Optimization of the pilot-to-data power ratio for DS-CDMA with linear interference suppression

We consider a Direct Sequence (DS-) CDMA system with orthogonally multiplexed pilot signals and minimum mean square error (MMSE) data and channel estimation. Large system analysis is used to optimize the pilot-to-data power ratio (PDR). Specifically, the PDR is selected to minimize the probability of error subject to a transmitted power constraint. Both flat and frequency-selective fading channels are considered. When the MMSE filter averages over the channels of the interferers, the optimal PDR is less than that for the matched filter. That is, the MMSE filter benefits from allocating more power to the data. For the case considered, when the MMSE filter directly incorporates channel estimates, the optimal PDR is greater than that for the matched filter.