This paper investigates the downlink spectral efficiency of low Earth orbit (LEO) satellite constellations, where spectral efficiency refers to the entire network’s total data rate per unit spectrum per unit area on the Earth’s surface. For practicality, all links employ single-user codebooks and treat interference as noise. A key finding is that, unlike terrestrial networks, the spectral efficiency of LEO constellations does not increase indefinitely with satellite density. Under typical assumptions about antenna array beam widths, this study explores the satellite density that maximizes spectral efficiency. As a special case, a regular deployment of satellites and ground terminals is analyzed across various densities. Simulation results reveal that regular configurations achieve higher spectral efficiency compared to random configurations. Furthermore, while the total downlink capacity of any LEO constellation remains significantly lower than that of terrestrial networks, there is substantial potential for growth-up to a few orders of magnitude-compared to current capacity levels.
