Delay-optimal multi-satellite collaborative computation offloading supported by OISL in LEO satellite network

By deploying the ubiquitous and reliable coverage of low Earth orbit(LEO)satellite networks using optical inter satel-lite link(OISL),computation offloading services can be provided for any users without proximal servers,while the resource limita-tion of both computation and storage on satellites is the impor-tant factor affecting the maximum task completion time.In this paper,we study a delay-optimal multi-satellite collaborative computation offloading scheme that allows satellites to actively migrate tasks among themselves by employing the high-speed OISLs,such that tasks with long queuing delay will be served as quickly as possible by utilizing idle computation resources in the neighborhood.To satisfy the delay requirement of delay-sensi-tive task,we first propose a deadline-aware task scheduling scheme in which a priority model is constructed to sort the order of tasks being served based on its deadline,and then a delay-optimal collaborative offloading scheme is derived such that the tasks which cannot be completed locally can be migrated to other idle satellites.Simulation results demonstrate the effective-ness of our multi-satellite collaborative computation offloading strategy in reducing task complement time and improving resource utilization of the LEO satellite network.

MULTI-CLASS TRAFFIC QOS ROUTING FOR LEO SATELLITE NETWORKS

Due to the diversified demands of quality of service（QoS） in volume multimedia application, QoS routings for multiservice are becoming a research hotspot in low earth orbit（LEO） satellite networks. A novel QoS satellite routing algorithm for multi-class traffic is proposed. The goal of the routing algorithm is to provide the distinct QoS for different traffic classes and improve the utilization of network resources. Traffic is classified into three classes and allocated priorities based on their QoS requirements, respectively. A priority queuing mechanism guarantees the algorithm to work better for high-priority classes. In order to control the congestion, a blocking probability analysis model is built up based on the Markov process theory. Finally, according to the classification link-cost metrics, routings for different classes are calculated with the distinct QoS requirments and the status of network resource. Simulations verify the performance of the routing algorithm at different time and in different regions, and results demonstrate that the algorithm has great advantages in terms of the average delay and the blocking probability. Meanwhile, the robustness issue is also discussed.

基于多种群混沌遗传算法的GEO目标服务任务规划

面向地球同步轨道(geosynchronous Earth orbit,GEO)空间目标碎片清除、燃料加注等不同在轨服务需求,研究了“固定储油站+往返航天器”相结合的航天器任务规划问题。首先,建立了多任务混合的燃料最优双层任务规划模型,外层为目标服务序列规划,内层为轨道机动规划。随后,针对该连续-离散混合变量组合优化问题,提出了一种多种群混沌遗传算法(multi-group chaotic genetic algorithm,MGCGA),采用混合编码表征决策变量,引入立方混沌映射算子提高初始种群质量,多种群及精英保留策略使得算法在求解过程中能更为显著地逼近全局最优解。最后,参考实际GEO目标构建了典型算例,规划结果表明所提算法具有全局收敛性好、收敛速度快的优点。

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.

基于CEI测量的GEO目标快速轨道恢复

连线干涉测量(Connected Element Interferometry,CEI)是一种全天时全天候的被动测角技术,已用于空间目标的跟踪监视.地球静止轨道(Geostationary Earth Orbit,GEO)卫星需要频繁机动以保持轨位或完成其他任务,其机动后的快速轨道恢复能力对于监视预警极为重要.针对基于CEI的GEO短弧定轨和预报,分析了定轨算法的形亏和数亏,在附加先验轨道约束的短弧定轨基础上,提出了轨道半长轴初值的自适应优化方法.利用亚太七号卫星的CEI仿真和实测数据进行了短弧定轨和预报,实验结果表明,采用优化后的半长轴初值,30min短弧定轨和10min预报的卫星位置分量精度均优于4km,能够满足非合作GEO目标机动后快速轨道恢复的需求.

A DISTRIBUTED QOS ROUTING BASED ON ANT ALGORITHM FOR LEO SATELLITE NETWORK

Low Earth Orbit (LEO) satellites provide short round-trip delays and are becoming in- creasingly important. One of the challenges in LEO satellite networks is the development of specialized and efficient routing algorithms. To satisfy the QoS requirements of multimedia applications, satellite routing protocols should consider handovers and minimize their effect on the active connections. A distributed QoS routing scheme based on heuristic ant algorithm is proposed for satisfying delay bound and avoiding link congestion. Simulation results show that the call blocking probabilities of this al- gorithm are less than that of Shortest Path First (SPF) with different delay bound.

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 multi-path routing algorithm of LEO satellite networks based on an improved ant colony system

Geography rectangle is used to reduce signaling overhead of the LEO satellite networks.Moreover,a multi-path routing algorithm based on an improved ant colony system(MPRA-AC) is proposed.Matrix indicating the importance of the link between satellites is introduced into MPRA-AC in order to find the optimal path more quickly.Simulation results show that MPRA-AC reduces the number of iterations to achieve a satisfactory solution.At the same time,the packet delivery ratio of LEO satellite networks when running MPRA-AC and DSR-LSN(dynamic source routing algorithm for LEO satellite networks) is compared.The packet delivery ratio is about 7.9%lower when running DSR-LSN.Moreover,because of the mechanism of active load balancing of MPRA-AC,simulation results show that MPRA-AC outperforms DSR-LSN in link utilization when data packets are transmitted in the networks.

Long Range Wireless Sensor Network Employing Cooperative Relaying-UAVs via LEO Satellite

In this study we proposed unique system model for wireless sensor network data telemetry in a wide area and long range. This system is made up with a wide area wireless sensor nodes, UAVs （unmanned aerial vehicles） and LEO （low earth orbit） communication satellite. Wirelessly data signals relaying from sensor nodes on ground to flying UAVs and relaying them to LEO satellite were studied. Three cases of studies were conducted： system without UAV-relay case, one UAV-relay case and two UAV-relay cases. In all the cases, the outage probabilities of data signal channel in Rayleigh fading environment were analyzed and overall system performance was quantified while considering an adaptive decode-and-forward relaying protocol scheme for UAVs. Then, the overall system channel signal-to-noise ratio required in order to achieve a predefined outage probability was analyzed at different channel data rate.

PACKET ROUTING ALGORITHM FOR LEO SATELLITE CONSTELLATION NETWORK

A novel distributed packet routing algorithm for Low Earth Orbit (LEO) satellite networks based on spiderweb topology is presented. The algorithm gives the shortest path with very low computational complexity and without on-board routing tables, which is suitable and practical for on-board processing. Simulation results show its practicability and feasibility.

Multicast Routing in Satellite Network

There are some problems in the dual-layer satellite MPLs metworks to be composed of LEO and MEO. In order to solve the problems, this paper presents a plan by means of unicast LSP to implement multicast in the dual-layer satellite MPLs networks. It has advantages of saving space and reducing extra charge.

A Handover Strategy in the LEO Satellite-Based Constellation Networks with ISLs

A new handover strategy named minimal-hops handover(MHH) strategy for the lowearth orbit(LEO) satellite constellations networks equipped with inter-satellite links(ISLs) is proposed.MHH strategy,which is based on the hops of the end-to-end connection paths and makes good use of theregularity of the constellation network topology,can appropriately combine the handover procedure withrouting and efficiently solve the inter-satellite handover issue.Moreover,MHH strategy can providequality of services(QoS) guarantees to some extent.The system performances of the MHH strategy,suchas time propagation delay and handover frequency,are evaluated and compared with that of otherprevious strategies.The simulation results show that MHH strategy performs better than other previoushandover strategies.

A Novel Probability-Based Handoff Strategy for Multimedia LEO Satellite Communications

A novel bandwidth allocation strategy and a connection admission control technique arc proposed to improve the utilization of network resource and provide the network with better quality of service （QoS） guarantees in multimedia low earth orbit （LEO） satellite networks. Our connection admission control scheme, we call the probability based dynamic channel reservation strategy （PDR）, dynamically reserves bandwidth for real-time services based on their handoff probability. And the reserved bandwidth for real-time handoff connection can also be used by new connections under a certain probability determined by the mobility characteristics and bandwidth usage of the system. Simulation results show that our scheme not only lowers the call dropping probability （CDP） for Class I real-time service but also maintains the call blocking probability （CBP） to certain degree. Consequently, the scheme can offer very low CDP for rcal-time connections while keeping resource utilization high.

GEO卫星对BDS中长基线精密定位的影响分析

针对北斗卫星导航系统(BDS)中特有的地球静止轨道(GEO)卫星存在轨道精度低和空间结构变化缓慢的问题,分析GEO卫星对BDS中长基线精密定位的影响:基于BDS中长基线精密定位算法,采用连续运行参考站系统(CORS)观测数据,对倾斜地球同步轨道(IGSO)+中圆地球轨道(MEO)+GEO组合和IGSO+MEO组合分别进行基线解算,探讨GEO卫星对BDS中长基线精密定位的卫星几何构型、宽巷模糊度固定效果、窄巷模糊度首次固定时间及定位精度的影响。实验结果表明,部分GEO卫星宽巷模糊度的小数部分存在系统性偏差,其宽巷模糊度需要5 h左右才能得到90%的固定率;加入GEO卫星后,窄巷模糊度首次固定时间从25缩短到16min,缩短了36%;BDS全星座组合的2h静态解算精度水平方向为2.1 cm,高程方向为3.5 cm;GEO卫星有利于提升BDS中长基线定位性能。

手机直连低轨卫星的应用场景及业务需求分析

手机直连卫星是低轨(low earth orbiting,LEO)星座系统的重要应用方向之一。概述了手机直连卫星的主要技术路线、应用场景及业务类型;分析了低轨星座的建设成本、承载能力、运营收入;提出了我国手机直连卫星通信的主要应用应以广覆盖、海量连接为主,而卫星大流量宽带上网应用存在商业闭环的风险;最后探讨了结合应用需求的技术发展建议。

北斗GEO卫星在磁暴电离层扰动分析中的应用

为了研究磁暴发生期间,电离层受其影响产生的异常扰动现象的特性,本文利用北斗系统中地球静止轨道(GEO)的特性,选取沿等纬度、经度和地磁纬度规则分布的地面站观测数据,针对2019年5月11日与5月14日发生的磁暴事件,对磁暴期间电离层扰动进行了分析,实验表明5月14日磁暴事件造成的电离层扰动在各点处有着更相似的时频特性;同时计算得到了磁暴沿纬线的平均传播速度为657.9 m/s,沿经线的平均传播速度为480.1 m/s,沿地磁纬线的平均传播速度为1 591.2 m/s。

星载6G核心网架构与网元功能设计及验证

为全面提升卫星的在轨服务能力,将6G核心网与卫星融合。针对6G核心网在低轨卫星部署的迫切需求,设计星载6G核心网体系架构,包括分布式架构、离线自治、网元智能化等功能。对星载6G核心网主要网元进行了优化设计,包括接入与移动性管理、会话管理、分布式服务注册与发现等。通过在轨部署和仿真试验,验证了所提星载6G核心网体系架构的有效性。仿真结果表明,集中式星载5G核心网网元之间的平均通信时延为109.3 ms,而分布式星载6G核心网的平均通信时延为60.3 ms,相较而言降低了44.8%;此外,5G集中式服务注册和服务发现的平均时延分别为40.53 ms和40.04 ms,而6G分布式服务注册和服务发现的平均时延分别为35.18 ms和34.91 ms,分别降低13.2%和12.8%。

低轨卫星网络服务质量保障路由方法综述

随着无线电和卫星小型化技术的进一步成熟,大规模低轨卫星网络得到了长足发展,面对网络传输业务的时延、带宽、丢包率等服务质量的差异化需求,如何在低轨卫星网络中实现服务质量保障路由,成为了研究关注的关键问题。通过介绍低轨卫星网络服务质量保障路由的场景与需求,总结并分析了当前的研究成果。首先,针对传统网络中的服务质量保障路由算法,总结了三类经典的路由计算方法。然后,对于软件定义网络和确定性网络中的服务质量保障路由算法,结合各自的网络特点,分析总结了各自场景下的路由算法。

手机直连低轨卫星通信:架构、关键技术和未来展望

借助低轨卫星星座全时全域覆盖优势,手机直连卫星通信预期成为6G重要特征之一。首先介绍了手机直连卫星的测试验证、标准化与商业项目发展现状。其次,介绍了基于透明转发、部分可再生处理、完全可再生处理、集成接入和回传的四种手机直连低轨卫星网络架构及组网方式。通过分析手机直连低轨卫星网络场景下高移动性与大传输时延等带来的接入与传输问题,提出对地面移动通信体制进行适应性改进的关键技术方案。最后,探讨了未来手机直连低轨卫星发展发向和潜在思路。通过上述阐述与分析,提供未来发展手机直连低轨卫星通信的可行路径。

面向6G通信的多层低轨卫星网络路由算法

在面向6G的移动通信网络中,低轨卫星网络(LEO,Low Earth Orbit)运行高度低、时延小,可大范围部署实现全球广域低时延通信。当前低轨卫星星座正朝着多层轨道面发展,多层轨道的跨层链路增加了数据传输路径,但跨层轨间链路的频繁通断,增大了多层LEO网络层间路由选择的难度。为此提出了一种面向6G移动通信的多层LEO卫星网络路由算法。首先建立跨层链路,面向端到端传输时延和可靠性需求,分析影响跨层轨间链路频繁通断的因素,基于LEO卫星网络虚拟位置思想,选择卫星节点对建立可靠跨层链路;然后实现路由选择,基于所建立的跨层星间链路,采用时空演化图模型刻画动态网络拓扑,设计最短路径算法计算最佳传输路径。最后,构建三层卫星网络场景对所提算法进行仿真验证。结果表明,相对于现有方法,所提算法在端到端时延和可靠性均有明显提升。