###### Abstract  
Direction-of-arrival (DoA) estimation methods are highly versatile and find extensive applications in satellite communication. DoA methods are employed across a range of orbits, from low Earth orbits (LEO) to geostationary Earth orbits (GEO). They serve multiple applications, including altitude determination, geolocation and estimation accuracy, target localization, and relative and collaborative positioning. This paper provides a framework for modeling the DoA angle in satellite communications with respect to the elevation angle. The proposed approach employs a closed-form expression that incorporates various factors, such as the antenna boresight angle, satellite and Earth station positions, and the altitude parameters of the satellite stations. By leveraging this formulation, the work accurately calculates the Earth station's elevation angle and effectively models the DoA angle. To the authors' knowledge, this contribution is unique and has not been previously addressed in the available literature. Furthermore, this paper studies the impact of spatial correlation in the channel on well-known DoA estimation techniques. As a significant part of this contribution, the authors introduce a signal model incorporating correlation in satellite communication. Although selected studies have presented spatial signal correlation models in satellite communications to analyze the performance metrics, such as the bit error or symbol error probability, outage probability, and ergodic capacity, this work stands out by presenting and adapting a correlation model in the signal specifically for studying DoA estimations. Accordingly, this paper evaluates DoA estimation performance using root mean square error (RMSE) measurements for different satellite communication link conditions (uplink and downlink) through extensive Monte Carlo simulations. The simulation's performance is evaluated by comparing it with the Cramer-Rao lower bound (CRLB) performance metric under additive white Gaussian noise (AWGN) conditions, i.e., thermal noise. The simulation results demonstrate that incorporating a spatial signal correlation model for DoA estimations significantly improves RMSE performance in satellite systems. direction-of-arrival (DoA) estimation; geostationary Earth orbit (GEO); low Earth orbit (LEO); multipath environment; Rician fading; spatial correlation +
Footnote †: journal: _Sensors_  
general, the satellite orbits are ellipses within the orbital plane, but, in the case of zero eccentricity, they are considered circular orbits [3]. Satellite altitude can vary significantly, from low Earth orbits (LEO) at heights of 180-2000 km to geostationary Earth orbits (GEO) at approximately 35,786 km above the Earth's surface [4]. DoA estimation methods have been extensively researched for satellite communication systems, as these methods have unique strengths and weaknesses concerning their techniques, speed, computational complexities, accuracy, and channel characteristics [5]. Consequently, DoA estimation methods find a wide range of applications in satellite communication systems, such as altitude determination [6], geolocation accuracy [7; 8], estimation accuracy [9], target localization [10], relative positioning [11], and collaborative positioning [12]. To enhance the DoA estimation performance and minimize errors, which, in turn, improves the communication system's performance and accuracy, it is crucial to model the DoA angle and satellite channel accurately. This paper provides a framework for modeling the DoA angle in satellite communications with respect to the elevation angle. The proposed approach is novel as it employs a closed-form expression utilizing the geographic coordinate system (i.e., latitude and longitude of the Earth station) and the satellite stations' altitude parameters and antenna boresight angle information to calculate the Earth station's elevation angle and accurately model the DoA angle.