## 8 Conclusions  
Assessing the performance of DoA estimation methods for satellite communication systems is crucial, as it involves various aspects that must be considered. This paper has provided a framework for modeling the DoA angle in satellite communications with respect to the elevation angle. It employed a closed-form expression incorporating the antenna boresight angle, satellite and Earth station positions, and altitude parameters of the  
Figure 14: RMSE \(\sigma(\theta)\) of downlink low Earth orbit satellite using the DAS technique for changes in decorrelation distance values in spatially correlated channels with AWGN and Rician fading (Case-vii).  
Figure 13: RMSE \(\sigma(\theta)\) performance of downlink low Earth orbit satellite using the DAS technique for change in \(K\) factor values in spatially correlated channels with AWGN and Rician fading (Case-vi).  
satellite stations to model the DoA angle. Furthermore, this work adapted a spatial signal correlation model to analyze the well-known DoA estimations performance for satellite communications. The study considered different geometries for both uplink and downlink scenarios, and the DoA estimation performance was evaluated under each condition, namely, a geographic coordinate system for the uplink and simplified geometries for the downlink. The analysis in this study primarily focused on downlink transmission due to the presence of fading and correlation, which are typically influenced by factors such as the terrain and receiver infrastructure. In contrast, the uplink transmission, lacking similar environmental influences, was simplified to an additive white Gaussian noise (AWGN) scenario. Additionally, the nature of free space in the uplink made correlation considerations unnecessary. Therefore, the study emphasized the downlink analysis while acknowledging the distinct characteristics and limitations of the uplink scenario. The numerical analysis considered a wide range of signal-to-noise ratio (SNR) values, sample sizes, decorrelation distance \(D_{0}\), and Rician \(K\) factor values. The simulation results indicate that the RMSE \(\sigma(\theta)\) performance is acceptable for higher SNR \((\gamma)\) values, specifically from 30 [dB], as the estimation error increases at lower SNR \((\gamma)\) values for the uplink scenario. The downlink scenario, including spatial correlation, resulted in a better RMSE \(\sigma(\theta)\) performance than the uncorrelated case, indicating parameter estimation for the line-of-sight (LoS) angle was more stable for all paths due to the reduced randomness in the correlation case. The outcomes also suggested that the spatially correlated case matched the AWGN case when there was no fading, i.e., a 100% correlation case, for instance, around K = 100 [dB].  
Conceptualization, M.H. and S.K.; methodology, M.H. and S.K.; software, M.H.; validation, M.H. and S.K.; writing--original draft preparation, M.H.; writing--review and editing, M.H., S.K., W.S.T.R. and A.A.-H.; supervision, S.K., W.S.T.R. and A.A.-H. All authors have read and agreed to the published version of the manuscript.  
This research received grant funding from the Australian Government under the Department of Industry, Innovation and Science grant AEGP000053. It has also received support through an Australian Government Research Training Program Scholarship.  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors declare no conflict of interest.