Non-reciprocal RIS-Aided Full-Duplex Communications: IoT Applications

The rapid growth of the Internet of Things (IoT) has increased the demand for efficient communication in scenarios where numerous devices sporadically transmit data to a base station (BS). This rise in wireless devices has led to spectrum congestion, driving the need for flexible and multifunctional full-duplex wireless systems. Reconfigurable Intelligent Surfaces (RIS) are particularly useful for enhancing data transmission in challenging environments, such as IoT devices in dead zones. RISs are programmable, ultra-compact, and can facilitate reciprocal and non-reciprocal signal transmissions in full-duplex mode, theoretically doubling the spectrum efficiency compared to half-duplex systems. Non-reciprocal RISs, with their independent transmission and reception paths, are ideal for full-duplex communication. This paper explores both reciprocal and non-reciprocal RIS configurations, deriving Signal-to-Interference-plus-Noise Ratio (SINR) metrics for both downlink and uplink scenarios. Optimal phase settings at the RIS are determined to maximize SINR, and simulation results demonstrate the advantages of RIS deployment in enhancing full-duplex communications for seamless connectivity in IoT systems. The study highlights the trade-offs between reciprocal and non-reciprocal RIS setups, with a focus on transmission power and RIS characteristics in system design. Additionally, the findings underscore the benefits of non-reciprocal RISs, particularly in leveraging directional transmission for improved system performance.