Salam Akoum

Full-dimensional MIMO for future cellular networks

Full-dimensional multiple input multiple output (FD-MIMO) is a practical implementation of massive MIMO in cellular communication systems. FD-MIMO relies on an active two-dimensional antenna grid at the base stations and harvests the benefits of both azimuth and elevation beamforming. This paper briefly introduces the concept of FD-MIMO, and surveys the recent research results and applications of active antenna systems (AAS) technology. The key concepts discussed range from antenna patterns and channel modeling to vertical sectorization and heterogeneous networks deployment. The paper focuses on the benefits of FD-MIMO in an urban environment with high rises and three-dimensional user deployment. It demonstrates the importance of FD-MIMO in enhancing the performance of cellular networks.

Optimizing vertical sectorization for high-rises

Vertical sectorization is a recent development of active antenna technologies, whereas cellular providers make use of sectors in the vertical domain in addition to the standard horizontal sectorization currently in place. In this paper, we develop a framework to analyze and optimize vertical sectorization for high-rise buildings in urban environments. We start with a generic urban network topology with high-rise buildings and use it to derive the distribution of the elevation angles of the user equipments (UEs) in a cell. Using this distribution, we derive the values of tilts that maximize the coverage of all the UEs for the cases of one and two vertical sectors. This work provides answers to how a cellular service provider should perform vertical sectorization for different base station heights, cell sizes and various urban environments.

Vertical beamforming for three-dimensional user placement

Full-dimensional multiple input multiple output (FD-MIMO) is a practical implementation of massive MIMO in cellular communication systems. FD-MIMO relies on a planar array of active antenna systems (AAS) at the base stations to harvest the benefits of both azimuth and vertical beamforming. In this paper, we analyze the network performance of per-user vertical beamforming with a special focus on the three-dimensional placement of the base stations and the users. We use tools from stochastic geometry to analyze the coverage performance of cellular networks with a three-dimensional radiation pattern at the base stations, using AAS. We show that the directionality achieved via dynamic antenna tilting provides multi-fold improvement in network performance as compared to omni-directional digital beamforming. We draw insights on the performance of the network as a function of the height difference between the base stations and the users, the number of antennas at the base station, and the various characteristics of the radiation pattern.