A Two-stage Spatial-oversampling Codebook and Field Trials of RIS-aided Wireless Communications

Reconfigurable intelligent surface (RIS) is a promising technology that has the potential to change the way we interact with the wireless propagating environment. In this paper, we propose a practical two-stage spatial-oversampling codebook algorithm for the beamforming of RIS, which is based on the spatial structure of the wireless channel. This algorithm has significantly lower complexity compared to the two-dimensional full-space searching-based codebook, yet with only negligible performance loss in the experiment. Then, a series of experiments are conducted with the fabricated RIS systems, covering office, corridor, and outdoor environments, to verify the effectiveness of RIS in both laboratory and current fifth generation (5G) commercial networks. In the office and corridor scenarios, the 5.8 GHz RIS provided a power gain of $\mathbf{1 0 - 2 0 ~ d B}$ at the receiver. In commercial 5G networks, the 2.6 GHz RIS improved indoor signal strength by 4-7 dB.