1.
Trinh, Phuc V.; Sugiura, Shinya; Xu, Chao; Hanzo, Lajos
Optical RISs Improve the Secret Key Rate of Free-Space QKD in HAP-to-UAV Scenarios Journal Article
In: IEEE Journal on Selected Areas in Communications, vol. 43, no. 8, pp. 2747–2764, 2025, ISSN: 1558-0008.
Abstract | Links | BibTeX | Tags: Atmospheric modeling, Drones, Fluctuations, Free-space optics (FSO), Global Positioning System, high-altitude platforms (HAPs), Laser beams, low-altitude platforms (LAPs), Optical beams, Optical reflection, Power distribution, quantum key distribution (QKD), reconfigurable intelligent surface (RIS), Reconfigurable Intelligent Surfaces, Satellites
@article{trinh_optical_2025,
title = {Optical RISs Improve the Secret Key Rate of Free-Space QKD in HAP-to-UAV Scenarios},
author = {Phuc V. Trinh and Shinya Sugiura and Chao Xu and Lajos Hanzo},
url = {https://ieeexplore.ieee.org/document/10993364},
doi = {10.1109/JSAC.2025.3568050},
issn = {1558-0008},
year = {2025},
date = {2025-08-01},
urldate = {2025-10-08},
journal = {IEEE Journal on Selected Areas in Communications},
volume = {43},
number = {8},
pages = {2747–2764},
abstract = {Large optical reconfigurable intelligent surfaces (ORISs) are proposed for employment on building rooftops to facilitate free-space quantum key distribution (QKD) between high-altitude platforms (HAPs) and low-altitude platforms (LAPs). Due to practical constraints, the communication terminals can only be positioned beneath the LAPs, preventing direct upward links to HAPs. By deploying ORISs on rooftops to reflect the beam arriving from HAPs towards LAPs from below, reliable HAP-to-LAP links can be established. To accurately characterize the optical beam propagation, we develop an analytical channel model based on extended Huygens-Fresnel principles for representing both the atmospheric turbulence effects and the hovering fluctuations of LAPs. This model facilitates adaptive ORIS beam-width control through linear, quadratic, and focusing phase shifts, which are capable of effectively mitigating the detrimental effects of beam broadening and pointing errors (PE). Consequently, the information-theoretic bound of the secret key rate and the security performance of a decoy-state QKD protocol are analyzed. Our findings demonstrate that quadratic phase shifts enhance the SKR at high HAP-ORIS zenith angles or mild PE conditions by narrowing the beam to optimal sizes. By contrast, linear phase shifts are advantageous at low HAP-ORIS zenith angles or moderate-to-high PE by diverging the beam to mitigate LAP fluctuations.},
keywords = {Atmospheric modeling, Drones, Fluctuations, Free-space optics (FSO), Global Positioning System, high-altitude platforms (HAPs), Laser beams, low-altitude platforms (LAPs), Optical beams, Optical reflection, Power distribution, quantum key distribution (QKD), reconfigurable intelligent surface (RIS), Reconfigurable Intelligent Surfaces, Satellites},
pubstate = {published},
tppubtype = {article}
}
Large optical reconfigurable intelligent surfaces (ORISs) are proposed for employment on building rooftops to facilitate free-space quantum key distribution (QKD) between high-altitude platforms (HAPs) and low-altitude platforms (LAPs). Due to practical constraints, the communication terminals can only be positioned beneath the LAPs, preventing direct upward links to HAPs. By deploying ORISs on rooftops to reflect the beam arriving from HAPs towards LAPs from below, reliable HAP-to-LAP links can be established. To accurately characterize the optical beam propagation, we develop an analytical channel model based on extended Huygens-Fresnel principles for representing both the atmospheric turbulence effects and the hovering fluctuations of LAPs. This model facilitates adaptive ORIS beam-width control through linear, quadratic, and focusing phase shifts, which are capable of effectively mitigating the detrimental effects of beam broadening and pointing errors (PE). Consequently, the information-theoretic bound of the secret key rate and the security performance of a decoy-state QKD protocol are analyzed. Our findings demonstrate that quadratic phase shifts enhance the SKR at high HAP-ORIS zenith angles or mild PE conditions by narrowing the beam to optimal sizes. By contrast, linear phase shifts are advantageous at low HAP-ORIS zenith angles or moderate-to-high PE by diverging the beam to mitigate LAP fluctuations.
2.
Trinh, Phuc V.; Sugiura, Shinya; Xu, Chao; Hanzo, Lajos
Toward Quantum SAGINs Harnessing Optical RISs: Applications, Advances, and the Road Ahead Journal Article
In: IEEE Network, vol. 39, no. 3, pp. 215–222, 2025, ISSN: 1558-156X.
Abstract | Links | BibTeX | Tags: Airplanes, Buildings, Drones, free-space optics, Low earth orbit satellites, next-generation network, Optical beams, Optical fiber networks, Optical fibers, optical reconfigurable intelligent surface, Quantum entanglement, quantum Internet, Relays, Satellites, Space-air-ground integrated network, Space-air-ground integrated networks
@article{trinh_toward_2025,
title = {Toward Quantum SAGINs Harnessing Optical RISs: Applications, Advances, and the Road Ahead},
author = {Phuc V. Trinh and Shinya Sugiura and Chao Xu and Lajos Hanzo},
url = {https://ieeexplore.ieee.org/document/10858146},
doi = {10.1109/MNET.2025.3536848},
issn = {1558-156X},
year = {2025},
date = {2025-05-01},
urldate = {2025-10-08},
journal = {IEEE Network},
volume = {39},
number = {3},
pages = {215–222},
abstract = {The space-air-ground integrated network (SAGIN) concept is vital for the development of seamless next-generation (NG) wireless coverage, integrating satellites, unmanned aerial vehicles, and manned aircraft along with the terrestrial infrastructure to provide resilient ubiquitous communications. By incorporating quantum communications using optical wireless signals, SAGIN is expected to support a synergistic global quantum Internet alongside classical networks. However, long-distance optical beam propagation requires line-of-sight (LOS) connections in the face of beam broadening and LoS blockages. To overcome blockages among SAGIN nodes, we propose deploying optical reconfigurable intelligent surfaces (ORISs) on building rooftops. They can also adaptively control optical beam diameters for reducing losses. This article first introduces the applications of ORISs in SAGINs, then examines their advances in quantum communications for typical SAGIN scenarios. Finally, the road ahead towards the practical realization of ORIS-aided NG quantum SAGINs is outlined.},
keywords = {Airplanes, Buildings, Drones, free-space optics, Low earth orbit satellites, next-generation network, Optical beams, Optical fiber networks, Optical fibers, optical reconfigurable intelligent surface, Quantum entanglement, quantum Internet, Relays, Satellites, Space-air-ground integrated network, Space-air-ground integrated networks},
pubstate = {published},
tppubtype = {article}
}
The space-air-ground integrated network (SAGIN) concept is vital for the development of seamless next-generation (NG) wireless coverage, integrating satellites, unmanned aerial vehicles, and manned aircraft along with the terrestrial infrastructure to provide resilient ubiquitous communications. By incorporating quantum communications using optical wireless signals, SAGIN is expected to support a synergistic global quantum Internet alongside classical networks. However, long-distance optical beam propagation requires line-of-sight (LOS) connections in the face of beam broadening and LoS blockages. To overcome blockages among SAGIN nodes, we propose deploying optical reconfigurable intelligent surfaces (ORISs) on building rooftops. They can also adaptively control optical beam diameters for reducing losses. This article first introduces the applications of ORISs in SAGINs, then examines their advances in quantum communications for typical SAGIN scenarios. Finally, the road ahead towards the practical realization of ORIS-aided NG quantum SAGINs is outlined.