However, integrating mobile devices with satellite networks is not without significant challenges.
- Doppler Effect and Signal Modulation: One of the primary challenges in connecting mobile devices to satellites arises from the relative motion between LEO satellites and devices on the ground. Due to the high velocity of LEO satellites, the Doppler effect causes a shift in the frequency of the signal, complicating the modulation and demodulation processes necessary for reliable communication [132]. This frequency shift can degrade signal quality, making real-time communication difficult.
- Latency: Another challenge is the latency introduced by the long distance between satellites and mobile devices. The time it takes for signals to travel to and from the satellite can introduce delays, which negatively impacts the quality of real-time applications, such as voice calls, video streaming, and emergency services. Reducing this latency is crucial for improving user experience and ensuring the practicality of satellite-based mobile communication.
- Antenna Limitations and Signal Processing: Mobile devices typically have small, low-power antennas (between 0.1 W and 2 W), which makes transmitting and receiving satellite signals a difficult task. To overcome this, satellites need to be equipped with advanced signal processing capabilities. For instance, satellites may require medium to large phased array antennas. These antennas can electronically adjust their beam direction without physical movement [133], enabling them to track multiple mobile devices and compensate for the Doppler shift caused by LEO satellite motion. By using an array of controllable antenna elements, these systems enhance signal quality, reduce communication latency, and support high throughput in dynamic environments [134]. Key benefits include improved reliability, better signal performance, and adaptability. However, these advanced systems significantly increase both the manufacturing and launch costs of satellites [135].
- Frequency Spectrum Compatibility: Ensuring compatibility between terrestrial and satellite communication frequencies is another critical issue. In densely populated areas, the risk of interference between these systems is particularly high, potentially causing service disruptions. Effective spectrum management is essential to ensure that both satellite and terrestrial communication networks can operate simultaneously without degradation in service quality [62]. For example, China Mobile, in collaboration with Huawei, has deployed dynamic spectrum sharing (DSS) in the NR 2.1 GHz band, enabling flexible spectrum allocation [136]. This boosts 5G data rates while maintaining service quality for 4G users. Similarly, the European Space Agency (ESA) studied the coexistence of 5G and satellite communications in the C-band, finding that adjusting base station power and satellite receiver antenna angles can reduce interference, supporting the ITU’s frequency allocation strategies [137].
- Security Concerns: Direct connections between mobile devices and satellites also raise concerns regarding security. Mobile devices that connect directly to satellite networks are vulnerable to potential attacks, such as signal spoofing, jamming, or the transmission of fake signals. These threats could lead to communication interruptions, loss of service, or even data breaches, making robust security protocols an essential part of future satellite communication systems [138].