The operation to secure future smart cities relies on cryptographic resistance against quantum computing threats. While satellite-based Quantum Key Distribution (QKD) offers a secure solution, current frameworks lack the scalable orchestration required for reliable service delivery in complex urban environments. The proposed adaptive QKD-as-a-Service (QKDaaS) framework addresses this issue as it combines dynamic coordination between quantum satellite constellations and smart city environment requests, such as “The Line” in Neom, Saudi Arabia. Low Earth Orbit (LEO) satellites and terrestrial networks are both considered in the framework along with Quantum Machine Learning (QML) optimization in the control plane routing. To maximize QKD performance based on user population, the satellite network is segmented to offer connectivity to the terrestrial demand. Unsupervised Quantum K-means (QK-means) clustering is applied in dynamic LEO networks to overcome dynamic movement difficulties. The analysis of benchmarking shows QK-means achieves a convergence time of 0.072 seconds, which is 3 times faster than K-means, and provides better clustering fidelity. Furthermore, Dijkstra performed better than Bellman-Ford in inter-cluster routing when analyzing routing algorithms, especially as the number of clusters increases, combining QK-means with Dijkstra in the upcoming generation of space-terrestrial networks in smart cities for stability and efficiency.
The operation to secure future smart cities relies on cryptographic resistance against quantum computing threats. While satellite-based Quantum Key Distribution (QKD) offers a secure solution, current frameworks lack the scalable orchestration required for reliable service delivery in complex urban environments. The proposed adaptive QKD-as-a-Service (QKDaaS) framework addresses this issue as it combines dynamic coordination between quantum satellite constellations and smart city environment requests, such as “The Line” in Neom, Saudi Arabia. Low Earth Orbit (LEO) satellites and terrestrial networks are both considered in the framework along with Quantum Machine Learning (QML) optimization in the control plane routing. To maximize QKD performance based on user population, the satellite network is segmented to offer connectivity to the terrestrial demand. Unsupervised Quantum K-means (QK-means) clustering is applied in dynamic LEO networks to overcome dynamic movement difficulties. The analysis of benchmarking shows QK-means achieves a convergence time of 0.072 seconds, which is 3 times faster than K-means, and provides better clustering fidelity. Furthermore, Dijkstra performed better than Bellman-Ford in inter-cluster routing when analyzing routing algorithms, especially as the number of clusters increases, combining QK-means with Dijkstra in the upcoming generation of space-terrestrial networks in smart cities for stability and efficiency.
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.
Quantum key distribution (QKD) has attracted much attention on secure communications across global networks. QKD over satellite networks can overcome the limitations of terrestrial optical networks, such as large attenuation over long distance fiber channel and difficulty of intercontinental domain communications. Different QKD networks (around the world) can intercommunicate through quantum satellites, leading to a global quantum network in near future. This raises a new resource allocation and management problem of QKD involving multiple satellite layers and distributed ground stations. Using existing schemes, a single satellite cannot perform QKD for ground stations for the whole day. Moreover, the research problem is more challenging due to limitations of satellite coverage: limited cover time of low earth orbit (LEO) satellite, high channel losses of geostationary earth orbit (GEO) satellite, etc. To overcome these limitations, our study proposes a double-layer quantum satellite network (QSN) implemented quantum key pool (QKP) to relay keys for ground stations. We propose a new architecture of trusted-repeater-based double-layer quantum satellite networks, comprising GEO and LEO satellites. We also address the routing and key allocation (RKA) problem for key-relay services over QSNs. We propose a novel joint GEO-LEO routing and key allocation (JGL-RKA) algorithm to solve the RKA problem. Simulative results show that the proposed scheme can increase success probability of key-relay services significantly. We also present the impact of different route selections mechanisms, number of satellite links, satellite node capability, and service granularity on network performance.
Mega low Earth orbit (LEO) satellite constellations are a key infrastructure for 6G global connectivity, but their high node density, fast orbital motion, and continuously changing inter-satellite topology make routing difficult. Clustering is widely used to reduce routing complexity by partitioning a constellation into routing domains. This paper evaluates, side by side, two quantum-ready clustering approaches for mega LEO constellations. The first is qc-kmeans, a hybrid quantum–classical compressive K-means algorithm that selects cluster centroids by solving small quadratic unconstrained binary optimization (QUBO) problems with the quantum approximate optimization algorithm (QAOA). The second, RS-QUBO, partitions the inter-satellite link (ISL) graph directly with a routing- and stability-aware QUBO that rewards compact, balanced routing domains and penalizes changes between consecutive snapshots. Both are compared with classical baselines under identical inputs, with every trial recorded. For qc-kmeans, selecting the best of repeated trials suggests better cluster quality than K-means, but over all trials the two are practically identical on a 10,687-satellite Starlink snapshot and on a synthetic benchmark; an ablation shows that the outcome is determined by the classical K-means seeding and refinement, while QAOA accounts for most of the runtime. For RS-QUBO, on a real, irregular 1454-satellite Starlink sub-network with time-varying links and 3% random link failures, it is the only method of the main comparison that keeps all routes inside their routing domains at every tested number of domains (0% routing failures, compared with 39–71% for K-means, 16–44% for a grid tiling, and 2–22% for recomputed METIS), with a delay stretch of 1.08–1.18 over the routed pairs and 4–11% of satellites changing domain between snapshots. A component ablation attributes the absence of failures to adapting the partition to the current links and repairing disconnected domains, which also removes the failures of recomputed METIS; the compactness objective lowers the delay stretch relative to cut-based partitioning in the recomputed pipelines at 8 and 32 domains but not at 16. Domain changes are costly for routing: under a link-state update model, RS-QUBO needs 0.6–1.2 times the update load of flat routing, mostly to announce satellites that change domain, whereas an incremental refinement of a static METIS partition is also free of routing failures and needs 0.3–0.4 times the flat load. QAOA solves 6–12-satellite instances of this QUBO better than random sampling in ideal simulation, but the benefit becomes marginal under an ibm_torino noise model, and the compiled circuits require up to 960 two-qubit gates. We conclude that, in the evaluated conditions, the benefit of quantum-ready clustering for satellite routing comes from the problem formulation and the classical pipeline around it, solved classically, and that domain stability matters as much for routing as domain quality; QAOA is demonstrated at small scale on current hardware and noise models.
Quantum Key Distribution (QKD) networks enable unconditionally secure key exchange using quantum mechanical principles. However, routing cryptographic keys across multi-hop quantum networks introduces challenges unique to quantum communication. This survey analyzes and classifies 26 routing strategies proposed between 2013 and 2024 for terrestrial, satellite, and hybrid QKD infrastructures. Dynamic, key-aware routing algorithms have been shown to reduce service rejection rates by 25-40% compared to static shortest-path methods by incorporating real-time key pool availability and link error rates. Multi-path strategies improve resilience against trusted-node compromise by distributing keys across disjoint routes, albeit with an increase in key consumption of 30-60%. SDN-based orchestration frameworks emerge as essential enablers of flexible, QoS-aware routing for hybrid networks integrating terrestrial fibers and intermittent satellite links. Critical research directions include reducing dependence on trusted nodes through quantum repeaters or post-quantum cryptography, developing standardized key management interfaces for interoperability, and adopting AI-driven predictive routing for adapting to fluctuating network states. This comprehensive synthesis of routing algorithms, performance trade-offs, and unresolved issues offers practical guidance for engineering secure, adaptable, and large-scale QKD networks capable of meeting real-world deployment demands.
Recently, large-scale quantum networks that connect metropolitan area quantum networks between cities have been realized by integrating free-space and fibre quantum key distribution (QKD) links, yet the fibre-based trusted nodes in such networks could be subject to constant surveillance and probes. To remove these fibre-channel risks, we consider a network in which a space-based relay, the Micius satellite, executes a sequence of key delivery missions, allowing any two cities to have a shared key. In this work, we develop a comprehensive framework integrated with precise orbital modelling and a cloud statistics model to enable a preassessment of satellite-based QKD applications. Using this framework, we consider three different scheduling strategies and estimate the keys that can be delivered to cities. The results show that the strategy of pursing the maximum number of final keys significantly embodies space-based QKD advantages, while the strategy of considering different levels of missions achieves the delivery of more keys to higher-priority missions. Most importantly, the targeted strategy of pursuing a distribution of final keys delivered that is coincident with the network traffic distribution guarantees individual needs, further promoting the utilization of the delivered keys in practice. We also provide a comparison of the total number of keys delivered by satellites with different-altitude orbits. It is demonstrated that the plan for constructing a low-Earth orbit (LEO) satellite constellation is more efficient than that for employing an expensive high-orbit satellite in terms of achieving potential applications. Our work not only provides a practical method in the near term but also gives the initial exploration to establish the quantum network.
With the rapid advancement of Low Earth Orbit (LEO) satellite constellations, ensuring the security of satellite-to-ground communication has become a critical concern. Traditional cryptographic techniques, while effective against classical attacks, face increasing threats from quantum computing. This paper proposes a quantum key secure transmission method tailored for LEO satellite-ground communication scenarios. The method integrates quantum key distribution (QKD) with dynamic channel estimation and orbital mobility prediction to support secure and low-latency key handshakes between satellites and ground stations. A hybrid encryption strategy is introduced, where QKD-generated keys are used to refresh symmetric session keys in real time, significantly enhancing resistance to eavesdropping and man-in-the-middle attacks. Simulation results demonstrate that the proposed method ensures stable key distribution under Doppler-shifted and intermittent link conditions, achieving improved secrecy capacity and resilience against quantum-level adversaries. This work provides a viable and scalable quantum-safe communication solution for future secure satellite networks.