Energy-efficient resource allocation with 3D beamforming in 3D MIMO-OFDMA systems

The paper investigates the energy efficiency of the 3D MIMO systems with Orthogonal Frequency Division Multiple-Access (OFDMA). In 3D MIMO-OFDMA communication systems, cellular users' specific downtilt angles are exploited through dynamic vertical beamforming. The objective of our proposed optimization problem is jointly concerning resource block assignment, power allocation and downtilt angles adjustment to maximize the energy efficiency measured by the metric of “bits-per-Joule”. We prove that the energy-efficient optimization problem can be transformed into an equivalent form which can be solved by an iterative algorithm. With the Lagrange dual method utilized in each iteration, we can obtain the closed-form solution. Simulation results validate that our proposed energy-efficient resource allocation algorithm outperforms the traditional algorithm in two-dimensional (2D) MIMO systems without considering the user's specific downtilt angle.