Earth Orbit Satellite Communication Research Articles

Optimal routing strategy based on extreme learning machine with beetle antennae search algorithm for Low Earth Orbit satellite communication networks

SummaryDue to the significant utilization of terrestrial communication, Low Earth Orbit (LEO) satellite network is a critical part of satellite communication networks owing to its several benefits. But the efficient and trustworthy routing for LEO satellite networks (LSNs) is a difficult process because of dynamic topology, adequate link changes, and imbalanced communication load. This study devises a new hybridization of extreme learning machine (ELM) with multitask beetle antennae search (MBAS) algorithm‐based distributed routing called the MBAS‐ELM model. The proposed model determines the routes based on traffic forecasting with respect to the level of traffic circulation on the earth. The proposed method is employed for traffic forecasting at the satellite nodes (SNs). To identify the optimal routes, mobile agents (MAs) are applied to concurrently and autonomously determine for LSNs and make a decision on routing data. The experimental outcome has showcased the effective performance of the proposed model over the compared models in terms of different measures, namely, average delay, packet loss ratio (PLR), and queuing delay. The results are validated under varying simulation time and data sensing rates. The obtained outcome pointed out the superior performance of the proposed MBAS‐ELM model compared with other methods.

Dynamic Channel Reservation Strategy Based on DQN Algorithm for Multi-Service LEO Satellite Communication System

In this letter, a dynamic channel reservation (DCR) strategy based on deep Q network (DQN) is proposed for multi-service low earth orbit (LEO) satellite communication system. We develop a novel modeling method to represent DCR problem of multiple services as a reinforcement learning (RL) task. Based on this model, we calculate the influence of current channel allocation results on future environment and take it as one of the factors for channel allocation decision. Moreover, a corresponding neural network is designed as a decision evaluator to provide an end to end mapping of decision to its value, which effectively avoids the influence of artificial preconditions. Simulation results show that the proposed strategy can improve the overall quality of service (QOS) of the system.

Design of polyrod antenna having isoflux radiation characteristic for satellite communication systems

In satellite communication, link margin and therefore antenna radiation characteristics are key factors to ensure providing a robust communication link between space and ground segment. For telemetry/telecommand and payload data transfer, isoflux antennas are employed widely in satellite communication systems to direct electromagnetic wave efficiently. To decrease complexity and manufacturing cost, simple antenna structures are preferred. In this study, after a detailed literature survey, a polyrod antenna has been designed to use in the space segment of Low Earth Orbit satellite communication subsystem. The proposed polyrod antenna has maximum gain at about 600 elevation angle of the antenna. Moreover, its impedance bandwidth is 750MHz (11%) that is fairly adequate to use in high data rate transmitters. By using CST Microwave StudioTM which is a commercially available 3-D electromagnetic time-domain solver, directivity, gain, axial ratio for elevation plane at X-Band, and return loss characteristic have been presented. Based on the obtained results, the designed polyrod antenna can be used where a conical shaped beam radiation pattern is needed.

Spatial Resource Management in LEO Satellite

Low Earth Orbit (LEO) satellite communication systems are known to have complicated spatial resource management. The problem occurs because of the impossibility to realize fully digital beamforming since its hardware implementation consumes too much power of the on-board battery. On another hand, analog beamforming can not provide enough system coverage in realistic user distribution scenarios. In this paper, we justify the choice of the hybrid multi-beamforming structure for some realistic user distributions. Such a structure guarantees enough coverage with minimal power consumption. For this structure, we propose a new spatial resource allocation intended to minimize handovers and to simplify the calculation of the time user spends inside each satellite beam spot. Numerical results with real system parameters are provided to confirm feasibility.

Massive MIMO Transmission for LEO Satellite Communications

Low earth orbit (LEO) satellite communications are expected to be incorporated in future wireless networks, in particular 5G and beyond networks, to provide global wireless access with enhanced data rates. Massive MIMO techniques, though widely used in terrestrial communication systems, have not been applied to LEO satellite communication systems. In this paper, we propose a massive MIMO transmission scheme with full frequency reuse (FFR) for LEO satellite communication systems and exploit statistical channel state information (sCSI) to address the difficulty of obtaining instantaneous CSI (iCSI) at the transmitter. We first establish the massive MIMO channel model for LEO satellite communications and simplify the transmission designs via performing Doppler and delay compensations at user terminals (UTs). Then, we develop the low-complexity sCSI based downlink (DL) precoder and uplink (UL) receiver in closed-form, aiming to maximize the average signal-to-leakage-plus-noise ratio (ASLNR) and the average signal-to-interference-plus-noise ratio (ASINR), respectively. It is shown that the DL ASLNRs and UL ASINRs of all UTs reach their upper bounds under some channel condition. Motivated by this, we propose a space angle based user grouping (SAUG) algorithm to schedule the served UTs into different groups, where each group of UTs use the same time and frequency resource. The proposed algorithm is asymptotically optimal in the sense that the lower and upper bounds of the achievable rate coincide when the number of satellite antennas or UT groups is sufficiently large. Numerical results demonstrate that the proposed massive MIMO transmission scheme with FFR significantly enhances the data rate of LEO satellite communication systems. Notably, the proposed sCSI based precoder and receiver achieve the similar performance with the iCSI based ones that are often infeasible in practice.

Downlink Coverage and Rate Analysis of Low Earth Orbit Satellite Constellations Using Stochastic Geometry

As low Earth orbit (LEO) satellite communication systems are gaining increasing popularity, new theoretical methodologies are required to investigate such networks' performance at large. This is because deterministic and location-based models that have previously been applied to analyze satellite systems are typically restricted to support simulations only. In this paper, we derive analytical expressions for the downlink coverage probability and average data rate of generic LEO networks, regardless of the actual satellites' locality and their service area geometry. Our solution stems from stochastic geometry, which abstracts the generic networks into uniform binomial point processes. Applying the proposed model, we then study the performance of the networks as a function of key constellation design parameters. Finally, to fit the theoretical modeling more precisely to real deterministic constellations, we introduce the effective number of satellites as a parameter to compensate for the practical uneven distribution of satellites on different latitudes. In addition to deriving exact network performance metrics, the study reveals several guidelines for selecting the design parameters for future massive LEO constellations, e.g., the number of frequency channels and altitude.

Beam-Space Multiplexing: Practice, Theory, and Trends, From 4G TD-LTE, 5G, to 6G and Beyond

In this article, the new term, namely beam-space multiplexing, is proposed for the former multi-layer beamforming for 4G TD-LTE in 3GPP releases. We provide a systematic overview of beam-space multiplexing from engineering and theoretical perspectives. First, we clarify the fundamental theory of beam-space multiplexing. Specifically, we provide a comprehensive comparison with antenna-space multiplexing in terms of theoretical analysis, channel state information acquisition, and engineering implementation constraints. Then, we summarize the key technologies and 3GPP standardization of beam-space multiplexing in 4G TD-LTE and 5G new radio (NR) in terms of multi-layer beamforming and massive beamforming, respectively. We also provide system-level performance evaluation of beam-space multiplexing schemes and field results from current commercial TD-LTE networks and field trial of 5G. The practical deployments of 4G TD-LTE and 5G cellular networks demonstrate the superiority of beam-space multiplexing within the limitations of implementation complexity and practical deployment scenarios. Finally, the future trends of beam-space multiplexing in 6G and beyond are discussed, including massive beamforming for extremely large-scale MIMO (XL-MIMO), low earth orbit (LEO) satellite communication, data-driven intelligent massive beamforming, and multi-target spatial signal processing, that is, joint communication and sensing, positioning, and so on.

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.

Deep Neural Network-Based Receiver for Next-Generation LEO Satellite Communications

This paper proposes a novel deep neural network (DNN)-based receiver for next-generation low Earth orbit (LEO) satellite communications. The DNN receiver can concurrently compensate for multiple imperfections of the satellite communication system to improve the quality of satellite-to-ground transmission. A special focus has been placed on handling the nonlinear distortion in the transmitted signal caused by space-borne high-efficiency radio frequency power amplifiers (RF-PAs), which is crucial in high-throughput satellite communications, but has been overlooked by existing relevant research. In this receiver, a DNN is designed and trained to learn the channel effects, nonlinearities of the RF-PAs, and digital modulation schemes in the received signal for demodulation and nonlinearity/channel effect compensation at the same time. The proposed receiver has been evaluated using five popular filtered orthogonal frequency division modulations with the nonlinear distortions experimentally extracted from a real gallium nitride (GaN) RF-PA and the additive white Gaussian noise channel generated by simulations. The validation results demonstrate that the DNN receiver can accommodate different modulation schemes and two typical groups of RF-PA classes with a satisfactory bit error rate performance. It has the potential to boost the performance of existing on-orbit LEO satellite communication systems with minimal system modifications and serves as a promising solution for future satellite communication services.

The Performance Analysis of Downlink NOMA in LEO Satellite Communication System

Non-orthogonal multiple access (NOMA) has the potential to provide higher throughput than conventional orthogonal multiple access (OMA), which has been considered as a key technology for 5G. NOMA in satellite communication system can provide anytime, anywhere access with improved spectral efficiency and system capacity because of its ubiquitous coverage. However, the characteristics of the satellite channels are different from that of the terrestrial network, i.e., huge time delay and Doppler shift. In this paper, different from the existing works, which mainly focus on the performance of NOMA in static terrestrial base stations and Geostationary orbit (GEO) scenarios, we investigate the performance analysis of downlink NOMA in dynamic low earth orbit (LEO) satellite communication system with Doppler shift considered. We combine NOMA and orthogonal frequency division multiplexing (OFDM) for better spectral efficiency. Our channel model includes both small scale model and large scale model. For simplify, we only consider two users in one spot beam. Besides, we express the performance analysis of downlink NOMA in LEO satellite communication system, like ergodic capacity, outage probability (OP) and mutual information. However, in traditional NOMA scheme, the proceeding error decision of the high power user will cause the deterioration of the subsequent detection performance. Therefore, a symmetrical coding (SC) scheme for different modulation mode is proposed for low power users to get better performance. Finally, simulation results validate the performance of the NOMA scheme is better than that of the OMA scheme. The proposed SC scheme can achieve a prominent increase performance contrasted to the traditional NOMA scheme.

A Prediction-Based Resource Matching Scheme for Rentable LEO Satellite Communication Network

The resource allocation strategy is a critical problem in the low earth orbit (LEO) satellite communication network (SCN) due to the limited resources and high movement. In this letter, we first introduce the rental service into LEO-SCN to improve the resource utilization by renting out unused resources. Secondly, we investigate a prediction-based resource matching scheme for rentable LEO-SCN. Specifically, a long-short-term memory (LSTM) based prediction framework is developed to predict the traffic value of local tasks, which is affected by the periodic motion and the inherent traffic law. Then, based on the predicted traffic, a task-driven joint resource allocation method is proposed to efficiently match power and spectrum resources. Finally, the simulation results verify the validity of the proposed approach compared with the pre-allocation strategy and the adaptive allocation strategy. Moreover, we analyze the key factors that affect the achievable performance of the proposed prediction-based resource matching scheme.

A Novel Low Profile Rectangular Microstrip Patch Antenna for L-Band Applications Using High Permittivity Substrate

A novel low-profile and miniaturized patch antenna on a substrate material of high dielectric constant has been designed, fabricated and tested in an indigenous laboratory. It is highly important to reduce the size of patch antenna as it limits the reduction of the sizes of the devices using this antenna. A number of techniques have been given for the size reduction of patch such as DGS (Defected Ground Structure), use of fractals and the use of metamaterials but in this paper the technique of high permittivity substrate has been implemented. The substrate as well as this conventional antenna has been prepared locally in Pakistan. A ceramic material of chemical composition {(Sr0.5Pb0.25Ca0.25)-Tio3-3Bi2O3.TiO2} having a high dielectric constant has beenused in the substrate of the antenna. The fabricated prototype was investigated experimentally for important parameters using Vector Network analyzer. The total measure of the antenna is 20.5x26.5x1.5 mm3. The antenna presented a large bandwidth of 186 MHz (1070-1256 MHz)in L-Band with a Return Loss of 21.10 dB at resonance. The VSWR (Voltage Standing Wave Ratio) remained under the standard value of 2 in the whole operating range. The proposed antenna may be employed in GPS (Global Positioning System) devices, Amateur Radio, Terrestrial Mobile Communication, Aeronautical and Maritime Mobile and other Military and Low Earth Orbit Satellite Communications.

An adaptive routing algorithm for integrated information networks

The integrated information network is a large capacity information network that integrates various communication platforms on the ground, at sea, in the air and in the deep air through the inter-satellite and satellite-ground links to acquire information accurately, process it quickly, and transmit it efficiently. The satellite communication, as an important part of integrated information networks, is one of main approaches to acquire, process and distribute communication information and resources. In this paper, based on current researches of the satellite communication network, we put forward a 3-layer satellite communication network model based on the Software Defined Network (SDN). Meanwhile, to improve current routing policies of the Low Earth Orbit (LEO) satellite communication network, we put forward an Adaptive Routing Algorithm (ARA) to sustain the shortest satellite communication link. Experiment results show that the proposed method can effectively reduce link distance and communication delay, and realize adaptive path planning.

Compensation System Design and Comparison of Very High Doppler Frequency Effect

One of the serious problems in the low earth orbit (LEO) satellite communication system is the very high Doppler frequency effect since the LEO satellite system runs very fast to keep the orbit altitude. Especially, this problem produces the critical performance degradation when the broad bandwidth is necessary for the very high speed satellite transmission of the very high resolution image data. As the data speed is increased, the higher efficient communication technology will be required to transmit the high-capacity of data to the ground station. In the LEO satellite communication systems, very large Doppler influence is generated because of the very fast movement of satellite. This Doppler spectrum shift effect, similar to the carrier frequency offset effect, can cause performance degradation in the satellite communication system. Therefore, it is very important to effectively compensate for this Doppler frequency shift. So, in this paper, we analyze this Doppler effect of LEO satellite receiver and propose an efficient compensation system design against the Doppler frequency. Two compensation methods are proposed: pilot method and phase locked loop (PLL) method. As simulation results show, when the SNR is approximately 5 dB or less, the pilot method provides better performance, compared with the PLL method. When the SNR is approximately 6 dB or more, it can be confirmed that the PLL method outperforms than the pilot method, which is almost same to the theoretical performances. Furthermore, it can be said that the PLL method is very spectrum-efficient than the pilot method since it does not require any pilots. However, it is very difficult and expensive to design the accurate, agile, broadband operating PLL system to compensate the very wide range of Doppler frequency shift.

On the performance of UNB for machine‐to‐machine low earth orbit (LEO) satellite communications

SummaryUltra narrow band (UNB) is a widely used technology for machine‐to‐machine and low‐power wide‐area communications. Its properties, long range with small RF power, make it naturally attractive for satellite communications but also draw new challenges compared with terrestrial systems where this technology is already deployed. Indeed, the main advantage of UNB signals, their small bandwidth, makes them more sensitive to frequency drifts that are particularly present in the case of LEO satellite systems. It also implies the use of a random access method in which the carrier frequency is a parameter unknown by the receiver. In this paper, we propose a general semianalytical model to evaluate the performance of a terrestrial or satellite system using UNB technology, taking into account the multiuser interference and the frequency drift. This model is then used to assess the performance (packet loss ratio and throughput) on the return link medium access control (MAC) of a representative LEO satellite system. With our model, we analyze the effect of frequency drift on the system performance. This paper also proposes to investigate more deeply the multiuser interference modeling in order to estimate accurately the performances of a UNB system in terms of bit error rate (BER). We propose a semianalytical approach to study the interference in presence of arbitrary power imbalance that includes the effect of frequency offset and frequency drift and applicable for any linear modulation and any pulse‐shaping filter. The expression of the multiuser interference is established in the general case. We then propose a methodology to compare this exact model to the Gaussian interference approximation (mainly used through the central limit theorem) in order to assess its accuracy.

Study of interference localization using single satellite based on signal strength distribution in multi-beam antenna for satellite communications system

Large onboard antennas with multi-beams are used almost in all the Geostationary Earth Orbit satellite communications systems, which are always disturbed by jams and inferences. However, there are lots of factors restricting interference localization in satellite communications system because the system is not designed for location-oriented. This article makes use of the characteristic that each spot beam of multi-beams antenna has different gain at the position of interference, establishes the localization equations set by using the ground projection model of multi-beams antenna pattern, and gives two methods of solving equations. Thus, it proposes interference localization algorithm using single satellite, based on antenna gain and the distribution of signal strength in multi-beam space. Because of not depending on extra onboard equipments and other facilities, it has no effect on the construction and operation of satellite communications system. From the results of analyses and simulations, the localization precision can satisfy the general practical requirement. The algorithm could be used in checking the interference of the system, decision supporting of anti-jamming, and improving operation and management of the system.

Addressing Subnet Division Based on Geographical Information for Satellite-Ground Integrated Network

To tackle the address aggregation problem for the low earth orbit (LEO) satellite communication system, a global geographical Internet Protocol subnet division model for space–ground integrated network addressing scheme is proposed in this paper. A 2-D spherical coordinate system based on spherical distance is applied to describe the LEO satellite track and the location information of geographical subnet zone. A mathematical framework for abnormal addressing users is constructed under the system. The size and division of geographical zone influence the expectation of abnormal user number through the ratio of logically covered and fully covered time. When the terrestrial regions are divided into small cells, the number of abnormal users reduces, as well as the partial routing cost. The simulation results confirm that the ratio of logically covered and fully covered time increase and the number of abnormal users decreases when the size of ground cells declines. The origin regions could be divided into smaller ground cells in order to reduce abnormal addressing users, balancing the cost on partial routing mechanism, mobility management, and satellite routing table items. This paper presented a solution and direction of addressing scheme and mobility management design for the space-terrestrial hybrid network.

A power reduction method for pilot channel of LEO satellite based on dynamic compensation

Since the lower power requirement of code division multiple access (CDMA) than that of other multiple access, the CDMA technology is suitable to be used in low earth orbit (LEO) satellite communication system whose space power is limited due to the small size of satellite. The pilot channel of CDMA technology is very important for earth mobile station (EMS) in LEO system to recover carrier and code, but the power requirement of pilot channel is very higher than that of other channels. In this paper, a power reduction method for pilot channel is proposed. By the new method, the power of pilot channel transmitted from LEO satellite is reduced to a lower level. For improving the signal to noise ratio (SNR) of pilot channel with lower power, coherent integration is employed in EMS at the pre-processing stage. Considering the high dynamic situation of LEO satellite, the long period of time for integration will deteriorate the receiving performance of EMS, therefore, a dynamic compensation module is added to carrier tracking loop against the high dynamic. Meanwhile, the transfer function of the new tracking loop and the condition for steady-state zero error are deduced. Numerical examples are provided to demonstrate effectiveness of the proposed approach.

Cooperative transmission over Rician fading channels for geostationary orbiting satellite collocation system

To enhance the spectral efficiency of geostationary Earth orbit (GEO) satellite communication systems with scarce GEO resources, cooperative transmission is widely used in GEO satellite collocation (GEOSC) systems. Current analysis on GEOSC channels is usually based on the hypothesis that channels are line-of-sight (LOS) ones, while multipath components are ignored. In this study, a more realistic cooperative transmission method is studied for GEOSC systems over Rician fading channels, where multipath components are taken into consideration in conjunction with LOS components. On the basis of this model, a practical user selection strategy with opportunistic beamforming is studied to optimise the capacity of GEOSC systems. Simulation results show that the GEOSC system using the techniques developed in this study has better performance comparing with the ones using existing approaches.

A Graph-Based Satellite Handover Framework for LEO Satellite Communication Networks

This letter proposes a graph-based satellite handover framework for the low earth orbit (LEO) satellite communication networks. In order to maintain the connection with the communicating counterpart, the user has to switch between consecutive satellites covering the very user. A directed graph with covering period of the satellite as its node, and the link representing the possible handover between two overlapping periods, is calculated in advance, and then, the satellite handover process can be viewed as finding a path in the directed graph. By setting the link weight according to different handover criterions, the graph-based framework can support a variety of satellite handover strategies, which shows the improved flexibility over the existing research. The application of the framework to find the shortest handover path conducted on two typical LEO satellite networks, viz., Iridium and Globalstar, also corroborates the effectiveness of the proposed handover framework.