Directional Modulation for Enhanced Privacy in Smartwatch Devices: Proposing a security solution compatible with Internet of Things devices

This article studies the security aspects of data transmission in on-body Internet of Things (IoT) devices through the use of Directional Modulation (DM) from a smartwatch integrated antenna. DM is a beam steering-based Physical Layer Security (PLS) method used to transmit baseband constellations to known secure locations while simultaneously scrambling them in other directions. However, in the state of the art, DM is implemented using large arrays, which are outsized for many on-body IoT devices. To overcome this challenge, this study proposes multimodal ultrathin compact antennas suitable for integration into smartwatches. These antennas present advanced beam steering capabilities that allow the implementation of DM from a low-thickness structure of up to 0.57 mm or 1/100th of the wavelength at the center operating frequency. Two different DM implementations (simultaneous multiport transmission and an energy-efficient single-port transmission) are tested using a multilayer phantom. Overall, secure steerable transmissions are realized, and experimental verifications are carried out to validate the proposed concept. Ultimately, this article demonstrates the feasibility of applying new energy-efficient and low-cost security techniques to enhance the privacy of resource-constrained IoT devices.