Multicarrier Code-Division-Multiple Access (MC-CDMA) is a promising candidate for the downlink for the fourth generation of mobile radio systems. MC-CDMA systems offer the spectral efficiency of orthogonal frequency division multiplexing (OFDM) combined with CDMA to combat multi-user interference losses and to offer a flexible multi-user access scheme. This paper from German Aerospace Center investigates rotated Walsh-Hadamard spreading matrices for a broadband MC-CDMA system with robust channel estimation in the synchronous downlink. The similarities between rotated spreading and signal space diversity are outlined. In a multi-user MC-CDMA system, possible performance improvements are based on the chosen detector, the channel code, and its Hamming distance.