Fast finger selection for GRAKE

This paper presents a low complexity finger selection method for the generalized RAKE receiver (GRAKE). GRAKE is an attractive receiver for CDMA systems, exhibiting nice gains over the standard RAKE receiver in dispersive channels, while maintaining the same structure. GRAKE is a linear whitening receiver, treating various sources of interference as colored noise. A GRAKE receiver makes use of so-called noise fingers (i.e. fingers not aligned with multipath delays) to effect interference suppression. Our method focuses on the selection of a subset of noise fingers to combine along with the standard signal fingers. We derive an exact expression for the SNR increment due to the placement of an extra finger, and an easily computed approximation to that expression. We describe two variants of a simple search algorithm based on the approximate SNR increment. We test the performance of our algorithm for the WCDMA system. Our simulation results show that GRAKE with our method exhibits gains of about 2 dB over RAKE. Our method also matches the performance of the more complex ML search algorithm, and it comes within 1/2 dB of an idealized GRAKE receiver.