Dynamic agile reconfigurable holographic MIMO: DoF, diversity gain, and array gain analysis

In this study, we propose a dynamic agile reconfigurable holographic multi-input-multi-output (DARH-MIMO) wireless communication system utilizing intelligent metasurfaces. By fully utilizing the ability of metasurfaces to dynamically manipulate electromagnetic signals, we deploy these structures as MIMO antennas with agile reconfiguration capabilities for both the transmitter and receiver. Subsequently, we introduce a spatial-temporal dynamic agile reconfigurable framework for this DARH-MIMO system. Within this framework, the phase response of each metasurface element is reconfigured multiple times within a single symbol duration, enabling the construction of an equivalent extended spatial-temporal channel and enhancing communication potential. We then analyze the system's multiplexing gain (degrees of freedom, DoF), diversity gain, and array gain under multipath fading channel conditions. The results highlight the following: (1) A clear relationship between the DoF and parameters such as agile frequency, angular spread, antenna size, and number of antennas. This conclusion indicates that when the number of receive antennas is smaller than that of transmit antennas, the dynamic agile reconfiguration of metasurface element phase response significantly enhances DoF. (2) A direct relationship between diversity gain, agile frequency, and DoF, indicating that diversity gain increases with higher agile frequency. (3) A proportional relationship between array gain and the size of the DARH-MIMO array size. These findings provide valuable insights into optimizing holographic MIMO systems for next-generation wireless communication.