RAKE finger placement for CDMA downlink equalization

We consider the problem of interference suppression in a multipath DS-CDMA downlink using a general RAKE receiver structure with M fingers and arbitrary finger delays. Utilizing asymptotically optimal sampling design theory, a new design approach that optimizes the receiver performance over the finger delays is proposed. It provides a set of delays which are asymptotically optimal for large M, and sheds light on the behavior of various finger placements' performance, as the number of fingers increases, and on the effect of the smoothness of the underlying chip pulse. Numerical results show that for certain Rayleigh fading channels and several chip pulses, the proposed finger placement is superior to the chip periodically-spaced finger placement.