Rake receiver
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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.
[edit] References
- Ziemer, R. E.; Tranter, W. H. (August 2001). Principles of Communications: Systems, Modulation, and Noise, 5th Edition. Wiley. ISBN 978-0-471-39253-8.
- Kyungwhoon Cheun (September 1997). "Performance of direct-sequence spread-spectrum RAKE receivers with random spreading sequences". IEEE Transactions on Communications 45 (9): 1130–1143. doi:. http://ieeexplore.ieee.org/iel3/26/13551/00623079.pdf?isnumber=13551∏=STD&arnumber=623079&arnumber=623079&arSt=1130&ared=1143&arAuthor=Kyungwhoon+Cheun. (See introduction for a description of what a rake receiver is.)
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