LEO Satellite Communication Systems Research Articles

Joint Optimization of Beam Placement and Transmit Power for Multibeam LEO Satellite Communication Systems

Joint Optimization of Beam Placement and Transmit Power for Multibeam LEO Satellite Communication Systems

Multi-dimensional resource allocation strategy for LEO satellite communication uplinks based on deep reinforcement learning

In the LEO satellite communication system, the resource utilization rate is very low due to the constrained resources on satellites and the non-uniform distribution of traffics. In addition, the rapid movement of LEO satellites leads to complicated and changeable networks, which makes it difficult for traditional resource allocation strategies to improve the resource utilization rate. To solve the above problem, this paper proposes a resource allocation strategy based on deep reinforcement learning. The strategy takes the weighted sum of spectral efficiency, energy efficiency and blocking rate as the optimization objective, and constructs a joint power and channel allocation model. The strategy allocates channels and power according to the number of channels, the number of users and the type of business. In the reward decision mechanism, the maximum reward is obtained by maximizing the increment of the optimization target. However, during the optimization process, the decision always focuses on the optimal allocation for current users, and ignores QoS for new users. To avoid the situation, current service beams are integrated with high- traffic beams, and states of beams are refactored to maximize long-term benefits to improve system performance.Simulation experiments show that in scenarios with a high number of users, the proposed resource allocation strategy reduces the blocking rate by at least 5% compared to reinforcement learning methods, effectively enhancing resource utilization.

Random Access Control and Beam Management Scheme for the 5G NR based Beam Hopping LEO Satellite Communication Systems

Random Access Control and Beam Management Scheme for the 5G NR based Beam Hopping LEO Satellite Communication Systems

Circularly Polarized Metasurface Phased Array Antenna System With Wide Axial-Ratio Beamwidth for LEO Mobile Satellite Communication

In this paper a millimeter waves LHCP 1×32 with dummy on both sides phased array antenna is proposed. Multi-layer structure and single feed are employed. The antenna patch adopts 3×3 metasurface. The measured impedance bandwidth is 20%, ranging from 22.5 to 27.5 GHz. The axial ratio bandwidth with an axial-ratio (AR) level < 3 dB achieves 3.35 GHz ranging from 24.15 GHz to 27.5 GHz. Relative 3 dB axial ratio bandwidth reaches 13.4%. A total of 37 beams were measured in the anechoic chamber. The results show that whether the phased array antenna system serves as transmitter or receiver, the 3dB beam angle coverage at 26 GHz reaches -42°-45° at φ= 0° and -42°-42° at φ= 90°. The 3 dB axial ratio beam angle ranges from -80° to 89° at φ= 0°, and from -45° to 45° at φ= 90°. Based on this linear array, it is easy to expand to circular polarization planar wide-angle scanning phased array. The antenna system realizes circular polarization with wide angle wide axial ratio beam scanning, which can be used in LEO satellite communication system.

Анализ применимости стандартных протоколов динамической маршрутизации в сетях спутниковой связи на основе низкоорбитальных космических аппаратов

One of the key components of communication networks, which determines the principles of their operation, are traffic routing protocols. The purpose of this article is to consider the possibility of using widely used dynamic routing protocols in LEO satellite communication systems. Based on the available publications, the analysis of the initial data was carried out and the conditions for the functioning of routing protocols in low-orbit satellite communication systems, as well as the basic requirements for such protocols, were formulated. The analysis of the functioning of the dynamic routing protocols in the given conditions is carried out. The disadvantages of the considered protocols are highlighted and characterized. The main conclusion of the article is the inexpediency of using the considered protocols in low-orbit satellite communication networks due to the high resource requirements and the insufficient speed of propagation of changes. The results can be used to substantiate technical solutions in the design of low-orbit satellite communication networks.

Broadband LEO Satellite Communications: Architectures and Key Technologies

This article aims to provide a comprehensive overview for key issues in broadband LEO satellite communication systems. First of all, the network architecture is introduced, which is the basis of the whole system. The space-based LEO system with ISL, which requires a small number of ground gateways, is the focus. In this system, the satellite constellation design is important with impact on key system performances such as coverage. Two popular LEO constellations, the walker Delta and Star constellations, are introduced. Given satellite constellations, proper beam coverage schemes should be employed at satellites to provide seamless coverage all over the world. A hybrid wide and spot beam coverage scheme is presented, where the LEO provides a wide beam for large area coverage and several steering spot beams for highspeed data access. Moreover, special coverage schemes should be designed in broadband LEO systems for the interference coordination between LEO and GEO. To protect GEO communications, LEO satellites should be turned off if they cause interference to GEO. In this case, to provide services for users covered by the turned-off LEO satellites, a progressive pitch method and a coverage expanding method can be employed. Finally, the coverage performance of LEO is also closely related to resource management schemes. The global resource management for broadband LEO systems is complicated, involving a large amount of data, and a two-level management structure should be employed. Using this structure, an NMC with powerful storage and processing capabilities is employed to carry out the first-level management, making strategies based on all information collected from the whole system. Then satellite base stations with limited capabilities are employed to respond to the strategies generated by NMC in real time.

G-BDP-ADC Model for Effectiveness Evaluation of Low Orbit Satellite Communication System in the Context of Poor Information

Effectiveness evaluation of LEO satellite communication system can not only guide the optimization of constellation program,but also play an important role in the stage of system design. In order to ensure the accuracy of the evaluation results, it is necessary to consider the impact of uncertain information on effectiveness evaluation, whether it is due to poor information or complex system.In order to solve this problem, this paper introduces birth and death process into satellite communication system.Firstly, according to the limit distribution of grey birth and death process with continuous time and limited state, we establish the availability model of the system.Then, the Kolmogorov forward equation is used to characterize the dependability of the system during operation.After that, a capability evaluation index system based on “four domains” is constructed. The attribute values of the index are unified into generalized standard interval grey numbers, and the weight allocation model of GSIGN-AHP-ME is established.The system capability is calculated according to the full probability formula.Subsequently,taking constellation X as an example, the system effectiveness is obtained by using the G-BDP-ADC model constructed in this paper.Finally, by comparing with the fuzzy evaluation method, it shows that the G-BDP-ADC model constructed in this paper is better than the fuzzy evaluation method, and can describe the LEO satellite communication system in the context of poor information more appropriately.

Possibility of using leo satellite communication systems for on-line data interchange

The paper presents the analysis of the possibility of using the information resource of the Globalstar LEO satellite communication system (LSCS) for rapid data exchange via the following channels: MCC Globalstar nanosatellite, nanosatellite Globalstar nanosatellite in order to receive telemetric information from a nanosatellite, to transmit necessary commands and information from MMC to a nanosatellite as well as to exchange data between two nanosatellites. The possibility of data transmission via the channels: MCC Globalstar nanosatellite, nanosatellite Globalstar nanosatellite is shown. The duration of communication sessions via the channel MCC Globalstar nanosatellite and the channel nanosatellite Globalstar nanosatellite is analyzed Potential volumes of data transmitted between two nanosatellites are determined. Stochastic analysis of the possibility of data transmission between two spacecraft is performed and the possibility of data transmission between two spacecraft, depending on the data volume and load level of the Globalstar system is assessed.

The Technology of LEO Satellite Communication Systems Utilization for the Rapid Exchange of Data with the Low-altitude Spacecraft: Scientific Technological Equipment “Kontakt-MKA” On the Small Spacecraft “AIST-2”

In this paper was analyzed thepossibility ofcommunication sessions withthe small spacecraftvia theGlobalstarsystem. Theduration of communicationsessions was estimated.It was made astochasticanalysis ofthe data transmission capabilitiesbetween the twospacecraftvia theGlobalstarsystem. The probability ofdata transmission between twospacecraft, depending on data volumeandworkload ofthe Globalstar system was estimated. The spaceexperiment on thesmall spacecraft “AIST-2” is planning to testthe results.

Interplex for Constant Envelope in LEO Satellite Communication System

In modern LEO satellite communication systems, numerous singnals have to be located in a same frequency band because of limited spectrum resources. Thus, a bandwidth-efficient modulation, which has constant envelope characteristics and can alleviate signal distortions when using saturated power amplifiers is necessary to combine several signals to share the frequency resource. This paper presents the analytic interplex modulation expression in LEO satellite spread spectrum communication systems, and obtains the relationship of modulation efficiency, error rate and power ratio. Lastly, the appropriate choice of power radio is obtained in the case of three signals or four signals multiplexing. The work of this paper is an important guideline for constant envelope combined methodologies in LEO satellite spread spectrum communication systems.

Study on ISL network structure in LEO satellite communication systems

Many parameters have to be taken into account in designing an LEO satellite constellation including transmission delay, service coverage, minimum elevation angle, and the effects of space radiation. We selected the 2 π constellation for the NeLS ISL study to maintain continuous ISL connections, which is expressed by using a Walker notation of 120/10/1 with 55° of inclination. The satellite orbit parameters were examined under conditions where at least two satellites were always visible from the user terminal to enable satellite diversity. The optimum inclination angle for the 2 π constellation was directly derived from the spherical triangle formed by three adjacent satellites. To evaluate the NeLS's ISL performance, the structure for ISL connections was simplified by using constellation parameters of 121/11/0 instead of 120/10/1. The ISL network had a bi-directional MSN structure with these parameters. The inter-orbital ISL, especially, achieved a ring network shaped like a figure-of-eight using n to n - 1 connections. The bi-directional MSN topology of ISL connections is also discussed. A combination of constellation parameters P , S , and F were found to have simple relations in the n to n - 1 connections of inter-orbital ISLs. Finally, optimum parameters for the NeLS constellation are discussed, and a candidate parameter ( T / P / F = 132 / 11 /- 1 , h = 1100 km , and I = 57 . 92 ∘ ) is proposed.

Impact of ionospheric scintillations on LEO satellite DS-CDMA communication system

The impact of ionospheric scintillations is investigated in terms of bit error rate for a multispot beam LEO satellite communication system employing direct sequence-code division multiple access (DS-CDMA) technique. Depending on the satellite orbit parameters and the earth station location, the effect of time-varying ionospheric scintillation on the system varies. Performance degradation can be substantial in times of severe scintillations.

A Generalized Gaussian User Distribution and a Modified Traffic Power Control (MTPC) for LEO Systems

This paper proposes the use of the generalized Gaussian as a user distribution model in LEO satellite communication systems. Evaluating the signal to interference ratio (SIR) for this more general function depicts the performance of a LEO system. It is shown that the performance of the system is sensitive to the assumed user distribution. Furthermore, since the discrepancy between the SIR of adjacent satellites is large especially in severe non-uniformity of the traffic, the use of a modified power control (MPC) is essential. A slight modification of this MPC is also suggested.

Adaptive bit loading scheme using COFDM at low elevation over LEO satellite communication channel

Much interest has been shown in employing LEO satellite communication systems. A novel algorithm is proposed for adaptive bit loading (multilevel modulation assignment) between COFDM subcarriers in a frequency selective fading channel. Two-dimensional alignment has been carried out. The system performance is greatly improved at low elevation angles compared to that using fixed bit loading. Furthermore, the comparison shows that this adaptive bit loading COFDM system is suitable for frequency selective slow fading channels, which have time-varying deep nulls in the frequency response.