A Passive Radar for Urban Ubiquitous Sensing: Building Facade Ranging With GNSS-IR

Smart city development today is focusing on urban digital twins, which require frequent data updates to connect digital models with the physical world. Ubiquitous sensing using RF signals has emerged as a cost-effective way to gather real-time spatial information with existing signals and sensors, though few studies have accurately measured urban building geometry through RF sensing techniques. To address the technical gaps, this article introduces global navigation satellite system interferometric reflectometry (GNSS-IR) as a potential ubiquitous sensing tool in urban areas. With multi-GNSS and effective quality control, the proposed method precisely measured the perpendicular distances (PD) to building facades in complex urban areas with only a smartphone. At least decimeter level accuracy and a detection range of more than 100 m is achieved in experiments. Statistical analysis of experimental results revealed characteristics of the method and influencing factors in applications. The retrieved PD measurements indicate the relative position between GNSS receivers and buildings, which shows large potential in building modeling and diverse urban applications.