Relaying Robust Beamforming for Device-to-Device Communication With Channel Uncertainty

In this letter, we study robust beamforming design in the scenario that user equipments (UEs) relay the messages from a base station (BS) to a destination UE out of the cellular networks, which is considered as a high-priority device-to-device (D2D) scenario in the 3rd Generation Partnership Project (3GPP) Long-Term-Evolution (LTE) standardization. We assume that another D2D UE, which receives data from another D2D transmission group, coexists in the network, and it is interfered by D2D relay UEs. Moreover, the channel links between D2D relay UEs and the interfered UE are supposed to suffer from Gaussian errors due to low accuracy of channel estimation. Our optimization objective is to minimize the total transmission power at the BS and D2D relay UEs, while satisfying the signal-to-interference-plus-noise ratio (SINR) requirement of the destination D2D receiver and keeping the probability of low SINR event of the interfered D2D receiver smaller than a predefined threshold. Finally, we present the joint BS and D2D relay UE beamforming design, the effectiveness of which is verified by computer simulations.