TAILIEUCHUNG - Adaptive WCDMA (P15)

Wideband CDMA network sensitivity THEORY AND PRACTICE OF MULTIUSER DETECTION Advanced wireless Code Division Multiple Access (CDMA) systems employing multiuser receivers described in Chapters 13 and 14 have gained a lot of attention during the recent years. In the beginning, the research was purely academic. In order to fully exploit CDMA capabilities, the third-generation wideband CDMA networks [1] have been planned to include interference cancellation (IC), as soon as it becomes feasible to implement (for details, see also Chapter 17). A number of overview papers [2–6] discuss basic features of multiuser detection (MUD) and IC techniques. Among linear IC schemes, decorrelating. | Adaptive WCDMA Theory And Practice. Savo G. Glisic Copyright 2003 John Wiley Sons Ltd. ISBN 0-470-84825-1 15 Wideband CDMA network sensitivity THEORY AND PRACTICE OF MULTIUSER DETECTION Advanced wireless Code Division Multiple Access CDMA systems employing multiuser receivers described in Chapters 13 and 14 have gained a lot of attention during the recent years. In the beginning the research was purely academic. In order to fully exploit CDMA capabilities the third-generation wideband CDMA networks 1 have been planned to include interference cancellation IC as soon as it becomes feasible to implement for details see also Chapter 17 . A number of overview papers 2-6 discuss basic features of multiuser detection MUD and IC techniques. Among linear IC schemes decorrelating detectors 7-9 belong to a major group of multiuser receivers. As it was discussed in Chapter 13 the basic idea of the decorrelator is to use the inverted cross-correlation matrix to subtract interference caused by other active users that is multiple access interference MAI . With perfect knowledge of code cross-correlations of all active users the effect of all MAI can be eliminated at the cost of noise enhancement. One important benefit of the ideal decorrelator is that it does not require knowledge of the users power levels or amplitudes and is thus robust to power fluctuations. On the other hand the complexity and need for updating the matrix inversion can become a bottleneck at high user populations and fast fading environment. Also in reality the cross-correlation matrix must be estimated and that will lead to further imperfections. These imperfections are the focus of this chapter. Although other options such as multistage or linear minimum mean square error LMMSE detectors discussed in Chapter 14 are also considered for these applications 4 in this chapter we will focus our attention on linear decorrelators and their operation in the presence of imperfections. In practice performance of

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