As the demand for global connectivity continues to rise, particularly in remote and underserved areas, non-terrestrial networks (NTN) are playing an increasingly vital role. These networks, which include satellites, Uncrewed Aerial Vehicles (UAVs) or drones, and High Altitude Platform Stations (HAPS), are expanding the boundaries of communication infrastructure. Among these, HAPS stands out as a unique and versatile solution, bridging the gap between terrestrial networks and space-based systems like satellites. But what exactly makes HAPS different than satellites, and how do they contribute to the broader NTN ecosystem, especially when considering the advancements in Low Earth Orbit (LEO) satellites like Starlink?
What Are HAPS?
High Altitude Platform Stations (HAPS) are airborne platforms operating in the stratosphere, typically at altitudes ranging from 18 to 22 kilometers (about 11 to 14 miles) above the Earth’s surface. These platforms, which can take the form of airships, balloons, or fixed-wing aircraft, are equipped with telecommunications payloads that provide connectivity services over a wide area, often covering hundreds of kilometers in diameter. HAPS offer unique performance characteristics due to their proximity to the Earth’s surface. With slight modifications, HAPS can function like a cell tower in the sky, delivering directly to devices the high bandwidth, high throughput, and low latency needed for 5G, and potentially 6G, applications. This makes them ideal for meeting the demands of mobile network operators (MNOs) in areas such as disaster recovery and augmenting terrestrial networks. With closer proximity to Earth compared to satellites, HAPS is also optimal for other service categories such as defense, remote sensing, and Earth observation.
How HAPS Fit into Non-Terrestrial Networks
Non-terrestrial networks are designed to complement and extend the reach of terrestrial communication networks, particularly in regions where deploying infrastructure like cell towers is challenging or impossible. This includes remote, rural, or disaster-stricken areas where traditional terrestrial networks may be limited or non-existent.
- Complementary to Satellites: HAPS and LEO satellites, such as those in the Starlink constellation, serve as critical components of NTNs but operate at different altitudes and fulfill distinct roles. While LEO satellites orbit at altitudes of around 500 to 1,200 kilometers, providing global coverage and lower latency internet services compared to Geostationary (GEO) satellites, HAPS operate much closer to Earth. This proximity allows HAPS to offer more localized, high-capacity connectivity with even lower latency, complementing the broader coverage provided by LEO satellites.
What Makes HAPS Unique?
While both HAPS and satellites share the goal of expanding connectivity beyond the limits of terrestrial networks, several key differences set HAPS apart:
- Altitude and Coverage:
- HAPS operate at altitudes of around 20 kilometers, much closer to Earth than LEO satellites, which orbit between 500 and 1,200 kilometers above the surface. This allows HAPS to cover smaller areas with greater precision, providing targeted, high-capacity services where they are needed most.
- Altitude and Signal Strength
- Operating at altitudes between 500 and 2,000 kilometers, LEO satellites are closer to the Earth than traditional GEO satellites but much higher than HAPS platforms. This relatively high altitude allows them to cover wide areas, but signal strength can be a challenge for direct-to-device (D2D) connections, especially for standard mobile devices without specialized antennas. HAPS: Positioned at around 20 kilometers in the stratosphere, HAPS are significantly closer to the ground. This shorter distance enables stronger, more direct signals to reach standard devices like smartphones without specialized hardware, making HAPS generally better suited for high-quality D2D connections with minimal latency.
- Cost:
- Launching LEO satellites involves high upfront costs due to the expense of rocket launches, satellite manufacturing, and related logistics. Despite advances reducing costs, like reusable rockets from companies like SpaceX, launching a satellite is still expensive. HAPS are typically uncrewed, high-altitude aircraft or balloons operating in the stratosphere (around 20 km). Their deployment is less costly than launching rockets, as they don’t require reaching orbit. HAPS can be launched and retrieved multiple times, enabling maintenance and upgrades without additional launches.
- Latency:
- The lower altitude of HAPS results in significantly lower latency compared to even LEO satellites. While Starlink satellites offer impressive latencies of around 20 to 40 milliseconds, HAPS can achieve latencies as low as 1 to 50 milliseconds. This makes HAPS ideal for applications that demand near-instantaneous communication, such as real-time video conferencing or online gaming.
- Flexibility and Deployment:
- One of the most significant advantages of HAPS are their flexibility. HAPS can be deployed more rapidly and can be repositioned or brought back for maintenance as needed. This adaptability makes HAPS highly suited for dynamic network demands, such as disaster recovery or temporary event coverage, where quick deployment is essential.
- Capacity and Frequency Reuse:
- HAPS platforms can provide high-capacity services with better frequency reuse due to their smaller coverage areas. In high-demand areas, this focused coverage can alleviate network congestion, complementing the broader coverage provided by LEO constellations, which, while extensive, may face challenges in densely populated regions.
- Upgradability:
- HAPS typically have shorter operational lifespans compared to LEO satellites, ranging from a few months to a few years. However, this is balanced by their ease of maintenance and the ability to upgrade or replace them relatively easily. LEO satellites are designed for longer-term operation but face significant challenges when it comes to maintenance and upgrades once in orbit.
The Future of HAPS in Non-Terrestrial Networks
In a world where staying connected is more important than ever, HAPS offers a flexible, scalable, and efficient solution to bridge the digital divide. Whether providing emergency connectivity, enhancing rural broadband, or supporting the next generation of mobile networks, HAPS is set to play a pivotal role in the future of global communications, working hand in hand with satellite constellations to ensure that no one is left out of the digital revolution.
| Type of Network | Bandwidth | Latency | Coverage | Mobility | Direct-to-Device |
| LEO satellites | High | Higher than terrestrial (20-100ms) | Global, lower capacity | Constantly moving | Emerging, but limited functionality |
| HAPS | Higher than LEO, less than terrestrial | Low, comparable to terrestrial | Localized, high capacity | Quasi-stationary | Yes |
| Terrestrial (4G/5G) | Very high | Very low | Limited, very high capacity | Stationary | Yes |