Wave Control for Wireless Communications: From Time-Reversal to Reconfigurable Intelligent Metasurfaces

Abstract

In this talk, I will show how the works performed at Langevin Institute have led 8 years ago to the seminal concept behind large reconfigurable intelligent surfaces (RIS) that is currently a topic of great interest in the wireless communication community and that is proposed as a new paradigm for the sixth generation (6G) of communication networks. Starting with the first demonstrations of ultrasonic time-reversal focusing in complex media, I will underline how these ideas were transposed later, for electromagnetic waves, into the concept of massive multi-user multiple-input multiple-output (MIMO) for the 5G communication networks. Then, I will explain how, working on the concept of wavefront shaping using spatial light modulators in optics, we propose an equivalent for the microwave domain, using tunable metasurfaces, a concept that would solve the drastic price problem of active techniques like time reversal MIMO. By smartly tuning the signal reflection of large metasurfaces, reconfigurable tunable metasurfaces are capable of dynamically altering wireless channels in disordered environments to enhance the communication performance. Using reconfigurable metasurfaces placed inside any complex environment, we tune the medium complexity to obtain the best communication performance. Compared to the well-known massive multiple-input multiple-output (MIMO) technique, RIS can provide excellent system performance without requiring power-hungry components such as power amplifiers.