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UMTS-FDD mode downlink system is in practice supposed to be partially loaded due to interference limitations. In other words, some of the orthogonal codes are not used. This indicates that the system is overdetermined and there exists a noise space which can be exploited to cancel the intracell and intercell interference. However, since the scramblers that differentiate the base stations are aperiodic, so are the noise spaces, which necessitates having receiver structures that vary by symbol period. In this work, interference cancellers are obtained by the interpretations of multistage multiuser detection (MUD) structures, whose time varying parts are limited to scramblers and descramblers. MUD equations are formulated from symbol level MMSE-ZF equalization followed by decorrelation among users via polynomial expansion. In the first order, a number of receiver components are replaced by their MMSE equivalents and supplements in order to obtain better SINR figures for the user of interest.
Date of Conference: 28-30 April 2004