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ADVANCING SECURE COMMUNICATIONS IN HIGH-MOBILITY ENVIRONMENTS: INTEGRATING QUANTUM KEY DISTRIBUTION, FREE SPACE OPTICS, AND HIGH-ALTITUDE PLATFORMS FOR ENHANCED IOT NETWORKS

Hasan Abbas Al-Mohammed

Published Jan 1, 2026• 0 citations
OpenAlex

Abstract

The emergence of massive, latency-sensitive Internet of Things (IoT) and high-mobility services in 6G networks amplifies long-standing limits of radio systems (bandwidth, interference, Doppler fragility) and exposes classical cryptography to quantum threats. This dissertation presents a framework that integrates Quantum Key Distribution (QKD) with Free-Space Optics (FSO) to provide quantum-resilient connectivity, while exploring applications to terrestrial Internet of Things (IoT), high-speed trains (HST), ultra-high-speed trains (UHST), and non-terrestrial networks (NTN) with high-altitude platforms (HAPs). On the physical layer, we build weather- and turbulence-aware FSO models (attenuation, beam propagation, pointing/beam-wander, scintillation) and derive fundamental link budgets. A core innovation for mobility is an optimization framework that maximizes the distance between base stations along a rail corridor subject to stringent Gbps-class data rate and availability constraints. This front-end optimization directly informs the subsequent design of robust FSO architectures and handover mechanisms for HST/UHST. The resulting system-achieved through divergence control, advanced acquisition-tracking-pointing (ATP), and geometry-aware handover zones-significantly reduces infrastructure density while sustaining high-capacity links. For IoT security, we propose two practical QKD delivery modes (rail-side and onboard) and quantify energy per secret bit and realistic key provisioning. For extended reach, we introduce HAP-assisted QKD via a standards-aligned trusted relay and a composable finite-key decoy-state pipeline using the Entropy Accumulation Theorem. A key contribution is a symmetry-aware altitude optimizer that selects the HAP height to bound the transmittance gap, complete with concavity proofs and implementable solvers. We show that-under realistic HAP turbulence-advanced measurement-device-independent (MDI-), twin-field (TF-), and Gaussian-modulated coherent-state continuous-variable (GM-CV-) QKD protocols all collapse, whereas the simpler per-hop BB84 with decoys remains feasible under finite-key constraints. Results include rate/feasibility maps, robust operating rules, and integrated "security dashboards," complemented by ML-based attacker detection. The framework adheres to tight size-weight-power (SWaP) constraints by prioritizing geometric control and efficient solvers over hardware escalation. Collectively, this dissertation bridges physics, security, and control into a deployable blueprint for quantum-secure communications, advancing FSO for HSTs/UHSTs through optimized base-station placement and highvelocity handovers to minimize infrastructure costs.

Related papers

Using Quantum Key Distribution With Free Space Optics to Secure Communications in High-Speed Trains

Hasan Abbas Al-Mohammed, Elias E. Yaacoub, Khalid Abualsaud +1 more

In the burgeoning era of quantum communications, Internet of Things (IoT) devices in high-speed train (HST) environments encounter formidable challenges. These devices are constrained by limited power and computational capabilities while needing to safeguard their data and communications against adversaries equipped with quantum-grade computational power. To counter such threats, Quantum Key Distribution (QKD) emerges as a vital solution, facilitating secure communication between servers and IoT controllers, thereby shielding the more vulnerable IoT sensors. This paper delves into the application of QKD within the unique scenario of HSTs, employing Free Space Optics (FSO) to establish high data rate communication channels. Our experimental setup involves the integration of FSO links for photon exchange essential to QKD. We meticulously explore the QKD process in the context of HSTs, detailing our methodology that involves the alignment of FSO transceivers on ground base stations with those on the moving trains, thereby enabling efficient photon exchange. The study presents quantitative results demonstrating that this approach allows for the exchange of a substantial number of keys, with negligible impact on FSO data throughput. These findings highlight that our proposed method can significantly enhance IoT communication security in HSTs without compromising the Quality of Service (QoS) offered to train passengers. Furthermore, we assess the system’s performance under various visibility conditions, which is crucial for FSO viability. Our results indicate the robustness of the proposed QKD method in diverse operational scenarios, underlining its practical applicability in securing IoT communications within HST environments. Through this study, we provide a comprehensive understanding of implementing QKD in high-speed mobile settings, contributing valuable insights into its effectiveness and feasibility.

IEEE Access•Jan 1, 2024•18 citations

Quantum Leaps in the Sky: Composable XOR–Relay QKD over HAPs for Next-Gen 6G Networks

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Quantum key distribution (QKD) via free-space optical (FSO) links suffers from severe turbulence losses and limited range in satellite-to-ground scenarios. We propose a two-hop XOR-relay architecture employing a high-altitude platform (HAP) to segment the link, reducing both geometric and atmospheric attenuation. Our simulation framework incorporates beam wandering, finite-key constraints, and realistic link geometry. Simulation results show up to a 55 times transmittance gain, 18% energy-per-bit savings, and a 64.2 kb/s secret key rate with under 3 ms latency. We formulate a constrained min–max optimization to minimize worst-case delay while meeting key rate, quantum bit error rate (QBER), and protocol overhead bounds. The XOR relay ensures composable secrecy with negligible information leakage, confirming the feasibility of stratospheric relays for low-latency, quantum-secure backhaul in future 6G non-terrestrial networks.

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This paper proposes a high-altitude platform (HAP)-aided relaying satellite free-space optics (FSO) quantumkey distribution (QKD) system for the secure vehicular networks supporting unmanned vehicles (UAV) and regular vehicles. The subcarrier intensity modulation (SIM) binary phase shift keying (BPSK) and dual-threshold/direct detection (DT/DD) receiver are employed. The relaying HAP is equipped with optical amplifyand-forward (OAF) relaying node. We analytically derive the ergodic secret-key rate of the proposed system under the impact of atmospheric turbulence and other noises. Gaussian beam model is used to evaluate the impact of geometrical spreading on the signal received by the legitimate users and the probability of being eavesdropped. The numerical results confirm the feasibility of the proposed system.

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Machine Learning for Specialized QKD Aspects: A Survey of Adaptive Protocols, Free-Space Links, 6G Integration, and Steerability-Aware Security

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Quantum Key Distribution (QKD) provides information-theoretic security grounded in the laws of quantum mechanics, yet practical deployment increasingly extends beyond conventional point-to-point fiber links. Several rapidly emerging QKD directions are often studied separately, including adaptive protocol and parameter support; free-space, satellite, UAV, and high-altitude platform (HAP) channels; integration with IoT and 6G networks; quantum-secured federated learning; Quantum Machine Learning (QML) assisted decision support; and steerability-aware estimation for one-sided device-independent QKD. This survey examines how Machine Learning (ML), Reinforcement Learning (RL), and QML address these specialized scenarios and organizes the literature into five thematic pillars: (I) adaptive protocol and parameter support; (II) free-space, satellite, UAV, and HAP-assisted QKD; (III) QKD for IoT, 6G, and quantum-secured federated learning; (IV) QML-assisted QKD functions; and (V) steerability-aware and one-sided device-independent QKD security estimation. For each theme, we follow a consistent problem, conventional solution, and ML/RL/QML solution structure and summarize reported gains using metrics such as accuracy, mean absolute percentage error, QBER reduction, and secret key rate improvement. We further provide thematic and cross-theme comparison tables and identify open challenges, including dataset scarcity, transferability across weather and mobility conditions, interpretability, trustworthy QML, and the boundary between ML-based decision support and security certification. This survey serves as a focused reference for adaptive, non-terrestrial, and application-integrated QKD systems.

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Quantum key distribution (QKD) is one of the most mature quantum technologies and can provide quantum-safe security in future communication networks. Since QKD in fiber is limited to a range of few hundred kilometers, one approach to bridge continental scale distances may be the use of high altitude pseudo satellites (HAPS) as mobile trusted nodes in the stratosphere. In parallel, free-space laser communication for high rate data transmission has been a subject of research and development for several decades and its commercialization is progressing rapidly. Important synergies exist between classical free-space communication and QKD systems since the quantum states are often implemented using the same degrees of freedom such as polarization or field amplitude and phase. These synergies can be used to benefit from the progress in classical free-space laser communication in QKD applications. In this paper, the use case of QKD in a stratospheric environment is described wherein HAPS may serve as relay station of secret keys and encrypted data. The mission scenario and HAPS capabilities are analyzed to derive special requirements on the stratospheric laser terminal, the link geometry and the ground segment with respect to a feasibility demonstration. To obtain a flexible and compatible system, discrete variable and continuous variable QKD protocols are considered to be implemented side by side in the HAPS payload. Depending on the system parameters, it can be beneficial to use the one or the other kind of protocol. Thus, a direct comparison of both in one and the same system is of scientific interest. Each of the protocols has particular requirements on coupling efficiency and implementation. Link budget calculations are performed to analyze possible distances, key rates and data transmission rates for the different schemes. In case of the QKD system, the mean coupling efficiency is of main interest, i.e. signal fluctuations arising from atmospheric turbulence must be taken into account in the security proof, but the buffered key generation relaxes real-time requirements. This is different to classical communications, where the corresponding fading loss must be assessed. A system architecture is presented that comprises the optical aircraft terminal, the optical ground terminal and the most important subsystems that enable implementation of the considered QKD protocols. The aircraft terminal is interfaced with the dedicated quantum transmitter module (Alice) and the ground station with the dedicated quantum receiver module (Bob). The optical interfaces are SMF couplings which put high requirements on the receiving optics, in particular the need for wave-front correction with adaptive optics. The findings of the system study are reviewed and necessary next steps pointed out.

•Oct 7, 2019•11 citations

Quantum Skyshield: Quantum Key Distribution and Post-Quantum Authentication for Low-Altitude Wireless Networks in Adverse Skies

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Recently, low-altitude wireless networks (LAWNs) have emerged as a critical backbone for supporting the low-altitude economy, particularly with the densification of unmanned aerial vehicles (UAVs) and high-altitude platforms (HAPs). To meet growing data demands, some LAWN deployments incorporate free-space optical (FSO) links, which offer exceptional bandwidth and beam directivity. However, without strong security measures in place, both conventional radio frequency channels and FSO beams remain vulnerable to interception and spoofing, and FSO in particular can suffer from turbulence, misalignment, and weather-related attenuation. To address these challenges in the quantum era, a quantum-secure architecture calledQuantum Skyshieldis proposed to enable reliable communication between the base transceiver station (BTS) and LAWN. The proposed design integrates BB84 quantum key distribution (QKD) with post-quantum authentication mechanisms. Simulation results confirm the reliable generation of a 128-bit symmetric key when the quantum bit error rate (QBER) remains below the threshold of 11%. Authentication is enforced using Lamport one-time signatures and hash-based message authentication codes (HMAC) to ensure message integrity. A Grover-inspired threat detection mechanism identifies anomalies with up to 89% probability in a single iteration, enabling real-time trust evaluation. Lastly, future research challenges have also been identified and discussed to guide further development in this area.

arXiv:2507.14822•IEEE Wireless Communications•Feb 2, 2026•2 citations
The emergence of massive, latency-sensitive Internet of Things (IoT) and high-mobility services in 6G networks amplifies long-standing limits of radio systems (bandwidth, interference, Doppler fragility) and exposes classical cryptography to quantum threats. This dissertation presents a framework that integrates Quantum Key Distribution (QKD) with Free-Space Optics (FSO) to provide quantum-resilient connectivity, while exploring applications to terrestrial Internet of Things (IoT), high-speed trains (HST), ultra-high-speed trains (UHST), and non-terrestrial networks (NTN) with high-altitude platforms (HAPs). On the physical layer, we build weather- and turbulence-aware FSO models (attenuation, beam propagation, pointing/beam-wander, scintillation) and derive fundamental link budgets. A core innovation for mobility is an optimization framework that maximizes the distance between base stations along a rail corridor subject to stringent Gbps-class data rate and availability constraints. This front-end optimization directly informs the subsequent design of robust FSO architectures and handover mechanisms for HST/UHST. The resulting system-achieved through divergence control, advanced acquisition-tracking-pointing (ATP), and geometry-aware handover zones-significantly reduces infrastructure density while sustaining high-capacity links. For IoT security, we propose two practical QKD delivery modes (rail-side and onboard) and quantify energy per secret bit and realistic key provisioning. For extended reach, we introduce HAP-assisted QKD via a standards-aligned trusted relay and a composable finite-key decoy-state pipeline using the Entropy Accumulation Theorem. A key contribution is a symmetry-aware altitude optimizer that selects the HAP height to bound the transmittance gap, complete with concavity proofs and implementable solvers. We show that-under realistic HAP turbulence-advanced measurement-device-independent (MDI-), twin-field (TF-), and Gaussian-modulated coherent-state continuous-variable (GM-CV-) QKD protocols all collapse, whereas the simpler per-hop BB84 with decoys remains feasible under finite-key constraints. Results include rate/feasibility maps, robust operating rules, and integrated "security dashboards," complemented by ML-based attacker detection. The framework adheres to tight size-weight-power (SWaP) constraints by prioritizing geometric control and efficient solvers over hardware escalation. Collectively, this dissertation bridges physics, security, and control into a deployable blueprint for quantum-secure communications, advancing FSO for HSTs/UHSTs through optimized base-station placement and highvelocity handovers to minimize infrastructure costs.
In the burgeoning era of quantum communications, Internet of Things (IoT) devices in high-speed train (HST) environments encounter formidable challenges. These devices are constrained by limited power and computational capabilities while needing to safeguard their data and communications against adversaries equipped with quantum-grade computational power. To counter such threats, Quantum Key Distribution (QKD) emerges as a vital solution, facilitating secure communication between servers and IoT controllers, thereby shielding the more vulnerable IoT sensors. This paper delves into the application of QKD within the unique scenario of HSTs, employing Free Space Optics (FSO) to establish high data rate communication channels. Our experimental setup involves the integration of FSO links for photon exchange essential to QKD. We meticulously explore the QKD process in the context of HSTs, detailing our methodology that involves the alignment of FSO transceivers on ground base stations with those on the moving trains, thereby enabling efficient photon exchange. The study presents quantitative results demonstrating that this approach allows for the exchange of a substantial number of keys, with negligible impact on FSO data throughput. These findings highlight that our proposed method can significantly enhance IoT communication security in HSTs without compromising the Quality of Service (QoS) offered to train passengers. Furthermore, we assess the system’s performance under various visibility conditions, which is crucial for FSO viability. Our results indicate the robustness of the proposed QKD method in diverse operational scenarios, underlining its practical applicability in securing IoT communications within HST environments. Through this study, we provide a comprehensive understanding of implementing QKD in high-speed mobile settings, contributing valuable insights into its effectiveness and feasibility.
Quantum key distribution (QKD) via free-space optical (FSO) links suffers from severe turbulence losses and limited range in satellite-to-ground scenarios. We propose a two-hop XOR-relay architecture employing a high-altitude platform (HAP) to segment the link, reducing both geometric and atmospheric attenuation. Our simulation framework incorporates beam wandering, finite-key constraints, and realistic link geometry. Simulation results show up to a 55 times transmittance gain, 18% energy-per-bit savings, and a 64.2 kb/s secret key rate with under 3 ms latency. We formulate a constrained min–max optimization to minimize worst-case delay while meeting key rate, quantum bit error rate (QBER), and protocol overhead bounds. The XOR relay ensures composable secrecy with negligible information leakage, confirming the feasibility of stratospheric relays for low-latency, quantum-secure backhaul in future 6G non-terrestrial networks.
This paper proposes a high-altitude platform (HAP)-aided relaying satellite free-space optics (FSO) quantumkey distribution (QKD) system for the secure vehicular networks supporting unmanned vehicles (UAV) and regular vehicles. The subcarrier intensity modulation (SIM) binary phase shift keying (BPSK) and dual-threshold/direct detection (DT/DD) receiver are employed. The relaying HAP is equipped with optical amplifyand-forward (OAF) relaying node. We analytically derive the ergodic secret-key rate of the proposed system under the impact of atmospheric turbulence and other noises. Gaussian beam model is used to evaluate the impact of geometrical spreading on the signal received by the legitimate users and the probability of being eavesdropped. The numerical results confirm the feasibility of the proposed system.
Quantum Key Distribution (QKD) provides information-theoretic security grounded in the laws of quantum mechanics, yet practical deployment increasingly extends beyond conventional point-to-point fiber links. Several rapidly emerging QKD directions are often studied separately, including adaptive protocol and parameter support; free-space, satellite, UAV, and high-altitude platform (HAP) channels; integration with IoT and 6G networks; quantum-secured federated learning; Quantum Machine Learning (QML) assisted decision support; and steerability-aware estimation for one-sided device-independent QKD. This survey examines how Machine Learning (ML), Reinforcement Learning (RL), and QML address these specialized scenarios and organizes the literature into five thematic pillars: (I) adaptive protocol and parameter support; (II) free-space, satellite, UAV, and HAP-assisted QKD; (III) QKD for IoT, 6G, and quantum-secured federated learning; (IV) QML-assisted QKD functions; and (V) steerability-aware and one-sided device-independent QKD security estimation. For each theme, we follow a consistent problem, conventional solution, and ML/RL/QML solution structure and summarize reported gains using metrics such as accuracy, mean absolute percentage error, QBER reduction, and secret key rate improvement. We further provide thematic and cross-theme comparison tables and identify open challenges, including dataset scarcity, transferability across weather and mobility conditions, interpretability, trustworthy QML, and the boundary between ML-based decision support and security certification. This survey serves as a focused reference for adaptive, non-terrestrial, and application-integrated QKD systems.
Quantum key distribution (QKD) is one of the most mature quantum technologies and can provide quantum-safe security in future communication networks. Since QKD in fiber is limited to a range of few hundred kilometers, one approach to bridge continental scale distances may be the use of high altitude pseudo satellites (HAPS) as mobile trusted nodes in the stratosphere. In parallel, free-space laser communication for high rate data transmission has been a subject of research and development for several decades and its commercialization is progressing rapidly. Important synergies exist between classical free-space communication and QKD systems since the quantum states are often implemented using the same degrees of freedom such as polarization or field amplitude and phase. These synergies can be used to benefit from the progress in classical free-space laser communication in QKD applications. In this paper, the use case of QKD in a stratospheric environment is described wherein HAPS may serve as relay station of secret keys and encrypted data. The mission scenario and HAPS capabilities are analyzed to derive special requirements on the stratospheric laser terminal, the link geometry and the ground segment with respect to a feasibility demonstration. To obtain a flexible and compatible system, discrete variable and continuous variable QKD protocols are considered to be implemented side by side in the HAPS payload. Depending on the system parameters, it can be beneficial to use the one or the other kind of protocol. Thus, a direct comparison of both in one and the same system is of scientific interest. Each of the protocols has particular requirements on coupling efficiency and implementation. Link budget calculations are performed to analyze possible distances, key rates and data transmission rates for the different schemes. In case of the QKD system, the mean coupling efficiency is of main interest, i.e. signal fluctuations arising from atmospheric turbulence must be taken into account in the security proof, but the buffered key generation relaxes real-time requirements. This is different to classical communications, where the corresponding fading loss must be assessed. A system architecture is presented that comprises the optical aircraft terminal, the optical ground terminal and the most important subsystems that enable implementation of the considered QKD protocols. The aircraft terminal is interfaced with the dedicated quantum transmitter module (Alice) and the ground station with the dedicated quantum receiver module (Bob). The optical interfaces are SMF couplings which put high requirements on the receiving optics, in particular the need for wave-front correction with adaptive optics. The findings of the system study are reviewed and necessary next steps pointed out.
Recently, low-altitude wireless networks (LAWNs) have emerged as a critical backbone for supporting the low-altitude economy, particularly with the densification of unmanned aerial vehicles (UAVs) and high-altitude platforms (HAPs). To meet growing data demands, some LAWN deployments incorporate free-space optical (FSO) links, which offer exceptional bandwidth and beam directivity. However, without strong security measures in place, both conventional radio frequency channels and FSO beams remain vulnerable to interception and spoofing, and FSO in particular can suffer from turbulence, misalignment, and weather-related attenuation. To address these challenges in the quantum era, a quantum-secure architecture calledQuantum Skyshieldis proposed to enable reliable communication between the base transceiver station (BTS) and LAWN. The proposed design integrates BB84 quantum key distribution (QKD) with post-quantum authentication mechanisms. Simulation results confirm the reliable generation of a 128-bit symmetric key when the quantum bit error rate (QBER) remains below the threshold of 11%. Authentication is enforced using Lamport one-time signatures and hash-based message authentication codes (HMAC) to ensure message integrity. A Grover-inspired threat detection mechanism identifies anomalies with up to 89% probability in a single iteration, enabling real-time trust evaluation. Lastly, future research challenges have also been identified and discussed to guide further development in this area.