Adaptive antennas for the TD-CDMA downlink under special consideration of high data rate services

Time division CDMA (TD-CDMA) is one of the air interfaces selected in the 3^rd Generation Partnership Project (3GPP) for 3^rd generation mobile radio systems (3G systems). In many investigations it has been shown that the uplink performance of TD-CDMA, or, more generally, of time slotted CDMA air interfaces, can be considerably enhanced by utilizing multi-element adaptive receiving antennas, for which mature algorithms of spatial-temporal signal processing are available. However, the application of adaptive multi-element transmit antennas in the downlink of such systems has not yet been extensively studied. In this paper, first a transmission model which allows the inclusion and consideration of adaptive transmit antennas in the TD-CDMA downlink is developed. Then, based on this model, an algorithm for implementing transmit antenna adaptivity is proposed; the crux of this algorithm is the determination of the antenna weights of the array feeding network based on an energy criterion. Finally, the efficiency of this algorithm is illustrated by simulation results. Special attention is paid to the support of higher data rates by CDMA code pooling