Programmable Metasurface Hybrid MIMO Beamforming: Channel Estimation, Data Transmission, and System Implementations at 28 GHz

With the development of wireless communication generations, multiple-input and multiple-output (MIMO) architectures have proven to be a solution to the higher required data rates for the increasing number of mobile users. As a matter of fact, better earnings can be gathered from a low-cost system with effective functions, which results in the hybrid beamforming architecture combining digital chains with large-scale antenna arrays. The programmable metasurface (PM) is a promising antenna array concept that realizes reconfigurable beamforming. It is raised to be an attractive antenna array architecture due to its low price and power consumption. However, experimental investigations combining PMs with modern wireless communication systems have not been intensively studied. Its challenges and difficulties of signal processing and system implementation remain uncertainties to be discovered. In this article, a PM hybrid MIMO beamforming system including the aforementioned important topics is presented as follows. First of all, the hybrid beamforming channel estimation algorithm adapted for PM is created by merging analog beam training and digital interleaved orthogonal frequency division multiplexing. Afterward, data transmissions based on the estimated channel state information utilizes variant signal recovery methods to examine the channel estimation accuracy and system feasibilities. To practically analyze the proposed system, the aforementioned aspects are implemented into system-level experiments using three PMs operating at 28 GHz for downlink wireless communication in both single-user and multiuser scenarios. Proper results are delivered, which successfully prove the PM hybrid MIMO beamforming system functionalities.