The optimal energy-efficient design of user-specific RIS-aided uplink communication system

Reconfigurable intelligent surfaces (RIS) has the potential to be an important technology for the sixth-generation (6G) communications in future. Especially, RIS can improve communication performance by extending coverage or improving the conditions for signal propagation. Most of the current work mainly focused on the reflective type RIS. In contrast, the recent emergence of user-specific reconfigurable intelligent surfaces (US-RIS) is a transmissive type. Unlike reflective RIS, which is typically deployed near the base station, US-RIS is deployed on the user side and is capable of adjusting the phase of the user's signal. In this paper, our research focuses on energy-efficient in the context of quality of service requirements. For this purpose, we formulate a joint optimization problem. As the optimization problem is non-convex, we separate and treat these variables in several sub-problems. The sub-problems are solved separately for the variables by alternating updates, either using closed-form solutions or using the semidefinite relaxation (SDR) method. In addition, it is clear from the simulation results that US-RIS is able to improve the energy efficiency of the communication system. Furthermore, the increased number of US-RIS elements can also improve the energy efficiency of the communication system.(c) 2023 Published by Elsevier B.V.