MC-CDMA system with double spreading codes for MAI reduction in the multi-path fading downlink channel

Most of the techniques for multiple access interference (MAI) reduction in code-division multiple access (CDMA) systems are applicable to the uplink, where the base-station knows the signature of all users and can apply a multi-user detection (MUD) strategy. A technique is proposed here to reduce the influence of MAI on the downlink of a multi-carrier CDMA (MC-CDMA) system, without resorting to MUD. The technique is based on the use of a spreading sequences pair for each subscriber. Its limiting factor is that the system capacity, in terms of the active users´ maximum number, is halved as compared to the case in which a single spreading code per user is adopted