Abstract: The minimum mean square error (MMSE) multiuser detectors based on signal-subspace are deeply investigated. Fast and stable yet another subspace tracker(FSYAST)and an improved MMSE multiuser detector is designed to solve the problems of detecting performance degradation caused by eigenvalue estimation errors. The simulation results showed that, the performance of the proposed MMSE detector approaches that of the singular-value decomposition-based subspace multiuser detectors.