STAR-IRS-Assisted MAC Protocol with Dynamic Element Allocation for Indoor IoT Networks

In dense indoor Internet of Things (IoT) environments, simultaneously transmitting and reflecting intelligent surfaces (STAR-IRS) can provide full-space coverage by steering energy to both sides of the surface. However, most STAR-IRS works focus on the physical layer and overlook medium access control (MAC) challenges, such as how to collect channel state information (CSI), dynamically assign each STAR-IRS element to either the reflection or transmission mode, and coordinate concurrent users. We propose a two-stage MAC protocol that couples carrier sense multiple access with collision avoidance (CSMA/CA) for contention and time division multiple access (TDMA) for scheduled data transmission. During contention, devices send extended request-to-send (eRTS) frames to enable CSI acquisition; during transmission, the access point (AP) configures the STAR-IRS, allocates TDMA slots, and pairs one reflection-region device (RD) with one transmission-region device (TD) for non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC). Analysis and simulations show that the proposed scheme increases throughput and reduces delay compared with reflective-only IRS baselines without NOMA, while remaining practical for dynamic indoor IoT.