RIS-Assisted Spectral Efficiency Enhancement for Vertical Sectorization Network

Vertical sectorization is a novel enabler to enhance cell capacity, however which results in strong interference and weak coverage issues when there are obstacles between inner and outer sector. To this end, this letter proposes a RIS-assisted vertical sectorization approach that formulates the issues to a inner-outer sector sum spectral efficiency (SSE) maximization problem. A fast and low-complexity alternating optimization (FLAO) algorithm is proposed to solve the problem. We firstly get a closed-form solution to active beamforming based on fractional programming (FP) and quadratic transform and reduce the computational complexity based on a prox-linear BCD update rule. And then we explore three methods to compute passive beamforming. Simulation results show that the proposed approach significantly improves capacity by 94% compared to the traditional vertical sectorization and FLAO is 65% faster than AO in SSE to 10 bps/Hz.

I. Introduction

With the explosive growth of wireless terminals and the increasing demand for high-capacity data transmission services, traditional MIMO technology can no longer meet the existing multi-user communication needs. Active antenna system (AAS) has the advantage of high integration and low power consumption [1], gradually replacing traditional passive antennas. Moreover, AAS with flexible and diverse remote electrical tilt (RET) brings vertical dimension angle information to the traditional MIMO, resulting in 3D MIMO [2]. The vertical sectorization is one of the specific applications of 3D MIMO. Specifically, a cell can be divided into inner and outer sectors through vertical sectorization, and since the inner and outer sectors have different IDs, it is possible to reuse the time-frequency resources, thereby increasing the overall system capacity of the network, which has attracted widespread attention in the academic community [3].