MMSE INTERFERENCE SUPPRESSION FOR DIRECT-SEQUENCE SPREAD-SPECTRUM CDMA

We consider interference suppression for direct-sequence spread-spectr um code-division multiple-access (CDMA) systems using the minimum mean squared error (MMSE) performance criterion. The conventional matched filter receiver suffers from the near-far problem, and requires strict power control (typically involving feedback from receiver to transmit ter) for acceptable performance. Multiuser detection schemes previousl y proposed mitigate the near-far problem, but are complex and require explicit knowledge or estimates of the interference parameters. In thi s paper, we present and analyze several new MMSE interference suppress ion schemes, which have the advantage of being near-far resistant (to varying degrees, depending on their complexity), and can be implemente d adaptively when interference parameters are unknown and/or time-vary ing. Numerical results are provided that show that these schemes offer significant performance gains relative to the matched filter receiver . We conclude that MMSE detectors can alleviate the need for stringent power control in CDMA systems, and may be a practical alternative to the matched filter receiver.