Active Reconfigurable MIMO Communications: Capacity Maximization Pattern Design

Reconfigurable Intelligent Surface (RIS) can improve the channel quality by smartly reconfiguring the wireless communication environment and has therefore received extensive research attention. In this paper, we propose to deploy the programmable metasurface at the base station of a cellular wireless communication system to formulate an active RIS system termed the pattern reconfigurable multi-input multi-output (PR-MIMO), which can modify the propagation environment actively by reconfiguring the radiation pattern of the transmit antenna array. We focus on the capacity maximization pattern design in PR-MIMO systems, where SDR-based solutions with Gaussian randomization are first discussed. We further propose an eigen-value optimization based pattern design scheme and a heuristic closed-form scheme based on the physical mechanism of the reconfigurable pattern on the wireless channel. Numerical results demonstrate that active radiation pattern design leads to an improved capacity performance for PR-MIMO over traditional MIMO systems with fixed radiation characteristics.