## 3 Challenges and Related Recommendation
### Future Research Challenges
#### 3.2.2 Space-Air-Ground-Sear (SAGS) Networks and Integrated Sensing and Computing Networks
Figure 12: UAV communication system tools. In addition, there is an immediate need for creativity in the following areas of the SAGS unified network: structure layout, movement administration, network procedure, resource placement, routing tactics, EE improvement, and beyond. To ensure that users have access to secure and dependable communication solutions, it is important to plan a network layout that is both effective and secure [101]. It is essential that the interconnected networks have efficient, secure, and transparent authentication mechanisms [102]. Advanced mobility control systems are necessary to ensure smooth mobility control between diverse and homogeneous networks, taking into account various forms of movement in different settings [46]. When planning network protocols, resource allocation, and routing techniques, it is important to keep in mind the SAGS combined network's flexible architecture and elevated movement features [103]. Preservation and improvement of SAGS-based networks necessitates taking into account the power provision of the connectivity base as well as the burden of UAVs and other equipment, all of which place high demands on the total EE of the system. Figure 13: Wireless and broadband applications in different scenarios. (**a**) UAV-to-ground communication in urban and rural areas, illustrating line-of-sight (LOS) and multi-bounce rays with a UAV trajectory over diverse building environments, (**b**) UAV-based communication over marine areas, depicting single-cluster and twin-cluster models, with evaporation duct effects and various signal propagation paths, and (**c**) an overview of various 6G transmission and reception scenarios, including UAV-to-UAV, UAV-to-ship, ship-to-land, underwater acoustic communication, vehicle-to-vehicle (V2V), ultra-massive MIMO, mmWave/THz/optical wireless, and IoT applications for industry and indoor hotspots. Simultaneously, it is essential to evaluate how to achieve a balance between enhancing network efficiency and controlling expenses [104]. Furthermore, the application of AI, deep learning, and other smart technologies to improve network structure and enhance entire network reliability [105] is a significant contemporary concern. The current network designs are inadequate for delivering customized network solutions tailored to various task kinds in SAGS. Furthermore, they are unable to effectively address numerous issues in SAGS, including diverse network separation, elevated network latency, sporadic interruptions, and imbalanced network traffic. Edge-cloud processing technology and networks might be employed to resolve the aforementioned issues, facilitating smart networking, and minimizing latencies. Various tasks operating within SAGS and their scheduling [52] may possess distinct network performance needs. SAGS cannot uniformly fulfil the requirements of all tasks. The user quality may be compromised, resulting in an imbalanced network load while addressing a more critical demand. Moreover, equipment roaming, and an inadequate connection setting may result in sporadic network outages and extended network reaction delay. The current network topologies are inadequate for SAGS in this complex environment. The conventional TCP/IP design is incapable of addressing link interruptions and exhibits drawbacks such as suboptimal bandwidth usage and inadequate security for the network. The information hub system [106], constrained by the extent and volume of data within SAGS, will result in a mass of material namespaces. This will result in significant latency cost for material extraction, hence extending network latency. Moreover, current network topologies do not address the issue of mixed network cooperation, resulting in suboptimal resource use, and proactive propagation is frequently neglected.