DS-SS Rake Receiver

Rake receiver for Direct-Sequence Spread-Spectrum (DS-SS) is to provide path diversity for reduce the effects of multipath selective fading. It can be done 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 the next stage it will combined to make use of the different transmission characteristics of each transmission path.
The multipath channel through which a radio wave transmits wirelessly can be viewed as the original transmitted wave plus many delayed copies of the original transmitted wave, each with a different magnitude and time-of-arrival at the receiver. Since each multipath component also contains the original information, at the receiver, if the magnitude and time-of-arrival (phase) of each multipath component can be known, then all the multipath components can be added coherently to bring up the information reliability. This could result in higher signal-to-noise ratio in a multipath environment.
In a mobile radio channel reflected waves arrive with small relative time delays, self interference will occurs. This can be overcome by Direct-Sequence Spread-Spectrum. As we know DS-SS is claimed to have the properties that makes it less vulnerable to multipath reception. The Rake receiver architecture allows an optimal combining of energy received over paths with different. This can avoid wave cancellation (fading of waves) if delayed paths arrive with phase differences and appropriately weights signals coming in with different signal-to-noise ratios.