For areas where terrestrial fiber or microwave links are impractical, expensive, or prone to disruption, non-terrestrial solutions become vital for establishing the fronthaul (connecting radio units to baseband units) and backhaul (connecting base stations to the core network). These solutions leverage aerial or space-based platforms.

Low Earth Orbit (LEO) satellites operate at altitudes typically ranging from 160 km to 2,000 km above the Earth's surface. Unlike geostationary (GEO) satellites that reside at a fixed point in the sky at 36,000 km, LEO satellites orbit the Earth rapidly (completing an orbit in 90-120 minutes). To provide continuous coverage over a large area, LEO systems require large constellations of satellites, sometimes numbering in the thousands (e.g., Starlink, OneWeb, Project Kuiper).

The primary driver for recent LEO constellations is to provide global broadband internet access, particularly to remote, rural, maritime, and aerial users who are underserved or unserved by terrestrial networks. Their relatively low altitude leads to significantly lower latency (typically 20-50 milliseconds round-trip time) compared to GEO satellites (which have latencies of 500-600 ms).

LEO satellites are increasingly crucial for providing backhaul connectivity for terrestrial 5G (and even 4G) cellular networks, especially in remote and rural regions where laying fiber optic cables or establishing microwave links is economically prohibitive or geographically challenging.

To provide truly global and lower-latency paths, LEO satellites within the same constellation can communicate with each other using inter-satellite links (often FSO or millimeter-wave links). This allows data to hop between satellites across vast distances (e.g., crossing oceans) before being downlinked to the nearest ground gateway.

LEO satellites offer advantages such as low latency, truly global coverage, high throughput with advanced antenna and multi-beam technologies, and relatively quick deployment of user terminals. However, they also face challenges including the need for very large constellations (high launch costs), complex constellation management, and ensuring reliable links under various weather conditions.

High-Altitude Platforms (HAPs) and Unmanned Aerial Vehicles (UAVs), commonly known as drones, represent a category of aerial communication platforms that can provide wireless coverage from the air, offering flexibility and rapid deployment for various scenarios.

HAPs can carry miniature 5G/6G base stations (gNBs) or provide backhaul services. They can serve as a cost-effective alternative to satellites or terrestrial towers for providing broadband access to remote rural communities. They are also ideal for rapidly deploying additional capacity over high-demand areas during major events or for providing emergency communication services when terrestrial infrastructure is damaged after a disaster.

Both HAPs and UAVs offer dynamic and adaptable solutions for extending and augmenting network coverage, providing critical connectivity in emergency situations, and enabling specialized applications beyond the reach of traditional terrestrial networks.