A base station adaptive antenna for downlink transmission in a DS-CDMA system

Multi-rate services are flexibly available by a DS-CDMA technique. Since high-bit rate signals have high transmitted power, they cause large multiple access interference (MAI) to low-bit rate users. A base station adaptive antenna has been studied to suppress the large MAI from the high-speed users. In an uplink case, the adaptive antenna for the low-speed user needs to reduce the received power of the high-speed signals. This is carried out by forming nulls toward the high-bit rate users. In the downlink case, however, the adaptive antenna for the high-speed user needs to reduce the transmitted power toward many low-bit rate users. If there are many low-speed users, we have a shortage of the freedom of the array pattern. That is, the interference to the low-bit rate users cannot be rejected. We propose a novel adaptive array structure to reduce the interference for many user environment