Spreading code optimization and adaptation in CDMA via discrete stochastic approximation

TitleSpreading code optimization and adaptation in CDMA via discrete stochastic approximation
Publication TypeJournal Article
Year of Publication2004
AuthorsKrishnamurthy, V., X. Wang, and G. Yin
JournalInformation Theory, IEEE Transactions on
Pagination1927 - 1949
Date Publishedsep.
Keywordsadaptive-step-size algorithm, CDMA, code division multiple access, code-division multiple-access system, codes, discrete stochastic approximation, fading channels, least mean squares methods, linear minimum mean-square error, MMSE receivers, multipath channels, multipath fading channels, multiuser detection, multiuser detector, optimisation, spreading code optimization, stochastic processes, time-varying channel conditions, time-varying channels, tracking analysis

The aim of this paper is to develop discrete stochastic approximation algorithms that adaptively optimize the spreading codes of users in a code-division multiple-access (CDMA) system employing linear minimum mean-square error (MMSE) receivers. The proposed algorithms are able to adapt to slowly time-varying channel conditions. One of the most important properties of the algorithms is their self-learning capability-they spend most of the computational effort at the global optimizer of the objective function. Tracking analysis of the adaptive algorithms is presented together with mean-square convergence. An adaptive-step-size algorithm is also presented for optimally adjusting the step size based on the observations. Numerical examples, illustrating the performance of the algorithms in multipath fading channels, show substantial improvement over heuristic algorithms.


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