Transmit array processing for CDMA downlinks operating in mixed service environments

It is expected that in the near future the demands for high-data-rate services, especially in the downlink of mobile radio systems, will dramatically increase. This expectation is currently being reflected by the lively high-speed-downlink-packet-access (HSDPA) standardization efforts within 3GPP. CDMA mobile radio standards, e.g. the UTRA-FDD mode, are especially prepared for such requirements by means of orthogonal variable spreading factor-codes allowing the coexistence of high- and low-data-rate users. To achieve high data-rates, low spreading factors have to be utilized, which goes along with the massive impact of interference and noise degrading the system performance. Moreover, a high system load has to he admitted to simultaneously support a sufficient number of mobile stations (MSs). To cope with these demands, currently the employment of adaptive antennas at the base station (BS) transmitters to enhance the carrier-to-interference and-noise-ratios (CINRs) at the receiver inputs of the MSs is under discussion. If among the MSs served by the same BS high and low data rate links coexist, MS specific minimum CINR requirements have to be fulfilled. Thus, transmit array processing and power control (PC) techniques should explicitly be prepared to cope with these demands. In the paper a PC which aims at adjusting equal ratios of the present CINR and the minimum MS specific CINR requirement at all MSs is derived. To act jointly with said PC a generalized interference reducing transmit array processing technique taking MS specific CINR requirements into account is introduced. The combination of PC and transmit array processing is discussed and analyzed by simulations.