Subspace Blind Multiuser Detectors In CDMA Communication System

Multiuser detection is one of the key technologies for Code Division Multiple Access communication systems. Blind multiuser detection can adaptively estimate the desired data transmitted by only the desired signature sequence. It can availably suppress Near-Far effect, eliminate multiple access interference and increase the user number. In this paper, the blind multiuser detectors based on subspace are proposed and applied in three CDMA systems. It is arranged as follows(1) Considering the synchronous Direct Sequence (DS) CDMA system through white Gaussian noise channel, the algorithm that tracks signal subspace eigenvalues and eigenvectors throughneural network is proposed. Emulation shows the blind detector using the proposed algorithm can be utilized to deal with the desired user's SNR lower. The algorithm improves the blind detector tracking capability.(2) Considering the asynchronous DS-CDMA system through fading multi-path channel, the blind detector based on subspace tracking is introduced following channel estimation. Though it increases computational complexity, it reduces the bit error rate and enhances its tracking capability.(3) Considering the asynchronous multi-rate DS-CDMA system through fading multi-path channel, it is proposed that the blind detector may use the Projection Approximation Subspace Tracking based on deflation (PASTd) or the adaptive eigenvalue-decomposition based on first-order perturbations. It suppresses Near-Far effect and enhances its tracking capability.