# Coexistence in Wireless Networks: Challenges and Opportunities
## 4 Spectrum Sharing and Coexistence
### Coexistence in Satellite Communication  
The rapid rise of internet applications and services has intensified the demand for high-speed, versatile, and reliable communication networks with minimal latency. Consequently, satellite communications have entered a critical phase of development [60]. Satellites can significantly contribute to meeting this demand, either as standalone systems or as integrated satellite-terrestrial networks, leveraging their unique capabilities and technological advancements [67]. Figure 7 illustrates the interference in satellite and terrestrial communication networks, where multiple signals overlap, causing disruptions. The satellite transmits signals to ground stations, but interference sources, such as overlapping frequency bands or environmental factors, introduce noise. Wireless communication devices and base stations also contribute to interference, affecting signal clarity and reception. The distorted signals can degrade communication quality, leading to data loss, increased latency, or connectivity issues. Facilitating communication across great distances and in isolated areas, satellite communication is an essential part of contemporary communication systems [68]. However, the coexistence of satellite communication systems has become an important issue because of the growing number of satellite systems and the limited amount of orbital space that is accessible [69]. 5G cellular systems operating below 6 GHz are provided in [70]. The study analyzes the potential impact of out-of-band emissions, receiver saturation, and active  
Figure 7: Coexistence of the 5G signal and satellite services. antenna systems on both the uplink and downlink performance. The outcomes will inform the assessment of how future 5G deployments may affect C-band satellite Earth station receivers and the related stakeholders. It suggests and tests possible ways that enable both systems to coexist more easily, such as turning off essential emitters or reducing the power of their transmission. [PERSON] [PERSON] and [PERSON] and [PERSON] (2020) developed a methodology to assess the compatibility of existing satellite networks and emerging 5G services within the millimeter-wave spectrum, aligned with the IMT-2020 framework. This study modeled signal propagation and analyzed interference between fixed satellite services (FSS) operating in the same band and adjacent-channel passive Earth exploration satellite services (EESS). The results indicate that FSS satellites may experience up to 7.9 dB of increased interference, while most EESS sensors fail to meet safety standards. To ensure coexistence, additional spectrum allocation or interference mitigation measures are necessary. This approach can also be applied to assess interference from non-terrestrial platforms such as airships, balloons, and UAVs. A smart antenna system employing the Recursive Least Squares (RLS) algorithm for adaptive beamforming is proposed in ([PERSON] et al., 2019) to facilitate coexistence between FSS and 5G networks. The RLS algorithm is utilized to generate a null beam directed toward FSS Earth stations, thereby mitigating interference. The simulation results demonstrate that this approach significantly reduces the required separation distance between 5G base stations and FSS Earth stations, enabling effective coexistence with minimal interference. Ensuring the coexistence of satellite communication systems is a complex challenge that necessitates a multi-disciplinary approach. This involves several key strategies, such as interference mitigation, spectrum management, and advanced signal processing techniques. Interference mitigation focuses on reducing the potential disruptions caused by overlapping signals, while spectrum management involves carefully allocating frequency bands to avoid conflicts. Advanced signal processing techniques are employed to enhance the clarity and reliability of the communication.