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In this paper, we discuss multiuser detection based on wideband code division multiple access (WCDMA) protocols. Multirate transmission and spreading method of WCDMA systems introduce a problem that characteristics of multiple access interference (MAI) change periodically. General adaptive algorithms will not work in that situation. An improved adaptive minimum mean-squared error (MMSE) multiuser detection algorithm is proposed to solve the problem. During our processing procedures, output vector sequence, which is cyclostationary, of matched filter is divided into several stationary vector sequences by down sampling. Then we respectively process those sequences using a bank of adaptive transversal filters using least-mean-square (LMS) algorithm. The improved algorithm is analyzed under FDD mode of WCDMA protocols, in which S(2) short scrambling codes are applied. Simulation result shows that improved multiuser detection algorithm solves multirate problems well and effectively suppresses MAI under AWGN channels and multipath time-varying channels according to IMT-2000 Vehicular Model A. The improved adaptive MMSE algorithm has better performance than conventional detector and improved constant modulus algorithm using the same thinking.