Multi-user detection in OFDM space time block code for high rate uplink application

In this paper, we propose a multi-user detector for space-time uplink transmission in multi-carrier CDMA systems using a new combination of STBC, OFDM and CDMA spreading. To achieve high rate, CDMA spreading codes are shared between a few users and we use linear STBC decoding to further separate users. The OFDM codewords are built from chips issued from different symbols. The STBC encoder and decoder are placed at the last stage of our multi-user transmitter and receiver respectively. We show that the system is particularly easy to implement when exploiting the space diversity after CDMA detection. Besides, the performance is comparable to the case of a single user STBC system. The proposed system allows for a very high rate multi-user system compared to the conventional CDMA system or combined array-processing technique previously proposed.