Joint transmission (JT), an alternative rationale for the downlink of time division CDMA using multi-element transmit antennas

In the 3^rd Generation Partnership Project (3GPP) time division CDMA (TD-CDMA) has been selected as the air interface for the TDD (time division duplexing) bands of 3^rd generation (3G) mobile radio systems. In the case of TDD the same channel impulse responses are valid for both the uplink and the downlink. In state-of-the-art TD-CDMA characterized by joint data detection (JD) this equality cannot be exploited for enhancing the system performance and reducing system complexity. A novel TD-CDMA downlink transmission scheme is proposed. This scheme is termed joint transmission (JT). It utilizes the knowledge of the channel impulse responses gained by channel estimation at the base station in such a way that channel estimators are no longer required at the mobile stations and the computational expense of data detection is dramatically reduced. The scheme easily lends itself to the utilization of multi-element transmit antennas. Further, its application is not restricted to systems of the type TD-CDMA