Low Earth Orbit Mobile Satellite Research Articles

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.

Forecast Based Handover in an Extensible Multi-Layer LEO Mobile Satellite System

Low earth orbit mobile satellite system (LEO-MSS) is the major system to provide communication support for the regions beyond the coverage of terrestrial network systems. However, passive handover happens frequently caused by the quick movement of LEO satellites in LEO-MSS. It not only causes the waste of radio resource, but also makes it hard to guarantee the quality of service (QoS), especially for user groups in hot-spot regions. To tackle this problem, we propose an extensible multi-layer network architecture to reduce the handover rate, especially group handover rate by introducing high-altitude platforms (HAPs) and terrestrial relays (TRs) to this system. We then propose a multi-layer handover management framework and also design different handover procedures based on handover forecast for different kinds of handovers according to the proposed architecture and framework to reduce handover delay and signalling cost. Furthermore, we propose a dynamic handover optimization to reduce the dropping probability and guarantee the QoS of mobile terminals. Numerical results show that the proposed architecture reduces group handovers significantly. The proposed handover procedures also provide better performance on delay and signalling cost compared with traditional handover protocols. With the proposed dynamic handover optimization, the proposed handover procedures provide better performance on dropping probability and throughput. The proposed dynamic handover optimization has an excellent performance on dropping probability while guaranteeing the QoS of mobile terminals.

On Channel Sharing Policies in LEO Mobile Satellite Systems

We consider a low earth orbit (LEO) mobile satellite system with “satellite-fixed” cells that accommodates new and handover calls of different service-classes. We provide an analytical framework for the efficient calculation of call blocking and handover failure probabilities under two channel sharing policies, namely the fixed channel reservation and the threshold call admission policies. Simulation results verify the accuracy of the proposed formulas. Furthermore, we discuss the applicability of the policies in software-defined LEO satellites.

An analytical framework in LEO mobile satellite systems servicing batched Poisson traffic

The authors consider a low earth orbit (LEO) mobile satellite system (MSS) that accepts new and handover calls of multirate service-classes. New calls arrive in the system as batches, following the batched Poisson process. A batch has a generally distributed number of calls. Each call is treated separately from the others and its acceptance is decided according to the availability of the requested number of channels. Handover calls follow also a batched Poisson process. All calls compete for the available channels under the complete sharing policy. By considering the LEO-MSS as a multirate loss system with ‘satellite-fixed’ cells, it can be analysed via a multi-dimensional Markov chain, which yields to a product form solution (PFS) for the steady-state distribution. Based on the PFS, they propose a recursive and yet efficient formula for the determination of the channel occupancy distribution, and consequently, for the calculation of various performance measures including call blocking and handover failure probabilities. The latter are much higher compared to the corresponding probabilities in the case of the classical (and less bursty) Poisson process. Simulation results verify the accuracy of the proposed formulas. Furthermore, they discuss the applicability of the proposed model in software-defined LEO-MSS.

Efficient Wideband Spectrum Sensing with Maximal Spectral Efficiency for LEO Mobile Satellite Systems.

The usable satellite spectrum is becoming scarce due to static spectrum allocation policies. Cognitive radio approaches have already demonstrated their potential towards spectral efficiency for providing more spectrum access opportunities to secondary user (SU) with sufficient protection to licensed primary user (PU). Hence, recent scientific literature has been focused on the tradeoff between spectrum reuse and PU protection within narrowband spectrum sensing (SS) in terrestrial wireless sensing networks. However, those narrowband SS techniques investigated in the context of terrestrial CR may not be applicable for detecting wideband satellite signals. In this paper, we mainly investigate the problem of joint designing sensing time and hard fusion scheme to maximize SU spectral efficiency in the scenario of low earth orbit (LEO) mobile satellite services based on wideband spectrum sensing. Compressed detection model is established to prove that there indeed exists one optimal sensing time achieving maximal spectral efficiency. Moreover, we propose novel wideband cooperative spectrum sensing (CSS) framework where each SU reporting duration can be utilized for its following SU sensing. The sensing performance benefits from the novel CSS framework because the equivalent sensing time is extended by making full use of reporting slot. Furthermore, in respect of time-varying channel, the spatiotemporal CSS (ST-CSS) is presented to attain space and time diversity gain simultaneously under hard decision fusion rule. Computer simulations show that the optimal sensing settings algorithm of joint optimization of sensing time, hard fusion rule and scheduling strategy achieves significant improvement in spectral efficiency. Additionally, the novel ST-CSS scheme performs much higher spectral efficiency than that of general CSS framework.

Wideband spectrum compressive sensing for frequency availability in LEO‐based mobile satellite systems

SummaryAvailability of L/S frequency band is a critical requirement for global communication provided by a constellation of low Earth orbit satellites. This paper investigates the issue of low Earth orbit mobile satellite system frequency availability, where wideband compressed signal detection approach is utilized to obtain active user subbands and their locations which should be avoided during frequency allocation. Compressed sensing can be achieved by exploiting the sparsity of wideband signal spectrum, whose useful frequency support occupies only a small portion of the entirely wide spectrum. An estimate of the signal spectrum can be obtained by using reconstruction algorithms. We define two novel wideband spectrum compressed sensing methods based on discrete cosine transform and Walsh–Hadamard transform, briefly named DCT‐WSCS and WHT‐WSCS, which significantly improve the performance of spectrum recovery and signal detection compared with conventional discrete Fourier transform‐based compressed spectrum sensing method. Furthermore, with the help of inter‐satellite links, the scheme of multiple satellites cooperatively sensing with a final decision according to OR and MAJ fusion rules is proposed, which can bring diversity gains. Finally, in‐depth numerical simulations under a particular scenario demonstrate the performance of the proposed scheme in the aspect of signal reconstruction precision, detection probability, and processing time. Copyright © 2017 John Wiley & Sons, Ltd.

Performance Analysis of Correlated Handover Service in LEO Mobile Satellite Systems

Analytical models for low earth orbit mobile satellite systems (LEO-MSSs) should consider service time correlation in adjacent satellite spot beams. This letter presents a simple analytical framework for the efficient performance evaluation of new and handover services in LEO-MSSs with correlated service times. When the fading channel is temporally correlated, channel characteristics in the preceding and succeeding spot beams do not change dramatically, especially for services with short transmission times. A closed-form solution of the correlated queue service time is derived using probability generating functions whose moments are used to derive the blocking probabilities of handover and new services. The system is then modeled as a queuing system with correlated service time and its performance investigated.

Space-borne BDS receiver for LING QIAO satellite: design, implementation and preliminary in-orbit experiment results

Known as China's first low earth orbit (LEO) mobile communication experimental satellite, the LING QIAO satellite was launched on September 4, 2014. In addition to the two global positioning system (GPS) receivers on board, which are the main navigation receivers supporting the synchronized LEO communication payload and other systems that require navigation input, a BeiDou navigation system (BDS) receiver is also installed on board as an experimental payload. We present the system design and preliminary in-orbit experiment results of the BDS receiver of the LING QIAO satellite. The results show that: (1) The root-mean-square positioning error of the BDS receiver is 13 m, while the GPS error is 1 m; (2) the in-orbit traced service area of BDS is from 55°S to 55°N, 70°E to 150°E, which matches the official announced service area; (3) for industrial-level chips and devices of the BDS payload which are vulnerable to space radiations, the single-event effect monitoring and combating measures, as presented in this work, have been effective for LING QIAO satellite.

Analysis of maximum traffic intensity under pre‐set quality of service requirements in low earth orbit mobile satellite system for fix channel reservation with queueing handover scheme

Maximum traffic intensity supported by a low earth orbit mobile satellite system (LEO-MSS) is important in practical application for providing satisfactory service. Applying fix channel reservation with first in first out queueing handover scheme into LEO-MSS, a novel analytical approach is proposed for determining the maximum traffic intensity under pre-set quality of service (QoS) constraints on new call blocking probability and handover failure probability. The relationship between QoS constraints and maximum traffic intensity is established. The expression of maximum traffic intensity is then deduced. The optimal number of reserved channels is obtained. By comparing the results between the proposed approach and existing method, the correctness of the proposed approach is verified. The proposed approach greatly reduces the calculation complexity. Lastly, the accuracy of the analysis has been verified by computer simulations.

Analysis of maximum traffic intensity for guaranteed handover and channel complete sharing scheme under pre-set QoS requirements in LEO-MSS

The maximum traffic intensity supported by a low earth orbit (LEO) mobile satellite system (MSS) (LEO-MSS) is important in practical application for providing satisfactory service. An analytical approach is proposed for determining the maximum traffic intensity of guaranteed handover (GH) scheme and channel complete sharing (CCS) scheme in LEO-MSS under quality of service (QoS) constraints. By evaluating performance of these two schemes, the relationship between the traffic intensity and the QoS constraints is established. The expressions of maximum traffic intensity of GH scheme and CCS scheme are deduced. Compared with the traditional method, the proposed analytical approach is more computationally efficient owing to the needlessness of the repeated iteration calculation. It also avoids the complex choice of the initial value of new call traffic intensity and its increment. Lastly, the accuracy and validity of the analysis approach have been verified by computer simulations.

On the Analysis of Random Coverage Time in Mobile LEO Satellite Communications

Deterministic models for coverage time evaluation of Low Earth Orbit (LEO) satellites constituting a mobile satellite network may tend to unreliable results due to arbitrary locations of mobile users within the satellite coverage area. This inevitable phenomenon necessitates a statistical model for coverage time assessment of LEO satellite networks. In this letter, we propose a novel approach for effective analysis of coverage times during LEO satellite visits. The analysis is particularly useful for probabilistic investigation of intersatellite handovers in LEO satellite networks and also in designing mobile satellite systems.

Optimal Channel Partitioning and Channel Utilization for Multiclass Traffic in a LEO-MSS

An optimal channel partitioning scheme that maximizes the channel utilization of low earth orbit mobile satellite systems serving multiclass traffic is presented. To this aim, the channel utilization was analytically derived and used as revenue function for the proposed optimization algorithm. The accuracy of the analysis and the effectiveness of the proposed optimization technique were verified by computer simulations.

A Trace-Time Framework for Prediction of Elevation Angle Over Land Mobile LEO Satellites Networks

Elevation angle is one of the most significant parameters of land mobile satellite channels, subject to rapid variations in the case of Low Earth Orbit (LEO) satellite systems. In this paper a novel trace-based framework is proposed and analyzed which is capable of predicting elevation angle as a function of time during satellite visibility window. Trace-time based modeling makes the framework practical for real-time evaluation of elevation angle and its alteration incurred by communication links in LEO satellite systems. The proposed method is particularly suitable for development of communication channel models and services in mobile LEO satellite networks where path variability is of great importance.

A Novel Method For evaluating Parameters Of Ongoing Calls In Low Earth Orbit Mobile Satellite System

In order to derive important parameters concerning mobile subscriber MS with ongoing calls in Low Earth Orbit Mo- bile Satellite Systems LEO MSSs, a positioning system had to be integrated into MSS in order to localize mobile subscribers MSs and track them during the connection. Such integration is regarded as a complex implementation. We propose in this paper a novel method based on advantages of mobility model of Low Earth Orbit Mobile Satellite System LEO MSS called Evaluation Parameters Method EPM which allows for such systems the evaluation of different information concerning a MS with a call in progress even if its location is unknown.

Channeling Partitioning Policies for Multi-Class Traffic in LEO-MSS

This paper studies channel partitioning policies and channel resource prioritization techniques for handovers, which efficiently support multi-class traffic in low Earth orbit mobile satellite systems (LEO-MSS). Analytical methods are developed for evaluating the performance of complete partitioning (CP) and complete sharing (CS) with and without fixed channel reservation (FCR) for multi-class traffic in LEO-MSS. Furthermore, a novel threshold call admission (TCA) scheme which achieves better channel utilization and fair channel access is introduced and analyzed.

Performance Analysis and Improvement Methods for Channel Resource Management Strategies of LEO–MSS With Multiparty Traffic

A novel analytical framework for the accurate and efficient evaluation of the performance of channel resource management strategies for low Earth orbit mobile satellite systems (LEO-MSSs) supporting multiparty traffic is presented. By considering a fixed channel reservation (FCR) scheme as a benchmark, an efficient and accurate analytical approach is developed for obtaining the performance of multiparty traffic under various quality-of-service (QoS) performance measure criteria. The proposed approach is based on a Markovian queuing model, and its correctness and accuracy have been verified by means of computer simulations. To improve the overall performance of LEO-MSS, two novel resource management techniques are introduced and analyzed. The first one is an efficient adaptive channel reservation (ACR) scheme, which allows priority to be given to handover requests that are generated by multiparty traffic. The second one is a new call queuing (NCQ) policy, which efficiently reduces the new call blocking probability with little impact on other system performance measures, such as call dropping probability and unsuccessful call probability. Various performance results show that when ACR is used in conjunction with NCQ, extremely low blocking and handover failure probabilities can be achieved for multiparty traffic.

Analysis of Maximum Traffic Intensity and Optimal Channel Reservation Under QoS Constraints in LEO-MSS

A novel analytical approach is developed for determining the maximum traffic intensity for Low Earth Orbit Mobile Satellite Systems (LEO-MSS) under preset Quality of Service (QoS) constraints such as call blocking and dropping probabilities. The proposed methodology also enables the optimization of channel reservation for handovers so that the traffic intensity supported by LEO-MSS is maximized.

New Cell Residence Time Models for Mobile LEO Satellite Cellular Networks

We propose new models for characterizing the cell residence time in a mobile low-Earth-orbit (LEO) satellite cellular network, which, unlike previous models, can accommodate the effect of the Earth's rotation in the teletraffic analysis. The speed of the satellite is typically much higher than that of the mobile; as such, the duration of a cell residence time is finite. Therefore, we use distributions with finite support to model the cell residence time. In particular, we model the residence time in the first (origination) cell with a right-truncated gamma distribution and the residence time in all the other cells with a generalized beta distribution. These distributions have finite support and are sufficiently flexible to accommodate the effects of different system conditions, including the Earth's rotation. To illustrate the use of the proposed models, we study the performance of a mobile LEO satellite cellular network based on the assumption that the residence time in the first cell follows the right-truncated gamma distribution, the residence times in all the other cells follow the generalized beta distribution, and the call duration is gamma distributed. The goodness of the proposed models is validated by computer simulation.

On the Performance Analysis of Dynamic Channel Allocation With FIFO Handover Queuing in LEO-MSS

The exact analysis of dynamic channel allocation (DCA) with first-in/first-out (FIFO) queuing of handover (QH) requests is highly complex, due to the dynamic nature of channel allocation to different cells. This letter presents an approximate but accurate analytical method to evaluate the performance of DCA in conjunction with FIFO-QH in low earth orbit mobile satellite systems. The accuracy of the proposed analysis has been verified by means of computer simulation.

QoS on LEO satellites

This paper discusses the role played by wireless network infrastructure in mobile commerce applications. The user's perception of service quality depends on the available resources and capabilities of the network. The new generation of low earth orbit (LEO) mobile satellite networks, deployed at altitudes ranging from 500 km to 2000 km, are well suited to handle multimedia traffic and to offer end-users equipped with hand-held devices at low cost-per minute access to network services. A wide range of multimedia services and applications are expected to provide users with QoS based asynchronous transfer mode (ATM) technology. LEO satellite networks provide significant wide area coverage, unique broadcast capability, ability to meet different QoS requirements, the ability to communicate with hand-held devices and low cost access. The main resources in the LEO networks are satellite radio bandwidth and the buffer capacity of the onboard ATM switch. The most important ATM resource management function is connection and call admission control. The real objective of this article is to introduce the general framework of resource reservation in multimedia LEO satellite networks which offers a unified approach to handle all the important aspects of resource reservation and radio-resource management functions required by E-commerce and mobile commerce applications.