Implementation of linear multiuser detectors for asynchronous CDMA systems by linear multi-stage interference cancellation

The decorrelating and the linear, minimum mean-squared error (MMSE) detectors for asynchronous code-division multiple-access communications ideally are infinite memory-length detectors. Finite memory approximations of these detectors require the inversion of a correlation matrix whose dimension is given by the product of the number of active users and the length of the processing window. With increasing number of active users or increasing length of the processing window, the calculation of the inverse may soon become numerically very expensive. In this paper, we prove that the decorrelating and the linear MMSE detector can both be realized by linear multi-stage interference cancellation algorithms with ideally an infinite number of stages. It is shown that for serial multi-stage interference cancellation, depending on the signal-to-noise ratio and the number of active users, only a few stages are necessary to obtain the same BER performance as the ideal detectors. Thus, the complexity can be reduced considerably.