A Low-Complexity Codebook-Based Physical Layer Security Framework for Ambient IoT Systems

This letter introduces a novel physical-layer security (PLS) mechanism for ultra-low-power ambient IoT (A-IoT) devices. The proposed system leverages on-off keying (OOK) signaling in combination with randomly modulated transmitter-side phases to generate a secure, channel-dependent detection pattern. This modulation technique causes the energy detector output of the A-IoT receiver to be highly sensitive to the unique properties of the wireless channel. Through a training stage, the transmitter learns a one-to-one mapping between transmitted sequences and observed binary outcomes, forming a secure codebook without requiring channel state information (CSI). To handle sparse multipath, random pre-filtering further enlarges the security gap. Analytical derivations and simulations show strong agreement, demonstrating a clear key disagreement rate (KDR) gap between legitimate devices and eavesdroppers under both rich and sparse multipath channels.