Universal code designs for widely-linear multiuser detection in downlink MC-CDMA

This paper deals with multiuser detection for multicarrier code-division multiple-access (MC-CDMA) systems, employing either zero-padded or cyclic-prefixed transmission techniques. For both systems, we consider widely-linear finite-impulse response (WL-FIR) estimators, which process both the received signal and its complex conjugate version. With regard to downlink configurations, it is shown that, if the number of users does not exceed a given threshold and their codes are appropriately designed, channel-irrespective WL-FIR zero-forcing symbol recovery is possible. In particular, some spreading code examples are provided, which satisfy our design rules.