Integration of Satellite and Terrestrial Networks in 6G

Integration of LEO with 5G, 6G and IoT networks, it is anticipated that the era of 5G networks is a significant juncture towards providing higher data rates while meeting stringent key performance indicators in terms of both continuity and ubiquity. Then, the 6G technology will come with further enhancement in terms of speed, connectivity, system capacity, communication reliability, intelligence, and other further services and enhancements. 

However, relying on terrestrial communications as theonly solution to provide wireless connectivity to users anywhere on the earth will not be feasible and achievable due to burdensome access point deployment that has led to 50% of the world having either no or poor Internet access. Also, the IoT connections in various environments and the number of mobile broadband connections are hugely increasing. This problem of limited coverage and capacity of terrestrial communications becomes more crucial if it is meant to support emerging technologies including IoT, Artificial Intelligence (AI), and cloud computing. In principle, the tremendous growth of number of User Equipment (UE) and associated services is yet another critical factor that calls for innovative paradigms other than depending solely on ground communications. 

On the other hand, satellite communications can provide seamless connectivity to underserved areas such as rural, mountain and ocean areas as well as harsh environmental conditions. Thus, the integration of 6G and IoT with satellite networks would bring lots of benefits including global coverage for radio users and IoT application. This integration also opens up doors for various applications such as earth observation and mapping, intelligent transportation, military operations, natural disaster rescue. With the fast advancement and deployment of LEO satellites, the LEO networks have been envisioned as a potential candidate to integrate with 6G and IoT networks to diversify the wireless connectivity sources. 

In the past decades, several LEO-ground integrated systems were employed to extend the wireless connectivity such as Iridium and Globalstar. Recently, there have been several LEO satellite projects and initiatives which aim at providing broadband Internet access such as SpaceX, and OneWeb, and their networks are expected to reach full operational capacity in the early 2020s.

The integration of satellite and terrestrial networks in 6G aims to create a seamless, global communication network that leverages the strengths of both systems. LEO satellite can be 6G networks to provide improved wireless connectivity due to its low propagation signal loss as compared to GEO.

1. Three-Dimensional Network Structure - 6G networks will expand into a three-dimensional structure, merging communication on the ground, in the air, and in space. This includes base stations, cars, drones, planes, High Altitude Platforms (HAPS), and satellites.

2. Enhanced Coverage and Connectivity - Satellite networks will complement terrestrial networks by providing coverage in remote and underserved areas, such as oceans and mountains, where terrestrial networks are insufficient. This ensures global connectivity and helps bridge the digital divide.

3. Key Technologies - Software-Defined Networking (SDN): This approach will help seamlessly integrate satellites into terrestrial networks, allowing for dynamic and flexible network management.

- Multicast Backhauling: This technique will be used to avoid congestion by sending data packets to multiple recipients simultaneously.

4. Challenges and Future Directions:

- Integrating these networks poses challenges such as ensuring seamless handovers between different network types, managing latency, and maintaining security. Future research is focused on addressing these issues and optimizing the performance of hybrid networks.