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Convergence analysis of chip- and fractionally spaced LMS adaptive multiuser CDMA detectors

Lim, T. J., Gong, Y. and Farhang-Boroujeny, B. (2000) Convergence analysis of chip- and fractionally spaced LMS adaptive multiuser CDMA detectors. IEEE Transactions on Signal Processing, 48 (8). pp. 2219-2228. ISSN 1053-587X

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To link to this item DOI: 10.1109/78.852003


This paper analyzes the convergence behavior of the least mean square (LMS) filter when used in an adaptive code division multiple access (CDMA) detector consisting of a tapped delay line with adjustable tap weights. The sampling rate may be equal to or higher than the chip rate, and these correspond to chip-spaced (CS) and fractionally spaced (FS) detection, respectively. It is shown that CS and FS detectors with the same time-span exhibit identical convergence behavior if the baseband received signal is strictly bandlimited to half the chip rate. Even in the practical case when this condition is not met, deviations from this observation are imperceptible unless the initial tap-weight vector gives an extremely large mean squared error (MSE). This phenomenon is carefully explained with reference to the eigenvalues of the correlation matrix when the input signal is not perfectly bandlimited. The inadequacy of the eigenvalue spread of the tap-input correlation matrix as an indicator of the transient behavior and the influence of the initial tap weight vector on convergence speed are highlighted. Specifically, a initialization within the signal subspace or to the origin leads to very much faster convergence compared with initialization in the a noise subspace.

Item Type:Article
Divisions:Faculty of Science
ID Code:19167
Uncontrolled Keywords:LMS filter, MSE, adaptive multiuser detectors, adjustable tap weights, bandlimited baseband received signal, chip rate, chip-spaced detection, code division multiple access, convergence analysis, convergence speed, correlation matrix, eigenvalue spread, fractionally spaced detection, fractionally spaced multiuser CDMA detectors, input signal, least mean square, mean squared error, noise subspace, sampling rate, signal subspace, tap-input correlation matrix, tap-weight vector, tapped delay line, transient behavior
Publisher:Institute of Electronic and Electronics Engineers

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