It is inevitable to generate cross term when calculating the cyclic spectrum estimation of complex electromagnetic environment interference signals. Aiming at the problem of cross term in multiple signal cycle spectrum in complex electromagnetic environment, this paper presents a method for cross-term suppression in cyclic spectrum estimation based on empirical mode decomposition(EMD).The effective information of complex electromagnetic environment signals is extracted by compression and reconstruction algorithm, and the effective information is decomposed by empirical mode. results of simulation and experiment show that the proposed method can effectively suppress the cross term.
Authors: jurong hu (Hohai University), Long Lu (Hohai University), Xujie Li (Hohai university),
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With the continuous development of Space Information Networks (SIN), there is an increasing demand for a cost-effective and high-fidelity tool to carry out research on related networking technologies. Neither the real testbed which is expensive nor the simulators which lack realism can meet our requirements. Therefore, this paper introduces MininetE to emulate space networking allowing relatively high-fidelity experiments that can run on the constrained resources of a single laptop. MininetE enhances the well-known Mininet emulator with adequate isolation and implements dynamic topology control with the original SDN capabilities. The validity of MininetE is verified by results of a Delay-/Disruption-Tolerant Networking (DTN) experiment.
Authors: Tao Lin (Nanjing University), Fa Chen (Nanjing University), Kanglian Zhao (Nanjing University), Yuan Fang (Nanjing University), Wenfeng Li (Nanjing University),
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This paper presents a research on the performance of packet layer coding for space streaming，which integrates Low Density Parity Check (LDPC) Code into space streaming service. By implementing LDPC code into higher layers, such as bundle layer or transport layer, the space streaming service can achieve stronger error correction capability, which improves the quality of experience of space streaming service. To evaluate the performance of packet layer coding for space streaming, emulation of data streaming in space are conducted. The results of the experiments show that compared with the original transmission scheme, space streaming service with packet layer coding has obvious improvements.
Authors: Xiaoyu Zhu (Nanjing University), Dongxu Hou (Nanjing University), Kanglian Zhao (Nanjing University), Wenfeng Li (Nanjing University), Yuan Fang (Nanjing University),
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This paper proposes an optimization-oriented design method for harmonic tuned power amplifier (PA) using particle swarm optimization (PSO). Optimal source and load impedances for achieving high efficiency are obtained at the package plane of a Wolfspeed CGH40010 transistor. PSO is employed to optimize match-ing networks for fitting the desired trajectories of impedances. The designed PA with optimized matching networks was simulated in Keysight's advanced design system for verification. The results showed that the saturation efficiency of the PA reaches 75% at 3.5GHz with associated output power of 42 dBm, which ver-ified that the method can be used to design high efficiency PA for 5G mobile communication systems.
Authors: chengxi bian (Jiangsu University), Weiqing Dong (Jiangsu University), Wa Kong (Jiangsu University), Jing Xia (Jiangsu University),
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This paper presents a method for constructing non-binary(NB) quasi-cyclic(QC) LDPC codes. First, the initial base matrix of NB-QC-LDPC code is constructed by two arbitrary subsets in a finite field. Then, through combining the number and connectivity of cycles jointly, the new masking method is proposed to construct a type of NB-QC-LDPC codes with larger ACE average values. The simulation illustrates that the proposed code has better error correction performance compared with binary LDPC codes and other NB-LDPC codes.
Authors: Xinting Wang (Army Engineering University of PLA), Kegang Pan (Army Engineering University of PLA), Rong Lv (The Sixty-third Research Institute), Ruixiang Zhao (Army Engineering University of PLA),
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As we all know, satellite communication has the advantages of wide coverage, large communication capacity, etc. compared to terrestrial communication, and is not easily affected by geographical natural disasters. But the coverage of one satellite is limited, so we often need a constellation satellite communication system composed of multiple satellites to communicate. Also, the cost of satellites is relatively high, and the satellite constellation usually needs to consider both cost and communication performance, how to use the least cost to achieve a best communication performance. We construct a design multi-objective optimization model of satellite constellation for a local high capacity, using the improved NSGA-II algorithm to solve model, using STK software to simulate the results of the solution.
Authors: Chao Zheng (Army Engineering University of PLA), Bing Zhao (Army Engineering University of PLA), Daoxing Guo (Army Engineering University of PLA),
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Licklider transmission protocol (LTP) was developed to provide reliable and highly efficient data delivery over unreliable space network channels. Some preliminary studies on LTP’s aggregation mechanism in space communication networks have been done. However, the effect on LTP aggregation of data losses caused by lossy space channels has been ignored. Data loss is one of the key features that characterize space networks, and therefore its effect on LTP transmission cannot be left out. In this paper, the LTP aggregation mechanism is studied with focus on its characterization and performance over lossy and highly asymmetric space channels. An analytical model is presented for calculating the minimum number of bundles that should be aggregated within an LTP block for transmission over a lossy channel to avoid report segment (RS) transmission delay caused by highly asymmetric channel rates. The model is validated by realistic file transfer experiments over an experimental testbed infrastructure and packet-level analysis of the results. It is concluded that the aggregation threshold derived from the analytical model functions effectively with respect to resolving RS delay effects and decreasing latency in file delivery, leading to higher transmission efficiency.
Authors: Yu Zhou (School of Electronics and Information Engineering, Soochow University, Jiangsu, P. R. China), Ruhai Wang (Phillip M. Drayer Department of Electrical Engineering, Lamar University, Beaumont, TX, USA), Lei Yang (School of Electronics and Information Engineering, Soochow University, Jiangsu, P. R. China), Siwei Peng (School of Electronics and Information Engineering, Soochow University, Jiangsu, P. R. China), Kanglian Zhao (Nanjing University),
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This paper studies the modulation recognition of digital communication signals based on neural networks. The method of the BP neural network ensembles is put forward, which is a linear composition of the BP neural networks. And, the recognition accuracy of ten different modulation signals is given according to model above in features extraction. The approach presented is superior to a neural network algorithm in existing articles. The result shows that the method proposed can recognize complex signal modulation formats availably, and the overall recognition accuracy is basically up to 100% in the sample data of this paper when the SNR is more than 8 dB.
Authors: Ma Ma (Army Engineering University of PLA), Zhang Zhang (Army Engineering University of PLA), Guo Guo (Army Engineering University of PLA), Cao Cao (Army Engineering University of PLA), Wei Wei (Army Engineering University of PLA), Ma Ma (HUAWEI TECHNOLOGIES CO., LTD),
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Optical communication is an important technology for future space networks. However, compared with inter-satellite optical communication, satellite-ground optical communication is more challenging because of weather, which are mostly cloud factors. To deal with this problem, an effective strategy is to achieve ground station site diversity. In this paper, we propose a method to determine the range of clouds that affects satellite-ground optical links for a certain ground station. Given the number of candidate ground stations, through processing the cloud products of the Himawari-8 GEO satellite, we obtained the cloud coverage data corresponding to each ground station. Then, by calculating the availability probability of possible combinations of ground stations, the network with the highest availability is chosen as the optimal optical ground station network. By calculating the availability probability with real cloud data, the results of ground station site selection in mainland China are obtained.
Authors: Yihua Wang (Nanjing University), Xiaoyong Zhuge (Nanjing University), Shulei Gong (Nanjing University), Kanglian Zhao (Nanjing University), Wenfeng Li (Nanjing University), Yuan Fang (Nanjing University),
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BGP is mainly used in inter-domain communication of ground network. However, when the traditional inter-domain routing protocol BGP is used in the space environment, slow routing convergence and inter-domain link in-terruption will often occur, which will not only greatly reduce the stability of the network, but also may lead to partial network interruption, resulting in unpredictable consequences. In order to solve a series of problems caused by slow routing convergence and inter-domain link interruption in satellite network, this paper proposes a new border gateway protocol based on BGP[1]. Firstly, the protocol adopts the NTD-BGP protocol[2] for the frequent dynam-ic changes of network topology in satellite network. For the unpredictable link break, modify the BGP neighbors finite state machine, and introduces a new link break detection mechanism, and combine the predictability of satel-lite motion, and introduce the backup routing mechanism, make the net-work link can always maintain the stability of the network, realizes the high stability of inter-domain routing. The experimental results show that the improved routing protocol is superior to the traditional BGP in reducing the detection time of link interruption and maintaining the network stability.
Authors: Huiwen Chen (Nanjing University), Kanglian Zhao (Nanjing University), Jiawei Sun (Nanjing University), Wenfeng Li (Nanjing University), Yuan Fang (Nanjing University),
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This paper designs an infrared cloud imaging system for satellite-to-earth laser communications. The imaging system provides a reliable service for establishing an effective satellite laser communication link by collecting the cloud images over a ground station site, processing and analyzing the time and space statistics of the cloud, and acquiring the optical depth of the cloud. To realize day and night automatic monitoring of cloud state information, the infrared cloud imager designed in this paper can effectively observe the fixed viewpoint of the sky, and the uncooled infrared focal plane array calibration model considering the working temperature effect of the detector can meet the radiation setting of sky cloud monitoring, which provides cloud state data information with higher temporal and spatial resolution. Preliminary observation experiments show that the infrared cloud imaging system proposed in this paper can get required real-time cloud image and information for space-terrestrial laser communications.
Authors: Zhi-yong Zhang (Nanjing University), Kang-lian Zhao (Nanjing University), Yuan Fang (Nanjing University), Wen-feng Li (Nanjing University),
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Exploiting unmanned aerial vehicles (UAVs) to locate the position of interferences has attracted intensive research interests, due to UAVs' flexibility and the feature of suffering less multi-path interference. However, in order to find the position of an interference source, off-the-shelf Q-learning-based schemes require the UAV to keep searching until it arrives at the target. This obviously degrades time efficiency of localization. To balance the accuracy and the efficiency of searching and localization, this paper proposes a collaborative search and localization approach, where search and remote localization are iteratively performed with a swarm of UAVs. For searching, a low-complexity reinforcement learning algorithm is proposed to decide the direction of flight (in every time interval) for each UAV. In the following remote localization phase, a two-stage clustering algorithm is proposed to estimate the position of the interference source, by processing intersections of the extensions of UAVs' trajectories. Numerical results reveal that in the proposed collaborative search and localization scheme, the proposed reinforcement-learning-based searching can benefit the collaborative localization, in terms of the accuracy of localization. Moreover, compared to the Q-learning-based approach, the proposed approach enables remote localization and can well balance accuracy, the robustness amd time efficiency of localization.
Authors: Guangyu Wu (College of Computer Science and Technology, Nanjing University of Aeronautics and Astronautics), Yang Huang (Key Laboratory of Dynamic Cognitive System of Electromagnetic Spectrum Space, Ministry of Industry and Information Technology, Nanjing University of Aeronautics and Astronautics), Simeng Feng (Key Laboratory of Dynamic Cognitive System of Electromagnetic Spectrum Space, Ministry of Industry and Information Technology, Nanjing University of Aeronautics and Astronautic),
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Aiming at the problem of low accuracy of traditional open-loop tracking and long time-consuming of closed-loop tracking, this paper proposes a joint open-loop and closed-loop tracking method of BeiDou B1C signal, which not only ensures the tracking accuracy, but also greatly reduces the time-consuming of signal tracking. In order to verify the effectiveness and feasibility of the proposed algo-rithm, this paper uses the 40 meter large aperture antenna system of Haoping ob-servation station to collect the measured satellite signal data for verification, and makes in-depth analysis from tracking time-consuming, correlation peak, correla-tion loss, zero crossing deviation of S-curve, etc. The results show that under the condition of the same tracking parameters, when the data length ratio of the open-loop and the closed-loop parts is 9:1, the time of the method is saved about 90 % compared with the closed-loop tracking method; at the same time, the difference of the three evaluation parameters is within 1 %, which verifies the effectiveness and feasibility of the proposed method. The research results can provide theoreti-cal basis and technical support for parallel processing of navigation signals and automatic quasi real-time signal quality monitoring and evaluation in the future.
Authors: Zhenyuan Hao (Chinese Academy of Science), Chengyan He (Chinese Academy of Science), Ji Guo (Chinese Academy of Science), Xiaochun Lu (Chinese Academy of Science), Yongnan Rao (Chinese Academy of Science), Meng Wang (Chinese Academy of Science),
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In satellite-to-ground laser communications, the laser beam is sus-ceptible to the effects of atmospheric media when it passes through the atmosphere. The main reason is that the laser beam will be ab-sorbed and scattered by the cloud when it passes through the cloud, causing the communication link to be blocked. In order to know the cloud cluster information around the laser beam in advance, this pa-per proposes a Cloud Prediction Network (CloudNet) model, which classifies first, then predict the cloud trajectory for the next 100 sec-onds by collecting clouds images over a ground station, so as to rea-sonably allocating the resources of the link and select the ground stations. The experimental results show that the prediction accuracy of the model is up to 81% under the condition of 5% error.
Authors: Zheng Dai (Nanjing University), Kanglian Zhao (Nanjing University), Wenfeng Li (Nanjing University),
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Driven by lacking of a low-cost, large-scale, flexible and reconfigurable general purpose network emulation platform for space networking, ISTIN laboratory of Nanjing University designed a flexible and fully reconfigurable space network emulation platform supporting emulation of multiple network architectures and network protocols. We have carried out some space network protocol research based on the platform, such as DTN and IP. This paper constructs a spatial network scenario to evaluate OSPF and OSPF+ routing performance on this platform The emulation results indicate the emulation platform has the ability of IP routing emulation, which guarantees considerable reliability and provides a reference for subsequent emulation work of IP protocols.
Authors: Jiawei Sun (Nanjing University), Peng Zhou (Advanced Institute of Information Technology, Peking University), Kanglian Zhao (Nanjing University), Wenfeng Li (Nanjing University),
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In this paper, we investigate the spectrum sensing of a weak signal based on multiple low earth orbit (LEO) satellites in the presence of a spectrum-sharing node, which can generate the interference imposed on the sensing LEO satellites. In order to improve the sensing ability of the weak signal, a cooperative spectrum sensing method relying on satellite formation is proposed. Specifically,firstly, some satellites will be chosen from multiple LEO satellites for formation purposes, where the specific number of satellites chosen can be adjusted by evaluating the probability of detection weak signal, as detailed later. Then, considering the object that both restraining the interference and magnifying the weak signal, the weighted value of each satellite for beamforming may be optimized with the aid of genetic algorithm, and the receive gains of the weak signal and the interference can be achieved. Finally, the probability of detecting the weak signal can be evaluated by calculating the signal to interference plus noise ratio (SINR), and the number of the chosen satellites can be decided accordingly. Simulation results show that the proposed method not only can suppress the interference imposed on the sensing satellites, but also can increase SINR of sensing satellites for the weak signal, resulting in improving the probability of detection.
Authors: Yu Zhang (Nanjing University of Posts and Telecommunications), Xiaojin Ding (Nanjing University of Posts and Telecommunications), Chaoran Sun (Nanjing University of Posts and Telecommunications), Jian Zhu (Nanjing University of Posts and Telecommunications), Gengxin Zhang (Nanjing University of Posts and Telecommunications),
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Recently beam hopping technique is considered as a potential key technology in the next generation of high throughput satellite (HTS) systems for its flexible resource allocation. This paper is focused on the downlink resource allocation of beam hopping in the HTS System. Firstly, the user traffic model which varies in geography and time is built. Then with the proposed uneven traffic distribution model, the beam hopping time slot optimization algorithm is provided based on fairness object function. Finally, the beam hopping pattern is designed to comb with precoding to suppress co-channel interference. The simulation results show that compared with the traditional methods, the proposed algorithm can dynamically adjust the resource allocation with the change of the traffic requirements, and eliminate the co-frequency interference of the beam as much as possible to meet the traffic requirements of each beam, thus improving the capacity of the satellite network.
Authors: Xudong Zhao (Nanjing University of Posts and Telecommunications), Chen Zhang (Nanjing University of Posts and Telecommunications), Yejun Zhou (Institute of Telecommunication Satellite, China Academy of Space Technology), Gengxin Zhang (Nanjing University of Posts and Telecommunications),
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With the advent of 5G, the energy consumption of communication industry also increases, among which the base station(BS) energy consumption accounts for 43% of the total energy consumption of mobile communication.In order to reduce the communication energy consumption, the BS sleep technology can make the BS with low load enter the sleep state, realize the energy saving and create the green communication. In this paper, the simulated annealing(SA) algorithm is used to determine the BS closing mode. The switching situation can effectively reduce the energy consumption, which has practical significance and conforms to the expectation. The simulation results show that the sleep strategy can reduce the energy consumption, and the optimization of the algorithm can get a better solution and a simpler traversal process.
Authors: Wenchao Yang (Harbin Institute of Technology), Xu Bai (Harbin Institute of Technology), Yulong Gao (Harbin Institute of Technology), Rui Wang (Harbin Institute of Technology),
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in this paper, to achieve high network throughput (NT) in the half-duplex mode, a virtual full-duplex multi-hop two-way relay network is developed (VFD-MH-TWRN) using physical network coding (PNC) and SOQPSK modulation for space exploration application in which do not need instantaneous channel state information. In the proposed VFD-MH-TWRN scheme, two full-duplex source nodes exchange their information with the help of multi half-duplex relay nodes. As the main contribution, at first we define a novel data transmission strategy and then analytically derive the end-to-end bit error rate (BER) and, which are validated by the simulation results. It is shown that network throughput is higher than all of the previously defined networks and the simulation results show that the proposed scheme with SOQPSK modulation is close to DF-TWRN the bit error rate and they have similar performance.
Authors: Alireza Mazinani (School of Electronic and Information Engineering, BeiHang University, Beijing, China), Vahid Tavakoli (Department of Engineering and Media Technology, IRIB University, Tehran, Iran), Qiang Gao (School of Electronic and Information Engineering, BeiHang University, Beijing, China),
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With the extensive applications of Unmanned Aerial Vehicle (UAV), traditional approaches such as Artificial Potential Field and A-star for UAV track planning are usually limited by their low efficiency and easy failure, especially in the three-dimensional complex environments with obstacles. Moreover, most of these works do not make careful considerations on the fine-grain smooth of track requird heavily by the realistic flight of UAV. Therefore, in this paper, we propose an improved Biogeography-Based Optimization (BBO) algorithm with Bats algorithm (BA), named BIBBO for UAV track planning, which allows a new generating method with continuous Bezier curve by using adaptive-step sampling of control points to smooth original track. The simulation results verify the effectiveness and robustness of the proposed algorithm with shorter and smoother 3-D tracks, compared with typical BBO and BA algorithms.
Authors: Jingzheng Chong (Communication Engineering Research Center, Harbin Institute of Technology (Shenzhen)), Xiaohan Qi (Harbin Institute of Technology (Shenzhen)), Zhihua Yang (Communication Engineering Research Center, Harbin Institute of Technology (Shenzhen), Pengcheng Laboratory, Shenzhen),
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The purpose of cross-project defect prediction is to predict whether there are defects in this project module by using a prediction model trained by the data of other projects. For the divergence of the data distribution between different projects, the performance of crossproject defect prediction is not as good as within-project defect prediction. To reduce the difference as much as possible, researchers have proposed a variety of methods to filter training data from the perspective of transfer learning. In this paper, we introduce a ”project-instancemetric” hierarchical filtering strategy to select training data for the defect prediction model. Using the three-level filtering method, the candidate projects that are most similar to the target project, the instances that are most similar to the target instance, and the metrics with the highest correlation to the prediction result are filtered out respectively. We compared three-level filtering with project-level filtering, instance-level filtering, and the combination of project-level and instance-level filtering methods in four classification algorithms using NASA open source data sets. Our experiments show that the three-level filtering method achieves more significant f-measure and AUC values than the single level training data filtering method.
Authors: Cangzhou Yuan (Beijing University of Aeronautics & Astronautics), Xiaowei Wang (Beijing University of Aeronautics & Astronautics), Xinxin Ke (Beijing University of Aeronautics & Astronautics), Panpan Zhan (Beijing Institute of Spacecraft System Engineering),
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Along with the expansion of space-based information network, the task cooperation and resource allocation of access nodes is important issues that need to be addressed in the context of multiple spacecraft access. For the problem of resource dynamic scheduling, based on the present situation and development trend of space-based information network construction, resource allocation on tasks is researched in this paper. Furthermore, network resource allocation model and method of resource dynamic allocation based on genetic algorithm are realized, comprehensively consider the consumption and profit of resources to meet the task demand. By establishing allocation model suitable for space-based network, and using simulated annealing process and adaptive method to design improved genetic algorithm, the advantages and disadvantages are analyzed and simulated. The simulation result indicated the algorithm has good result in improving effectiveness and timeliness of network resource scheduling.
Authors: Wang Rui (China Academy of Space Technology), Han Xiao-dong (China Academy of Space Technology), An Wei-yu (China Academy of Space Technology), Song Ke-zhen (China Academy of Space Technology), Han Huan (China Academy of Space Technology),
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Monolithic fault detection methods have low accuracy for comprehensive faults detection, because they can only detect specific type of faults. Therefore, it is necessary to study the combination of fault detection methods to improve the detection accuracy. In this paper, based on the fault propagation on component-based aerospace embedded software architecture, we analyze occur reasons, manifestations and effects of instruction-, component- and system-level faults whose root cause is single event upset(SEU) which is the main reason of aerospace embedded software, and propose a hierarchical fault model to specify characteristics of the three levels faults. And based on the hierarchical fault model, a hierarchical detection method is proposed to combine the three levels monolithic fault detection methods. The experimental results show that the hierarchical fault detection method has higher fault detection accuracy than the monolithic fault detection methods for comprehensive faults detection.
Authors: Cangzhou Yuan (Beijing University of Aeronautics & Astronautics), Kangzhao Wu (Beijing University of Aeronautics & Astronautics), Ran Peng (Beijing University of Aeronautics & Astronautics), Panpan Zhan (Beijing Institute of Spacecraft System Engineering),
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As a efficient random access scheme, contention resolution diversity slotted ALOHA (CRDSA) improves the system throughput greatly, although deadlock problem limits the maximum throughput of system. To address this issue, in this paper, a non-orthogonal multiple access (NOMA) technique is proposed with random access (RA) scheme for supporting multiple terminals access in satellite IoT-oriented networks, by utilizing a code domain NOMA called Sparse Code Multiple Access (SCMA). In the proposed scheme, the throughput is mainly improved by physical (PHY) decoding and iterative decoding. Through mathematical analysis, theoretical and practical throughput lower bound of our scheme are shown and the result proves the proposed scheme is efficient in enhancing RA throughput.
Authors: Bo Zhang (Communication Engineering Research Center, Harbin Institute of Technology (Shenzhen)), Yue Li (Communication Engineering Research Center, Harbin Institute of Technology (Shenzhen)), Yunlai Xu (Communication Engineering Research Center, Harbin Institute of Technology (Shenzhen)), Zhihua Yang (Communication Engineering Research Center, Harbin Institute of Technology (Shenzhen), Pengcheng Laboratory, Shenzhen),
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Recently, to acquire the programmability, flexibility and reconfigurability of network, the technologies of software-defined networking (SDN) are utilized to design new architectures for LEO satellite networks, where control plane is realized by several GEO satellites, and suppose that each LEO satellite can directly connects with GEO controllers. This is unreasonable when the LEO data plane is a large-scale LEO satellite constellation, as the number of GEO controllers and antennas of each GEO controller are limited. In this work, we propose a design of software defined large-scale LEO satellite networks with limited GEO controllers, where the communication between GEO control plane and LEO data plane is achieved by limited cross-layer links. In this model, the selection of cross-layer links directly affects the load balance among GEO controllers and the latencies of control paths, which will deeply influence the latency of routing response. Thus, we propose a switching-aware dynamic control path planning scheme to handle this, where we propose a switching-time selection scheme to handle the impact of switching and a multi-objective optimi-zation problem to deal with the selection of cross-layer links, and finally present a particle swarm optimization based algorithm to solve it. Simulation results demonstrate the better performance on reducing the bad influence of switching, optimizing the load balance among controllers and the average latencies of control paths.
Authors: Tingting Zhang (Beijing Institute of Satellite Information Engineering, Beijing, China), Fan Bai (Beijing Institute of Spacecraft System Engineering), Tao Dong (Beijing Institute of Satellite Information Engineering, Beijing, China), Jie Yin (Beijing Institute of Satellite Information Engineering, Beijing, China), Zhihui Liu (Beijing Institute of Satellite Information Engineering, Beijing, China), Yuwei Su (Beijing Institute of Satellite Information Engineering, Beijing, China),
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Visual image transmission during power descent or landing segment is needed in deep space probes, while the bandwidth of transmission channel is limited and the information transmission rate is low in deep space communication. In view of this contradiction, a rate-adaptive visual image transmission scheme is designed in this paper. Key problems such as frame extraction and playback, frame format identification, joint scheduling are solved. Visual transmission of image under the condition of limited communication rate is realized by the scheme, with the characteristics of real-time performance, rate adaptation, image integrity, etc. At the same time, the concrete implementation and experimental verification of the scheme in engineering are given, which provide reference for the design on spacecraft data management system.
Authors: Cuilian Wang (Beijing Institute of Spacecraft System Engineering), Yin Li (DFH Satellite Co. Ltd), Ke Li (Beijing Institute of Spacecraft System Engineering), Dong Zhou (Beijing Institute of Spacecraft System Engineering),
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Recently, tremendous progress has been made in the research on space infor-mation networks, which also inspires the development of general or dedicated emulation systems. As an important part in emulation of the space information networks, the research on traffic generation system is still in the preliminary stage. In view of the insufficient research in this area, a multi-service traffic gen-eration system dedicated for emulation of space information networks is pro-posed in this paper. The system is designed based on software-defined network-ing technology to decouple the traffic generation part from the traffic transmission part, avoiding the complicated configuration problems in emulation of large scale space information networks, and making the entire system flexible and extensible. At the same time, the traffic generation part of the system uses a variety of busi-ness models, which is helpful for the research in future space information net-works.
Authors: Feng Jiang (Nanjing University), Qi Zhang (Nanjing University), Yuhang Du (Nanjing University), Kanglian Zhao (Nanjing University), Wenfeng Li (Nanjing University), Yuan Fang (Nanjing University),
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At present, the research on the single satellite frequency measurement and localization technology mainly focuses on the use of multiple satellite obser-vation positions in a single flight orbit to forward the ground target source signals, but there are many limitations in locating the interference source with limited field of view. In this paper, based on the single-orbit single-satellite time-division frequency-measuring localization technology, a localization technology of single-satellite time-division Doppler frequency measurement in different orbits is proposed, which is based on the optimal observation satellite position. Firstly, the positioning model and the positioning equation of the single-satellite time-division Doppler frequency measurement and lo-calization technology in different orbits are constructed. Secondly, a calcula-tion formula for GDOP is derived and the optimal model of the observation satellite position is constructed. Finally, based on the positioning process, the minimum positioning error is targeted. Computer simulation results show that the availability and accuracy of the technique are improved significantly in the scene with limited field of view.
Authors: Hui Ji (“Telecommunication and Network” National Engineering Research Center, Nanjing Uni-versity of Posts and Telecommunications), Dexin Qu (“Telecommunication and Network” National Engineering Research Center, Nanjing Univer-sity of Posts and Telecommunications), Gengxin Zhang (Telecommunication and Network” National Engineering Research Center, Nanjing Universi-ty of Posts and Telecommunications),
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The recent decades have seen an increasing interest in Medium Earth Orbit and Low Earth Orbit satellite constellations. However, there is little information on the delay variation characteristics of these systems and the resulting impact on high layer protocols. To fill this gap, this paper simulates a constellation that exhibits the same delay characteristics as the already deployed Iridium but considers closer bandwidths to constellation projects'. We identify five major sources of delay variation in polar satellite constellations with different occurrence rates: elevation, intra-orbital handover, inter-orbital handover, orbital seam handover and Inter-Satellite Link changes. We simulate file transfers of different sizes to assess the impact of each of these delay variations on the file transfer. We conclude that the orbital seam is the less frequent source of delay and induces a larger impact on a small file transfers: the orbital seam, which occurs at most three times during 24 hours, induces a 66% increase of the time needed to transmit a small file. Inter-orbital and intra-orbital handovers occur less often and reduce the throughput by approximately ~ 8% for both low and high throughput configurations. The other sources of delay variations have a negligible impact on small file transfers, and long file transfers are not impacted much by the delay variations.
Authors: Amal Boubaker (IRIT/ENSEEIHT/TéSA), Emmanuel Chaput (IRIT/ENSEEIHT), Nicolas KUHN (CNES), Jean-Baptiste Dupé (CNES), Renaud Sallantin (TAS), Cédric Baudoin (TAS), André-Luc Beylot (IRIT/ENSEEIHT),
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The design and optimization of fade mitigation techniques in Q / V bands satellite communications require rain attenuation time series in the propagation channel. Methods for synthesizing short-term and long-term rain attenuation time series at Q/V bands are integrated in this paper. Firstly, based on the ‘Event-on-Demand’ model, assuming that the rain attenuation value obeys the log-normal distribution, the rain attenuation process is transformed into a first-order stationary Markov process after nonlinear transformation. The generation steps of short-term rain attenuation time series are analyzed by using the characteristic parameters of rainfall attenuation time series. Then according to the Dirac lognormal distribution model, based on the mixed Dirac log-normal distribution of the rain attenuation complementary cumulative probability distribution function CCDF, the steps of generating long-term rain attenuation time series are given using a stationary Gaussian process. Finally, the short-term and long-term rain attenuation time series at Q / V bands are obtained by combining the simulation results of ITU-R static model. The power spectrum estimation of the series shows the validity of the rain attenuation time series.
Authors: Jiangtao Yang (Nanjing University of Posts and Telecommunications), Chen Zhang (Nanjing University of Posts and Telecommunications,), Yonghua Huang (CETC38 China Electronic Technology Group Corporation), Gengxin Zhang (Nanjing University of Posts and Telecommunications),
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With the increasing scale of low Earth orbit (LEO) satellite networks, the satellite network topology may become more and more complex. In order to cope with local congestion and link disruption with the aid of path planning, a virtual topology based improved routing (VTIR) scheme is proposed, which can be considered as a kind of node feedback routing (NFR) To be specific, in the proposed VTIR scheme, the orbit-period is divided into time slices, and the dynamic topology is also converted into a static topology. Moreover, both queue buffer state feedback and connection state feedback are considered in routing-path computation, resulting in that the link cost may be determined by a combination of distance, congestion, and link state. Simulation results show that compared with the conventional snapshot scheme, the proposed VTIR scheme can alleviate local congestion by extending traffic to idle links, without increasing packet loss rate.
Authors: Chaoran Sun (Nanjing University of Posts and Telecommunications), Yu Zhang (Nanjing University of Posts and Telecommunications), Jian Zhu (Nanjing University of Posts and Telecommunications),
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Based on the frequency division multiplexing principle of the multi-beam antenna, this paper proposes a new method for locating interference sources by only one single satellite. According to the antenna pattern function ex-pression of multi-beam antennas, the positioning equations are derived and established by analyzing the link that interfering signal arrives at the space-borne multi-beam antenna from the ground. Importantly, some errors are in-troduced in the positioning process when we evaluate the performance of this positioning method, including gain error, beam center position devia-tion, and elevation error. Considering the difficulty of solving nonlinear po-sitioning equations, a new algorithm combining the Particle Swarm Optimi-zation (PSO) and grid search is proposed. At the same time, in this paper, in order to analyze the feasibility of this new algorithm, we introduce the Mon-te Carlo method in the process of this experiment. Finally, this new algo-rithm is compared with the traditional Particle Swarm Optimization in terms of speed and accuracy, which shows the superiority of this new algorithm.
Authors: Cen Ruan (Nanjing University of Posts and Telecommunications), Laiding Zhao (Nanjing University of Posts and Telecommunications), Gengxin Zhang (Nanjing University of Posts and Telecommunications), Jidong Xie (Nanjing University of Posts and Telecommunications),
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Most of transmitted signals of satellite Internet of Things (IoT) terminals have the characteristics of low baud rate, short packet length and burstiness. The collision of massive access of IoT terminals can be solved by a random multiple access technology in company with an efficient and reliable collision separation method in the receiver. However, most existing signal separation technologies are proposed for continuous signals, and the receiving structure is designed based on the phase-locked loop. In this paper, a short burst signal separation method based on adaptive minimum mean square error (MMSE) filtering is proposed for the classical contention resolution diversity slotted Aloha (CRDSA). The proposed method estimates the frequency and phase difference between copies by amplitude and phase estimation (APES) firstly and cancels the collision signal based on a MMSE filter. The theoretical analysis and simulation results verify the feasibility of the proposed method.
Authors: Yixin Hu (Nanjing University of Posts and Telecommunications), Ziwei Liu (Nanjing University of Posts and Telecommunications), Jing Zeng (Nanjing University of Posts and Telecommunications), Gengxin Zhang (Nanjing University of Posts and Telecommunications),
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The principle of wavelet threshold de-noising is described in detail. Daubechies wavelet function is selected to denoise the sinusoidal signal with noise. The relationship between the order of wavelet function, the number of decomposition layers, the number of signal samples and the signal-to-noise ratio of denoised signal is demonstrated. At the same time, the calculation methods of fixed threshold, unbiased risk estimation threshold, mixed threshold and mini threshold max threshold are summarized, and then the denoising effects of hard threshold, soft threshold and semi soft threshold functions are compared. By analyzing the distribution of wavelet decomposition coefficients and combining with the characteristics of other threshold functions, a new wavelet threshold function is designed and compared with other threshold functions.
Authors: Shulin Xiao (Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences), Lintao Han (Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences), Jiabian An (Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences), Luyao Gao (Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences), Changhong Hu (Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences),
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Near-field source localization is a potential research topic in next-generation wireless communications. Most existing methods focus on traditional subspace based methods or on-grid sparse methods. In this paper, we propose an off-grid sparse representation localization method. First, by obtaining a high order cumulant matrix we construct an angle based off-grid signal model and then employ the alternatively iterating optimization method to estimate the angles. For range estimation, a range based off-grid signal model is constructed by using the angle estimations and solved by alternatively iterating method. Simulation results reveal that, the proposed method not only enjoys high estimation accuracy, but also can realize auto-pairing of angles and ranges.
Authors: Yang Li (China Academy of Space Technology of Xian), Jin Yi (China Academy of Space Technology of Xian), Xu Changzhi (China Academy of Space Technology of Xian), Li Xiaoran (China Academy of Space Technology of Xian), Zuo Jinzhong (China Academy of Space Technology of Xian), Wang Dizhu (China Academy of Space Technology of Xian),
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This paper presents a design scheme of space-borne multi-functional integrated hardware processing platform. This platform is characterized by low power consumption, small size and light weight. At the same time, the scheme has the feature of reconfiguration, which maximizes the function of software. Different software is loaded according to different application to build hardware platforms for satisfying requirements in different environments. It provides a new way to solve the problem of traditional hardware specialization, which is the trend of hardware platform in the future.
Authors: Ping Yi-Fan (China Academy of Space Technology, Xi’an 710100), Wang Su-jun (China Academy of Space Technology, Xi’an 710100), Wen Wei (China Academy of Space Technology, Xi’an 710100), Xu Chang-zhi (China Academy of Space Technology, Xi’an 710100), Shao Ying-zhao (China Academy of Space Technology, Xi’an 710100),
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With the fierce competition for electromagnetic spectrum, the development of intelligent satellite communication systems with intelligent waveform generation and reconstruction capabilities is an effective means to adapt satellite communication system to the harsh electromagnetic environment. In this paper, a 10-layer deep autoencoder network(DAN) is designed, and 2-ary to 64-ary modem are implemented based on this 10-layer DAN. During this process, a unified loss function and a a unified optimization algorithm are utilized to train and test the 10-layer DAN. Finally , the demodulation performance, that is close to, consistent with or better than that of traditional MPSK or QAM is obtained. The above-mentioned DAN and its training method provide a new way for waveform generation and reconstruction in intelligent communication satellites. In addition, the high-order modulation constellation generated by this 10-layer DAN is quite different from the traditional modulation method and very difficult to distinguish linearly, which is beneficial to improve the anti-intercept ability of the satellite communication waveform.
Authors: Peng Wei (63rd Research Institute, National University of Defense Technology), Ruimin Lu (63rd Research Institute, National University of Defense Technology), Shilian Wang (College of Electronic Science, National University of Defense Technology), Shijun Xie (63rd Research Institute, National University of Defense Technology),
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Low Earth Orbit satellite communication system has the characteristics of low latency and wide coverage, and is widely used in the non-terrestrial communication systems. But at the same time, the characteristic of its fast-changing topology also brings the complex problem of network performance evaluation. In this paper, we propose a Minimum Delay Maximum Capacity algorithm based on Minimum Cost Maximum Flow algorithm to evaluate the performance of the LEO satellite networks. We analyze the performance of several different constellation configurations by using the algorithm.
Authors: Xuan Li (College of Aerospace Science and Engineering, National University of Defense Technology), Quan Chen (College of Aerospace Science and Engineering, National University of Defense Technology), Lei Yang (College of Aerospace Science and Engineering, National University of Defense Technology), Xianfeng Liu (College of Aerospace Science and Engineering, National University of Defense Technology), Lihu Chen (College of Aerospace Science and Engineering, National University of Defense Technology),
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Cognitive radio and artificial intelligence are hot research topics in the field of communication. This article discusses how to efficiently and reliably transmit space-based information from satellites to the ground. Related theories of cognitive radio and artificial intelligence are used to study the intelligent transmission of space-based information. This article also proposes ideas and strategies to improve the transmission efficiency and reliability of the satellite-earth data link. Several key issues including spectrum sensing and cognition, waveform reconstruction, the design of the intelligent decision engine, the massive data processing, spaceborne reconfigurable transmission platform, and signaling parameters transmission were analyzed. The research results can provide help for real-time and reliable transmission of space-based information in the future.
Authors: Tao Guan (National University of Defense Technology), Rong Lv (The Sixty-third Research Institute, National University of Defense Technology, China.), Ganhua Ye (The 63rd Research Institute, National University of Defense Technology), Wei Huang (National University of Defense Technology), Xin Ma (National University of Defense Technology), Ruimin Lu (National University of Defense Technology),
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Satellite-assisted Internet of Things (IoT) communications, artificial intelligent (AI) empowered wireless communications have been expected as two of the key enablers for 6G visions, since they can help 6G achieve better intelligence, cover-age in diverse scenarios besides faster transmission speed than 5G. A straight-forward way to enable this vision is moving computation facilities onto the satel-lites using the edge computing paradigm. At its current state, existing satellite edge computing proposals only describes a rudiment of the satellite design with revealing the service architecture of the edge computing empowered satellite-territorial networks. In this backdrop, this paper presents a service architecture of edge computing empowered satellite-territorial networks, which is a layered structure contains two pools and five layers. To exhibit the benefit of the service architecture, a satellites-based spectrum sensing use case is detailed, and the nu-merical test results are given and analyzed. Finally, several open issues in imple-menting our proposed architecture are outlined.
Authors: Xianglin Wei (National University of Defense Technology), Rong Lv (National University of Defense Technology), Shiyun Yu (National University of Defense Technology), Yongyang Hu (National University of Defense Technology),
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In general, the problem of the resource management in the MF-TDMA satellite communication system can be divided into two phases: a timeslot calculation phase for each connection request and a timeslot allocation phase in the frame structure. In this paper, we propose algorithms to solve this two-phases problem. In the former phase, we first allocate each connection re-quest on an appropriate carrier based on the traffic demand of each connection request, and next dynamically adjust the coding and modulation mode of each connection request, according to the channel condition and state of the system resource usage. Then we calculate the number of timeslots required to be as-signed to each connection request. In the latter phase, we propose an algorithm called Best Fit (BF)-modified to allocate the timeslots in the MF-TDMA frame structure. Simulation results show that although the total traffic demands gener-ated by all the connection requests are various, the timeslot is sufficiently uti-lized due to the dynamical adjustment of the coding and modulation mode. Moreover, the performance of the proposed (BF)-modified algorithm is better than that of the existing algorithm.
Authors: Heng Wang (The 63rd Research Institute, National University of Defense Technology), Shijun Xie (The 63rd Research Institute, National University of Defense Technology), Ganhua Ye (The 63rd Research Institute, National University of Defense Technology), Bin Zhou (The 63rd Research Institute, National University of Defense Technology), Yonggang Wang (The 63rd Research Institute, National University of Defense Technology),
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Traditional satellites are designed and developed according to specific functions, resulting in large size, high price and long development cycle. With the rapid development of small satellite technology, the satellite has higher and higher degree of modularization. Similar to smartphones, satellites can dynamically upload “Apps” in-orbit, achieving the transition from “function satellites” to “smart satellites”. In view of the rapid, efficient and reliable development of on-board software, a model-driven software development framework and a development tool chain are proposed in this paper. To solve the problems of lack of standardized architecture in on-board software development, poor communication of various development stages, serious coupling of software and hardware, and low automation, the framework adopts unified architecture, standardized components, configurable integration and automatic code generation. The development tool chain provides a complete set of tools for entire on-board software development. It improves the software reusability by decoupling software design from hardware platform and shortens the development period by automatically connecting the various development stages. Finally, this paper demonstrates the process of developing iSat-1, which is a CubeSat for function in-orbit defined experiment.
Authors: Junxiang Qin (College of artificial intelligence of the National University of Defense Technology), Ninghu Yang (College of artificial intelligence of the National University of Defense Technology), Yuxuang Wang (College of artificial intelligence of the National University of Defense Technology), Jun Yang (The Sixty-third Research Institute, National University of Defense Technology, China.), Jinliang Du (Xi'an satellite control center),
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Approximate computing is an innovative circuit paradigm for lower power and real time image processing architecture within an intelligent satellite. Multiplication is often a fundamental function for many of image processing applications. Based on previous approximate compressor designs, a recursive type multiplier is proposed. Extensive simulation results show that the proposed designs achieve significant reductions in area, power and delay compared with an exact recursive multipliers as well as other approximate multipliers found in the technical literature. An image processing application is performed to further show that the performance of the proposed approximate multipliers for image processing achieves a very good accuracy (measured by the peak signal to noise ratio) as well as substantial reductions in power dissipation and delay.
Authors: Zhixi Yang (National Innovation Institute of Defense Technology, Academy of Military Science, China), Rong Lv (The Sixty-third Research Institute, National University of Defense Technology, China.), Xianbin Li (National Innovation Institute of Defense Technology, Academy of Military Science, China), Jian Wang (National Innovation Institute of Defense Technology, Academy of Military Science, China), Jun Yang (The Sixty-third Research Institute, National University of Defense Technology, China.),
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The global navigation satellite system(GNSS) includes satellites of multiple types, ground facilities with multiple functions, and various user terminals. The docking test of multiple systems in ground is an important part for managing the design, construction, and deployment of the satellite navigation system. To achieve efficient parallel docking of multiple systems, this paper designs a platform for remote docking test. Specifically, the architecture, operating process, and functional performance of the docking test platform are designed according to the task and characteristics of the docking test for satellite navigation. Besides, some key techniques are also analyzed including the management of command and dispatch for multi-node system as well as the interconnection of remote fiber. This paper implements the effective interconnection between the simulation verification system and real engineering system, and realizes command control and timing scheduling with high-precision. The designed platform has the capability of full coverage test for signal and information projects, and the capability of remote docking test for multi-systems that work in parallel. By applying our platform, the docking efficiency can be improved, the docking cost can be reduced, and the implementation of high-density networking for satellite can be promoted.
Authors: Wang wei (Beijing Institute of Tracking and Communication Technology), Chai qiang (China Academy of Aerospace Electronics Technology), Gao weiguang (Beijing Institute of Tracking and Communication Technology), Lu jun (Beijing Institute of Tracking and Communication Technology), Shao shihai (University of Electronic Science and Technology of China), Bai yu (China Academy of Aerospace Electronics Technology), Niu jingyi (China Academy of Aerospace Electronics Technology), Feng wenjing (Beijing Institute of Spacecraft System Engineering), Li shaoqian (Shanghai Engineering Center for Microsatellites),
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In recent years, the research in the multiple fields of representation learning has led to the emergence of many excellent Network Embedding algorithms. Here we propose attr2vec, a completely unsupervised algorithmic framework for learning the latent representations for nodes. In attr2vec, we have adopted an attribute processing method similar to GCN, that is, taking the average of the attribute of the node’s neighbors as the attribute for the node. We also consider first-order neighbors and second-order neighbors separately to achieve an effect similar to multiple convolutional layers in GCN. In summary, our algorithm utilizes similar attribute processing idea of GCN, which can learn the graph topology and node attribute to generate latent representations for nodes, but implemented it with a completely unsupervised way. In some experiments on citation networks we demonstrate that our algorithm outperforms related unsupervised techniques by a significant margin.
Authors: Pengkun Zheng (College of Computer Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China), Yan Wen (College of Computer Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China), Ming Chen (State Grid shandong Electric Power Company, Qingdao Power Supply Company,Qingdao, 266500, China), Geng Chen (College of Electronic and Information Engineering, Shandong University of Science and Technology, Qingdao 266590, China),
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As the key technology of connected intelligence, the importance of artificial intel-ligence has increased rapidly. It is important to note that the most critical chal-lenge is the secure data sharing which is stored in different area and belonged to different organization. With this in mind, a hashgraph based federated learning for secure data sharing model is proposed to protect user privacy and detect the dishonest model provider. In terms of technologies, a detection of local model is added to the hashgraph consensus processing, and only if the supermajority (more than 2/3) of the participants agree, the local model could be adopted. There-fore, the accuracy and convergence rate of the federated learning both increased largely. On the other hand, the asynchronous working mode of hashgraph can greatly reduce the network overload. Simulation results show that the hashgraph based federated learning enables the data sharing more secure and relia-ble.
Authors: Xiuxian Zhang (Nanjing University of Posts and Telecommunications, Nanjing Xiao zhuang University), Lingyu Zhao (Nanjing University of Posts and Telecommunications), Jinfeng Li (Nanjing University of Posts and Telecommunications), Xiaorong Zhu (Nanjing University of Posts and Telecommunications),
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In order to achieve fast decoding and improve the throughput, this paper uses the polar code to encode the spin transfer torque MARAM (STT-MRAM) channel. Based on the Fast-SSC algorithm, a (256, 220) hardware architecture is designed, including the controller, processing element, Kronecker product and memory module. This paper reduces the complexity of data process by splitting the data of nodes, and reduces the memory bandwidth by increasing the reusability of data. The decoder is synthesized on Stratix V 5SGXEA7N2F45C2, the decoding latency is 0.68us, and it can achieve 375Mbps at 167MHz.
Authors: Jianming Cui (Shandong University of Science and Technology), Zengxiang Bao (Shandong University of Science and Technology), Xiaojun Zhang (Shandong University of Science and Technology), Hua Guo (Shandong University of Science and Technology), Geng Chen (Shandong University of Science and Technology),
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Compared with the SC decoder, BP decoder provides a higher throughput and lower decoding latency for its inherent parallel nature. However, the functional units of existing BP decoders are not fully utilized. In this paper, we propose a new update scheduling scheme and hardware optimization design to improve the hardware efficiency of BP decoder. First, a pipelined decoder architecture is proposed to reduce the consumption of functional units. Then, a new update scheduling scheme is proposed, when updating the messages, both new-value and old-value approaches are used to improve the utilization of functional units and reduce the decoding latency. The analysis and synthesis results have shown that, compared with the existing methods, the proposed decoder suffers from a slight the decoding performance degradation, but the utilization rate of basic computational blocks (BCB) can be increased to 50.58%. The storage resource dissipation can be reduced by 20.1%-34.09%.
Authors: Xiaojun Zhang (Shandong University of Science and Technology), Na Li (Shandong University of Science and Technology), Jun Li (Shandong University of Science and Technology), Chengguan Chen (Shandong University of Science and Technology), Hengzhong Li (Shandong University of Science and Technology), Geng Chen (Shandong University of Science and Technology),
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With the advent of the Internet era, the recommendation system has devel-oped rapidly. Heterogeneous information networks representation learning is widely used in recommendation systems due to its advantages in complex in-formation modeling. Although the performance of the recommendation sys-tem has been improved, there are still two shortcomings: 1. There is a lot of noise data in the instances of the meta-path generated by random walks of meta-paths, which will reduce the performance of the recommendation sys-tem. 2. Traditional recommendation algorithms fail to make full use of the relevant meta-path information in heterogeneous in-formation networks, which makes the recommendation results lack of interpretability. To solve these problems, we propose a recommendation system based on heterogene-ous network representation learning and neural network model. Firstly, use the matrix factorization and the similarity calculation to select the meta-path instances with good quality as the pre-training vectors of the recommenda-tion system. Then, we combine LSTM with Attention mechanism to learn the user, item and meta-path embeddings, and use MLP to make prediction after fusion to jointly improve the recommendation effect. We conduct-ed exper-iments on Movielens datasets to evaluate the performance of our proposed recommendation.
Authors: Cong Zhao (College of Computer Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China), Yan Wen (Shandong University of Science and Technology, Qingdao, China), Ming Chen (State Grid Shandong Electric Power Company, Qingdao Power Supply Company, Qingdao, 266500, China), Geng Chen (College of Electronic and Information Engineering, Shandong University of Science and Technology, Qingdao 266590, China),
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In the paper, we explore the spectrum-data reconstruction of a spectrum-sensing system. In order to decease the demand on the sensed spectrum data, we proposed a deep convolutional neural network (DCNN) based spectrum data reconstruction scheme relying on three stages, thus the satellites are allowed to perform spectrum sensing with the aid of down-sampling, and transmit the low-resolution (LR) and small amount of high-resolution (HR) spectrum data to earth stations. Specifically, in the first stage, the received LR and HR spectrum data will be first preprocessed. Then, the preprocessed HR spectrum data will be sent into the DCNN model for training purposes in the second stage. In the third stage, the preprocessed LR spectrum data will be fed into the trained model with the aid of the optimized hyperparameters, and the trained DCNN can generate the HR spectrum data. Additionally, performance results show that the proposed reconstruction scheme can obtain the reconstructed HR spectrum data in terms of the low mean absolute error.
Authors: Xiaojin Ding (NUPT), Lijie Feng (NUPT),
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Mobile edge computing (MEC) networks can provide a variety of services for different applications. End-to-end performance analysis of these services serves as a benchmark for the efficient planning of network resource allocation and routing strategies. In this paper, we propose a performance analysis framework for the end-to-end data-flow in MEC networks based on stochastic network calculus (SNC). Due to the random nature of routing in the MEC networks, we introduce a probability parameter set in our proposed analysis model to characterize this randomness into our derived expressions. Taking actual communication scenarios into consideration, we analyze the end-to-end performance of video with the interference with voice over internet protocol (VoIP) and file transfer protocol (FTP) . For scheduling of these network data-flows, we consider the preemptive priority scheduling scheme. Based on the arrival processes of these video-flows, the effect of interference on its performances and the service capacity of each node in the MEC network, we derive closed-form expression for showing the relationship between delay upper bound and violation probability of the video-flow. Simulation and analytical results show that delay performances of the video-flow is influenced by the number of hops in the network and the random probability parameters of interference-flow.
Authors: Jindou Shi (Nanjing University of Posts and Telecommunications), Xiaorong Zhu (Nanjing University of Posts and Telecommunications),
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Efficient wireless access of a large number of nodes is one important issue for large scale self-organizing wireless networks. In order to achieve this goal, collision problem between nodes must be resolved. Bio-inspired algorithms provide some significant characteristics such as stability, adaptability, and scalability, and hence many researchers have attempted to apply bio-inspired algorithms to solve some problems in networks. In this paper, we propose a smart access algorithm for large scale self-organizing wireless networks, which is inspired by Stigmergy, which is able to make group members implement information interaction symmetry in some ways, and members are able to influence and interact with each other to avoid collision. Then we build an analysis model based on Markov chain for the proposed algorithm. Simulation results show that the proposed algorithm can maintain a low collision probability with the increasing number of competing nodes even in a dynamically changing network topology. In addition, the results show that compared with traditional algorithms, the proposed algorithm has better performances on channel throughput and access delay.
Authors: Enfu Jia (Nanjing University of Posts and Telecommunications), Jiaming Cao (Nanjing University of Posts and Telecommunications), Xiaorong Zhu (Nanjing University of Posts and Telecommunications), Jinfeng Li (Nanjing University of Posts and Telecommunications),
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In order to improve the efficiency and quality of service of the network, network convergence and the development of heterogeneous network have became inevitable. It is a challenge to detect and diagnose the various network faults efficiently in the complex network environment. To solve this problem, a network fault detection and diagnosis algorithm based on deep Q-learning is proposed. Combining deep learning and reinforcement learning model to classify network faults, we can classify some obvious network states via using less features, and filter irrelevant or redundant features at the same time. Results show that the algorithm can use less features to achieve higher classification accuracy, and the accuracy can reach 96.7%.
Authors: Peipei Zhang (Nanjing University of Posts and Telecommunications), Mingxiao Wu (Nanjing University of Posts and Telecommunications), Xiaorong Zhu (Nanjing University of Posts and Telecommunications),
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With the previous method based on the signal strength of the three-beam in-terference source[1], after studying and deriving the antenna gain pointing model, this paper proposes a single-star interference source localization method based on the signal strength of the four-beam interference source. As for solving the nonlinear directional equations, this paper proposes an improved particle swarm optimization algorithm to obtain its numerical so-lution, which is compared with the previous ordinary particle swarm optimi-zation algorithm[2]. Then, using the least square method, the multi-group data is used to determine the interference source with the smallest error. First orientation and then positioning. After the simulation test of the pro-posed positioning method, the feasibility of the algorithm for positioning is proved. The method proposed in this paper is compared with the previous positioning method to prove the robustness of the algorithm.
Authors: Laiding Zhao (Nanjing University of Posts and Telecommunications), Zhiwei Li (ZheJiang University), Cen Ruan (Nanjing University of Posts and Telecommunications), Yue Zheng (Nanjing University of Posts and Telecommunications),
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In order to improve the efficiency and stability of SpaceTerrestrial integrated network resource management and control, a multielement multi-domain network management protocol (MMMP) is proposed. Based on MMMP, Space-Terrestrial integrated network management and control system (STi-NMCS) is designed. By abstracting network management objects, the efficiency of network management is greatly improved. Experiments are carried by comparing the overhead and the success rate of network management between MMMP, simple network management protocol(SNMP) and common management information protocol(CMIP). The results show that by using MMMP rather than SNMP as well as CMIP, the Space-Terrestrial integrated network management system archives high success rate and low management overhead.
Authors: Ling Teng (Institute of Software Chinese Academy of Sciences), Li Shen (Institute of Software Chinese Academy of Sciences), Wang Xiaoting (Beijing Institute of Tracking and Teleconmulations Technology), Wu Lielei (Beijing Institute of Tracking and Teleconmulations Technology), Zhou Hui (Beijing Information Science & Technology University), Yang Fei (Beijing Information Science & Technology University), Wu Guangyang (Institute of Software Chinese Academy of Sciences), Hu Hailong (Institute of Software Chinese Academy of Sciences), Liu Lixiang (Institute of Software Chinese Academy of Sciences), Zheng Changwen (Institute of Software Chinese Academy of Sciences),
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In order to overcome the high mobility problem of nodes in vehicular ad hoc networks (VANETs), the clustering algorithm can effectively improve the overall communication performance. This paper proposes an optimized timer-based passive clustering algorithm (OTPCA) for VANETs. Vehicles can choose to actively leave the cluster or not join the cluster based on the communication environment and performance. The vehicle can choose to communicate directly with the road side unit (RSU) and force it to remain for a timer. After the timer expires, it is re-evaluated whether it is suitable to join a cluster, and then repeat the operation. This can effectively solve the problem of node state stuck and improve the average communication performance. Simulation results show that the proposed algorithm is better then the passive multi-hop clustering algorithm in terms of average communication delay and control information transmission ratio.
Authors: Yang Lu (Beihang University), Kai Liu (Beihang University), Tao Zhang (Beihang University), Xiling Luo (Beihang University), Feng Liu (Beihang University),
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To solve the high transmission collisions and channel resource wastage problems in unbalanced traffic conditions of VANETs, an adaptive and on-demand TDMA-based MAC (AODMAC) protocol is proposed. A dynamic frame is partitioned into equal slot sets according to the lane numbers, and each lane has its own disjoint time slot set for vehicles to access. The key operation of AODMAC is that it can adaptively adjust the size of slot set according to the different traffic density in each lane. Due to each lane can acquire its slot set on-demand, AODMAC can be efficient in both balanced and unbalanced traffic load scenarios. Before a vehicle can acquire a time slot, it should judge the traffic load of its lane. If the density has exceeded a threshold, the node should augment its slot set size from the other lane. Simulation results show that the proposed AODMAC protocol can achieve a better performance than VeMAC and MoMAC in terms of the transmission collision rate and channel utilization, especially in high traffic load and unbalanced conditions.
Authors: Yaodong Ma (Beihang University), Kai Liu (Beihang University), Xiling Luo (Beihang University), Tao Zhang (Beihang University), Feng Liu (Beihang University),
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A dynamically modified load balancing routing strategy, named Dynamic Modified routing table based on Load Balance (DMLB) was proposed in this manuscript for the problem of congestion and packet loss, which was caused by uneven distribution of business traffic in the low earth orbit (LEO) satellite network. Different from the traditional routing protocol for a single satellite, the strategy forms a kind of fast forwarding through the steps of geographical location-based traffic prediction, calculation of the entire network routing forwarding table based on weighted shortest path and dynamic correction of load balancing based on priority. These lead to an efficiently updated routing protocol. Simulation results show that the proposed DMLB strategy has better load balancing capabilities and smaller rerouting convergence time, ensuring the reliability of delay-sensitive service transmission, reducing link management overheads, and saving on-board computing resources.
Authors: Li Shen (Space Engineering University), Yuanqin Wang (Space Engineering University), Lixiang Liu (Institute of Software Chinese Academy of Sciences), Shuaijun Liu (Institute of Software Chinese Academy of Sciences), Dapeng Wang (Institute of Software Chinese Academy of Sciences), Yuanyuan Fan (Institute of Software Chinese Academy of Sciences), Huanren Zhou (Institute of Software Chinese Academy of Sciences), Teng Ling (Institute of Software Chinese Academy of Sciences),
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Power system is one of the important sub-systems that directly impact the in-orbit safe and affection of satellites. Satellite solar array determine the current output of whole satellite. The paper shows the solar array current prediction method based on unsupervised learning which can solve the low-orbit satellite solar array current prediction problem. This method introduces the competition elements that establish the mapping relation between the historical data and the competition element, obtains the best sample through the competition between the competition elements in the prediction processes, the relation functions take the best sample data as the benchmark which can realize the prediction of solar cell array output. Through competition the information of temperature, earth reflection, conversion efficiency and attenuation factors in the sample data are introduced effectively, and the description of such factors in the prediction process is avoided. Through the actual data analysis, we realize the extrapolation of the one-year current mean error is not more than 0.4 a, and the maximum error is not more than 0.5 a. The prediction algorithm for the solar cell array of low orbit satellites without the mathematical description of temperature, earth reflection, conversion efficiency and attenuation factors can predict the reasonable introduction of the above factors.
Authors: Wu Guan (Key Laboratory for Fault Diagnosis and Maintenance of Spacecraft in-orbit), Chen Jun (Key Laboratory for Fault Diagnosis and Maintenance of Spacecraft in-orbit), Zhang Wei (Key Laboratory for Fault Diagnosis and Maintenance of Spacecraft in-orbit), Hu Xing (Key Laboratory for Fault Diagnosis and Maintenance of Spacecraft in-orbit), Zhao Jing (Key Laboratory for Fault Diagnosis and Maintenance of Spacecraft in-orbit),
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Low-orbit space debris removal path planning can be decomposed into optimization problems of debris removal sequences and optimization of transfer orbit design between debris. In this paper, a two-level planning model is established, and the corresponding group intelligent optimization algorithm is proposed. The upper-level optimization problem takes the debris removal sequence as the design variable, considers the task time constraints, and takes the minimum total task energy consumption as the optimization goal, and uses the discrete ant colony algorithm to solve the optimal debris removal sequence. The lower optimization problem takes the maneuvering time and impulse of the inter-debris transfer orbit mission as the design variables, considers the influence of the earth's non-spherical perturbation, and adopts the single-circle perturbation Lambert algorithm for the constraint processing method of terminal state satisfaction, and proposes a method based on continuous ant colony. Optimized path planning algorithm. Simulation results show that the strategy and algorithm proposed in this paper are efficient and feasible, which can save fuel to the greatest extent and maximize the benefits of space debris mitigation. The research results of this paper provide technical reserves for the follow-up exploration of the integrated design optimization of debris transfer orbits and debris removal sequences.
Authors: Na Fu (State Key Laboratory of Astronautic Dynamics, Xi’an Satellite Control Center), Tian-Jiao Zhang (State Key Laboratory of Astronautic Dynamics, Xi’an Satellite Control Center), Lai-Jian Zhou (State Key Laboratory of Astronautic Dynamics, Xi’an Satellite Control Center), Yan-Yan Zeng (State Key Laboratory of Astronautic Dynamics, Xi’an Satellite Control Center), Chen Zhang (State Key Laboratory of Astronautic Dynamics, Xi’an Satellite Control Center),
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Gearbox is one of the most important parts of the rotating machinery, so health monitoring of the gearbox is essential. The accurate positioning of tooth failure of gear is an important function of the fault diagnosis system. This paper proposes a detection strategy based on designed convolutional neural networks to detect and locate gear tooth failure. The detection strategy aims to compare the characteristic gap between the normal gear and the faulty gear in the same period extracted by the convolutional neural network, and assign weights to the faulty gear vibration signal to obtain the weight sequence of the faulty vibration signal, so as to obtain the faulty tooth weight. Finally, the health condition of the gear can be evaluated by comparing the weight between all teeth of the gear. The proposed detection strategy is tested through simulation vibration signal and experiment vibration signal. The result shows that the proposed method can successfully identify gear failure and effectively detect single tooth failure on gear.
Authors: Xiaoqiang Du (Northwestern Polytechnical University), Yongbo Li (Northwestern Polytechnical University), Shubin Si (Northwestern Polytechnical University),
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In this paper, a trajectory design algorithm via convex optimization has been proposed for the 6-DoF asteroid powered landing problem. The main contribution is that the algorithm combines the time-optimal and the fuel-optimal trajectory optimization to give a fuel-optimal trajectory in the optimal flight time. First, two constrained nonconvex optimal control problems of the time-optimal and the fuel-optimal are proposed, then the original nonconvex continuous-time infinite dimensional problems are turned to convex discrete-time finite dimensional optimization problems through linearization and discretization of the nonlinear dynamics and the nonconvex state, control constraints. By developing the successive convexification, the final trajectory is achieved by solving a sequence of convex fuel-optimal sub-problems using the optimal flight time and the time-optimal trajectory given by solving the time-optimal optimization problem in successive manner. The validity of proposed algorithm of generating the fuel-optimal trajectory in the optimal flight time is verified through numerical simulations for landing on an irregular asteroid.
Authors: Yingying Zhang (Harbin Institute of Technology, School of astronautics), Jiangchuan Huang (Harbin Institute of Technology, School of astronautics), Yang Tian (Harbin Institute of Technology, School of astronautics), Hutao Cui (Harbin Institute of Technology, School of astronautics),
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Satellites are very expensive to manufacture and require high reliability. Moni-toring a large amount of telemetry data during the satellite orbit operation, the telemetry data are an important data source for analyzing the internal correla-tion of the satellite system and detecting anomalies. Telemetry data is in the form of time series, and there may be mutual influence and correlation be-tween these time series. Due to the diversity of its influence and association forms, it is necessary to establish an effective model to determine the associa-tion relationship between them in order to detect anomalies on this basis and identify the cause of anomalies. In this paper, we use Granger causality model to analyze correlation between time series of telemetry data and establish a causality model. Detecting anomalies according to the causality which under normal circum-stances and find out the cause of the anomalies. The case study shows that our method is effective.
Authors: Siya Chen (National University of Defence Technology), Jin Guang (National University of Defense Technology), Sun Peng (National University of Defense Technology), Lulu Zhang (National University of Defence Technology),
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This paper reviews the state of the art in fault detection and diagnosis in satellite power subsystem. Different algorithms are compared, and some examples are given. Finally, the existing problems and the future development trend are given.
Authors: Bo Sun (Beijing Institute of Spacecraft System Engineering, Beijing 100094, China), Weihua Jin (Research Center of Satellite Technology, Harbin Institute of Technology, Harbin 150080, China), Zhidong Li (Beijing Institute of Spacecraft System Engineering, Beijing 100094, China), Lei Zhang (Beijing Institute of Spacecraft System Engineering, Beijing 100094, China),
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Since the beginning of the 21st century, the increasing requirements of mankind for spacecraft technology have forced spacecraft technology to become more and more complex and increase investment. Most current fault detection methods only use single features and features or single fault detection data, and do not involve satellite fault monitoring under multi-parameter conditions. This paper proposes a satellite fault detection method that can be used in a multi-parameter state. The multivariate state estimation algorithm (MSET) is used to obtain the residual between the multivariate state and historical health data, and then the actual residual of the data to be measured is input into the sequential rank sum probability ratio test method (SRPRT) to test. This paper verifies the effectiveness of the combination of MSET algorithm and SRPRT algorithm through experiments, and finds the optimal parameters and accuracy relative to SPRT method.
Authors: sun Peng (National University of Defense Technology), Jin Guang (National University of Defense Technology),
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Onboard observation task planning plays an important role in satellite autonomy, which has attracted considerable attention from researchers in recent years. Most of the existing studies solve the Satellite Onboard Observation Task Planning (SOOTP) problem by searching algorithms. However, the limited computing resources and the change of onboard conditions present a challenge for these methods. In this paper, we propose a data-driven onboard planning framework to decide the observation task to execute in real-time using machine learning techniques. Based on the framework, the satellite can learn how to make optimal decisions from the historical planning results. What is more, we design five types of features and employ three ensemble learning algorithms to solve the SOOTP. A comparison of the proposed method against two online searching algorithms indicates that the former has smaller profit gap and shorter response time, which verify the feasibility of our method.
Authors: Shuang Peng (National University of Defense Technology), Jiangjiang Wu (National University of Defense Technology), Chun Du (National University of Defense Technology), Hao Chen (National University of Defense Technology), Jun Li (National University of Defense Technology),
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This paper studies and analyzes quantitative model-based fault diagnosis method, and then presents a design of quantitative model-based fault diagnosis structural strategy. It can isolate the faults of actuator and sensor with reduced quantitative models. The strategy is proposed based on the analysis of traditional quantitative model-based fault diagnosis method. By redefining the analytical model-based method, the process of fault isolation is studied with the conception of support component. The effectiveness of the proposed strategy is also analyzed in the paper. Finally, the proposed structural strategy is applied for fault diagnosis of satellite attitude control system.
Authors: Yao Cheng (Beijing Institute of Spacecraft System Engineering), Yang Jin (Civil Aviation University of China), Jingyan Wang (Beijing Institute of Spacecraft System Engineering),
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A data-driven satellite telemetry data anomaly detection method is proposed. The gradient boosting regression algorithm combined with feature selection including feature scoring and recursive lowest-score feature elimination can automatically mine the correlative telemetry variables through iterations, and establish a nonlinear regression model for their functional association, which can be used as a health baseline for anomaly detection of telemetry data. This method requires no expert to specify correlative telemetry variables based on domain knowledge beforehand and has the advantage of self-adaption for satellite operating conditions, which can overcome the problem of functional association altering under different operating conditions caused by orbit or sunshine condition changes. The validity and effectiveness of the method is verified by telemetry data of power subsystem.
Authors: Zhidong Li (Beijing Institute of Spacecraft System Engineering, Beijing 100094, China), Bo Sun (Beijing Institute of Spacecraft System Engineering), Weihua Jin (Research Center of Satellite Technology, Harbin Institute of Technology), Lei Zhang (Beijing Institute of Spacecraft System Engineering), Rongzheng Luo (Beijing Institute of Spacecraft System Engineering),
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Compared with other spacecrafts, there are many bus networks and many interactive data. Moreover, it has the bus network connection and data management functions among the three space station capsules, and the manned spaceships and cargo spaceships. Aiming at the problem of data management of space station bus network which can be combined and separated dynamically, through the design of multi-level bus networks and docking bus networks in the capsule, the data management solution is given from the system level. The process of telemetry management, telecommand management and interactive data management between subsystems are described in detail. Through the unified protocol design and routing management, the integrated networking and data communication between the spacecrafts are realized, which reduces the complexity and test difficulty of the system. This method has been tested and verified in the space station task, which not only ensures the reliability of docking and separation between the space station capsules, but also takes into account the flexibility and expansibility of data management.
Authors: Panpan Zhan (Beijing Institute of Spacecraft System Engineering), Xin Liu (Beijing Institute of Spacecraft System Engineering), Yating Cao (Beijing Shenzhou Aerospace Software Technology Co., Ltd.), Lan Lu (Beijing Institute of Spacecraft System Engineering), Xiongwen He (Beijing Institute of Spacecraft System Engineering), Yong Sun (Beijing Institute of Spacecraft System Engineering),
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In order to improve the capability of on-demand customization and agile re-configuration of space network, and to improve the scalability and reliability of space network, this paper proposed a method of spacecraft software in-orbit high-reliability maintenance method that is suitable for space network. This method is based on the electrical erasable memory of the onboard computer, uses various methods to improve the reliability, writes the reconfiguration data into the memory, and realizes the non-volatile reconfiguration of onboard software based on multiple granularities such as parameters, modules, processes or complete software. In addition, this method uses the hardware EDAC function to detect and correct errors in the memory during operation, which further improves the robustness. The in-orbit application and a large number of tests show that the method is suitable for on-demand customization of space network and can realize in-orbit reconfiguration of onboard software with high reliability.
Authors: Liang Qiao (Beijing Institute of Spacecraft System Engineering, China Academy of Space Technology), Ying Wu (Beijing Institute of Spacecraft System Engineering, China Academy of Space Technology), Xiaoyi Zhou (School of Computer Science and Engineering, Beihang University), Lijun Yang (Beijing Institue of Spacecraft System Engineering),
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Targeting the needs of low-earth orbit (LEO) Internet constellations for the high performance, high reliability, and high functional density of satellite-borne integrated electronics, the study was implemented on domestic LEO mobile constellation satellite-borne integrated electronic technology. Upon benchmarking foreign advanced LEO mobile constellation satellite-borne integrated electronic products, we analyzed the architecture of the domestic ones, and proposed solutions based on domestic devices; For the requirements of long service life and high reliability, the reliability analysis was carried out on several working modes with the components and parts stress analysis method, and a reliability improvement plan was proposed on the basis of software and programmable devices. Finally, we obtained a design plan of a satellite-borne integrated electronic system for LEO mobile constellation applications. With the overall performance comparable to those of advanced foreign solutions, the processing performance trebling that of existing domestic satellite-borne computers, and the 10-year reliability of 0.99999, it meets the needs of domestic LEO mobile constellation services.
Authors: Ying Wu (Beijing Institute of Spacecraft System Engineering), Zhenlong Xu (Beijing Institute of Spacecraft System Engineering),
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The application of CCSDS telecommand space data link protocol in the Chinese space field is still limited to intra-spacecraft communication recently, and the re-search on the standardized protocols and layered system architecture which is suitable for inter-spacecraft telecommand data forwarding is still insufficient. In this paper, we introduce a new protocol based on telecommand space data link protocol and a novel layered implementation of the protocol, which enables inter-preting and forwarding uplink data, device management command and manual control command through unified protocols, processes and modules. Comparing to traditional protocol and implementation of spacecraft telecommand, the new protocol and corresponding implementation has great advantage in terms of standardization, flexibility and extensibility, and has been applied to a large spacecraft assembly.
Authors: Lan Lu (Beijing Institute of Spacecraft System Engineering), Xin Liu (Beijing Institute of Spacecraft System Engineering), Xiongwen He (Beijing Institute of Spacecraft System Engineering),
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A wired/wireless distributed on-board data management system is proposed in this paper, in which Distributed IO Modules are embedded in all kinds of on-board equipment that need to be measured and controlled, and provides interface services such as measurement and control, Low-speed serial data, 1-wire Temperature measurement, etc. The distributed information management device is used to replace the traditional integrated electronic centralized telemetry acquisition and control architecture to form a distributed satellite information acquisition and control network. The wireless Wi-Fi channel or a standardized control bus is used to replace hundreds or even thousands of analogy signal cable networks, which makes the external interface of satellite electronic equipment with different forms and functions standardized To be possible, it simplifies the process of field integration and assembly, and is an important support technology for the standardization and rapid assembly of electronic interface of satellite equipment.
Authors: Yong XU (Beijing Institute of Spacecraft System Engineering), Lei ZHANG (Beijing Institute of Tracking and Telecommunication Technology), Ke YIN (Beijing Institute of Spacecraft System Engineering), Long JI (Beijing Institute of Spacecraft System Engineering), Ling TONG (Beijing Institute of Spacecraft System Engineering), Zheng Qi (Beijing Institute of Spacecraft System Engineering, CAST), Xiangyu Lin (Beijing Institute of Spacecraft System Engineering),
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At present, the space network is booming. In the face of an increasingly large space network, how to monitor the network status with high real-time performance becomes increasingly important. This paper is directed to the space network, and proposes a highly real-time technology scheme for space constellation network status monitoring, which supports real-time acquisition of various types of space network status information. Based on the idea of the integration of the satellite and the ground, the design and implementation of both the satellite and the ground are carried out.
Authors: Jiaxiang Niu (China Academy of Space Technology), Liang Qiao (China Academy of Space Technology), Hongcheng Yan (China Academy of Space Technology), Ruijun Li (China Academy of Space Technology), Bo Zhou (China Academy of Space Technology), Sheng Yu (China Academy of Space Technology),
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