מושגי ליבה
The core message of this paper is to propose a novel approach to jointly optimize active and passive beamforming as well as mutual coupling (MC) in RIS-assisted multi-user MIMO wireless communication systems, leading to enhanced system performance.
תקציר
The paper presents a novel framework to optimize the RIS phase configuration and base station (BS) active precoders using a physically-consistent end-to-end channel model that incorporates mutual coupling (MC). The authors propose an offline optimization method, applied to a class of wireless channels, to design the MC at the RIS, as opposed to state-of-the-art approaches that did not perform MC optimization.
The key highlights and insights are:
The authors formulate a novel joint optimization problem for active and passive beamforming as well as MC for RIS-aided multi-user downlink transmission based on a physically-consistent RIS model.
The offline MC optimization exhibits a complex nested structure within the overall optimization problem, involving both outer and inner optimization problems. The inner problem deals with the optimization of the RIS phase configuration and the BS active precoding, while the outer problem involves optimizing MC based on the scattering S-parameters.
The authors propose a solution approach that decomposes the overall system design into two sub-problems and deploys an alternating optimization approach. The first sub-problem is solved using the method described in prior work, while the second sub-problem is solved via a combination of the projected gradient descent method and the method of Lagrange multipliers.
The simulation results showcase that the system performance is further enhanced through joint beamforming and MC optimization. This improvement is achieved even with the proposed offline process for optimizing the MC at the RIS, emphasizing the effectiveness beyond real-time MC adjustments.
סטטיסטיקה
The transmit power P is varied from 30 dBm to 50 dBm.
The number of RIS elements M is varied from 64 to 100.
The number of users K is varied from 6 to 8.
The number of BS antennas N is 32.
ציטוטים
"Mutual Coupling (MC) is an unavoidable feature in Reconfigurable Intelligent Surfaces (RISs) with sub-wavelength inter-element spacing."
"We particularly formulate a novel problem to jointly optimize active and passive beamforming as well as MC in a physically consistent manner."
"Our simulation results showcase that the system performance is further enhanced through joint beamforming and MC optimization."