DocumentCode :
1302653
Title :
Performance of constrained and unconstrained adaptive multiuser detectors for quasi-synchronous CDMA
Author :
Iltis, Ronald A.
Author_Institution :
Dept. of Electr. & Comput. Eng., California Univ., Santa Barbara, CA, USA
Volume :
46
Issue :
1
fYear :
1998
fDate :
1/1/1998 12:00:00 AM
Firstpage :
135
Lastpage :
143
Abstract :
It has previously been shown that multiuser interference in a quasi-synchronous code-division multiple-access (QS-CDMA) system can be effectively rejected using a nonadaptive decorrelator. However, the QS decorrelator is orthogonal to the inflated subspace spanned by the undesired users with arbitrary delays in the QS uncertainty interval and, hence, does not perform as well as a decorrelator with a priori knowledge of the delays. Here, we consider a constrained adaptive linear suppression filter which implicitly estimates the delays of the QS undesired signals, and thus approaches the ideal decorrelator of Lupas and Verdu (1990). For QS-CDMA, it is shown through analysis and simulations that the constrained recursive least-squares (C-RLS) algorithm converges faster than an unconstrained RLS adaptive filter, and generally outperforms the nonadaptive QS decorrelator. A cellular quasi-synchronous system is discussed in the present paper
Keywords :
adaptive filters; adaptive signal detection; cellular radio; code division multiple access; convergence of numerical methods; correlation methods; delays; interference suppression; land mobile radio; least squares approximations; radio receivers; radiofrequency interference; recursive filters; synchronisation; C-RLS algorithm; QS decorrelator; QS uncertainty interval; QS-CDMA; a priori knowledge; constrained adaptive linear suppression filter; constrained adaptive multiuser detectors; constrained recursive least-squares algorithm; delays; inflated subspace; multiuser interference; performance; quasi-synchronous CDMA; quasi-synchronous code-division multiple-access; unconstrained RLS adaptive filter; unconstrained adaptive multiuser detectors; undesired signals; Adaptive filters; Algorithm design and analysis; Analytical models; Decorrelation; Delay estimation; Interference constraints; Multiaccess communication; Multiple access interference; Nonlinear filters; Uncertainty;
fLanguage :
English
Journal_Title :
Communications, IEEE Transactions on
Publisher :
ieee
ISSN :
0090-6778
Type :
jour
DOI :
10.1109/26.655412
Filename :
655412
Link To Document :
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