# Optimal Progressive Pitch for OneWeb Constellation with Seamless Coverage
For the OneWeb system, a progressive pitch-based approach is proposed, where the OneWeb satellite shifts its coverage area to lower latitudes by changing its attitude as the latitude of the satellite decreases, thus maintaining an angular separation between the OneWeb [29] system and the GSO satellite system. Seamless global coverage is a key benefit of large-scale LEO satellite constellations. Due to the large-scale constellation, the Starlink system can provide multiple coverage of the Earth's surface. It is possible to achieve a blind spot-free coverage of the Earth despite the presence of exclusion zones. For OneWeb's progressive pitch technology, it is easy to lead to communicate blind spots between adjacent satellites because the satellite coverage area is changed. Communication blind spot elimination also makes the design of the progressive pitch strategy more complicated. The interference avoiding approaches based on spatial isolation are used in both of them, but they are totally different from each other as a result of different beam patterns and antennas. Recently, a progressive pitch scheme based on the OneWeb system to avoid interference to the GSO satellite system in the downlink is given in the literature [30], but the scheme does not guarantee seamless coverage of LEO satellite systems. In this paper, the progressive pitch technique is redesigned based on the seamless coverage characteristics of the LEO satellite constellation. One of the most important features of the broadband LEO satellite constellation is to provide Internet access for seamless global coverage. When considering interference avoidance for GSO satellite systems, it is necessary to ensure that no blind spots exist within its coverage. Although there is a t of literature on interference to GSO system from LEO constellations, there is still very little research on interference avoidance techniques that can guarantee seamless coverage. This article proposes an interference avoidance scheme that enables seamless coverage. * We analyze the downlink EPFD of the NGSO satellite system on the orbital plane and evaluate each satellite's contribution to the EPFD. Based on the results of this analysis, the focus is on the EPFD in the inline scenario. * Based on the spectrum coexistence scenario of the LEO constellation and GSO satellite system, the inline interference and seamless coverage are modeled. The average total communication capacity of the LEO system is maximized under the constraints of no harmful interference to the GSO system and no blind spots between adjacent satellites. Finally, the corresponding optimization problem is created. * In order to obtain the optimal interference avoidance strategy, the problem is first discretized and reformulated. Then we solve the problem with a genetic algorithm that includes the design of the fitness function, encoding and operators. * Based on the inline interference model and OneWeb system parameters, the off-axis angle thresholds are obtained without harmful interference. The variation of various metrics with satellite latitude is also given, which includes the total satellite communication capacity, the range of the coverage overlap between adjacent satellites and the minimum off-axis angle. The rest of the paper is organized as follows. In Section 2, the inline interference and seamless coverage are modeled, and the corresponding optimization problem is formulated by maximizing the average total satellite communication capacity. In Section 3, the optimization problem is reformulated and solved by genetic algorithm. In Section 4, we evaluate the proposed algorithms by simulations. In Section 5, we conclude the study and provide an outlook on future research directions.