A paper published in Nature addresses one of the more persistent engineering problems facing future 6G radio access networks: how to cut the energy consumed by aerial base stations while they serve mobile users on the ground.

The study, titled "Joint optimization of HBS 3D trajectory and power allocation transmission for energy-efficient NOMA downlink in 6G networks," focuses on high-altitude platform stations (HAPS) acting as hovering base stations, or HBS. These aerial platforms are expected to carry transmitters in future network architectures, providing coverage from the air rather than from towers.

What the researchers modeled

The paper's core contribution is a joint optimization framework. Instead of treating flight path and radio transmission as separate engineering problems, the researchers model them together. The framework optimizes two variables simultaneously: the three-dimensional trajectory of the aerial base station and the power it allocates across users on the downlink.

The multiple access scheme under study is NOMA — non-orthogonal multiple access. NOMA allows a base station to serve several users on the same time-frequency resource by splitting them in the power domain, with successive interference cancellation at the receiver. Researchers have long promoted NOMA as a spectral-efficiency tool for dense networks, and this work applies it to the aerial-base-station scenario that 6G proponents frequently cite as a use case for HAPS deployments.

The objective function is energy efficiency. By adjusting both where the platform flies in three dimensions and how much transmit power it dedicates to each user, the system aims to deliver downlink throughput while minimizing total energy expenditure — a trade-off that matters for platforms with limited onboard power budgets.

Why trajectory and power interact

The coupling between the two variables is the reason joint optimization is difficult. An aerial base station's position determines its channel conditions to every user on the ground: fly closer, and the link budget improves, but the platform may drift away from other users it also needs to serve. Power allocation, in turn, depends on those channel conditions, which shift continuously as the platform moves.

Solving the two problems independently leaves performance on the table. The paper's contribution is a method that treats trajectory planning and power assignment as a single optimization problem, which the authors evaluate for the downlink direction of a 6G NOMA system.

Context: HAPS, NOMA and the 6G research agenda

The work sits at the intersection of two active research tracks. The first is aerial network infrastructure. Regulators have already moved on this front: the International Telecommunication Union has allocated spectrum for HAPS, and standards bodies including 3GPP have studied non-terrestrial networks (NTN) in recent releases, work that brought satellite and high-altitude platforms into cellular standardization. Aerial base stations are a natural extension of that trajectory, positioned as a way to deliver coverage where terrestrial builds are uneconomic.

The second track is NOMA itself. Despite extensive academic literature, NOMA did not make the cut as a mainstream feature in 5G specifications, where orthogonal schemes dominated. 6G research programs have revived interest in non-orthogonal approaches, and energy efficiency — rather than raw spectral gain alone — has become a more prominent criterion in that discussion. Positioning NOMA within an energy-constrained aerial platform scenario is consistent with that shift.

Research result, not deployment

The Nature paper is a theoretical and modeling study, not a product announcement or operator trial. It proposes an optimization method and evaluates it analytically; it does not report field measurements, vendor contracts, or commercial deployments. For telecom operators and vendors tracking 6G readiness, the relevant takeaway is methodological: joint trajectory-and-power optimization appears to improve the energy efficiency of aerial NOMA downlinks compared with approaches that separate the two problems.

That distinction matters. Vendors and platform operators have made expansive claims about HAPS-based connectivity over the past decade, with several high-profile programs scaled back or shut down after commercial results failed to match the projections. Peer-reviewed optimization work like this paper addresses the underlying physics and resource-allocation questions that will determine whether such platforms can operate efficiently at all — questions that marketing materials tend to skip.

Energy efficiency has also become a regulatory and cost issue in its own right. Network operators face rising energy bills and mounting scrutiny of power consumption across radio access networks. Any architecture that adds aerial transmitters to the network must clear an energy-efficiency bar that terrestrial infrastructure already struggles to meet.

Outlook

For 6G standardization, studies of this kind feed the research phase that precedes any specification work. ITU's framework development for 6G — IMT-2030 — is underway, with candidate radio technologies expected to be assessed in the coming years before standards converge around 2028–2030. Research on joint optimization of aerial platform trajectories and NOMA power allocation will inform which non-terrestrial and non-orthogonal techniques make it into that process, and how energy-efficient 6G aerial coverage might eventually become.