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.
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.
Quantum key distribution (QKD) offers unconditional security for mobile aerial networks, but existing protocols face challenges in low-altitude, continuously moving aerial networks because of hardware complexity and sensitivity to channel noise. This paper proposes mobile aerial semi-quantum communication (MASQC), a novel lightweight protocol that integrates and adapts decoy state analysis with time-batched polarization encoding over free-space optics to enable secure key distribution among aerial vehicles (AVs) and base stations. MASQC introduces six key innovations tailored for aerial networks: (1) a decoy state semi-quantum protocol implementation requiring only passive single-photon detection on AVs while providing robust security against photon-number-splitting attacks, (2) time-batched polarization encoding with 1-5 ms windows and real-time trajectory prediction to compensate for Doppler effects, (3) comprehensive post-quantum authentication infrastructure using CRYSTALS-Dilithium signatures and CRYSTALS-Kyber key encapsulation, (4) adaptive security thresholding (0.08-0.12) with dual-layer error analysis combining conventional QBER and decoy state bounds, (5) hybrid quantum-classical resilience with emergency key pools and perfect forward secrecy mechanisms, and (6) encrypted relay capabilities through neighboring AVs during line-of-sight disruptions. Unlike prior semi-quantum or decoy-state protocols designed for static environments, MASQC provides a holistic system solution addressing the unique constraints of low-altitude aerial networks. Comprehensive simulation results using the Qiskit framework demonstrate the effectiveness of MASQC with an 85.3% network success rate, high bits/second key generation rate per AV, and robust security validation including a high attack detection probability against sophisticated eavesdropping attempts.
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.
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.
As the demand for better security and higher capacity grows, quantum key distribution (QKD) using free-space optics (FSO) presents an innovative solution for 5G networks and beyond. The Innovate-UK AirQKD project explores how FSO–QKD could enable quantum-secure connections at a metropolitan scale, focusing on the critical “last-mile” of connectivity. However, implementing FSO–QKD in the real world brings several engineering challenges, spanning software, hardware, system integration, and security. This paper dives into the complexities of system architecture and integration, QKD transmission over FSO, and the post-processing of keys. We showcase a cohesive system design that blends the quantum and classical domains, incorporating cutting-edge FSO–QKD hardware and software. The system’s functionality is demonstrated for key processes such as transmission, post-processing, network control, and key management. As a case study, we tested an FSO–QKD link over 135 m at BT’s Adastral Park in Suffolk, UK. The setup achieved a photon count rate of up to 585 kcps through a channel with 15.9 dB of loss and 12 kHz of background noise, resulting in a security key rate (SKR) of up to 84.3 kbps using two detectors. We also conducted simulations to estimate the SKR and compared them with the experimental results. Both approaches confirm the system’s ability to generate keys and successfully transmit orthogonal polarization states, highlighting its potential for practical application.
Due to the recent rapid growth of computing technologies, today's encrypted information based on classical computational complexities will soon no longer remain secure. Quantum cryptography, or quantum key distribution (QKD), relying on the physical laws of quantum mechanics, stands out as a more powerful cryptographic solution that enables the secret key to be shared securely over publicly unsecured communication channels in the presence of eavesdroppers. QKD can be possibly implemented over both optical fiber and free-space optical (FSO) links. Compared to optical fiber, FSO has the immediate advantage of flexibility and cost-effectiveness in terms of infrastructure deployment. More interestingly, recent advancements in satellite communications using FSO links promise the future of a global QKD network for highly secure applications. This paper reviews the development of QKD over FSO for both terrestrial and satellite channels, which highlights the most up-to-date QKD protocols. Owing to how the information is encoded, different QKD protocols are classified into technology-focused categories, where their properties are reviewed and compared. The feasibility of current QKD protocols is then investigated with respect to its specific application scenarios for terrestrial and satellite FSO links, equipped with results from both theoretical and experimental studies. Based on the latest free-space QKD achievements, novel perspectives for future developments and challenges to enhance the secrecy performance and reduce implementation cost are then summarized and comprehensively discussed. The potential combination of QKD and physical layer cryptography for the newly emerging wireless mobile communications networks involved with unmanned aerial vehicles (UAV) is also introduced.
Abstract The increasing demand for secure communications in mobile and critical infrastructure networks has led to the emergence of Quantum Key Distribution (QKD) as a promising technique for enhancing cryptographic security in next-generation systems. This paper reviews recent progress in integrating QKD within mobile and wireless networks. It focuses on key enabling technologies, such as Software-Defined Networking (SDN), satellite-based, and aerial networks. The paper critically analyzes how these frameworks can address evolving security requirements in sixth-generation (6G) networks and smart city infrastructures. Additionally, it examines the role of Machine Learning (ML) in improving QKD performance and adaptability. Challenges such as key management, mobility support, scalability, and interoperability are explored. These challenges help identify current barriers and research directions. By consolidating developments and highlighting unresolved issues, this study offers researchers valuable insights. It discusses the convergence of quantum communication and advanced mobile architectures, facilitating the design of secure and resilient future communication infrastructures.