Reduced-rank minimum variance receiver for asynchronous CDMA systems

The minimum variance receiver has been proposed to blindly suppress the multiple-access interference in CDMA channels by minimizing the receiver´s output variance based on constrained optimization. We consider the reduced-rank minimum variance receiver in asynchronous CDMA channels. The reduced-rank detector uses a reduced-rank approximation of the covariance matrix of the received data. When the covariance is known, the reduced-rank receiver cannot perform better than the full-rank receiver. However, when the covariance matrix is estimated, we demonstrate that the optimal reduced-rank receiver outperforms the full-rank receiver. The reduced-rank receiver is implemented adaptively using a subspace tracking algorithm; its performance is better than the conventional full-rank recursive least-square adaptive receiver