Fast Wide Beam Adjustment of Reconfigurable Intelligent Surfaces in Practical Deployments

Abstract

Reconfigurable Intelligent Surface (RIS) is a promising way to increase the coverage and capacity of existing and future wireless systems. For that, the RIS reflection coefficients need to be properly adjusted. However, cellular systems demand RIS adjustment algorithms to use low-complexity feedback such as signal power measurements. Moreover, the multipath signal propagation in urban cellular systems, especially in the sub-6 GHz band, dictates the necessity to consider the destructive interference of reflected and direct channels at the Mobile Station. This paper tackles these problems and proposes a fast hierarchical RIS configuration algorithm with two novel features. First, on each level of the hierarchy, the reflecting coefficients are adjusted to compensate for destructive interference of reflected and direct channels at the Mobile Station. Second, it relies on a novel approach to synthesizing 2D reflected beams with a given width and direction based on narrow beam phase stitching. The proposed algorithm showcases superior performance, surpassing existing solutions by up to 5 dB while requiring only 100 signal power measurements for the RIS with 4096 elements.

Keywords

• Beam synthesis
• intelligent reflecting surface
• reconfigurable intelligent surface
• sub-6 GHz band