Rake receiver

Rake receiver

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.

References

Citation
last1 = Ziemer | first1 = R. E.
last2 = Tranter | first2 = W. H.
title = Principles of Communications: Systems, Modulation, and Noise, 5th Edition
publisher = Wiley
date = August 2001
year = 2001
isbn = 978-0-471-39253-8

cite journal
author = Kyungwhoon Cheun
title = Performance of direct-sequence spread-spectrum RAKE receivers with random spreading sequences
journal = IEEE Transactions on Communications
volume = 45
issue = 9
pages = 1130–1143
date = September 1997
url= http://ieeexplore.ieee.org/iel3/26/13551/00623079.pdf?isnumber=13551∏=STD&arnumber=623079&arnumber=623079&arSt=1130&ared=1143&arAuthor=Kyungwhoon+Cheun
doi = 10.1109/26.623079 (See introduction for a description of what a rake receiver is.)


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