Thermosphere joint observations by TM-1 constellations and Swarm-B during the April 2023 geomagnetic storm

The response of thermosphere density to geomagnetic storms is a complicated physical process.Multi-satellite joint observations at the same altitude but different local times(LTs)are important for understanding this process;however,until now such studies have hardly been done.In this report,we analyze in detail the thermosphere mass density response at 510 km during the April 23−24,2023 geomagnetic storm using data derived from the TM-1(TianMu-1)satellite constellation and Swarm-B satellites.The observations show that there were significant LT differences in the hemispheric asymmetry of the thermosphere mass density during the geomagnetic storm.Densities observed by satellite TM02 at nearly 11.3 and 23.3 LTs were larger in the northern hemisphere than in the southern.The TM04 dayside density observations appear to be almost symmetrical with respect to the equator,though southern hemisphere densities on the nightside were higher.Swarm-B data exhibit near-symmetry between the hemispheres.In addition,the mass density ratio results show that TM04 nightside observations,TM02 data,and Swarm-B data all clearly show stronger effects in the southern hemisphere,except for TM04 on the dayside,which suggest hemispheric near-symmetry.The South-North density enhancement differences in TM02 and TM04 on dayside can reach 130%,and Swarm-B data even achieve 180%difference.From the observations of all three satellites,large-scale traveling atmospheric disturbances(TADs)first appear at high latitudes and propagate to low latitudes,thereby disturbing the atmosphere above the equator and even into the opposite hemisphere.NRLMSISE00 model simulations were also performed on this geomagnetic storm.TADs are absent in the NRLMSISE00 simulations.The satellite data suggest that NRLMSISE00 significantly underestimates the magnitude of the density response of the thermosphere during geomagnetic storms,especially at high latitudes in both hemispheres.Therefore,use of the density simulation of NRLMSISE00 may lead to large errors in satellite drag calculations and orbit predictions.We suggest that the high temporal and spatial resolution of direct density observations by the TM-1 constellation satellites can provide an autonomous and reliable basis for correction and improvement of atmospheric models.

Uniquely Decomposable Constellation Group-Based Sparse Vector Coding for Short Packet Communications

Sparse vector coding(SVC)is emerging as a potential technology for short packet communications.To further improve the block error rate(BLER)performance,a uniquely decomposable constellation group-based SVC(UDCG-SVC)is proposed in this article.Additionally,in order to achieve an optimal BLER performance of UDCG-SVC,a problem to optimize the coding gain of UDCG-based superimposed constellation is formulated.Given the energy of rotation constellations in UDCG,this problem is solved by converting it into finding the maximized minimum Euclidean distance of the superimposed constellation.Simulation results demonstrate the validness of our derivation.We also find that the proposed UDCGSVC has better BLER performance compared to other SVC schemes,especially under the high order modulation scenarios.

Local-State Routing in Satellite Constellation Networks from the Perspective of Complex Network

Routing algorithms in satellite constellation networks usually make use of the local state information to adapt to the topology and traffic dynamics,since it’s difficult to obtain the global states in time due to the spatial large-scale feature of constellation networks.Furthermore,they use different range of local states and give these states distinct weights.However,the behind design criterion is ambiguous and often based on experience.This paper discusses the problem from the perspective of complex network.A universal local-state routing model with tunable parameters is presented to generalize the common characteristics of local-state routing algorithms for satellite constellation networks.Based on this,the impacts of localstate routing algorithms on performance and the correlation between routing and traffic dynamics are analyzed in detail.Among them,the tunable parameters,the congestion propagation process,the critical packet sending rate,and the network robustness are discussed respectively.Experimental results show that routing algorithms can achieve a satisfactory performance by maintaining a limited state awareness capability and obtaining the states in a range below the average path length.This provides a valuable design basis for routing algorithms in satellite constellation networks.

Low Altitude Satellite Constellation for Futuristic Aerial-Ground Communications

This paper discusses the significance and prospects of low altitude small satellite aerial vehicles to ensure smooth aerial-ground communications for next-generation broadband networks.To achieve the generic goals of fifthgeneration and beyondwireless networks,the existing aerial network architecture needs to be revisited.The detailed architecture of low altitude aerial networks and the challenges in resource management have been illustrated in this paper.Moreover,we have studied the coordination between promising communication technologies and low altitude aerial networks to provide robust network coverage.We talk about the techniques that can ensure userfriendly control and monitoring of the low altitude aerial networks to bring forth wireless broadband connectivity to a new dimension.In the end,we highlight the future research directions of aerial-ground communications in terms of access technologies,machine learning,compressed sensing,and quantum communications.

A Unified Bit-to-Symbol Mapping for Generalized Constellation Modulation

Gray mapping is a well-known way to improve the performance of regular constellation modulation,but it is challenging to be applied directly for irregular alternative.To address this issue,in this paper,a unified bit-to-symbol mapping method is designed for generalized constellation modulation(i.e.,regular and irregular shaping).The objective of the proposed approach is to minimize the average bit error probability by reducing the hamming distance(HD)of symbols with larger values of pairwise error probability.Simulation results show that the conventional constellation modulation(i.e.,phase shift keying and quadrature amplitude modulation(QAM)with the proposed mapping rule yield the same performance as that of classical gray mapping.Moreover,the recently developed golden angle modulation(GAM)with the proposed mapping method is capable of providing around1 d B gain over the conventional mapping counterpart and offers comparable performance to QAM with Gray mapping.

A Performance Evaluation Platform for Mega Satellite Constellation Network

With the rapid development of satellite technology, mega satellite constellations have become a research hotspot. A large number of related techniques have been developed on orbit topology, network routing, energy balance and resource control. However, it is difficult to accurately compare the performance of similar studies due to differences in the means of validation. Especially for invulnerability studies in many military applications, a unified evaluation system is essential. This paper proposes a network evaluation system for mega satellite constellations. Evaluation parameters include orbit topology, communication network, energy balance and invulnerability. Different application algorithms and traffic models were used to validate the specific system. .

Constellation玻切机使用中的维护与保养

玻切机是用于眼前段(超声乳化白内障吸出术和白内障摘除术)和眼后段(玻璃体视网膜术)手术不可或缺的基本设备,也是最昂贵的手术设备之一。最新一代Constellation玻切机自2010年上市以来,一直以高安全、高效率、高智能化占居全球玻切设备市场第一,受到了广大医护人员的欢迎。Constellation玻切机的正常运行直接影响着手术的效率和效果,所以对Constellation玻切机使用中的维护与保养显得尤为重要。

Analysis of detection capabilities of LEO reconnaissance satellite constellation based on coverage performance

In the design problem of low earth orbit(LEO) reconnaissance satellite constellation, optimization of coverage performance is the design goal in most current methods. However,in the using process, the user only concerns with the detection capabilities rather than coverage performance. To establish the relationship between these two aspects, the reconnaissance processes of normal stochastic targets are considered and the mathematic models of detection processes are built. The indicators of coverage performance are used to evaluate the detection probability and expectation of detection time delay, which are important factors in reconnaissance constellation estimation viewed from military intelligence discipline. The conclusions confirmed by the final simulation will be useful in LEO reconnaissance constellation design, optimization and evaluation.

COVERAGE PERFORMANCES ANALYSIS ON COMBINED-GEO-IGSO SATELLITE CONSTELLATION

The Combined-GEO-IGSO constellation is the combination of Geostationary Earth Orbit(GEO) satellite and Inclining GeoSynchronous Orbit(IGSO) satellite.The Combined-GEO-IGSO constellation can integrate the advantages of GEO and IGSO to achieve regional coverage.In order to discuss the performances of the Combined-GEO-IGSO constellation,the performances of coverage,elevation,diversity,and transmission are simulated in China and surrounding regions by Satellite Tool Kit(STK).The simulation results show that:the combined constellation can reach higher multi-satellite coverage and higher communication elevation in China and surrounding areas;the Doppler shift,delay,and propagation loss of this constellation have little impact on the system.As regional coverage constellation,the Combined-GEO-IGSO is feasible.

Sensor management of LEO constellation based on covariance control

This paper studies the multi-sensor management problem for low earth orbit(LEO) infrared warning constellation used to track a midcourse missile. A covariance control approach, which selects sensor combinations or subset based on the difference between the desired covariance matrix and the actual covariance of each target, is used for sensor management, including some matrix metrics to measure the differentia between two covariance matrices. Besides, to meet the requirements of the space based warning system, the original covariance control approach is improved. Simulation results demonstrate that the covariance control approach is able to provide a better tracking performance by providing a well-designed desired covariance and balance tracking performance goals with system demands.

AI-Enhanced Constellation Design for NOMA System: A Model Driven Method

Grant-free Non-orthogonal Multiple Access(GF-NOMA)is a promising technology for massive access users and sporadic small-packet transmission for Beyond the 5th Generation mobile communication system(B5G)/the 6th Generation mobile communication system(6G).One of the key aspects in GF-NOMA system is the signature/constellation design.However,due to the channel variation and random activation of users,conventional optimization approaches seem unsuitable for such complex models.In this paper,as an initial attempt,we propose a human intelligence(HI)-guided artificial intelligence(AI)-enhanced signature/constellation design method.By separate design of modulation and power allocation inspired by prior knowledge,the proposed deep neuron network(DNN)for NOMA signature/constellation design not only has smaller size of DNN and less training data,but also has stronger interpretability.In the last section,via simulations we demonstrate that in terms of bit error rate,the proposed scheme can achieve significant performance gain over the conventional NOMA schemes.

6G Service Coverage with Mega Satellite Constellations

The rapid development and continuous updating of the mega satellite constellation(MSC)have brought new visions for the future 6G coverage extension, where the global seamless signal coverage can realize ubiquitous services for user terminals. However, global traffic demands present nonuniform characteristics. Therefore, how to ensure the on-demand service coverage for the specific traffic demand, i.e., the ratio of traffic density to service requirement per unit area, is the core issue of 6G wireless coverage extension exploiting the MSC. To this regard, this paper first discusses the open challenges to reveal the future direction of 6G wireless coverage extension from the perspective of key factors affecting service coverage performance, i.e., the network access capacity, space segment capacity and their matchingrelationship. Furthermore, we elaborate on the key factors affecting effective matchings of the aforementioned aspects, thereby improving service coverage capability.

Polar-Coded Modulation Based on the Amplitude Phase Shift Keying Constellations

In this paper, we investigate the polarization effect of the amplitude phase shift keying(APSK) constellations. We find that the polarization effect of the APSK constellations is affected by the bit mapping and the bit loading. Traditionally, the Gray mapping is usually adopted in APSK constellations. Based on the given Gray mapping, we firstly propose the bit interleaved coded modulation polar-APSK(BICM-PA) scheme, which neglects the correlations between the bit levels by using the bit interleaver. In the BICM-PA scheme, a new metric called cumulative Bhattacharyya parameter is introduced to optimize the bit loading of the APSK constellations under the Gray mapping. Second, the multilevel coded modulation polar-APSK(MLCM-PA) is proposed to further improve the performance. A twostage optimization approach is adopted to select the bit mapping and the bit loading in the MLCM-PA scheme. The semi-set partitioning mapping is introduced to achieve a better system performance in the MLCM-PA scheme. Simulation results verify the effectiveness of all the proposed metrics. In addition to this, BICM-PA and MLCM-PA both outperform the coded modulation Turbo-APSK scheme up to 1 dB.

Simulation of earth gravity field using satellite constellation with variable inclination configuration

Based on a satellite constellation composed of two GRACE-type satellite formations with different inclinations(near polar orbit + low inclination) and the theory of repeat orbit cycle, we discuss the methods for selecting medium-low inclinations for global and local gravity fields. The effects of this constellation configuration on gravity field inversion are comparatively analyzed using a whole-course dynamics simulation. The results show that compared with the single GRACE-type satellite formation,the use of satellite constellations with different inclination configurations improves the gravity solution precision by 34%. The inclusion of multi-directional observations can improve the spatio-temporal resolution of the satellite missions, and yield gravity field solutions with higher isotropic sensitivity.Furthermore, it is necessary to select the optimal low inclination according to the study area, which will have a significant influence on the gravity field solution.

Optimal reconfiguration of constellation using adaptive innovation driven multiobjective evolutionary algorithm

Constellation reconfiguration is a critical issue to recover from the satellite failure,maintain the regular operation,and enhance the overall performance.The constellation reconfiguration problem faces the difficulties of high dimensionality of design variables and extremely large decision space due to the great and continuously growing constellation size.To solve such real-world problems that can be hardly solved by traditional algorithms,the evolutionary operators should be promoted with available domain knowledge to guide the algorithm to explore the promising regions of the trade space.An adaptive innovationdriven multi-objective evolutionary algorithm(MOEA-AI)employing automated innovation(AI)and adaptive operator selection(AOS)is proposed to extract and apply domain knowledge.The available knowledge is extracted from the final or intermediate solution sets and integrated into an operator by the automated innovation mechanism.To prevent the overuse of knowledgedependent operators,AOS provides top-level management between the knowledge-dependent operators and conventional evolutionary operators.It evaluates and selects operators according to their actual performance,which helps to identify useful operators from the candidate set.The efficacy of the MOEAAI framework is demonstrated by the simulation of emergency missions.It was verified that the proposed algorithm can discover a non-dominant solution set with better quality,more homogeneous distribution,and better adaptation to practical situations.

Conceptual Design Process for LEO Satellite Constellations Based on System Engineering Disciplines

Satellite design process is an interdisciplinary subject in which the need for collaboration among various science and engineering disciplines is evident.Meanwhile,finding an optimal process for conceptual design of a satellite,which can optimize time and cost,is still an important issue.In this paper,based on system engineering approach,an optimal design process is proposed for LEO satellite constellations.In the proposed method,design process,design sequences,and data flow are established.In this regard,the conceptual design process is divided into two levels of mission(or constellation)and system(or satellite)as well as 15 main activities based on the mission profile,previous experiences of the authors,and existing literature.Then,the relationships between these activities have been determined by considering the importance of relationships according to their priority.Finally,these relations are optimized based on design structure matrix(DSM).By utilizing this approach,system design process of a telecommunication satellite constellation in LEO is formulated in conceptual design phase.Performance and capability of the proposed approach in optimal design process of the satellite constellation are investigated by comparing the outcome with existing results in the literature.

Adaptive Turbo Equalization for Probabilistic Constellation Shaped Underwater Acoustic Communications

To increase the spectral efficiency of the underwater acoustic(UWA)communication system,the high order quadrature amplitude modulations(QAM)are deployed.Recently,the prob-abilistic constellation shaping(PCS)has been a novel technology to improve the spectral efficiency.The PCS with high-order QAM is introduced into the UWA communication system.A turbo equal-ization scheme with PCS was proposed to cancel the severe inter-symbol interference(ISI).The non-zero a priori information is available for the equalizer and decoder before turbo iteration.A pri-ori hard decision approach is proposed to improve the detection performance and the equalizer con-vergence speed.At the initial turbo iteration,the relation between the a priori information and the probability of the amplitude of 16QAM symbols in one dimension is given.The simulation results verified the efficiency of the proposed method,and compared to the uniform distribution(UD),the PCS-16QAM had a significant improvement of the bit error rate(BER)performance with PCS-ad-aptive turbo equalization(PCS-ATEQ).The UWA communication experiments further verified the performance superiority of the proposed method.

An analysis method for ISL of multilayer constellation

The multilayer satellite network has high spatial spectrum utilization, flexible networking, strong survivability, and diversified functions. The inter-satellite links(ISLs) and crosslayer ISLs(CLISLs) enable direct communication paths between satellites, which improves the spatial autonomy of the constellation. Due to the existence of perturbation, ISLs are affected for a long time, which impacts reliable inter-satellite transmission. The stability and complexity of ISL establishment are related to the static and dynamic characteristics of range and azimuth. This paper presents a model of ISLs in a perturbed multilayer constellation. Series of theoretical derivation, simulation, and numerical calculation are carried out. A more comprehensive multilayer constellation ISL model is obtained. The work of this paper provides some theoretical foundations for constellation networking research.

Progress of Radiation Belt Exploration by a Constellation of Small Satellites TGCSS/SGRB,COSPAR

A COnstellation of Radiation BElt Survey(CORBES)program is proposed by the Sub-Group on Radiation Belt(SGRB)of TGCSS,COSPAR.The CORBES mission is expected to have a constellation of 10-plus small/Cube Sats to take an ultra-fast survey of the Earth’s radiation belt.The general science goal for CORBES is to investigate two groups of physical processes related to the radiation belts:wave-particle interactions and radial transport.This mission is an international multilateral cooperation mission,an open and sharing data policy will be implemented.The data set of observations will be shared within the contributors of the constellation and the broad research community at large,then would be of great use for comprehensively understanding the dynamics of magnetospheric energetic populations and developing more standard models of the Earth’s radiation belts.Furthermore,from the application perspective,the ultra-fast survey of the radiation belt could serve as an important facility for monitoring space weather of the Earth as well.

New bounds on the mutual information for discrete constellations and application to wireless channel estimation

The lack of closed-form expressions of the mutual information for discrete constellations has limited its uses for analyzing reliable communication over wireless fading channels.In order to address this issue,this paper proposes analytically-tractable lower bounds on the mutual information based on Arithmetic-Mean-Geometric-Mean(AMGM)inequality.The new bounds can apply to a wide range of discrete constellations and reveal some insights into the rate behavior at moderate to high Signal-to-Noise Ratio(SNR)values.The usability of the bounds is further demonstrated to approximate the optimum pilot overhead in stationary fading channels.