Near-far resistance of multicarrier CDMA systems

Multicarrier (MC) CDMA systems have been developed and rapidly gained popularity as they capitalize on both the resilience of MCM (multicarrier modulation) to MUI and the robustness of direct-sequence (DS) CDMA against frequency selectivity to mitigate both MUI and the intersymbol interference (ISI) caused by time dispersive channels. However, the well-known near-far problem in a multiuser setting still places fundamental limitations on the performance of MC-CDMA communication systems, and this issue has been considered by very few papers. We derive the theoretical near-far resistance of the MMSE detector in the MC-CDMA uplink (with and without cyclic prefix, CP). It turns out that the near-far resistance of MC-CDMA without CP has the same form as that of DS-CDMA, except that the user codes are IFFT transformed. Our formulation for near-far resistance is applied to either blind or non-blind MMSE detectors. Computer simulations confirm our theoretical findings.