Multiuser receivers that are robust to delay mismatch

We investigate a new robust multiuser signal detector for asynchronous code-division multiple-access uplink channels under delay mismatch. We first formulate a robust decorrelating detector by dividing each user into two virtual users with rectangular chip pulse shapes. To increase the system capacity, a multistage version of the robust decorrelating detector is derived, which can achieve capacity of up to M/(M+1) of the spreading factor, where M is the observation block length. We further propose a robust successive interference cancellation (SIC) implementation. The proposed robust SIC detector adds only a residual error estimation procedure onto the standard SIC detector, so its computational complexity is of the same order of that of the SIC. Performance is investigated via analysis and simulation. Computer simulation results showed that our proposed robust SIC detector outperforms the conventional decorrelating detector when delay estimation error is present, and its performance is close to that of the decorrelating detector with perfect time-delay information. Finally, we generalize the robust SIC detector to the case of nonrectangular chip pulse shapes.