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Power from Space: Coordinated Satellite Charging for Off-Grid Wireless Systems
Osmel M. Rosabal, Amirhossein Azarbahram, Mateen Ashraf, Mohammad Shehab, Abdul Basit Khattak, Onel L. A. López, Mohamed-Slim Alouini
TL;DR
Off-grid IoT deployments need energy provisioning where traditional infrastructure and UAV systems are constrained, motivating satellite-based WPT. The paper reviews long-distance microwave and laser links, proposes coordinated multi-satellite charging, evaluates received power and spillover, and discusses metasurfaces and research challenges. Its reported results connect coordinated received-power levels with representative application requirements, while experiments show long-distance feasibility but reduced efficiency at 10 km.
Problem
Off-grid missions require rapid, infrastructure-free energy provisioning, while long propagation distances and limited visibility make charging low-power IoT devices from space challenging.
Method
The paper reviews long-distance WPT, characterizes representative IoT use cases, evaluates coordinated satellite charging and inter-satellite laser links, and discusses metasurfaces.
Results
Received power ranges from sub-mW with few non-coherently coordinated satellites to tens of mW with coherent coordination, while a microwave system achieved 1% end-to-end efficiency over 10 km.
Takeaways & Limitations
Coordinated satellite charging can theoretically support representative low-duty-cycle applications when received power reaches their stated requirements, including all three applications above 4.18 mW.
Abstract
from arXiv · showhide
Satellite-enabled wireless power transfer (WPT) may be a transformative solution for charging Internet of Things (IoT) devices in off-grid scenarios where traditional technologies struggle to efficiently meet urgent energy demands. In this article, we review the advantages and limitations of microwave-based long-distance charging for satellite-enabled WPT. We then introduce our vision of coordinated space-based WPT, where multiple satellites jointly serve networks of ground devices. Potential use cases are presented highlighting application requirements. We evaluate the average received power at the target locations using two coordination schemes and perform a statistical characterization of the power spillover on undesired locations. We also shed light on the performance of inter-satellite laser WPT for different operating distances and transmit-receive apertures of the peer satellites. Moreover, we explore the integration of metasurfaces on satellite apertures and ground networks to boost energy conversion efficiency, scalability, and beam management. Finally, we outline relevant challenges and research directions towards implementing our vision.
I. INTRODUCTION
WPT could support heterogeneous IoT energy demands and off-grid deployments, but space-based charging remains difficult because of long distances and limited visibility. The paper proposes coordinated multi-satellite charging and examines its enabling technologies, use cases, and challenges.
- WPT wirelessly recharges IoT energy-harvesting devices, potentially reducing maintenance costs and e-waste while enabling smaller or temporary deployments.
- Off-grid missions such as battlefield logistics, remote monitoring, and disaster relief need rapid, infrastructure-free energy provisioning beyond traditional WPT limits.UAV-based energy transmitters can support time-critical missions, but limited autonomy constrains remote or rapidly changing operations.
- Space-based charging remains challenging because long propagation distances and limited visibility windows constrain low-power IoT device charging.These constraints motivate combining energy contributions from multiple satellites.
- Increasingly dense satellite constellations create opportunities for jointly charging ground devices when multiple satellites are simultaneously visible.
- The proposed framework dynamically selects visible or soon-to-be-visible satellites to jointly charge low-power IoT devices through ground supervision or inter-satellite links.Coordination may provide higher beamforming gains, longer service windows, lower per-satellite requirements, and spatial diversity against fading.
- The article reviews long-distance WPT, characterizes off-grid IoT power requirements, evaluates coordinated charging and inter-satellite laser WPT, and identifies research directions.
II. LONG-DISTANCE WPT
Microwave WPT is suited to space-to-ground charging because it can serve multiple users without strict direct LoS, whereas long-distance links face severe propagation and atmospheric impairments. Experiments show technical feasibility, but efficiency generally declines as distance increases.
- Microwave WPT uses directive antennas to transmit electromagnetic energy and rectennas to convert incident signals into electrical power.Its broadcast nature enables simultaneous charging of multiple ground users without a direct LoS link.
- Space-to-ground WPT experiences cloud attenuation, rain and gas absorption, scattering, turbulence-induced scintillation, and ionospheric dispersion or polarization rotation.
- Severe free-space path loss requires optimizing hardware, onboard constraints, satellite geometry, diffraction, and spillover to ensure sufficient received power.Ground-supported metasurfaces can enlarge the energy-capturing aperture and enable indirect LoS links.
- More than 50% end-to-end efficiency has been demonstrated for tens of kW over kilometer-scale distances, while a reported microwave system achieved 1% over 10 km.The evidence preserves a sharp contrast between high efficiency at short range and degraded efficiency over longer distances.
- The paper considers microwave WPT for space-to-ground charging and laser WPT for inter-satellite charging.The division reflects the different requirements of space-ground and inter-satellite links.
III. USE CASES
Satellite-based WPT targets dispersed, difficult-to-access devices where local infrastructure is impractical or costly and service availability outweighs maximum delivered power. Representative applications span inventory, monitoring, emergencies, and intermittent edge AI.
- Satellite-based WPT is most advantageous for geographically dispersed, hard-to-access devices when local charging infrastructure is impractical or costly.Terrestrial and UAV systems remain preferable when higher received power and feasible deployment are required.
- Outdoor inventory: Outdoor inventory applications involve widely distributed sensing or tracking devices for which dense terrestrial transmitters or frequent UAV charging may be inefficient.
- Remote monitoring: Remote monitoring requires long-term operation with minimal intervention in protected regions where terrestrial infrastructure may be impractical or environmentally intrusive.
- Emergency management: After disasters damage terrestrial communications and energy infrastructure, satellite WPT can charge sparse low-power emergency sensors, alarm tags, and backscatter devices.
- Edge AI inference: Edge AI devices may use satellite WPT for occasional energy-intensive inference bursts when battery replacement and persistent local charging are impractical.Required power varies substantially: lightweight CPUs may consume 5-10 µW actively, while high-performance AI processors may require more than 100 mW.
IV. COORDINATED SPACE-BASED WPT
Coordinated satellite WPT uses dynamically selected serving sets and optimized transmission to deliver power to ground devices, while coordination, synchronization, geometry, and onboard constraints shape performance. The section also evaluates inter-satellite laser transfer and identifies pointing and operational challenges.
- Coordination architecture: Ground control stations update the serving satellite set in real time as LEO satellites enter or leave visibility windows.This aims to reduce charging interruptions and unnecessary satellite energy expenditure.
- Coordination strategies: Coherent coordination uses common phase-aligned signals, whereas non-coherent coordination combines independent satellite transmissions without inter-satellite phase alignment.Both strategies use jointly optimized array precoders under individual satellite power budgets.
- Received power: Received power ranges from sub-mW with a few non-coherently coordinated satellites to tens of mW with coherent coordination, larger arrays, and more satellites.The evaluated configuration thresholds indicate that 1.20–2.50 mW can theoretically support outdoor inventory, at least 2.50 mW can also support remote monitoring, and more than 4.18 mW can satisfy all three applications.
- Synchronization: Coherent coordination requires sub-nanosecond timing accuracy at 12 GHz to keep residual phase errors below approximately 20°.Increasing residual phase-error standard deviation reduces coherent received power, potentially producing partially coherent or non-coherent operation.
- Inter-satellite laser WPT: Inter-satellite laser pointing loss first decreases and then increases with transmit aperture, while increasing with link distance because of beam spreading.The resulting optimal aperture motivates adaptive techniques such as variable beam expansion.
- Operational constraints: Lower-altitude operation requires orbit-decay correction, collision avoidance, power-management strategies, and thermal control that can strain onboard batteries.The section also highlights solar-panel optimization and emergency GCS energy supply as operational considerations.
V. METASURFACE-ASSISTED WPT
Metasurface-assisted WPT can add beam-control and propagation capabilities to coordinated satellite charging. Its deployment requires balancing efficiency and adaptability against hardware, structural, synchronization, and calibration constraints.
- Satellite apertures: Satellite metasurfaces can provide additional spatial degrees of freedom for coherent beam concentration and improve individual-link directivity under non-coherent coordination.Coherent operation still requires inter-satellite phase and timing synchronization.
- Reconfigurable surfaces: Dynamic metasurface antennas and reconfigurable holographic surfaces offer low-power, scalable beamforming using fewer RF chains and many fed elements.High-power handling remains necessary because intense surface currents can cause dielectric heating or breakdown.
- On-orbit deployment: Large effective apertures must be balanced against satellite mass and launch-volume constraints, motivating planar, foldable, or deployable surfaces.Deployment deformation, attitude errors, changing LEO geometry, and coherent synchronization require calibration and adaptive phase compensation.
- Receiver-side surfaces: Receiver-side reflective surfaces such as RISs can capture and redirect otherwise lost energy, creating virtual LoS links in blocked environments.Limited phase resolution, tunable-element nonlinearity, and mutual coupling can reduce beamforming accuracy and efficiency.
VI. CONCLUSION & OUTLOOK
The article frames coordinated satellite charging as an opportunity for off-grid energy provision while identifying beamforming, autonomy, safety, tracking, efficiency, and control challenges that require further work.
- Conclusion & Outlook: The article reviews RF- and laser-based space WPT and examines coordination, array size, satellite count, laser pointing, and metasurface integration.It presents coordinated satellite charging for low-power ground devices and discusses representative applications and service requirements.
- Distributed Beamforming Management: LEO motion changes propagation delays, Doppler shifts, and serving-set geometry, so beam management must track and compensate these variations to avoid synchronization and beamsteering errors.Suggested measures include redundancy, adaptive re-optimization, predictive beamforming, and potentially optimization or reinforcement learning at the ground control station.
- Satellite Autonomy: WPT power allocation must preserve primary satellite functions, while high-power operation can increase aperture, amplification, storage, thermal-management, mass, and hardware requirements.The article recommends reusing communication apertures and RF hardware and adapting WPT to onboard energy and thermal conditions.
- Safety Concerns: Pointing errors can send high-power inter-orbital laser beams toward Earth, creating potentially hazardous exposure that motivates feedback-based interruption and further safety studies.Transmission could be interrupted when alignment is lost and resumed after the receiver link is re-established.
- Laser WPT Challenges: Accurate laser alignment requires timely target-satellite positions, but temporal gaps in TLE data may limit arcsecond-level pointing accuracy and create a microwave-positioning versus laser-power allocation trade-off.The paper also identifies changing receiver temperature as a source of variable optical-to-electrical conversion efficiency, making constant transmit power potentially suboptimal.
- Channel Acquisition and Beam Control: Rapidly varying geometry, Doppler shifts, propagation delays, and large metasurface element counts make channel acquisition and beam-control overhead important implementation challenges.Perfect instantaneous CSI may overestimate coherent beamforming gains.
BIOGRAPHIES
The authors are researchers and academics affiliated mainly with the Centre for Wireless Communications at the University of Oulu, with additional affiliations at the German University in Cairo and KAUST.
- Author Affiliations: Osmel M. Rosabal, Amirhossein Azarbahram, Mateen Ashraf, Abdul Basit Khattak, and Onel L. A. López are affiliated with the Centre for Wireless Communications at the University of Oulu, Finland.Their research areas include RF localization and sensing, AI-enabled wireless communications, long-distance wireless charging protocols, and RF wireless power transfer.
- Author Affiliations: Mohammad Shehab is an Assistant Professor of Networks at the German University in Cairo, Egypt.
- Author Affiliations: Mohamed-Slim Alouini is a Distinguished Professor of Electrical Engineering at KAUST, Saudi Arabia.