Energy Efficiency Optimization for D2D Communication Underlaying Distributed Antenna System

In this paper, the energy efficiency (EE) performance of a downlink distributed antenna system with device-to-device (D2D) underlay communication is investigated over a composite Nakagami fading channel. The optimal power allocation (PA) schemes are developed for improving the EE performance. Under the minimum rate constraint of cellular user (CU), the maximum power constraints of CU and D2D pair, an optimization problem for maximizing the system EE is formulated. The Karush-Kuhn-Tucker conditions are used to solve the optimization problem. Based on the 1-D search method and the bisection method, two schemes and corresponding algorithms are, respectively, proposed to obtain the optimal solutions of PA. For a given transmit power of D2D pair, the closed-form PA of remote antennas (RAs) and the number of active RAs are derived, which greatly simplifies the optimization. It is shown that the proposed two schemes can obtain the same EE performance, and the scheme with the bisection method has lower complexity than that with the 1-D search method. Computer simulation verifies the effectiveness of these two schemes, and superior EE performance can be achieved.