Location Awareness Via Intelligent Surfaces: A Path Toward Holographic NLN

Location information is critical for numerous applications, such as smart cities, autonomous vehicles, and Industry 4.0. In this article, we present the paradigm of holographic network localization and navigation (NLN), namely NLN with holographic radios. We describe holographic NLN enabled by reconfigurable intelligent surfaces (RISs), where the phase responses of the RISs are controlled to create desirable electromagnetic (EM) environments for wireless communications. Specifically, we present a mathematical model for signal transmission and reception in the presence of RISs. This model applies to both continuous intelligent surfaces (CISs) and discrete intelligent surfaces (DISs) and accounts for the polarization and directivity of antennas. We review recent research progress on RISs and summarize their characteristics that benefit communication and localization. We present key ingredients of NLN and describe how RISs can be employed to enable holographic NLN. We quantify the performance of RIS-enabled holographic NLN with a case study, showing that RISs can significantly improve localization accuracy, especially in scenarios where line-of-sight (LOS) paths between agents and anchors are obstructed.