Multi-satellite Networks Research Articles

Fault Diagnosis and Prognosis for Satellite Formation Flying: A Survey

Fault diagnostics and prognosis are vital functions of engineering systems, mainly fault prognosis, which is a relatively novel area and requires further development. By applying these methods, the system can be enriched with the ability to detect and isolate faults before they result in failures; in addition, fault propagation can be predicted, and maintenance can be considered to reduce the risk of severe failure. This paper focuses on the problem of satellite formation fault diagnosis and prognosis in the literature. Multi-satellite networks that cooperate as multi-agent systems are primarily used to implement cutting-edge technologies and improve future Earth and space observing missions. Space systems constantly encounter numerous failures due to the hazards and challenges of the space environment that need to be tackled. The current starts with an overview of the main concepts and motivations behind the deployment of small satellites in constellation settings and the detection and prediction of their faults. Next, recent papers on fault diagnosis and prognosis of single and multiple agent(s) or satellite(s), working individually or in collaboration, are reviewed. Comprehensive comparisons and categorization of the reviewed literature are included throughout the paper leading to existing research gaps for future work.

基于中短距离星间链路的可见光通信及性能分析

To meet constraints on size, weight, and power consumption in small satellite platforms and explore alternative solutions for radio frequency and laser-based communication in medium- and short-distance inter-satellite links, this study explores the feasibility of visible-light communication (VLC) based medium- and short-distance inter-satellite communication in multi-satellite networks. Using the satellite tool kit (STK), the binary star formation flying configuration is constructed, background-light noise introduced by the sun and stars is quantitatively analyzed, and a medium- and short-range inter-satellite VLC link model is constructed. Then, to improve the link capacity and reliability, the VLC link is further developed into a single-input multi-output VLC (SIMO-VLC) system. The influences of different diversity merging algorithms on the link's performance are evaluated by numerical simulation. Simulation results show that the stray light power introduced by solar radiation is below 10 μW throughout most of the time period, and the background light power introduced from the ground is reduced by 75%. In order to achieve a data transmission rate of 112.5 Mbit/s and a bit error rate of 1×10-6 within 20 km, the light power required by the system is at least 4.55 W. Compared with the single-input single-output system, the SIMO-based diversity detection scheme can achieve better performance, and the required transmission power and communication distance are effectively improved with the increase of the receiving branch, which can provide a reference for the design of VLC-based inter-satellite links and extending their outdoor application scenarios. © 2019, Chinese Lasers Press. All right reserved.

Blind Modulation Classification for Cognitive Satellite in the Spectral Coexistence Context

The scarcity of the usable satellite spectrum has led to a need for advanced communication techniques. Among them, multisatellite networks have been promoted for their ability to reuse the frequency bands in a more aggressive manner. This is made possible by sharing both the spectral and spatial degrees of freedom. Meanwhile, the concept of cognitive satellite was deeply investigated to make the best of these novel architectures. In this context, very few blind signal processing methods were proposed to tackle the co-channel interference issues entailed by such systems. Herein, we develop a novel low-complexity algorithm for blind automatic modulation classification and parameters estimation in the strongly interfering scenario. The proposed method relies on an Analytical study of the M ${\text{th}}$ -Power nonlinear Transformation (A $M$ PT) of the co-channel mixture. Theoretical analysis and extensive simulations show the effectiveness of the proposed method in various scenarios.

Networked Control of Cooperating Distributed Pico-Satellites

In spacecraft engineering a paradigm shift is emerging with the tendency from traditional, single, large, and multifunctional satellites towards cooperating, distributed small spacecraft systems. In particular modern miniaturization techniques allow realization of satellites with continuously smaller masses, and thus enable cost-efficient implementation and launch of distributed multi-satellite systems. This raises challenges in control approaches at each individual spacecraft by required compensation of limitations and of increasing noise effects due to miniaturization of the satellite components. The higher noise susceptibility is to be counterbalanced by filtering and robust control approaches on-board. At the level of formation control, innovative orbit control approaches for multi-satellite networks based on relative position and attitude control of each satellite are to be developed. This contribution addresses related technology approaches, which have been tested with UWE-satellites in orbit, and reports about the obtained performance results.

Time Interference Alignment via Delay Offset for Long Delay Networks

The potential of Time Interference Alignment is investigated in this work, with particular reference to the attainable degrees of freedom. The K-user interference channel is considered, in which transmitters and receivers are placed randomly in a Euclidean space. A model for long delay networks is introduced and the degrees of freedom for different cases (with and without transmitter delay coordination) are evaluated. It is shown how time interference alignment can provide more degrees of freedom than TDMA when the transmitters jointly coordinate their transmission delay and the number of pairs is K ≥ 5. Closed form expressions are derived for several cases of interest which provide insight and useful predictions. This work is concluded with an investigation of the achievable degrees of freedom for multi-satellite networks, where it is shown that the results obtained under several assumptions do predict accurately the degrees of freedom in a real setting.

Satellite communications networks

The evolution of satellite communication systems over the past two decades from simple point-to-point links with unique subcarrier-defined paths between points to today's multipoint, satellite-switched, multi-satellite networks tying together hundreds of earth stations, and transmitting voice and data increasingly in the time domain is considered. Examples of the methods used to manage network resources efficiently through terrestrial control and monitoring of information flow together with on-board switching are given. These examples are choosen mostly from the INTELSAT experience which will soon include a sixth generation of space segment. The paper concludes with a discussion of the future directions of satellite network development made possible by the technology being planned for NASA's Advanced Communications Technology Satellite. This design anticipates the needs of both high-volume trunking and thin-route service.