Core Concepts
The authors propose a double self-sustainable reconfigurable intelligent surfaces (RISs) aided multi-user multiple input multiple output (MIMO) communication system to minimize the transmission power at the base station while guaranteeing the quality of service requirements of the users and meeting the power consumption requirements of the RISs.
Abstract
The authors consider a multi-user MIMO communication system assisted by two self-sustainable RISs. The system comprises a base station (BS) with multiple antennas, RIS1 deployed at the BS side with reflection elements, RIS2 deployed at the users' side with reflection elements, and multiple single-antenna users.
To achieve self-sustainable transmission of the RISs, the RISs are equipped with energy harvesting circuits to harvest energy from the BS. The authors aim to minimize the transmission power at the BS by jointly optimizing the active beamforming at the BS, as well as the phase shifts and amplitude coefficients of the RISs.
The authors employ a block coordinate descent (BCD) algorithm based on the penalty-based method and successive convex approximation (SCA) to alternatively optimize the active beamforming at the BS and the phase shifts, as well as amplitude coefficients of the two RISs. The SCA framework is used to address the quality of service (QoS) and power consumption constraints of the RISs, while the penalty-based method is used to transform the non-convex constraints related to the phase shifts of the RISs.
Simulation results show that the proposed double self-sustainable RISs system can achieve significantly lower power consumption at the BS compared to conventional RIS systems.
Stats
The authors provide the following key figures and metrics:
The transmission power at the BS decreases as the total number of reflection elements increases, but starts to increase when the total number exceeds 140.
The minimum transmission power can be achieved by uniformly distributing the number of reflection elements between the two RISs.