EAGER SARE: Physical-Layer Security of THz Communication Using Orbital Angular Momentum and Rapid Frequency Hopping

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With the ever-growing number of wireless devices handling personal health, finance, and other private data, the security associated with the over-the-air data transmission becomes a major concern. At present, the protection of data transmission almost entirely relies on digital encryption, which has various drawbacks and vulnerabilities. For high-volume data transmission, energy-efficient and fast symmetric encryption (e.g., advanced encryption standard, AES) is commonly used, but its cipher secret key, which needs to be wirelessly shared between the transmitter and receiver, is susceptible to eavesdropping. Asymmetric encryption with a public-key infrastructure (e.g., RSA cryptography) can be used to secure key distribution, but it requires energy-consuming computation and complex two-way communication protocols. As a result, additional non-digital security approaches using the physical properties of wireless hardware and electromagnetic waves become attractive. Transmission using narrow beams at millimeter-wave and terahertz (THz) frequencies is expected to reduce the chance of eavesdropping. However, due to the inherently non-ideal beam shape generated by actual antenna arrays, leakage of information still occurs. To address the above issues, this project will investigate the design, analysis, and experiments of a new approach for secured wireless transmission of secret keys. It is expected to significantly increase the capabilities of wireless backhaul infrastructures, especially the future “beyond-5G” networks, against eavesdropping and attacking. It will also advance the interdisciplinary research and education across the fields of THz technologies, microelectronics, and wireless security.The project will use a scheme that encodes the data onto various spatial-distribution patterns (i.e., orbital-angular momentum, OAM) of the wave-front phases in a THz beam. The decoding of such a scheme requires the receiver to be precisely located along the axis of the OAM wave, making eavesdropping very hard and prone to be detected. The project will study approaches that utilize superposition of multiple OAM modes, which further enhances security with the additional information ambiguity induced to illegitimate receivers. To avoid any possible selective jamming, a bit-level rapid frequency hopping scheme will also be applied. The researchers will not only investigate the theoretical security performance limits of the “laser-like” transmission scheme against various sophisticated hacking scenarios, but also provide experimental demonstrations using custom-designed microelectronic chips. Operations such as the generation, detection, coding, frequency-hopping, and beam-steering of THz OAM waves will be performed. The one-way, high-security transmission of secret key to be enabled by this project will complement the existing digital encryption schemes and further the understanding of the THz technologies and applications in wireless security systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.