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Short note: RAKE receiver

Short answer

A RAKE receiver is a CDMA receiver that exploits multipath by assigning a correlator finger to each resolvable path. Each finger correlates with the appropriate delayed PN code, and the outputs are co-phased, weighted by path strength, and summed, converting destructive multipath into diversity gain. Used in IS-95 and WCDMA.

Write a short note on RAKE receiver.

A RAKE receiver is a receiver used in CDMA (DSSS) systems that collects and combines the energy of several multipath components of the same signal, providing multipath (time) diversity. It is named after a garden rake because it has several "fingers".

       +->[Finger 1: corr, τ1]-Z1-(xα1)-+
r(t) --+->[Finger 2: corr, τ2]-Z2-(xα2)-(Σ)-> decide
       +->[Finger M: corr, τM]-ZM-(xαM)-+
  • Each finger is a correlator using the PN code delayed to match one multipath component. Paths more than one chip apart are uncorrelated, so each finger isolates one path.
  • Outputs are weighted by path strength, α_m = Z_m²/ΣZ_m², co-phased and summed: Z' = Σ α_m Z_m.
  • If one path fades, others still contribute, so fading is greatly reduced.
  • Turns multipath, normally harmful, into a gain. Used in IS-95 (3 fingers in the mobile, 4 at the base station) and WCDMA.

✓ Answer checked by Claude Opus 5.5 (high effort)

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