An optimal MIMO mode selection method for D2D transmission in cellular networks

Device-to-Device (D2D) communication is one of the new features introduced for Long Term Evolution-Advanced (LTE-A) and beyond networks. In this paper we address the problem of communication mode selection for a pair of User Equipments (UEs). In particular we assume that the paired UEs can choose from the reuse, dedicated, and cellular modes. While this problem was treated in the literature for Single-Input-Single-Output (SISO) case, we derive models for networks where UEs and evolved-Node-Bs (eNBs) exploit Multiple-Input-Multiple-Output (MIMO) techniques with four antennas at each side. This approach requires design of the pre-coding matrices at each node which poses a challenge in the reuse mode due to the non-convexity problem. To solve this issue we propose a distributed iterative algorithm. The numerical study compares the performance of the MIMO based approach with that of the SISO case, and the results show that the presented MIMO based mode selection method provides significantly higher network throughput than that of the SISO based mode selection method for the same D2D transmission range.