On Beam Widening for RIS-Assisted Communications Using Genetic Algorithms

As future wireless communication systems aim to achieve increased data rates, system capacity, and reduced latency and power consumption, they have shifted towards higher frequency bands such as Millimeter Wave (mmWave) and Terahertz spectrums. However, these spectrums pose challenges in terms of the quality of the communication link, including large path-loss and limited coverage, as well as difficulties in system and antenna design. Reconfigurable Intelligent Surfaces (RISs) have recently been proposed as a promising low-cost and low-power consumption solution to enhance the performance of wireless communication systems. However, beamforming with RISs can be difficult, especially in the presence of beam widening requirements, which aim to produce wide beams for cell or sectorwide broadcasting, among other applications. In this paper, a new approach for beam widening in RIS-assisted communications using genetic algorithms is proposed. The focus is on using phaseonly tapering to achieve wide beams while minimizing sidelobes (SSL) and beam ripple. To address this problem, two cost functions are developed and optimized using genetic algorithms. The optimization results in a codebook of 1-bit phase patterns with varying beamwidths, making it possible to widen the beams without requiring extra controllers or specific element designs. The proposed approach is evaluated through simulation results, which demonstrate its effectiveness in achieving wide beams while maintaining a low level of sidelobes and beam ripple.