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.