RAKE receivers suffer degradation in performance under fast fading due to errors in channel state estimation. The wide-sense stationary uncorrelated scatterer channel model lends itself to time-frequency canonical representation, and provides additional diversity in the frequency axis. Using the joint spatial-multipath-Doppler diversity model based on this canonical representation, we propose a nonlinear space-time-frequency decorrelating decision-feedback multiuser detector for synchronous CDMA which utilizes decisions of the stronger users when forming the decisions for the weaker ones. Simulation results based on realistic fast-fading assumptions demonstrate that the proposed decorrelating decision-feedback multiuser detector promises substantially improved bit-error-rate performance compared to space-time-frequency decorrelating multiuser detector for the weaker users, while the error probability of the weakest user approaches the single-user bound as the interferers grow stronger. The proposed detector exhibits strong resistance to the near-far effect for all users and the time-complexity-per-bit is linear in the number of users.