关于RAKE接收技术

关于RAKE接收技术

RAKE不是英文缩写，因此也没有全名。一般在通讯领域指RAKE接收机。

RAKE接收机是一种能分离多径信号并有效合并多径信号能量的最终接收机。

原理

多径信号分离的基础是采用直接序列扩展频谱信号。当直扩序列码片宽度为TC时，系统所能分离的最小路径时延差为TC。RAKE接收机利用直扩序列的相关特性，采用多个相关器来分离直扩多径信号，然后按一定规则将分离后的多径信号合并起来以获得最大的有用信号能量。这样将有害的多径信号变为有利的有用号。 应用 RAKE 接收机主要应用在直扩系统中，特别是在民用CDMA（码分多址）移动通信系统中。下图示出一个RAKE接收机，它是专为CDMA系统设计的多径最佳接收机。

以下为英文的定义以及介绍：

A rake receiver is a radio receiver designed to counter the effects of multipath fading. It does this by using several "sub-receivers" called fingers, that is, several correlators each assigned to a different multipath component. Each finger independently decodes a single multipath component; at a later stage the contribution of all fingers are combined in order to make the most use of the different transmission characteristics of each transmission path. This could very well result in higher signal-to-noise ratio (or Eb/N0) in a multipath environment than in a "clean" environment.

The multipath channel through which a radio wave transmits can be viewed as transmitting the original (line of sight) wave plus a number of multipath components. Multipath components are delayed copies of the original transmitted wave traveling through a different echo path, each with a different magnitude and time-of-arrival at the receiver. Since each component contains the original information, if the magnitude and time-of-arrival (phase) of each component is computed at the receiver (through a process called channel estimation), then all the components can be added coherently to improve the information reliability.

The rake receiver is so named because it reminds the function of a garden rake, each finger collecting symbol energy similarly to how tines on a rake collect leaves.

Rake receivers are common in a wide variety of CDMA and W-CDMA radio devices such as mobile phones and wireless LAN equipment.