Low Orbit Satellite Networks Research Articles

An Adaptive Routing Algorithm for Inter-Satellite Networks Based on the Combination of Multipath Transmission and Q-Learning

In a satellite network, the inter-satellite link can facilitate the information transmission and exchange between satellites, and the packet routing of the inter-satellite link is the key development direction of satellite communication systems. Aiming at the complex topology and dynamic change in LEO satellite networks, the traditional single shortest path algorithm can no longer meet the optimal path requirement. Therefore, this paper proposes a multi-path routing algorithm based on an improved breadth-first search. First, according to the inter-satellite network topology information, the improved breadth-first search algorithm is used to obtain all the front hop node information of the destination node. Second, all the shortest paths are obtained by backtracking the path through the front hop node. Finally, according to the inter-satellite network, the bandwidth capacity of the traffic and nodes determines the optimal path from multiple shortest paths. However, due to the high dynamics of low-orbit satellite networks, the topology changes rapidly, and the global topology of the network is often not available. At this time, in order to enhance the adaptability of the algorithm, this paper proposes an inter-satellite network dynamic routing algorithm based on reinforcement learning. Verified by simulation experiments, the proposed algorithm can improve the throughput of the inter-satellite network, reduce the time delay, and the packet loss rate.

Toward Efficient Geolocation in SAGIN: A Single-Satellite Geolocation Method Combined with Bandlimited Signal Extrapolation

The satellite network, as an essential part of space-air-ground integrated network (SAGIN) with high coverage and mobility, not only expects a promising development but faces increasing interference and tenser satellite spectrum resources. The geolocation function of single satellite is widely used in the low-orbit satellite network but limited to the long measuring duration, which cannot adapt the flexiblity in SAGIN scenario. In this paper, an efficient single satellite geolocation method is proposed combined with bandlimited signal extrapolation in order to save more operation time and ensure the positioning accuracy. Due to the bandlimited characteristic of the radiated signal, information received from the satellite can be further extrapolated so that more doppler frequency values are obtained. The estimated accuracy can be improved with the extra information input to grid search method. Besides, short-term single-satellite geolocation can be realized to meet the higher efficiency requirement of SAGIN. Simulation results demonstrate the superiority of the proposed method in terms of the positioning accuracy compared to the geolocation method without extrapolation.

INTERLINK: A Digital Twin-Assisted Storage Strategy for Satellite-Terrestrial Networks

Recently, low-orbit satellite networks have gained lots of attention from the society due to their wide coverage, low transmission latency, and storage and computing capacity. Providing seamless connectivity to users in different areas is envisioned as a promising solution, especially in remote areas and for marine communication. However, when jointly used with terrestrial networks composing satellite-terrestrial networks, the satellite moving speed is much faster than the ground terminal, which can cause inconsistent service from a single satellite, and therefore lead to frequent satellite handover. Moreover, due to the dynamic and time slot visibility of satellites, the topology of an intersatellite changes frequently, which results in loops during satellite handover, thereby reducing the utilization of links. To address these problems, we propose a digital twin-assisted storage strategy for satellite-terrestrial networks (INTERLINK), which leverages the digital twins (DTs) to map the satellite networks to virtual space for better communication. Specifically, we first propose a satellite storage-oriented handover scheme to minimize the handover frequency by considering the limited access time and capacity constraints of satellites. Then, a multiobjective optimization problem is formulated to obtain the optimal satellite by genetic algorithm. Finally, considering the timing visibility of the satellite links, a digital twin-assisted intersatellite routing scheme is introduced to improve the quality of data delivery between satellites. Simulation results demonstrate that the proposed INTERLINK can reduce both handover times and average propagation delay compared with its counterparts. Meanwhile, benefitting from integrated DT, both the quality of data delivery and the delay of intersatellite links are considerably improved.

Satellite Network Task Deployment Method Based on SDN and ICN.

With the rapid development of 5G and the Internet of Things, satellite networks are emerging as an indispensable part of realizing wide-area coverage. The growth of the constellation of low-orbit satellites makes it possible to deploy edge computing services in satellite networks. This is, however, challenging due to the topological dynamics and limited resources of satellite networks. To improve the performance of edge computing in a satellite network, we propose a satellite network task deployment method based on SDN (software-defined network) and ICN (information-centric network). In this method, based on the full analysis of satellite network resources, a mission deployment model of a low-orbit satellite network is established. The genetic algorithm is then used to solve the proposed method. Experiments confirm that this method can effectively reduce the response delay of the tasks and the network traffic caused by task processing.

Orbital collaborative learning in 6G space-air-ground integrated networks

Currently, 6G is being proposed as a new next-generation communication architecture. The inclusion of satellite communication networks makes it possible to genuinely space-air-ground integrated networks, especially the combination of 6G with machine learning algorithms, which has attracted increasing attention. Of particular note is the combination of collaborative learning with the Internet of Everything, which improves the intelligence and collaboration of devices with more robust privacy protection, higher computing power, and greater energy savings. However, the airspace environment in 6G is extraordinarily dynamic and delay-sensitive for services, and traditional federation learning is a synchronous aggregation model with slow convergence. To address this problem, the paper proposes a hierarchical satellite-ground collaborative architecture with three roles: remote cloud center, orbital edge computing server, and data node. We use the advantages of orbital edge computing and low-orbit satellite network communication to manage the parameter transfer problem during the collaboration process. Meanwhile, we propose an asynchronous adaptive collaborative aggregation algorithm (AFLS) for the satellite-ground architecture, enabling the federated members to update the model parameters in time during the dynamic joining aggregation process. Experiments show that our architecture and algorithm excel in training performance with 95%accuracy and fewer communication rounds in image classification when the roles are in good collaboration.

Effects of gas supply direction on the discharge characteristics of a low-power Hall thruster

Micro-nano satellites show considerable potential in the application of low-orbit satellite networks, and low-power Hall effect thrusters (HETs) that provide the impetus for them have also attracted considerable attention worldwide. However, the relatively large surface-to-volume ratio of low-power HETs leads to significant loss of ions on the wall surface. After the channel width is increased or the ionization area is moved outward, ensuring sufficient ionization of the propellant is very difficult, and thus its integrated performance is not high. Thus, in this study, a 100-W permanent magnet HET with an aft-magnetic field is considered as the carrier to investigate the effect of gas supply direction on the thruster discharge characteristics through a simulation and experiments. Results indicate that under the same working conditions, adopting the circumferential direction gas supply mode effectively increases the density of the propellant in the ionization zone (up to 7%), improves the propellant ionization rate (up to 12.7%), and improves integrated discharge performance (the anode efficiency can be increased by up to 5.3%). In addition, the performance optimization effect of this mode is more evident under the working condition of low flow. When combined with an aft-magnetic field, this method is an effective means to ensure high-efficiency discharge of a low-power HET, which can be used as a reference for the miniaturization development of HETs.

Virtual Agent Clustering Based Mobility Management Over the Satellite Networks

Due to the high dynamic characteristics of the low-orbit satellite networks, the frequent handovers of the users led to heavy mobility management load and large handover delay. To solve these problems, one mobility management mechanism based on the virtual agent domain (VAD) is proposed. In this mechanism, a virtual agent cluster (VAC) is designed to co-manage the network architecture of users in the corresponding VAD. With the on-board processing and switching capabilities, the architecture of the distributed mobility management mechanism is adopted to support the information sharing between the VACs, which reduces the performance requirements for single satellite and improves the system scalability. Then, we construct the home mobile-agent-anchor (HMAA) and the local MAA. In this way, the MN triggers a binding update to the HA only when the home MAA is lost, and the MN's switching within the VAD only needs to update its intra-domain relations, which reduces the overhead of mobility management and switching delay. Furthermore, the proposed scheme is theoretically evaluated in terms of the signaling overhead and handover latency. Finally, the numerical simulation results are presented to verify the efficacy of our scheme. The experimental platform also demonstrates the availability and efficiency of the new mechanism.

Link Resource Allocation in Counter-Rotating Seam of Low-Orbit Satellite Network

This paper studies the communication problem at the counter-rotating seam of the low-orbit satellite based on the walker constellation. The counter-rotating seam has a short life cycle, low capacity, and dynamic geometric parameters. To better utilize the scarce link resources at the seam, increase network throughput, and approach the physical limits of the link throughput at the seam, an initial phase condition that maximizes the relative rotational joint link throughput is calculated. In the experimental simulation results using the Iridium system as an example, it is shown that better throughput can be obtained under the initial conditions, and the throughput is improved by about 30%.

Packet switching for mobile earth stations via low-orbit satellite network

A potentially valuable implementation of a satellite computer communication packet switched network is one which is survivable and distributed. That is, a system which dynamically adapts to changing network element connectivities, changing interconnections of users, and is not dependent on any central unit for its own internal command and control. A laboratory prototype of such a system has been constructed of a group of computers which when given communication circuits between them will, acting autonomously, create a computer communication packet switching network and which will continually adapt to changes in connectivity. In this paper, an adaptive computer communication routing algorithm is described, its application in space including a space segment design is presented, its actual implementation in real physical hardware is discussed, and system performance results as parameters are varied are presented.