Novel multiuser interference canceling scheme in TDD-CDMA systems

Conventional multiuser interference canceling is always done in the uplink. A novel multiuser processing scheme for the downlink of TDD-CDMA (time division duplex-code division multiple access) systems was proposed. The downlink multipath channel parameter can be estimated from the uplink. The instantaneous channel parameter is used to calculate the spreading and despreading codes for different users. The optimal criterion of the generation of these codes was presented, so that the multiple access interference can be greatly reduced. Numerical results show that the scheme can increase the signal to noise ratio as compared with conventional CDMA systems which use Gold sequence as spreading code.