Time-Modulated EM Skins for Integrated Sensing and Communications

An innovative solution, based on the exploitation of the harmonic beams generated by timemodulated 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 toward 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, both BSs localize the user terminal and, as a by-product, establish a communication link with it by leveraging on the “sum” reflected beam. Toward 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.