Resource Allocation in STAR-RIS-Aided Pinching-Antenna Systems (PASS)

This paper investigates a pinching-antenna systems (PASS)-enabled wireless-powered non-orthogonal multiple access (NOMA) system with the aid of a simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS), where two energy-constrained users first harvest energy from PASS and then upload the information using the harvested energy. A resource allocation problem is formulated for the maximization of the system sum rate by jointly optimizing the baseband energy transfer and information receive beamforming, the positions of pinching antennas (PAs), STAR-RIS coefficient matrices, user uploading power, and time allocation. To address this highly-coupled non-convex problem, a block coordinate descent (BCD) algorithm is developed. In particular, for the joint baseband energy transfer beamforming, user uploading power, and time allocation optimization, the subproblem is shown to be convex and can be optimally solved. The PA positions, STAR-RIS coefficient matrices, and baseband information receive beamforming are then alternatingly optimized by employing the gradient descent method, Dinkelbach's method, and Newton's method, respectively. Simulation results demonstrate that (i) the system performance is highly correlated with the PASS waveguide length. A reasonable design can enhance resource utilization efficiency, while STAR-RIS further improves communication quality; and (ii) the joint design of PASS and STAR-RIS boosts the system sum rate, effectively demonstrating its superiority in improving communication performance.