A Novel Two-Step Beam Alignment Method Based on Narrowband Power-Only Measurements with Reconfigurable Intelligent Surface

Future communication systems are expected to employ high-gain, beam-steerable antenna arrays to track the dominant path in the channel to compensate for higher path loss and maintain the communication link. The advent of reconfigurable intelligent surfaces (RIS) has made dynamic wave manipulation possible to improve coverage by bypassing blockage objects, with the cost of high beam alignment overhead due to exhaustive beam search among the base station (BS), RIS, and user equipment (UE). This letter proposes a two-step beam alignment method that only requires narrowband power-only signals to find the dominant paths in RIS-aided communication systems. The first step comprises RIS channel estimation via a fast power-only calibration method, followed by an RIS beamforming design. In the second step, the best BS and UE beams for reliable communication can be determined via conventional beam alignment methods. Simulation and experimental results validate the accuracy and effectiveness of the proposed method.