We consider uplink multi-carrier code-division multiple access (MC-CDMA) systems in a multi-cell environment. It is assumed that all intra-cell users employ Alamouti's simple space-time block coding (STBC), which is known to the base station receiver, but the receiver has no information on whether inter-cell users employ STBC or not. In this case we propose a blind adaptive minimum output energy (MOE) receiver for uplink STBC MC-CDMA, which is designed to perfectly remove the interference from intra-cell users by using the spreading sequence information on all intra-cell users and to reduce the interference from inter-cell users by minimizing the constrained output energy. Analysis and simulation results show that the proposed adaptive receiver has a faster convergence rate and higher steady-state signal-to-interference plus noise ratio (SINR) than a conventional scheme in which only the spreading code information of the desired user is utilized.

We consider device-to-device (D2D) direct communication underlying cellular networks where the D2D link reuses the frequency resources of the cellular downlink. In this paper, we propose a linear precoder design scheme for a base station (BS) and D2D transmitter using the weighted sum-rate of the cellular downlink and D2D link as a cost function. Because the weighted sum-rate maximization problem is not convex on the precoding matrices of BS and D2D transmitters, an equivalent mean-squared error (MSE) minimization problem which is convex on the precoding matrices is proposed by introducing auxiliary matrices. We show that the two optimization problems have the same optimal solution for the precoding matrices. Then, an iterative algorithm for solving the equivalent MSE minimization problem is presented. Through a computer simulation, we show that the proposed scheme offers better weighted sum-rate performance that a conventional scheme.