## 1 Introduction
To confirm whether the satellite communication system can provide 5G service, 3 GPP analyzed the uplink link budget for NTNs. Unfortunately, the analysis showed that the carrier-to-noise ratio is insufficient to provide voice-over NR (VoNR) service (4.75 kbps) at an elevation angle of 30 degrees for LEO 1200 km satellites with the existing PUSCH repetition method [11; 12]. Thus, 3 GPP discussed and supported joint channel estimation for NR NTN in Release-18. Moreover, 3 GPP did not consider interference; interference leads to worse coverage performance. The interference mitigation scheme must be studied to provide ubiquitous coverage in the QEFC satellite communication system. One of the well-known interference mitigation solutions for satellite communication is frequency reuse. The frequency reuse scheme divides the frequency band into sub-bands so that the adjacent beams have disjoint frequency bands [13]. Although frequency reuse significantly mitigates the interference, it reduces the available bandwidth for each beam. Furthermore, frequency reuse does  
Figure 1: Service link types (**a**) earth-moving cells and (**b**) quasi earth-fixed cells. not solve the severe path loss problem; the performance still degrades at low elevation angles due to high path loss. Another interference mitigation scheme is beamwidth control. SpaceX in [14] mentions that the increasing size of the spot on the ground increases the potential for interference with other beams using the same frequencies. SpaceX controls the half-power beamwidth between \(2.15^{\circ}\) and \(2.45^{\circ}\) in the Ku-band to mitigate interference by controlling the active antenna elements at various steering angles [14]. The authors of [15] controlled the beamwidth and altitude of the satellite to maximize uplink coverage probability. The controlled beamwidth mitigates interference by limiting the interference region and improves the uplink coverage probability. However, the authors of [15] did not consider the antenna pattern effect, an essential issue in directional antenna systems. Based on the above discussion, this paper evaluates the performance of QEFC LEO satellites, an area that has received relatively less attention. We analyze serving and interference power for each elevation angle by considering the antenna gain, antenna pattern, and large-scale fading. To improve the uplink coverage probability and solve the low SINR problem highlighted in [7; 8], especially at low elevation angles, we propose the optimal beamwidth maximizing uplink coverage probability scheme. The proposed scheme maximizes uplink coverage probability with target SINR for QEFC LEO satellites by tuning beamwidth for different elevation angles. The remainder of the paper is organized as follows. The primary notations in this paper are listed in Table 1. Section 2 introduces the system model, which is the large-scale channel model described in [16]. Section 3 introduces the proposed optimal beamwidth maximizing uplink coverage probability. Three parts are included in the proposed scheme: beam boresight direction, uplink coverage probability analysis model, and beamwidth optimization. The numerical results and discussion of the proposed scheme are shown in Section 4. Finally, the concluding remarks are in Section 5.