Quantum key resources in quantum satellite networks are fundamental to confidential data forwarding, which highly depends on the network topology. In this paper, we propose a network topology construction scheme via formulating the dynamic link establishment among network nodes as an integer linear programming to maximize the number of available quantum keys in the topology. Then we solve this topology optimization problem through subgradient method based on the Lagrange duality theory. Under the optimized topology, we further propose a key-based routing and resource allocation (KRRA) algorithm to forward secret keys for ground stations. The simulation results show that our scheme performs better than the benchmark method with the minimum route distance in terms of the number of quantum keys and the success probability of real-time secret key forwarding service.
Quantum key resources in quantum satellite networks are fundamental to confidential data forwarding, which highly depends on the network topology. In this paper, we propose a network topology construction scheme via formulating the dynamic link establishment among network nodes as an integer linear programming to maximize the number of available quantum keys in the topology. Then we solve this topology optimization problem through subgradient method based on the Lagrange duality theory. Under the optimized topology, we further propose a key-based routing and resource allocation (KRRA) algorithm to forward secret keys for ground stations. The simulation results show that our scheme performs better than the benchmark method with the minimum route distance in terms of the number of quantum keys and the success probability of real-time secret key forwarding service.
In quantum satellite networks, routing is an important task for providing key relay services to ground stations (GSs). For the demand of quantum keys for multiple concurrent requests between GS pairs, we formulate a multi-objective optimization routing (MOOR) problem to allocate the quantum key and time-slot resources to find routes for simultaneous services. The proposed optimization scheme maximizes the number of successful requests while minimizing the routing cost. Specifically, we consider that the fewer available quantum keys on the link, the greater the cost of occupying the link. Then we use the reciprocal of the number of available keys on links to represent link costs, and find the route with the minimum link costs. Simulation results show that the success probability of MOOR scheme is higher than that of the comparison routing strategy based on Dijkstra algorithm, especially when the number of keys forwarded by a request is not too large, the improvement is significant.
Multicast is an important service type in both terrestrial and space communication networks but has security issues because more than one destination node can receive information. Point-to-point quantum key distribution can be achieved end-to-end over long distances by using a quantum satellite (e.g., Micius) as a relay node. Hence, how to provide secret keys for remote multicast services and efficiently distribute secret keys between the source node and multiple destination nodes for long-distance secure multicast services (SMSs) has become a critical problem. In this paper, a quantum satellite network with a special node structure is designed to complete point-to-multipoint key distribution, and a point-to-multipoint satellite relay scheme is proposed. The weight information of the link is dynamically described by the method of auxiliary topology, and a satellite relay tree is constructed. Finally, this paper proposes a satellite relay algorithm for multicast services to route and allocate key resources to solve the problem of long-distance point-to-multipoint key relay and improve the success probability of multicast service requests. Simulation results show that the proposed algorithm can improve the success probability of SMS requests by about 51.32% in a static scenario and 17.33% in a dynamic scenario.
Quantum key distribution (QKD) is a promising technique to resist the threat against quantum computers. However, the high loss of quantum signals over a long-distance optical fiber is an obstacle for QKD in the intercontinental domain. In this context, the quantum satellite network is preferred over the terrestrial quantum optical network. Due to the mobility of satellites, the satellite topology is dynamic in the quantum satellite network, which remains a challenge for routing. In hybrid geostationary-earth-orbit (GEO)/low-earth-orbit (LEO) quantum satellite networks, the lack of an efficient scheduling scheme for GEO/LEO satellites also limits the construction of quantum satellite networks. Therefore, this paper provides a topology abstraction-based routing scheme for secret-key provisioning, where the dynamic physical topology is translated into a quasi-static abstracted topology. This scheme contributes to saving the precious secret key resources. In order to improve the success probability of long-distance QKD requests, three novel resource-scheduling heuristic algorithms are proposed in hybrid GEO/LEO quantum satellite networks. Simulation results indicate that the proposed algorithms can improve the success probability of QKD requests by 47% compared to the benchmark.
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.
Quantum Key Distribution (QKD) is a technology that enables the exchange of private encryption keys between two legitimate parties, using protocols that involve quantum mechanics principles. The rate at which secret keys can be exchanged depends on the attenuation that is experienced. Therefore, it is more convenient to replace many terrestrial fiber segments (and repeaters) by just few optical satellite links that would enable flexible global coverage. Then, the satellite nodes can take the role of trusted-relays, forwarding the secret keys from source to destination. However, since the rate at which secret keys can be generated in each quantum link is limited, it is very important to select the intermediate satellite nodes to inter-connect ground stations efficiently. This paper studies the most convenient allocation of resources in a QKD network that combines complementary connectivity services of GEO and LEO satellites. The aim of the centralized routing algorithm is to select the most convenient trusted-relays to forward the secret keys between pairs of ground stations, verifying the constraints that satellite-to-ground and inter-satellite quantum channels have.
Satellite-based quantum key distribution (QKD), especially relying on low Earth orbit (LEO) satellites, overcomes the geographical limitations of fiber-based QKD and enables global secure communications. However, existing QKD link establishment schemes for LEO quantum satellite networks fail to fully consider practical scenarios (e.g., multi-layer constellations as well as heterogeneous satellite–ground and inter-satellite QKD links) along with realistic constraints (e.g., different illumination conditions and the need to avoid frequent link switching). To address this gap, this work focuses on the adaptive establishment of satellite–ground and inter-satellite QKD links in single- and dual-layer LEO quantum satellite networks. We describe the network structures of single- and dual-layer constellations, as well as formulate the corresponding network model, secret key rate model, and secret key volume model. To realize adaptive QKD link establishment, we develop two integer linear programming (ILP) models and design three heuristic algorithms. The two ILP models are denoted as ILP-G and ILP-R, respectively, where ILP-G aims to maximize the generated key volume, and ILP-R is dedicated to optimizing global key resource balance by prioritizing QKD links with lower remaining key volume. The three heuristic algorithms are designed based on maximum key rate (MaxKR), maximum generated key volume (MaxGKV), and minimum remaining key volume (MinRKV). Simulation results verify the applicability of the proposed approaches across single- and dual-layer LEO quantum satellite networks. Comparative evaluations against two benchmarks, i.e., random fit (RF) and first fit (FF), show that ILP-G and MaxGKV achieve the largest cumulative key volume, while ILP-R and MinRKV outperform the other approaches in key volume distribution, quantum satellite availability, and total number of established QKD links. Specifically, the cumulative key volume of ILP-G is 44.0% and 33.8% higher than that of RF in single- and dual-layer LEO quantum satellite networks, respectively. Furthermore, the dual-layer constellation generates more key resources, with the cumulative key volume reaching approximately five times that of the single-layer constellation. It also exhibits a more balanced global key resource distribution, where key resources are distributed across a broader set of node pairs rather than concentrated on a limited subset of nodes.