Two-dimensional block-spread CDMA relay using virtual-four-antenna STCDTD

Cooperative communication networks can exploit the spatial diversity inherent in a multiuser system by allowing users to cooperate and relay other users' messages to a destination. Avoiding the multiple-access interference (MAI) while taking full advantage of the multiuser cooperative multiple-input-multiple-output (Co-MIMO) is still an interesting problem. In this paper, we propose a relay scheme that combines the source user's two antennas and the relay user's two antennas to form a virtual-four-antenna space-time cyclic delay transmit diversity (STCDTD), and explore 2-D block-spread code-division multiple access (CDMA) to achieve MAI-free uplink transmission. The theoretical error probability of the proposed scheme is described, when a signal is transmitted through a multiple-access Rayleigh fading channel. Computer simulations indicate that the proposed scheme is able to avoid the MAI over a slow fading channel and to improve the bit error rate (BER) significantly.