EURASIP Journal on Applied Signal Processing
Volume 2002 (2002), Issue 12, Pages 1365-1376
doi:10.1155/S1110865702209087

Blind Reduced-Rank MMSE Detector for DS-CDMA Systems

Xiaodong Cai,1 Hongya Ge,2 and Ali N. Akansu2

1Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis 55455, MN, USA
2Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark 07102, NJ, USA

Received 18 March 2002; Revised 14 August 2002

Copyright © 2002 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We first develop a reduced-rank minimum mean squared error (MMSE) detector for direct-sequence (DS) code division multiple access (CDMA) by forcing the linear MMSE detector to lie in a signal subspace of a reduced dimension. While a reduced-rank MMSE detector has lower complexity, it cannot outperform the full-rank MMSE detector. We then concentrate on the blind reduced-rank MMSE detector which is obtained from an estimated covariance matrix. Our analysis and simulation results show that when the desired user′s signal is in a low-dimensional subspace, there exists an optimal subspace so that the blind reduced-rank MMSE detector lying in this subspace has the best performance. By properly choosing a subsspace, we guarantee that the optimal blind reduced-rank MMSE detector is obtained. An adaptive blind reduced-rank MMSE detector, based on a subspace tracking algorithm, is developed. The adaptive blind reduced-rank MMSE detector exhibits superior steady-state performance and fast convergence speed.