Symbol rate processing for the downlink of DS-CDMA systems

Many services of third-generation (3G) mobile radio systems will have higher data rates in the downlink than in the uplink. We propose to utilize adaptive antennas at the base stations because spatial interference suppression is able to reduce the near-far effect in the downlink of single-user detection direct-sequence (DS) code division multiple access (CDMA) systems. Besides the channel parameters in terms of directions of arrival, delays, and medium-term average path attenuations which are estimated in the uplink, we also take into account the correlation properties of the spreading and scrambling codes. In DS-CDMA the users are distinguished by different spreading codes, which change over time due to scrambling. In Brunner et al. (see Proc. EPMCC, p.375-80, 1999), the beamforming vectors at the base station were computed slotwise, whereas in this paper, we favor a symbol-rate beamforming at the base station. The new approach optimizes the actual values of the decision variables of the RAKE demodulators at the receivers. The superiority of the symbol rate beamforming algorithm compared to slotwise beamforming is shown by bit error rate (BER) simulations.