Research on Energy Efficiency of Hybrid Networks Based on Massive MIMO and D2D

In this paper, based on massive MIMO and device-to-device (D2D) techniques, a two-tier hybrid network is considered as well as the energy efficiency analysis, and a novel wireless energy-harvesting scheme for DUs (D2D users) is proposed. In the interested hybrid networks, the base stations of macro cells are equipped with massive MIMO antenna array. The macro cells are overlaid by D2D networks and share spectrum with D2D. To guarantee D2D communications, the dedicated power beacons (PBs) are deployed, which are equipped with small-scale MIMO. By using zero-forcing precoding scheme, the dedicated PBs transfer energy for energy-constrained D2D transmitters. At the same time, in order to improve the energy efficiency of the networks, the DUs also harvest the energy from the ambient radio frequency (RF) interference of cellular users (CUs). For the proposed hybrid network models and energy-harvesting schemes, we model the positions of CUs, DUs, and PBs are the independently Poisson point processes, respectively. By applying stochastic geometry, based on inverse power control scheme we derive the sufficient probability that a typical D2D transmitter harvests sufficient energy to establish communication links, which is presented in a simple integral form. Both the analytical and numerical results show that the proposed wireless energy-harvesting schemes not only guarantee the reliability of D2D communications by equipping PBs, but also improve the sufficient probability of DUs harvesting energy by exploiting the ambient RF interference of CUs. As a result, the power of PBs is saved, and the energy efficient of networks is improved greatly.