HAPS IMT Base Station

Description

HIBS, the HAPS IMT Base Station, is a Rel-20 concept studied in 3GPP TR 22.870 that defines how an IMT (International Mobile Telecommunications) base station can be deployed on a High Altitude Platform Station (HAPS). A HAPS is an airborne platform — such as a solar-powered aircraft, airship, or balloon — operating in the stratosphere at altitudes typically between 18 and 25 km, quasi-stationary over a service area. By mounting a base station on such a platform, the network can provide wide-area coverage comparable to a terrestrial macro cell but from the sky, without the cost and delay of building ground infrastructure.

Architecturally, HIBS is treated as part of the radio access network. The airborne base station communicates with user equipment (UE) on the ground using licensed IMT spectrum, while connecting back to the core network through a backhaul link. That backhaul may be provided by a satellite, a ground station gateway, or another airborne relay, depending on the deployment. The HAPS platform itself is not a 3GPP-defined node; 3GPP specifies the base station functions and the interfaces that allow the airborne node to integrate with the 5G system as a gNB or similar access node.

The key technical challenge HIBS addresses is the propagation environment. At stratospheric altitude, the radio link to the ground has a long line-of-sight path with different delay, Doppler, and path-loss characteristics than a terrestrial cell. HIBS studies therefore examine timing advance, mobility management, and beamforming implications, as well as how to manage interference with terrestrial cells sharing the same spectrum. Because the platform moves slowly relative to the ground, mobility is quasi-static, but the large coverage footprint means many UEs may be served simultaneously.

HIBS is closely related to NTN (Non-Terrestrial Networks) work in 3GPP, but it is distinct: NTN covers satellite and airborne platforms broadly, while HIBS specifically addresses the base station function on a HAPS platform. The Rel-20 study in TR 22.870 focuses on use cases and service requirements, including coverage extension in rural, remote, and disaster-affected areas, as well as temporary capacity augmentation for events. HIBS is therefore positioned as a complement to terrestrial RAN and satellite NTN, filling a coverage gap at intermediate altitude.

For network operators, HIBS offers a way to serve low-density or hard-to-reach areas economically, and to restore service quickly after a disaster when terrestrial infrastructure is damaged. For regulators and standards bodies, it raises questions of spectrum sharing, cross-border interference, and coordination with terrestrial and satellite systems. The Rel-20 study is the first step toward normative specifications that would allow commercial HIBS deployments integrated with 5G networks.

Purpose & Motivation

HIBS exists to solve a persistent problem in mobile networks: the economics of coverage. Terrestrial base stations require land, power, backhaul, and maintenance, which makes serving remote, rural, maritime, or disaster-affected areas expensive or impractical. Satellite NTN can cover these areas but has high latency and limited capacity in some configurations. HIBS fills the gap by placing a base station at stratospheric altitude, where it can cover a large footprint with lower latency than satellite and lower cost than building many terrestrial sites.

The concept was motivated by advances in high-altitude platform technology — solar-powered aircraft and airships capable of staying aloft for weeks or months — and by 3GPP's broader NTN work in Releases 17 and 18. Those earlier releases established NTN architecture and channel models for satellite access; Rel-20's HIBS study in TR 22.870 extends the thinking to airborne IMT base stations specifically, defining service requirements and use cases.

HIBS also addresses resilience. When earthquakes, floods, or conflicts destroy terrestrial infrastructure, a HAPS-based base station can be deployed or repositioned quickly to restore connectivity. This makes HIBS valuable not only for routine coverage extension but also for emergency communications, a priority in 3GPP service requirements.