Performance of adaptive antennas for the TD-CDMA downlink under special consideration of multi-directional channels and CDMA code pooling

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 radi o systems (3G systems), In many investigations it has been shown that the u plink performance of TD-CDMA, or, more generally, of time slotted CDMA air interfaces, can be considerably enhanced by utilizing multi-element adaptiv e receiving antennas, for which mature algorithms of spatial-temporal signa l processing are available. However, the application of adaptive multi-elem ent transmit antennas in the downlink of such systems has not yet been exte nsively studied. In this paper, first a transmission model which allows the inclusion and consideration of adaptive transmit antennas in the TD-CDMA d ownlink is developed. Then, based on this model, an algorithm for implement ing 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 illus trated by simulation results. Special attention is paid to the support of h igher data rates by CDMA code pooling.