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This paper proposes and investigates a novel code-division multiple-access (CDMA) system. This two-layer spreading CDMA (TLS-CDMA) system can combat multiple-access interference (MAI) and multipath interference (MPI) simultaneously and effectively in a multiuser scenario over frequency-selective fading channels. Moreover, a two-layer cell-specific scrambling code is proposed for the TLS-CDMA system in the uplink transmission to efficiently suppress other-cell interference (OCI) in a multicell environment. The proposed TLS-CDMA system allows the two-layer spreading factors to be adapted to the cell structure, the channel conditions, and the number of active users to support variable data rate transmission among multiple users. The superior performance of the TLS-CDMA system over other uplink transmission systems, such as cyclic prefix CDMA (CP-CDMA) and multicarrier CDMA (MC-CDMA), is also illustrated using performance analysis and simulation results.