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Rake receiver, as the name suggests, try to get multiple copies of the transmitted signal. These multiple copies then to be combined to produced better estimate compared if you just have one copy. The philosophy behind it is that if you have multiple copies then you can expect that at least one of it is in good condition, so you get better chance to decode the transmitted signal perfectly.
Rake receiver is conventional receiver and you can find the detail how it works from many standard textbook like digital communication by proakis, etc.
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" each delayed slightly in order to tune in to the individual multipath components. Each component is decoded independently, but at a later stage 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 radio wave transmits wirelessly can be viewed as the original transmitted wave plus many delayed copies of the original transmitted wave but with different magnitude and time-of-arrival at the receiver. Since each multipath component also contains the original information, so at the receiver, if the magnitude and time-of-arrival (phase) of each multipath component can be known (through a process called channel estimation), then all the multipath components can be added coherently to bring up the information reliability.
The rake receiver is so named because of its analogous function to a garden rake, each finger collecting bit or 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.