On Age of Information and Energy‐Transfer in a STAR‐RIS‐Assisted System

ABSTRACT Battery‐limited devices and time‐sensitive applications are considered as key players in forthcoming wireless sensor network. So, the main goal of the network is two‐fold; charge battery‐limited devices, and provide status updates to users where information‐freshness matters. In this paper, a multi‐antenna base station (BS) in assistance of simultaneously‐transmitting‐and‐reflecting reconfigurable intelligent surface (STAR‐RIS) transmits power to energy harvesting (EH) devices while controlling status update performance at information users by analysing age of information (AoI) metric. Therefore, we derive a scheduling policy at BS, and analyse joint transmit beamforming and amplitude‐phase optimization at BS and STAR‐RIS, respectively, to reduce average sum‐AoI for the time‐sensitive information users while satisfying minimum required energy at EH users. Moreover, two different energy‐splitting and mode‐switching policies at STAR‐RIS are studied. Then, by use of an alternating optimization algorithm, the optimization problem is studied and non‐convexity of the problem is tackled by using the successive convex approximation technique. Through numerical results, AoI‐metric and EH requirements of the network are analysed versus different parameters such as number of antennas at BS, size of STAR‐RIS, and transmitted power to highlight how we can improve two‐fold performance of the system by utilizing STAR‐RIS compared to the conventional RIS structure.