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Multiuser detection in multirate DS/CDMA communications

In this paper, multiuser detection in multirate long-code DS/CDMA systems is considered. Regarding the slower transmission rate of a symbol in the system as repeated transmission of the symbol at the fastest rate in the system, we reduce the multirate transmission model to a single-rate one with repeated transmission of symbols which can be viewed as a binary repetition code or a form of time-diversity signaling. Thus, traditional multiuser detection for single-rate encoded data can be applied. Several typical multiuser detection methods, such as decorrelating, MMSE and parallel interference cancellation (PIC), are investigated for multirate systems. An integrated preconditioned soft decision PIC (PSD-PIC) structure is proposed to improve the performance of partitioned decorrelating (or MMSE) multirate detector. Numerical simulations show that the performance of integrated PSD-PIC is better than that of integrated hard decision PIC (HD-PIC) for multirate systems.