Blind Reduced-Rank MMSE Detector for DS-CDMA Systems
- PDF / 931,850 Bytes
- 12 Pages / 600 x 792 pts Page_size
- 3 Downloads / 201 Views
Blind Reduced-Rank MMSE Detector for DS-CDMA Systems Xiaodong Cai Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, USA Email: [email protected]
Hongya Ge Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA Email: [email protected]
Ali N. Akansu Department of Electrical and Computer Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA Email: [email protected] Received 18 March 2002 and in revised form 14 August 2002 We first develop a reduced-rank minimum mean square 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 reducedrank MMSE detector lying in this subspace has the best performance. By properly choosing a subspace, 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. Keywords and phrases: CDMA, blind multiuser detection, reduced-rank, MMSE, subspace tracking.
1.
INTRODUCTION
The major limitation on the performance and channel capacity of direct-sequence (DS) code division multiple access (CDMA) system is the multiple-access interference (MAI) due to simultaneous transmissions. The conventional matched filter (MF) detector cannot suppress MAI effectively, and it suffers from the near-far problem. Since CDMA is not fundamentally MAI limited [1], multiuser detection (MUD) techniques can substantially improve the performance of a CDMA system. While the optimal multiuser detector, which is essentially a maximum-likelihood (ML) sequence detector, has prohibitive complexity, many other multiuser detectors with relatively low complexity such as decision feedback detector, successive or parallel interference canceler, and linear multiuser detectors have been developed [1]. The linear decorrelator removes all cross-correlations between active users and thereby eliminates MAI at the price of enhancing noise [2]. The linear minimum mean square error (MMSE) detector is the optimal linear detector that
maximizes signal-to-interference ratio (SIR) [3, 4]. The blind MMSE detector proposed in [5] minimizes the receiver’s mean output energy (MOE) while constraining the response of the desired user to a constant. It was shown that MOE and MMSE are directly related and minimizing one is equivalent to minimizing the other [5]. In [6], both blind decorrelator and blind MMSE dete
Data Loading...
