一下子衰下去了或者说落下去了。我们学通信原理最常见的一个图就是误码率相对信噪比的“瀑布”图，可见随着信噪比的下降误码率就会增大 影响信号的正常接收，所以衰落会严重影响信号的误码率。。。这个“衰落”按功率下降的快慢可以分为大尺度衰落（long term fading）和小尺度衰落（short term fading）。大尺度衰落是在一个较大的范围上考察功率的渐变过程，而小尺度衰落是在小范围内的急剧变化，一般是波长数量级。举例来说，从我国的西部往东部走，海拔是逐渐降低的，这就是“大尺度衰落”，在离基站越远的地方一般信号也就越弱，这是我们看到的一种宏观上的变化趋势。而从我国的西部到东部 同一个城市海拔也不是一样的 这里有个小山坡 隔了没多远又是一个小河。这是就所谓的“小尺度衰落”，在小范围内的突变，这是在整体的变化趋势上又叠加上去的变化细节。大尺度衰落按原因分为路径损耗（path loss） 阴影效应（shadowing）…而造成小尺度衰落的原因就是多径问题，很多书上都将小尺度衰落分为两类来讲：多径效应和多普勒扩展。其实产生衰落的根本原因只是多径（不同相位的时延信号进行叠加产生相加或相消），多普勒扩展只是在多径的基础之上使得衰落问题更加复杂并带来的更大的随机性。只有多普勒扩展而没有多径效应是不会产生衰落问题的，我们可以以声波的多普勒效应来类比，迎面而来的火车的声音频率会变高，我们听起来声音会变尖，但不会出现声音强度忽高忽低的现象。衰落问题中引入多普勒扩展的概念目的是为了讨论信道变化快慢的问题。因为信道变化快慢会直接影响电磁波的传播路径，从而影响衰落。于是我们通过多普勒扩展引入相干时间这个参数，其实多普勒频移Fm和衰落也是没有直接关系的，只不过多普勒频移是由移动台的运动引起的，直接受移动速度的影响，而移动速度又反应了信道的变化。所以多普勒频移反应了信道的变化，就这样，多普勒频移就间接和衰落拉上了关系。其实归根结底，多普勒扩展只是一个"衰落事故"发生时的“目击者”。。。有些书上在讲衰落的时候还讨论了多普勒频移产生随机调频的问题，当然这个说法本身没有问题，多普勒扩展确实会产生随机调频的问题，但随机调频和衰落其实是没有关系的，这样讨论很容易让大家误解。。。
希望我的理解能对你有帮助。
参考资料：引自http://bbs.c114.net/viewthread.php?tid=399952&highlight=%CB%A5%C2%E4
《小幸运》的歌词就和《我的少女时代》的情节一样。学生时代纯真的友情和爱情，错过了，成长了，开始怀念叹息。能够遇见他很幸运，但是当时没有珍惜，失去后不再有流泪的权利。希望他可以遇见他心爱的人，羡慕那个女孩拥有他，拥有他是种小幸运，并给予对方无尽的祝福。
小幸运
我听见雨滴落在青青草地
我听见远方下课钟声响起
可是我没有听见你的声音
认真呼唤我姓名
爱上你的时候还不懂感情
离别了才觉得刻骨铭心
为什么没有发现遇见了你
是生命最好的事情
也许当时忙着微笑和哭泣
忙着追逐天空中的流星
人理所当然的忘记
是谁风里雨里一直默默守护在原地
原来你是我最想留住的幸运
原来我们和爱情曾经靠得那么近
那为我对抗世界的决定
那陪我淋的雨
一幕幕都是你
一尘不染的真心
与你相遇好幸运
可我已失去为你泪流满面的权利
但愿在我看不到的天际
你张开了双翼
遇见你已注定
她会有多幸运
青春是段跌跌撞撞的旅行
拥有着后知后觉的美丽
来不及感谢是你给我勇气
让我能做回我自己
也许当时忙着微笑和哭泣
忙着追逐天空中的流星
人理所当然的忘记
是谁风里雨里一直默默守护在原地
原来你是我最想留住的幸运
原来我们和爱情曾经靠得那么近
那为我对抗世界的决定
那陪我淋的雨
一幕幕都是你
一尘不染的真心
与你相遇好幸运
可我已失去为你泪流满面的权利
但愿在我看不到的天际
你张开了双翼
遇见你的注定oh
她会有多幸运
歌曲名:Fading (Acoustic)
歌手:Anouk
专辑:Lost
The Title - Fading
i'm sure that you're writing it off
and if you're fighting with the idea
that the meaning is lost
then you should stop by
maybe drop me a line
and if it's not too much to ask
then maybe save me some time
'cause i can't spend a day
without a thought about you
and the things i'd like to say
i just can't make come out
when your eyes meet mine
we're standing in the fading moonlight
making the most of the brightest stars in the sky
and of you at my side
i've been sitting counting the days
from the moment that we met
until the second you stayed in my arms
so sure that we knew who we were
in the sense of what it meant to feel completely secure
'cause i can't spend a day
without a thought about you
and the things i'd like to say
i just can't make come out
when your eyes meet mine
we're standing in the fading moonlight
making the most of the brightest stars in the sky
and of you at my side
http://music.baidu.com/song/2870657
歌曲名:Fading
歌手:Anouk
专辑:Hotel New York Live Edition
The Title - Fading
i'm sure that you're writing it off
and if you're fighting with the idea
that the meaning is lost
then you should stop by
maybe drop me a line
and if it's not too much to ask
then maybe save me some time
'cause i can't spend a day
without a thought about you
and the things i'd like to say
i just can't make come out
when your eyes meet mine
we're standing in the fading moonlight
making the most of the brightest stars in the sky
and of you at my side
i've been sitting counting the days
from the moment that we met
until the second you stayed in my arms
so sure that we knew who we were
in the sense of what it meant to feel completely secure
'cause i can't spend a day
without a thought about you
and the things i'd like to say
i just can't make come out
when your eyes meet mine
we're standing in the fading moonlight
making the most of the brightest stars in the sky
and of you at my side
http://music.baidu.com/song/2824327
自己翻译的哦！
Fading - Fenech-Soler
Was it just a faded night
这难道是一个普通的夜晚吗？
Serpents in the sky
连空中都出现了蛇
We can’t hide anymore
我们无处可藏
Was it just a bridge to far
这是到远方的一座桥吗
Strangers with lonely hearts
孤独的心，陌生的人
A world apart she said
一个分离的世界，她说
We’ve gone started over
我们重新开始
I can’t take it anymore
我再也受不了了
Cause we keep facing into a storm
我们直面暴风雨
Watch the rise and fall
看着日升日落
Could’ve had it all
所有的都经历过了
Ocean and rising stars
海洋的升起的星星
Close your eyes and bleed
血正在流，闭上你的眼睛吧
Drifting always sleep
在睡梦中中漂流
Letting go of who we are
不要在意我们是谁
The sun is a fading star
太阳是颗褪色的星星
If I could just feel one time
如果我能再感受一次
Made you by design I find you there
故意在那找到你
Or is it all in my head
这都在我的脑海里
The words that were left unsaid
剩下的话，不必再说
They feel dead to me
他们感觉我要死了
Watch the rise and fall
看着日升日落
Could’ve had it all
所有的都经历过了
Ocean and rising stars
海洋的升起的星星
Close your eyes and bleed
血正在流，闭上你的眼睛吧
Drifting always sleep
在睡梦中中漂流
Letting go of who we are
不要在意我们是谁
The sun is a fading star
太阳是颗褪色的星星
The sun is a fading star
太阳是颗褪色的星星
（Rising）升起
（Rising）升起
（Rising）升起
We’ve gone started over
我们重新开始
I can’t take it anymore
我再也受不了了
Cause we keep facing into a storm
我们直面暴风雨
Watch the rise and fall
看着日升日落
Could’ve had it all
所有的都经历过了
Ocean and rising stars
海洋的升起的星星
Close your eyes and bleed
血正在流，闭上你的眼睛吧
Drifting always sleep
在睡梦中中漂流
Letting go of who we are
不要在意我们是谁
The sun is a fading star
太阳是颗褪色的星星
The sun is a fading star
太阳是颗褪色的星星
望！thank you！have a nice day!
更多扩展补充
扩展
十分感谢呢，你会做LRC歌词么？
补充
不会，不好意思啊。
扩展
没事，已经很谢谢了
You say you love me but they feel like
你说你爱我但是他们觉得那之于我
words to me
就是浮云
But this just aint workin, still thinkin
朋友的劝说似乎不起作用，我还是傻乎乎的想着
you can run over me
你会回心转意
Drifting, settling up to a foreign place.
独自一人来到一个完全陌生的地方
If i can't see what's in front of me,
在我眼前的景象
It's a mystery, but then apparently
似乎是秘密 话说回来 又像单纯的表面
Things just aint the same, and i'm ready
结局马上就要峰回路转，我为改变
for change.
蓄势待发
Go on, be gone, bye bye, so long.
出发吧，向以前的自己说声再见
Can't you see that you're fading fading
你难道没有发现你已经渐渐的消失
fading faaading away away away away.
在我的生活，消失，消失。
I opened up my eyes and i finally
当我睁开眼睛，我才意识到眼前的
realized today,
美好
Today is too late, you're fading away.
如果你能离开的早点，我就能更早的发现生活的
美好
Put a sock in it, just stop running your
闭嘴，该死的，你能不能安静点，
mouth, got my mind made up,
让我的大脑清醒一点
I aint comin back again, no way, no way,
我拒绝回到从前，绝不！没门！你想都别想！
no way, no way.
Cuz i'm so fed up boy, you got me messed
喂，我已经受够了，你让我的生活一团
up
糟
If we're hookin back up, don't press your
某天如若我们在转角处相遇，不要期望我还会和
luck today.
你有什么瓜葛
I'm blowing you away.
这回换我甩开你
Things just aint the same, and i'm ready
结局马上就要峰回路转，我为改变
for change.
蓄势待发
Go on, be gone, ta ta, so long.
走吧，谢谢你，你可以滚了。
Can't you see that you're fading fading
你难道没有发现你已经渐渐的消失
fading faaading away away away away.
在我的生活，消失，消失。
I opened up my eyes and i finally
当我睁开眼睛，我才意识到眼前的
realized today,
美好
Today is too late, you're fading away.
如果你能离开的早点，我就能更早的发现生活的
美好
Saw you turn into a ghost right in front
我的眼睛看到的是你已经
of my eyes.
成为一个魔鬼
Tell me what's a girl to do when she's
告诉我当一个女孩已经被逼到走投无路时
crying inside?
她会做出什么极端的事？
I'm about to go insane, i'm jumping off
哈，就算要我变成神经病，我也要跳出
this train,
这种绝境
Whether wrong or right, i'll be gone by
管他对不对，今夜我就要
night.
离开
Can't you see that you're fading fading
你难道没有发现你已经渐渐的消失
fading faaading away away away away.
在我的生活，消失，消失。
I opened up my eyes and i finally
当我睁开眼睛，我才意识到眼前的
realized today,
美好
Today is too late, you're fading away.
如果你能离开的早点，我就能更早的发现生活的
美好
歌曲名:Fading
歌手:Kelly Clarkson
专辑:Don'T Waste Your Time
The Title - Fading
i'm sure that you're writing it off
and if you're fighting with the idea
that the meaning is lost
then you should stop by
maybe drop me a line
and if it's not too much to ask
then maybe save me some time
'cause i can't spend a day
without a thought about you
and the things i'd like to say
i just can't make come out
when your eyes meet mine
we're standing in the fading moonlight
making the most of the brightest stars in the sky
and of you at my side
i've been sitting counting the days
from the moment that we met
until the second you stayed in my arms
so sure that we knew who we were
in the sense of what it meant to feel completely secure
'cause i can't spend a day
without a thought about you
and the things i'd like to say
i just can't make come out
when your eyes meet mine
we're standing in the fading moonlight
making the most of the brightest stars in the sky
and of you at my side
http://music.baidu.com/song/7877267
掌声衰落