Self-Adaptive Power Control Mechanism in D2D Enabled Hybrid Cellular Network with mmWave Small Cells: An Optimization Approach

Millimeter wave (mmWave) and Device-to-Device (D2D) communications have been considered as the key enablers of the next generation networks. We consider a D2D-enabled hybrid cellular network compromising of $\mu W$ macro-cells coexisting with mmWave small cells. We investigate the dynamic resource sharing in downlink transmission to maximize the energy efficiency (EE) of the priority, or cellular users (CUs), that are opportunistically served by either macrocells or mmWave small cells, while satisfying a minimum quality-of-service (QoS) level for the D2D pairs. In order to solve this problem, we first formulate a self-adaptive power control mechanism for the D2D pairs subject to the interference threshold constraint set for the CUs, while maintaining its minimum QoS level. Subsequently, the original EE optimization problem, which aimed at maximizing the EE for both CUs and D2D pairs, has been broken up into two subproblems that manage the radio resource allocation for D2D pairs and maximize EE exclusively for CUs, in that order. We then propose an iterative algorithm to provide a near-optimal EE solution for CUs.