Rake receiver finger placement for realistic channels

This paper deals with finder placement for Rake receivers, which is a key aspect in the design of receivers for spread-spectrum communications. Finger placement is typically performed using a path searcher, which estimates the power/delay profile (PDP) of the received signal to determine where signal energy is present. A commonly used finger placement approach is to place fingers at delays corresponding to the peaks of the PDP, with a restriction that fingers he no closer than some minimum spacing. Another approach is to place fingers on an equally-spaced grid of delays. For the typical urban (TU) channel model, we quantify performance of the two approaches in terms of acquired signal-to-noise ratio (SNR) and modem bit- error-rate (BER). We show that performance depends primarily on minimum finger spacing and number of fingers. The grid approach performs well when there are enough fingers to collect most of the signal energy. For a channel model in which path delays vary dynamically, we find that the grid approach provides robust performance.