## 3 Challenges and Related Recommendation
### Future Research Challenges
#### 3.2.2 Space-Air-Ground-Sear (SAGS) Networks and Integrated Sensing and Computing Networks  
Realizing the dream of 6G worldwide coverage will require the SAGS integrated network, which is both a trend and a critical technology. There are numerous technical and theoretical concerns with network design, building, preservation, and optimization that need to be addressed before the SAGS integrated network can be considered fully operational. Developing and researching communication systems and networks relies on first establishing communication channels. A prevalent channel structure [73] must take into account how to incorporate distinct channel properties in satellite [91], unmanned aerial vehicle (UAV) [92], ocean [93; 94], and ground scenarios, among others, due to the significant difficulties posed by different frequency bands and scenarios when measuring and predicting channels [95]. Satellite networking stands apart due to its extensive support coverage qualities and the fact that it is a proven and operational technology with a lengthy history. Several fields have begun to rely on communications via satellite in recent years, including the broadcasting industry, directions, and earth monitoring. There is a lot to explore in using next-gendomestic wireless communication infrastructure, which means that satellite networks have to meet greater standards for things like bandwidth, QoS, and ubiquitous connection if integrated with 6G networks. Predicting the fundamental genuine transmission channel properties requires a generic, precise, and low-complexity approach, which is essential for the development and efficiency assessment of communications satellites [96]. In addition to dependable control and non-payload communication links, several emerging UAV uses, like distant sensing and aerial snapshots, necessitate a significant transmission data rate for payload connectivity [97]. The vast range and enormous capacity of existing and upcoming 6G networks make it a viable option to use future cellular networks to meet UAV communication requirements. Visions of future 6G wireless communication network deployments point to UAVs acting as base stations for mobile devices as a key component in expanding network reach [39]. Figure 12 shows some tools that enables the UAV system. An attractive option for providing ubiquitous access from above to ground user equipment in some situations and locations (such as hotspot regions, big public spaces, and isolated places without network service) is the installation of aerial BSs [39]. The worldwide Internet of Things or global reach via 6G SAGS connected networks can be realized by integrating UAVs with other critical innovations pertaining to satellite, terrestrial, and ocean telecommunications [98]. Multipath elements (MPEs) produced by ground-level landscapes and structures are the root source of small-scale channel fading. Figure 13a shows a conventional UAV-to-ground channel situation that incorporates all conceivable forms of MPCs. Two possible paths for the broadcast data to reach are the LoS route and the multibounce route. To improve the accuracy of the UAV-to-ground channel simulation while decreasing computational complexity. In Figure 13b, we can see a simplified representation of the network structure for UAV-to-ship connectivity in maritime settings. A transceiver is attached to the UAV side, while a receiver is attached to the ship side, where SB refers to a single bounce, while MB is a multi-bounce. It is possible to place several antennas on each side. While sub-6 GHz is the most common frequency for UAV-to-ship communication, mmWave bands are also an option for seamless integration with future 6G networks [99]. Ocean surface roughness increases reflections and causes fading of multiple paths as a result of water fluctuation [100]. Figure 13c shows that there are numerous possible uses for UAVs and 6G wireless channels across various frequency bands. There is a striking disparity between the sounders and features of each channel.