Optimal sequences combined with antenna arrays to suppress the multiuser interference

Conventional CDMA systems use the PN sequences as the spreading waveforms. In this paper, the spreading and despreading waveforms of different users are optimized by using the instantaneous channel parameters. The maximum receive signal to interference plus noise ratio criterion under the constraint of the fixed transmission power is used to optimize the spreading and despreading waveforms. We find that the proposed scheme can be understood as an adaptive frequency hopping systems. The numerical results indicate that, compared with the conventional spreading waveforms such as Gold sequences, the optimal waveforms can greatly decrease the multiaccess interference. When the optimal waveforms are combined with the antenna arrays, the system performance can be further improved.