## 1 Introduction  
The fifth-generation mobile network (5G) is expected to provide high-quality communications, such as a high sum rate, low latency, extended coverage, and low power consumption [1]. However, ubiquitous coverage remains a significant challenge to solve. According to [2], an estimated 34 percent of the global population cannot use the Internet. To ensure the anytime and anywhere 5G service, satellite communication, also called non-terrestrial networks (NTNs), was proposed and is becoming increasingly popular. The satellite communication system provides a comprehensive coverage area, an attractive solution for ubiquitous wireless coverage for next-generation wireless networks, especially in areas where terrestrial networks are difficult to deploy or are cost-prohibitive [3]. The Third-Generation Partnership Project (3 GPP), an international standardization organization for mobile telecommunications, started studying and standardizing how to implement satellite communication on the 5G New Radio (NR) system in Release 15 and 17. Compared with medium-earth and geostationary orbit, low-earth orbit (LEO) satellites, with altitudes less than 2000 km, they are an attractive solution to achieving ubiquitous wireless coverage and high spectral efficiency by considering propagation delay and channel attenuation. Two types of LEO service links are introduced in the 3 GPP standard (as shown in Figure 1):* Quasi earth-fixed cells (QEFC): satellites can compensate and steer the beams at the same position on the earth while satellites move. * Earth-moving cells (EMC): satellites cannot provide steerable beams. The position of beams changes while satellites move. Since the earth-moving LEO satellite moves very fast and each provides many beams, user equipment (UE) can stay inside the beam footprint for only a few seconds [4]. The rapid footprint location change creates problems for paging and handover [5]. Although 3 GPP reduces the neighbor cell measurements for handover procedures with predictable satellite locations using ephemeris information in Release 17, the network still needs to spend a lot of resources on random access procedures to handle the frequent handovers of numerous UEs. The QEFC LEO satellites are designed to steer beams to specific areas on Earth within configurable time frames, solving frequent handover issues. Over the years, 3 GPP has developed various handover strategies for the QEFC scenario, such as conditional handover in Release 17 and satellite switch with re-sync in Release 18 [6]. The QEFC scenario holds significance for the cellular satellite communications network. However, despite this importance, only a few studies have discussed and analyzed the performance of QEFC satellites. The authors of [7] evaluated the throughput and reference signal received power with different beam-fixed time durations, and the authors of [8] evaluated different elevation angles' downlink signal-to-noise-plus-interference ratio (SINR). The evaluation results show that UEs have low communication quality at low elevation angles. However, they did not delve into the reasons behind this performance drop or propose any solutions. Hence, addressing the issue of low SINR to enhance signal quality for mobile satellite communications in the QEFC scenario is essential. This paper aims to fill this gap by evaluating and analyzing the SINR of QEFC LEO satellites and proposing solutions to mitigate the low SINR problem, ultimately striving towards achieving ubiquitous coverage. Since the max transmission power of a handheld user devices is limited to 0.2 watts, it is hard for the receiver to decode the uplink signal successfully with the long-distance communication system. Some uplink coverage enhancements were proposed to strengthen the receiving power in the 3 GPP NR standard, including physical uplink shared channel (PUSCH) repetition [9], joint channel estimation [9], and peak-to-average-power ratio reduction [10].