Power-Aware Maximization of Ergodic Capacity in D2D Underlay Networks

Abstract

Device-to-device (D2D) underlay networks enable high data rates and low end-to-end delay and improve spectral/energy efficiency and offload cellular traffic. However, D2D communication also results in interference between CUs and D2D terminals, negatively impacting capacity. Is there a critical set of system parameters (density of D2D users (DUs), cellular base stations (BSs), transmit power, etc.) that can ensure that the benefits of D2D underlay operation can outweigh its drawbacks? We seek to address this fundamental question in the context of the tradeoff between ergodic capacity and power consumption. Toward this end, we first quantify the ergodic capacity metric for a realistic network where D2D pairs are spaced randomly and experience Rician fading. Based on a stochastic-geometry-based network model, we derive, for the first time, closed-form results for ergodic capacity of both cellular users (CUs) and DUs. Second, we identify the D2D user density and transmit power that maximizes the ergodic capacity of the network. Specifically, a two-stage scheme is proposed to optimize ergodic capacity while minimizing overall power consumption. The results from this analysis provide a framework to uncover desirable system design parameters that offer the best gains in terms of capacity.