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We develop a novel multistage group-blind multiuser detection technique for reverse link in multi-cell direct sequence (DS) code-division multiple access (CDMA) systems. This approach fully utilizes all known users' information, performs interference cancellation (IC) to suppress the interferers within the cell, and exploits blind adaptive decision-directed (DD) MMSE detector to suppress the inter-cell interference. This process can be made iterative and in the multistage process, the tentative decision bits from DD-MMSE detectors can be fed back to the IC part to make interference regeneration more accurate. A simplified RLS (SRLS) algorithm is derived particularly for DD-MMSE detectors and steady-state SIR performance of the SRLS algorithm is analyzed. It is shown that the proposed detector with SRLS algorithm is sufficient to perform accurate multiuser detection and has significant performance gain over that of the pure blind detectors and the non-blind detectors for the given scenario. Moreover, compared with the conventional RLS algorithm, the SRLS algorithm has lower computational complexity and the convergence speed is faster. We also develop two group-blind channel estimation methods to estimate the effective signature waveforms in multipath fading channel. It is seen that the group-blind channel estimation methods using updated received signal correlation matrix can effectively combat the mismatch problem faced by pure blind detectors.