Post by Robert Heath

I am pleased to see that the tri-hybrid MIMO architecture is being further developed by the research community. This architecture extends hybrid MIMO by adding reconfigurable antennas as an electromagnetic precoding layer. A tri-hybrid MIMO system includes three layers of precoding: digital, analog, and electromagnetic, at the transmitter and the receiver. I want to highlight some recent work that I have seen posted on arXiv in the past few months. Mengzhen Liu, Ming Li, Rang Liu, and Qian Liu, in “Tri-Timescale Beamforming Design for Tri-Hybrid Architectures with Reconfigurable Antennas,” propose to optimize the three layers of beamforming on different time scales, with the antenna layer operating on the slowest scale. Together with Lee Swindlehurst, they have also written “Reconfigurable Antenna Arrays: Bridging Electromagnetics and Signal Processing.” In that paper, the authors describe a dynamic connected tri-hybrid architecture, which was not included in my magazine paper, and summarize several open challenges including cross-domain design. Pinjun Zheng, Yuchen Zhang, Tareq Al-Naffouri, Md. Jahangir Hossain, and Anas Chaaban, in “Tri-Hybrid Multi-User Precoding Using Pattern-Reconfigurable Antennas: Fundamental Models and Practical Algorithms,” study the effect of discrete and continuous pattern reconfigurability on multiuser MIMO communication. They also examine how reconfigurable antennas can reduce the number of RF chains. Yinchen Li, Chenhao Qi, Shiwen Mao, and Octavia A. Dobre, in “Tri-Hybrid Beamforming for Radiation-Center Reconfigurable Antenna Array: Spectral Efficiency and Energy Efficiency,” analyze precoding with a radiation-center reconfigurable array implemented using reconfigurable pixel antennas. They compare selection among fixed-position antennas and fully digital systems and show improvements in energy efficiency. Jiangong Chen, Xia Lei, Yuchen Zhang, Kaitao Meng, and Christos Masouros, in “Integrated Sensing and Communication with Tri-Hybrid Beamforming Across Electromagnetically Reconfigurable Antennas,” explore the benefits of the tri-hybrid architecture for integrated sensing and communication. They formulate and solve optimization problems that configure the three layers of precoding to balance communication and sensing objectives, showing clear benefits from antenna reconfiguration. Zhenqiao Cheng, Chongjun Ouyang, and Nicola Marchetti, in “On the Performance of Tri-Hybrid Beamforming Using Pinching Antennas,” connect the tri-hybrid architecture to the emerging area of pinching antennas, which are a form of reconfigurable antenna. They formulate an optimization that configures the pinching mechanism to serve multiple users over a large area and demonstrate improvements compared with hybrid-only systems. Much more work can be viewed through the framework of the tri-hybrid MIMO architecture. These papers are only a few that mention it explicitly. Links to the papers are in the comments.