Scattering Matrix Design of Reconfigurable Intelligent Surface Based on Group Connected Impedance Network in MU-MIMO System

Reconfigurable intelligent surface (RIS) is considered as a promising technology for next-generation 6G wireless system by controlling the propagation environment that degrades the quality of received signals in wireless communication. In contrast to the conventional RIS architecture in which an impedance of each RIS element is grounded, the general architecture having an impedance network connected to each other element can more flexibly control the signal. The computational complexity by optimization of the scattering matrix of the general RIS architecture increases according to the size of the channel matrix. Therefore, as the number of users increases, high computational complexity is paid for optimizing the scattering matrix. This paper proposes the effective scattering matrix design for RIS based on group connected impedance network in multi-user multiple-input multiple-output(MU-MIMO) wireless communication systems. By limiting the number of supported users per group to one, it is possible to effectively reduce computational complexity and ensure appropriate performance compared to the optimization of the scattering matrix that maximizes the channel gain of all users.