Communication and Localization in Networks at Sub-6 GHz aided by Frequency Shifting-RIS

Frequency-shifting reconfigurable intelligent surfaces (FS-RISs) can be developed using a new generation of meta-materials that shift the original frequency spectrum of sent signals, it is also known as frequency conversion. Their application in wireless communications and localization remains in the early stages of development. This work proposes the FSRIS to provide localization services in an existing cellular network operated at sub- 6 GHz. It can up-convert the signal transmitted by the base station (BS) to the millimetre Wave and forward it to the user, allowing this to estimate its position thanks to the use of narrow directive beams. The proposed method significantly outperforms the existing solution based on multiple BSs in terms of the Cramér-Rao lower bound, which is analytically derived. An efficient data-aided beam-sweeping is provided to reduce the beam-training delay at FS-RIS without sacrificing the data rate. This work introduces a novel approach to utilizing FS-RIS in wireless systems, with the potential to reshape how we view spectrum and interference management, paving the way for more efficient communication and localization applications.