I. Introduction
As 5th generation (5G) cellular networks are becoming fully commercial all around the globe, characterizing 6G challenges and requirements has recently attracted significant attention [1]–[3]. Providing ubiquitous and high-capacity connectivity, as promised in 6G, requires enabling and development of non-terrestrial networks. Among non-terrestrial networks low Earth orbit (LEO) satellite systems have gained increasing popularity due to providing seamless connectivity with lower round-trip delay—compared to geostationary satellites—especially for remote regions where the deployment of terrestrial networks is not economically reasonable [4], [5].