Editing Rake receiver

{{Short description|Radio receiver}}
{{Use dmy dates|date=January 2022}}
A '''rake receiver''' is a radio [[receiver (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 propagation|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 (telecommunications)|transmission]] characteristics of each transmission path. This could very well result in higher [[signal-to-noise ratio]] (or [[Eb/N0|E<sub>b</sub>/N<sub>0</sub>]]) 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 propagation|line of sight]]) wave pulse through 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.<ref name="ref 1">{{cite book| title=Principles of Spread-Spectrum Communication Systems, 4th ed.| year=2018|last1=Torrieri|first1=Don}}</ref><ref name="ref 2">{{cite book| title=Principles of Mobile Communication, 4th ed.| year=2017|last1=Stuber|first1=Gordon L.}}</ref><ref name="ref 3">{{cite book| title=Digital Communications, 5th ed.| year=2008|last1=Proakis|first1=John G.|last2=Salehi|first2=Masoud}}</ref>

== Mathematical definition ==
A rake receiver utilizes multiple correlators to separately detect the ''M'' strongest multipath components. Each correlator output may be quantized using several bits. Demodulation and bit decisions are then based on the weighted outputs of the ''M'' correlators, which provide a better estimate of the transmitted signal than is provided by a single component. 

== History ==
Rake receivers must have either a general-purpose [[CPU]] or some other form of [[digital signal processing]] hardware in them to process and correlate the intended signal. Rake receivers only became common after 16-bit CPUs capable of signal processing became widely available.  The rake receiver was patented in the US by [[Robert Price (engineer)|Robert Price]] and [[Paul Green (engineer)|Paul E. Green]] in July 1956,<ref>{{cite web|title=UMTS / 3G History and Future Milestones|url=http://www.umtsworld.com/umts/history.htm|access-date=12 November 2010}}</ref> (U.S. Pat. No. 2,982,853) but it took until the 1970s to design practical implementations of the receiver.

Radio astronomers were the first substantial users of rake receivers in the late 1960s to mid-1980s as this kind of receiver could scan large sky regions yet not create large volumes of data beyond what most data recorders could handle at the time. [[Astropulse]], which is part of the [[SETI@Home]] project, uses a variant of a rake receiver as part of its sky searches—so this kind of receiver is still current for the needs of radio astronomy.

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

Rake receivers are also used in [[radio astronomy]]. The [[Australia Telescope National Facility|CSIRO Parkes radio telescope]] and [[Jodrell Bank Observatory|Jodrell Bank telescope]] have [[filter-bank]] recording formats that can be processed in real time by software-based rake receivers.

In a Flexible rake Receiver, [[signal (electrical engineering)|signal]] reception is performed with a single [[Cross-correlation|correlator]] engine and a [[stream (computing)|stream]] [[buffer (computer science)|buffer]] storing the entire delay spread of [[baseband]] [[input/output]] (I/O) [[sample (signal)|sample]]s. The primary advantage of the rake receiver is flexible [[Multipath propagation|multipath]] allocation supporting enhanced [[modularity (programming)|modularity]] of the receiver and resource sharing among multiple [[channel (communications)|channel]] decoders.

== References ==
{{Reflist}}

{{DEFAULTSORT:Rake Receiver}}
[[Category:Telecommunications equipment]]
[[Category:Radiofrequency receivers]]
[[Category:Code division multiple access]]