Time-Modulated EM Skins for Integrated Sensing and Communications

TL;DR

This work addresses ISAC in a SMART electromagnetic environment by employing time-modulated EM skins (TM-EMS) to generate a carrier sum beam ($h=0$) and a first-harmonic difference beam ($h=1$) through harmonics controlled by time-varying meta-atom reflections. The design casts the problem as optimizing a time-modulation sequence $\mathcal{T}$ via a cost function $\Phi(\mathcal{T})$ with $h=0,1$ beam masks, solved by a PS-based evolutionary strategy, and leverages column-wise simplifications to reduce hardware complexity. Numerical full-wave simulations and experimental measurements on a $16\times16$ TM-EMS prototype validate that the proposed approach can robustly localize a terminal and simultaneously sustain a communication link, even under non-ideal hardware. The work demonstrates a practical ISAC pathway that integrates sensing and communication in SEME with minimal BS/terminal modifications, enabling azimuthal sensing and data exchange through controllable harmonic beams. This has significant implications for next-generation wireless networks operating in challenging non-line-of-sight and dynamic environments.

Abstract

An innovative solution, based on the exploitation of the harmonic beams generated by time-modulated electromagnetic skins (TM-EMSs), is proposed for the implementation of integrated sensing and communication (ISAC) functionalities in a Smart Electromagnetic Environment (SEME) scenario. More in detail, the field radiated by a user terminal, located at an unknown position, is assumed to illuminate a passive TM-EMS that, thanks to a suitable modulation of the local reflection coefficients at the meta-atom level of the EMS surface, simultaneously reflects towards a receiving base station (BS) a "sum" beam and a "difference" one at slightly different frequencies. By processing the received signals and exploiting monopulse radar tracking concepts, the BS both localizes the user terminal and, as a by-product, establishes a communication link with it by leveraging on the "sum" reflected beam. Towards this purpose, the arising harmonic beam control problem is reformulated as a global optimization one, which is successively solved by means of an evolutionary iterative approach to determine the desired TM-EMS modulation sequence. The results from selected numerical and experimental tests are reported to assess the effectiveness and the reliability of the proposed approach.