STAR-RIS-enabled UAV Wireless Systems: A Stochastic Geometry Approach

The recent deployment of unmanned aerial vehicles (UAVs) to enhance network coverage has emerged as an essential enabler in the beyond fifth-generation and sixth-generation (6G) communication paradigms. Moreover, advances in metasurfaces, i.e. reconfigurable intelligent surfaces (RISs), are expected to significantly enhance 6G wireless communications by enabling a smart radio environment through passive subwavelength scat-tering. RISs which are capable of transmitting and reflecting signals simultaneously, so-called STAR-RISs, have emerged as a promising solution, offering <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$360^{\circ}$</tex> wireless coverage and serving users on both sides of the transmitter, unlike traditional RIS which only reflects signals. This paper investigates a stochastic geometry approach for STAR-RIS-enabled unmanned aerial vehicle-assisted wireless systems, where a UAV communicates simultaneously with two users via the aid of a STAR-RIS. To evaluate system performance, we approximate the probability density function (PDF) and cumulative distribution function (CDF) of the received channel gains based on random variable approximation theory. Accordingly, two performance metrics, outage probability and ergodic capacity, are derived. Extensive simulations verify the accuracy of our theoretical analysis. Notably, numerical results indicate that increasing the number of STAR-RIS elements can help the system overcome performance disadvantages when expanding the UAV's movement area.