Blind multiuser detectors for dual rate DS-CDMA systems over frequency selective channels

Linearly constrained optimization techniques based on the minimization of the output energy have been proposed for the design of single rate DS-CDMA detectors. The goal of this paper is to apply this approach to dual rate systems where low rate users have symbol periods which are multiples of those of high rate users. It is observed that a high rate (HR) user experiences the same frequency selective communication channel during its M consecutive symbol periods corresponding to one symbol period of low rate (LR) users. A bank of M detectors can be derived to detect those M symbols for a HR user by minimizing the total output power of these detectors subject to a common constraint for all M detectors. The unknown constraint can be obtained by further maximizing the resulting power. To detect a LR user, one possible solution is to similarly design M such detectors in its one symbol period and combine all outputs based on some criterion such as maximum ratio combining. An alternative is to directly apply existing constrained optimization methods. It is shown that the performance of the proposed detectors tends to be close to that of the MMSE detector at high SNR.