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