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Multiuser detection for direct-sequence code-division multiple-access (DS/CDMA) multipath frequency-selective fading channels with intersymbol interference (ISI) is considered. The concept of expanded signal subspace is introduced to characterize the unique property of the CDMA systems in multipath channels. By fully exploiting the structure of the expanded signal subspace, novel expanded approaches are developed to jointly suppress ISI and multiple access interference (MAI). Simulations have verified that the proposed detectors are immune to MAI and ISI and are near-far resistant, significantly outperforming the conventional multiuser detectors.