A Positioning Method and Realization on Single Satellites in Different Orbits Using TDOA

The main geolocation technology currently used in COSPAS-SARSAT system is TDOA/FDOA or three-star TDOA,the principle is to determine the location of the signal source by using the difference in arrival time and frequency of the wireless signal between different receivers.Therefore,ground monitoring stations need to be equipped with more than two antenna receiving stations,and multiple satellites should be able to simultaneously relay the distress signal from the target source in order to achieve the geolocation function.However,when the ground receiving system has only one antenna receiving station,or the target source is in a heavily obscured environment,the ground side is unable to receive the forwarded signals from multiple satellites at the same time,which will make it impossible to locate.To address these problems,in this paper,a time-sharing single satellite geolocations method based on different orbits is proposed for the first time.This method uses one or several low-earth orbit satellites(LEO)and mediumearth orbit satellites(MEO)in the visible area,and the receiving station only needs one pair of receiving antennas to complete the positioning.It can effectively compensate for the shortcomings of the traditional TDOA using the same moment and have better positioning accuracy compared with the single satellite in the same orbit.Due to the limited experimental conditions,this paper tests the navigation satellite using different orbit time-sharing single satellite geolocations,and proves that the positioning method has high positioning accuracy and has certain promotion and application value.

Joint Precoding Schemes for Flexible Resource Allocation in High Throughput Satellite Systems Based on Beam Hopping

Beam hopping technology provides a foundation for the flexible allocation and efficient utilization of satellite resources,which is considered as a key technology for the next generation of high throughput satellite systems.To alleviate the contradiction between resource utilization and co-frequency interference in beam hopping technology,this paper firstly studies dynamic clustering to balance traffic between clusters and proposes cluster hopping pool optimization method to avoid inter-cluster interference.Then based on the optimization results,a novel joint beam hopping and precoding algorithm is provided to combine resource allocation and intra-cluster interference suppression,which can make efficient utilization of system resources and achieve reliable and near-optimal transmission capacity.The simulation results show that,compared with traditional methods,the proposed algorithms can dynamically adjust to balance demand traffic between clusters and meet the service requirements of each beam,also eliminate the co-channel interference to improve the performance of satellite network.

Spectrum Sensing via Temporal Convolutional Network

In this paper,we investigate a spectrumsensing system in the presence of a satellite,where the satellite works as a sensing node.Considering the conventional energy detection method is sensitive to the noise uncertainty,thus,a temporal convolutional network(TCN)based spectrum-sensing method is designed to eliminate the effect of the noise uncertainty and improve the performance of spectrum sensing,relying on the offline training and the online detection stages.Specifically,in the offline training stage,spectrum data captured by the satellite is sent to the TCN deployed on the gateway for training purpose.Moreover,in the online detection stage,the well trained TCN is utilized to perform real-time spectrum sensing,which can upgrade spectrum-sensing performance by exploiting the temporal features.Additionally,simulation results demonstrate that the proposed method achieves a higher probability of detection than that of the conventional energy detection(ED),the convolutional neural network(CNN),and deep neural network(DNN).Furthermore,the proposed method outperforms the CNN and the DNN in terms of a lower computational complexity.

Stochastic Dynamic Modeling of Rain Attenuation: A Survey

Satellite communication systems(SCS) operating on frequency bands above 10 GHz are sensitive to atmosphere physical phenomena, especially rain attenuation. To evaluate impairments in satellite performance, stochastic dynamic modeling(SDM) is considered as an effective way to predict real-time satellite channel fading caused by rain. This article carries out a survey of SDM using stochastic differential equations(SDEs) currently in the literature. Special attention is given to the different input characteristics of each model to satisfy specific local conditions. Future research directions in SDM are also suggested in this paper.

Performance Analysis of Spectrum Sensing Based on Distributed Satellite Clusters under Perturbation

In this paper,we investigate the spectrum sensing performance of a distributed satellite clusters(DSC)under perturbation,aiming to enhance the sensing ability of weak signals in the coexistence of strong and weak signals.Specifically,we propose a cooperative beamforming(BF)algorithm though random antenna array theory to fit the location characteristic of DSC and derive the average far-field beam pattern under perturbation.Then,a constrained optimization problem with maximizing the signal to interference plus noise ratio(SINR)is modeled to obtain the BF weight vectors,and an approximate expression of SINR is presented in the presence of the mismatch of signal steering vector.Finally,we derive the closedform expression of the detection probability for the considered DSC over Shadowed-Rician fading channels.Simulation results are provided to validate our theoretical analysis and to characterize the impact of various parameters on the system performance.

Intelligent Interference Management and Secure Communications for Satellite-Terrestrial Integrated Systems

Satellite-terrestrial integrated(STI)systems represent the right solution to meet complex requirements of several services and sharing of the limited spectral resources between satellite systems and terrestrial ones must be considered to optimize performance.Network architectures and traffic demand are different for the satellite component and for the terrestrial 5G/6G one,so that the requirements of spectral resources for satellite and terrestrial systems are expected to vary dynamically in a significant range.

SPACE INTERNET

Internet over satellites has been a hot research topic for some times.In addition to the development of the Internet applications and services over satellite,there are also significant developments in satellite communication systems and networks with Ka band and high throughput satellites(HTS).These developments enhance greatly the role of

Improving SINR via Joint Beam and Power Management for GEO and LEO Spectrum-Sharing Satellite Communication Systems

In this paper,we investigate a geosynchronous earth orbit(GEO)and low earth orbit(LEO)coexisting satellite communication system.To decrease the interference imposed on the GEO user caused by LEO satellites,we propose a joint beammanagement and power-allocation(JBMPA)scheme to maximize signal-to-interference plus noise ratio(SINR)at the GEO user,whilst maintaining the ongoing wireless links spanning from LEO satellites to their corresponding users.Specifically,we first analyze the overlapping coverage among GEO and LEO satellites,to obtain the LEO-satellite set in which their beams impose interference on the GEO user.Then,considering the traffic of LEO satellites in the obtained set,we design a beam-management method to turn off and switch interference beams of LEO satellites.Finally,we further propose a deep Q-network(DQN)aided power allocation algorithm to allocate the transmit power for the ongoing LEO satellites in the obtained set,whose beams are unable to be managed.Numerical results show that comparing with the traditional fixed beam with power allocation(FBPA)scheme,the proposed JBMPA can achieve a higher SINR and a lower outage probability,whilst guaranteeing the ongoing wireless transmissions of LEO satellites.

Preparation of V2O5 Porous Hollow Spheres and Study on Excellent Cycling Stability of Lithium Battery

Through one-step simple polyol-assisted (ethylene glycol) process, V2O5 hollow mi-cro-spheres about 3 micrometres in size were successfully synthesized. The structure is neat, the outer wall were porous. Testing its electrochemical properties with V2O5 hollow materials as cathode materia of lithium ion battery, the results showed that under the ratio of 1 C, the initial charge and discharge specific capacity were 236.8 mAh g^-1, 213 mAh g^-1, even if after 100 cycles, the charge and discharge specific capacity were still 220 mAh g^-1 and 219.7 mAh g^-1 respectively. Relative to the charge and discharge capacity of the second cycle, the keep rate were 93.2%, 92.9% respectively, has good cycle stability.

碳周转时间驱动了青藏高原和北极苔原表层土壤有机碳密度的差异

素有"世界屋脊"之称的青藏高原是除了北极苔原之外最大的冻土分布带,且该区域存储着大量的土壤有机碳.然而,这两大冻土分布带的土壤有机碳密度却存在着很大的差别.表层土壤扮演着连接地表植被和下层冻土的桥梁作用,但是我们对于两者表层土壤有机碳密度的差别及其驱动机制的理解却十分匮乏.本研究基于多源观测数据发现青藏高原草地表层土壤有机碳密度仅为北极苔原的一半,然而两者的潜在碳输入之间却没有明显差异.基于^(14)C数据的进一步分析表明北极苔原表层土壤碳周转时间(1609年)约为青藏高原草地(547年)的3倍,这一结果意味着碳周转时间驱动了这两个区域土壤有机碳密度的差异.该研究强调了碳周转时间对于理解不同冻土分布带土壤碳差异的重要性,也指示了未来的生态系统模型应该进一步提升对土壤碳周转过程的模拟能力.

Dynamic Channel Allocation Aided Random Access for SDN-Enabled LEO Satellite IoT

Considering the global demands on Internet of things(IoT),and the limitation of constructing base stations for the terrestrial IoT,the satellite IoT approach is a realizable and powerful supplement to the terrestrial IoT.Meanwhile,in order to dynamically access the available terrestrial and satellite networks,IoT terminals may have the ability of accessing both the terrestrial IoT and the satellite IoT,leading to great challenges on the access-control of the IoT.In this paper,we design a satellite-terrestrial integrated architecture for the IoT relying on the software defined network(SDN).Moreover,based on this architecture,we further propose a dynamic channel resource allocation algorithm to control the access of the IoT terminals with different priorities.Simulation results show that the demands on the probabilities of successful access of IoT terminals with various priorities can be simultaneously met if the access of the IoT terminals are well controlled.