LEO Satellite Research Articles

Omnidirectional Optical Crosslinks for CubeSats: Transmitter Optimization.

CubeSat swarm in LEO orbit is an attractive alternative to present-day expensive and bulky satellite-based remote sensing systems. This paper presents the design and optimization rules to achieve omnidirectional, high speed, long-range (more than 100 km) data communication among CubeSats. The unprecedented size, weight, power, and cost constraints imposed by the CubeSat platform and the availability of the commercial-off-the-shelf components are considered in the analyses. Analytical studies related to the scanning mirror-based beam steering system as well as scanning mirror's smallest step angle requirement are presented. In addition, we demonstrate the relations and dependencies among scanning mirror's smallest step angle, laser beam divergence, optics dimensions, communication distance, and scanning area filling efficiency, etc. Furthermore, the optimization challenges of the transmit laser beam size considering the interplay among beam divergence, beam clipping, and scattering are studied in detail. This paper also presents the effect of laser peak power, initial beam size, and communication distance on effective communication beam width to maintain a long-distance (more than 100 km) communication with SNR ≥ 10 dB at a data rate greater than 500 Mb/s.

Determination the optimum orbit for low Earth satellites by changing the eccentricity

The main objective of this paper is to determine an acceptable value of eccentricity for the satellites in a Low Earth Orbit LEO that are affected by drag perturbation only. The method of converting the orbital elements into state vectors was presented. Perturbed equation of motion was numerically integrated using 4th order Runge-Kutta’s method and the perturbation in orbital elements for different altitudes and eccentricities were tested and analysed during 84.23 days. The results indicated to the value of semi major axis and eccentricity at altitude 200 km and eccentricity 0.001are more stable. As well, at altitude 600 km and eccentricity 0.01, but at 800 km and eccentricities (0.01, 0.05 and 0.1) the stability of the orbit was not depending strongly on eccentricity value, because the effect of the drag is too small.

Research on the Performance of Multi-GNSS Medium Length Baseline RTK with LEO-Augmented

In this letter, we simulate GNSS/LEO measurements and propose a process strategy for LEO-augmented GNSS medium length baseline RTK. Experiments show that, the performance of GNSS medium length baseline RTK can be significantly improved by introducing LEO satellites. The convergence speed of LEO-augmented GPS or BDS float solution maybe better than GPS/BDS combined under the conditions of similar satellite geometry. Besides, the RMS error of fixed solutions are improved to better than 4 cm from sub-decimeter level.

Numerical Simulation of Spacecraft Charging Attributed to Ionospheric Plasma in Polar and Equatorial Environment

The presence of spacecraft in ionospheric plasma can change plasma properties, vice versa plasma can lead to charge buildup on spacecraft. The level of charging, through electric potential of spacecraft, initially depends on plasma density. However, simulations done on four LEO satellites, i.e. ERS 1, MIDORI, ASCA and FUSE 1, showed that charging level depends on plasma electron temperature rather than plasma density which satisfied the Boltzmann’s relation in the absence of high-energy electrons from aurora. The higher the plasma electron temperature the more spacecraft exposed to negative charging. It is assumed that plasma ions and electrons are collisionless or in Maxwellian distribution. It is found that there is no strong relation between density and charging level. Furthermore, there exists insignificant different of charging between polar and equatorial satellites. It means that the placement of satellite in polar or equatorial region, as long as the presence of auroral electrons is excluded, will suffer similar level of charging which is less than 5V (negative). Since spacecraft are exposed to negative charge, electric field generated by spacecraft potential, together with mesothermal motion effects, deflects ion trajectory into donwstream region leading to ion void region. The ion density is reduced compared to electron density, but there is no significant different of ion void feature between polar and equatorial satellites.and capacity building of beneficiaries.

Untangling the Incoherent and Coherent Scattering Components in GNSS-R and Novel Applications

As opposed to monostatic radars where incoherent backscattering dominates, in bistatic radars, such as Global Navigation Satellite Systems Reflectometry (GNSS-R), the forward scattered signals exhibit both an incoherent and a coherent component. Current models assume that either one or the other are dominant, and the calibration and geophysical parameter retrieval (e.g., wind speed, soil moisture, etc.) are developed accordingly. Even the presence of the coherent component of a GNSS reflected signal itself has been a matter of discussion in the last years. In this work, a method developed to separate the leakage of the direct signal in the reflected one is applied to a data set of GNSS-R signals collected over the ocean by the Microwave Interferometer Reflectometer (MIR) instrument, an airborne dual-band (L1/E1 and L5/E5a), multi-constellation (GPS and Galileo) GNSS-R instrument with two 19-elements antenna arrays with 4 beam-steered each. The presented results demonstrate the feasibility of the proposed technique to untangle the coherent and incoherent components from the total power waveform in GNSS reflected signals. This technique allows the processing of these components separately, which increases the calibration accuracy (as today both are mixed and processed together), allowing higher resolution applications since the spatial resolution of the coherent component is determined by the size of the first Fresnel zone (300–500 meters from a LEO satellite), and not by the size of the glistening zone (25 km from a LEO satellite). The identification of the coherent component enhances also the location of the specular reflection point by determining the peak maximum from this coherent component rather than the point of maximum derivative of the incoherent one, which is normally noisy and it is blurred by all the glistening zone contributions.

System for space materials evaluation in LEO environment

This paper describes the conception and experimental setup of a new concept for a Vacuum Ultraviolet with extreme Thermal Vacuum Cycle system and the evaluation of LEO satellites materials with the equipment. The system was developed in the framework of a study of spacecraft debris generation due to satellites materials degradation, when exposed to space environment. The study was developed in the framework of an ESA project. Its main purpose was to evaluate the characteristics and the quantity of debris resulting from surface of satellites due spacecraft materials degradation and provide input to space debris models. The experimental setup developed partially simulates the space environment, on an accelerated mode, as endured by a spaceship in Low Earth Orbit, allows the testing of materials to a Vacuum, Ultraviolet and thermal cycles. This thermal cycling provided to the sample holder was implemented using an innovative mechanical thermal switching architecture. This architecture allows temperature cycling of +200 °C to −200 °C without the use of LN2. The experimental setup design, manufacture and final characterization is presented.

Terminal location method with NLOS exclusion based on unsupervised learning in 5G‐LEO satellite communication systems

SummaryWe investigate the terminal location method in 5G‐Low Earth Orbit (5G‐LEO) satellite communication systems. To overcome the dependence on the external Global Navigation Satellite System (GNSS), we propose to use a single LEO satellite in 5G‐LEO satellite communication systems for terminal location and utilize the downlink synchronization detection for pseudorange differential measurement. Then, a data clustering method of unsupervised machine learning is proposed to classify the measured data into line‐of‐sight (LOS) and non‐line‐of‐sight (NLOS) signals. Furthermore, the NLOS data are excluded, and the Taylor series expansion iteration method is used to calculate the terminal coordinates. Simulation results show that the proposed method can effectively reduce the influence of NLOS error on measurement results and improve the accuracy of terminal location. In simulated urban scenario, the average location accuracy is improved from 10 km by traditional methods to 0.7 km and the convergence time is reduced from 400 to 250s.

An optimal delay routing algorithm considering delay variation in the LEO satellite communication network

In the LEO satellite communication network, delay is not fixed but varying in a regular manner. Moreover, traditional routing planning algorithms lose sight of delay variation and need intensive computation. These have led to incomprehensive performance assessment of the satellite network and large resource occupancy. Effective routing scheme with uncertain delay information is the novel problem that we solve in this paper. An optimal delay routing algorithm called delay queuing graphical evaluation and review technique minimal path set is proposed. First, based on the delay queuing graphical evaluation and review technique (DQ-GERT) and the minimum path set, the satellite network is characterized and all valid candidate paths are selected. Second, the delay evaluation index that includes delay and its variation to evaluate possible routes is derived. Simulation results show the superiority of the proposed algorithm by comparing with existing algorithms.

Experimental Study on Doppler Performance of Satellite Emergency Communicator Based on LoRa System

Aiming at the propagation loss and Doppler frequency shift problems faced by LEO satellite in realizing Internet of Things, the LEO satellite emergency communication machine is tested. The emergency communication machine adopts SX1280 chip as the transceiver unit, analyzes the bit error rate and Doppler frequency shift index of LoRa signal generated by SX1280, and proposes a test scheme combining satellite channel simulator and emergency communication machine. In the range of Doppler frequency shift less than 53 kHz, changing Doppler frequency and its change rate has less than 4 dB effect on signal communication sensitivity. Reducing signal transmission rate and bandwidth can improve communication sensitivity. It proves that LoRa signal generated by SX1280 chip can be effectively used in LEO satellite Internet of Things.

Multi-QoS adaptive routing algorithm based on SDN for satellite network

With the development of communication services, satellite network services have developed from the traditional single type of services to multiple types of services. Different types of services need to meet different Quality of Service (QoS) requirements. The traditional satellite network algorithm does not distinguish the services, so the high QoS service in the network cannot get timely service. However, the architecture of Software Defined Satellite Networking (SDSN) can solve this problem well. The controller in the SDSN has a global view and can obtain the node and link information of LEO satellites. Therefore, the SDSN can more effectively meet the demand of data service for QoS. In this paper, a satellite network architecture based on Software Defined Networking (SDN) is firstly established. Then an adaptive routing algorithm that can meet various QoS requirements is proposed. The final simulation results show that compared with SDRA algorithm and Dijkstra algorithm, this optimization algorithm has better performance in QoS satisfaction rate and bandwidth utilization.

Analytical Study of Earth Tides on Low Orbits Satellites

The main objective of this paper is to calculate the perturbations of tide effect on LEO's satellites . In order to achieve this goal, the changes in the orbital elements which include the semi major axis (a) eccentricity (e) inclination , right ascension of ascending nodes ( ), and fifth element argument of perigee ( ) must be employed. In the absence of perturbations, these element remain constant. The results show that the effect of tidal perturbation on the orbital elements depends on the inclination of the satellite orbit. The variation in the ratio decreases with increasing the inclination of satellite, while it increases with increasing the time.

Design and implementation of a star-tracker for LEO satellite

An important task of the attitude determination and control subsystem (ADCS) is the determination of attitude of the satellite in reference to the Earth or any other planetary and correct any deviation from the expected attitude. In order to determine the attitude of the satellite, sensors are needed to sense the orientation of the satellite. The star-tracker is able to determine the attitude from the view field of the star set without any prior knowledge of sensor information. In this paper, the design, simulation and implementation of a star-tracker is presented for LEO satellites. For capturing image data, the MT9P031 CMOS image sensor from Aptina Imaging was used. The star tracker uses a Texas Instrument OMAP3530 using an ARM Cortex A8. The processor supports powerful graphic interfaces resulting in reduction of the size and consumption power of the star-tracker. For storage and processing, the star tracker used NAND flash memory. The communication interface to the satellite is done through CAN Bus. One of the key features of this sensor is processing various algorithms for image processing, positioning, and tracking according to mission requirements. Quaternion estimator (QUEST) algorithm was utilized for positioning. The tracking algorithm utilizes information from the previous frame of the star-tracking. This algorithm is a high-speed, low cost, and low memory implementation. In the field tests, the identification success rate of this system was 96.81 %.

On the Occurrence of GPS Signal Amplitude Degradation for Receivers on Board LEO Satellites

AbstractTransient signal loss of the global positioning system (GPS) has been frequently observed by receivers on board the European Space Agency's Swarm mission when the satellites encounter ionospheric plasma irregularities. In this study we provided the first comparison of the GPS signal amplitude degradations from receivers on board low Earth orbiting satellites at different altitudes. Intense carrier phase variations but almost no amplitude fades (less than 2 dB Hz) are observed when the spaceborne receiver lies right inside the ionospheric plasma irregularities, like the case for the Swarm and CHAMP satellites flying at about 400–500 km. This indicates that the strong phase variation, but not the amplitude fades, causes the receivers to stop tracking the GPS signals. When the receiver is located 100–200 km below the slab of plasma irregularities, like the case for the GOCE satellite flying at about 250 km, signal amplitude fades exceeding 10 dB Hz are observed, in addition to strong phase variation. Our results suggest that a considerable distance of the receiver to the plasma irregularity slab is needed to affect the Fresnel diffractive process and further causes GPS signal amplitude fades.

20Gbit/s-40 GHz OFDM based LEO-GEO Radio over Inter-satellite optical wireless communication (Ro-IsOWC) system using 4-QAM modulation

This work discusses the modeling and the numerical investigation of Ro-IsOWC link between a low earth orbit LEO and geosynchronous earth orbit GEO satellite. 4-level quadrature amplitude modulation 4-QAM signal with orthogonal frequency division multiplexing OFDM technique has been used to transmit high-speed data between two satellites separated at 35,000 km link distance in outer space. The proposed link performance has been numerically evaluated under the impact of operating wavelength, transmission distance, input power, pointing errors, additional losses, and receiver aperture diameter. Signal-to-noise ratio SNR and received electrical power of the information signal are considered as the performance metrics to evaluate the link performance. Through numerical simulations, we report a successful transportation of 20Gbit/s-40GHz information between two satellites over a transmission distance of 35,000 km using the proposed Ro-IsOWC system. Also, an improved link performance has been investigated in this work by using a Square root module SRm technique at the receiver terminal for non-linearity compensation.

A Dynamic Resource Scheduling Scheme in Edge Computing Satellite Networks

The LEO satellite network has been a valuable architecture due to its characteristics of wide coverage and low transmission delay. Utilizing LEO satellites as edge computing nodes to provide reliable computing services for access terminals will be the indispensable paradigm of integrated space-air-ground network. However, the design of resource division strategy in edge computing satellite (ECS) is not easy, considering different accessing planes and resource requirements of terminals. Moreover, network topology, available resources and relative motion need to be analyzed comprehensively to establish ECS collaborative network for emergency situations. To address these problems, a three-layer network architecture combined with software defined networking (SDN) model is proposed to guide the inter-satellite link (ISL) connection and ECS resource scheduling. The advanced K-means algorithm (AKG) and breadth-first-search-based spanning tree algorithm (BFST) are provided to realize ECS resource division and ISL construction respectively. Simulation results show that the proposed dynamic resource scheduling scheme is feasible and effective.

A Hierarchical Approach to Resource Allocation in Extensible Multi-Layer LEO-MSS

Low earth orbit mobile satellite system (LEO-MSS) is the major system to provide communication support for mobile terminals beyond the coverage of terrestrial communication systems. However, the quick movement of LEO satellites and current single-layer system architecture impose restrictions on the capability to provide satisfactory service quality, especially for the remote and non-land regions with high traffic requirement. To tackle this problem, high-altitude platforms (HAPs) and terrestrial relays (TRs) are introduced to cover hot-spot regions, and the current single-layer system becomes an LEO-HAP multi-layer access network. Under this setup, we propose a hierarchical resource allocation approach to circumvent the complex management caused by the intricate relationships among different layers. Specifically, to maximize the throughputs, we propose a dynamic multi-beam joint resource optimization method in LEO-ground downlinks based on the predicted movement of LEO satellites. Afterwards, we propose the dynamic resource optimization method of HAP-ground downlinks when LEO satellites and HAPs share the same spectrum. To solve these problems, we use the Lagrange dual method and Karush-Kuhn-Tucker (KKT) conditions to find the optimal solutions. Numerical results show that the proposed architecture outperforms current LEO-MSS in terms of average capacity. In addition, the proposed optimization methods increase the throughputs of LEO-ground downlinks and HAP-ground downlinks with an acceptable complexity.

LEO IoT based big data management and analysis platform design for intermodal containers

In view of the global information management requirements of intermodal containers, combined with the development status, this paper proposes an IoT model based on LEO satellites, and a big data management and analysis platform based on the model. This paper designs and analyses the scheme of the platform, and proposes a middleware approach to solve the problem of multi-source heterogeneous data access of containers intelligent terminals. Then, this paper designs business processes such as user and device registration, middleware registration, historical data access, and timely data access for the platform. The big data analysis and management platform has been prototyped and verified; the platform has the advantages of compatibility, openness and convenience. This study has certain value.

A Load Balancing Routing Strategy for LEO Satellite Network

The LEO network composed of massive satellite nodes is a hot research field at present. In such a network, the problem of load balancing should be reconsidered due to the large number of satellite nodes, the frequently changing topology, and the uneven distribution of global ground users. To solve such problem, a selective iterative Dijkstra algorithm (SIDA) is proposed to optimize the path finding process by reducing the reuse frequency of nodes. On the basis of SIDA, a selective split load balancing strategy (SSLB) is proposed to solve the link congestion problem in low latitude LEO network. SSLB is a distributed strategy, which diverts the traffic flow of congestion nodes to neighboring nodes. SSLB reduces the burden of neighbor nodes, which need the less demand of computing resources and signaling interaction. Simulation results show that SIDA reduces the number of congestion links and balances the load distribution, while SSLB can effectively suppress the number of new congestion links after traffic diversion. These algorithms provide a load balancing solution for LEO satellite network.

A Safe and Reliable Routing Mechanism of LEO Satellite Based on SDN

Satellite networks have high requirements for security and data processing speed. In order to improve the reliability of the network, software-defined network (SDN) technology is introduced and a central controller is set... | Find, read and cite all the research you need on Tech Science Press

Corrections to “Beam Coverage Comparison of LEO Satellite Systems Based on User Diversification”

In the above article [1] , there is a misquotation in Section I, part A, paragraph 6, the fourth sentence. It should read: “The DRA will be able to form at least 16 beams in the uplink direction and at least 16 additional beams in the downlink direction and will have the capability of beamforming, its power, bandwidth, size, number, and boresight dynamically assigned to each beam to maximize system performance and minimize interference with GSO and NGSO satellites [2] .”