Coordinated multi-antenna processing for cellular underlay device-to-device communication

We propose linear coordinated transmit-receive beamforming methods for spatial underlay direct device-to-device (D2D) communication in cellular networks where the user terminals (UTs) employ multiple antenna elements. For a D2D terminal pair, direct communication is a beneficial alternative compared to the cellular mode, where the UTs communicate to each other via a base station (BS) that acts as a relay. For mode selection, spatial scheduling, and transmitter-receiver design, we formulate a joint weighted sum-rate (WSR) maximization problem, and adopt an optimization framework where the WSR maximization is carried out via weighted sum mean-squared-error (MSE) minimization. Furthermore, we propose to connect the uplink and downlink design problems - for the case when the BS relays the data - via scalar weight optimization. According to the results, D2D communication can provide very high data rates for the D2D pair and at the same time save resources for other UTs that employ regular cellular connections.