CDMA downlink transmission with transmit antenna arrays and power control in multipath fading channels

Wireless code-division multiple-access (CDMA) cellular downlink communications with transmit antenna arrays in multipath fading channels is studied. Various array signal processing techniques at the transmit end are investigated and compared under various settings, in conjunction with power control. No instant downlink channel information is assumed; however, the obtained results are also compared with results assuming ideal feedback. The study is carried out for both circuit-switched and packetswitched systems, where different goals are pursued and different conclusions are drawn. In particular, it is found that the traffic type impacts the algorithm choice in downlink transmission, and that there is no need to seek optimum power control/allocation schemes, which are either too complex or infeasible in practice. Another interesting conclusion is that, even though feedback does not help much for packet-switched systems, it does help for circuit-switched systems, the gain of which increases with the number of antennas.