Low Earth orbit (LEO) satellite–based positioning, navigation, and timing (PNT) has emerged as a promising way to complement traditional global navigation satellite systems (GNSS), such as GPS and Galileo. Conventional GNSS satellites operate at altitudes of around 20,000 km, whereas LEO satellites orbit just a few hundred kilometers above the Earth. As a result, LEO signals arrive at the receiver tens of times stronger than those of traditional GNSS. Moreover, large-scale LEO constellations, which comprise hundreds to thousands of satellites, offer more favorable geometric conditions. However, because LEO satellites travel at approximately 7–8 km/s—faster than a rifle bullet—their visibility over an urban area is limited to a few minutes. This short visibility window leads to frequent blockages, making it challenging to achieve stable positioning.

To overcome these limitations, increasing attention has been paid to the use of reconfigurable intelligent surfaces (RISs), which exploit reflected signals as virtual anchors to improve positioning accuracy under blockage conditions. Nonetheless, the high mobility of LEO satellites introduces several technical challenges. In particular, the large Doppler shift can distort the reflected signal paths from RISs and degrade positioning performance. To address these issues, we are developing LEO–RIS-based urban positioning technologies.