I. Introduction
Satellite communication systems have the advantage of wide coverage and low construction cost, which is the trend of next-generation communication systems [1], [2], [3], [4]. Recently, non-geostationary orbit (NGSO) constellations have developed rapidly, such as Oneweb, Starlink, Telesat, etc [5]. In order to provide broadband transmission and seamless coverage, the NGSO constellation needs to achieve multiple coverage, that is, some areas are covered by multiple satellites. In addition, due to the non-uniform geographic distribution of the ground users and high mobility of NGSO satellites, the traffic demands in the area seen by the satellite show temporal and spatial non-uniformity. Therefore, how to make full use of the feature of multiple coverage to match limited satellite resources to non-uniform services is a major challenge for NGSO satellite systems [6], [7].