低轨卫星星座快速响应链路损毁路由算法

设计高效弹性的卫星路由算法是未来低轨(Low Earth Orbit, LEO)卫星通信技术的一个重要发展方向。为解决低轨卫星星座网络中星间链路发生故障后存在的传输中断和数据安全问题,提出了一种低轨卫星星座快速响应链路损毁路由算法(Quick-response Link Destruction Routing Algorithm for LEO Satellite Constellation, QRLDRA)。QRLDRA以星座可预测拓扑作为星间路由计算基础,增加星地回传路由设计,快速将星间链路异常回传至地面计算中心处理;引入多优先级动态队列,根据节点链路状态调整星间链路不同数据传输的优先级;综合路由计算、路由上注、链路检测等功能,完成对拓扑变化的及时响应。通过仿真实验与传统算法的比较发现,所提算法有效提高了数据端到端传输的成功率,为用户业务服务质量(Quality of Service, QoS)提供了可靠保障。     

面向低轨卫星的星地信道特性研究与仿真

随着5G的应用与6G的研究,构建空天地一体化网络已经成为未来通信系统的发展方向。低轨(Low Earth Orbit,LEO)卫星网络可以提供大容量、低时延、广覆盖的通信能力,是未来天基网络的重要组成部分。然而星地信道传播距离长,电磁环境复杂,其传播特性与地面蜂窝网络有着很大不同。介绍了目前低轨卫星关于星地链路信道的标准化进展,分析了影响星地链路信道特性的因素及计算方法。在仿真平台上利用Starlink卫星数据对星地链路传播中的各种损耗进行了仿真,为低轨卫星星地链路设计提供了参考。     

TCP和XTP协议传输性能仿真与分析

针对卫星链路的特点,利用仿真技术,采用NS2仿真软件建立仿真模型,设计仿真场景,给出了软件实现方法,分别在固定误码率和信道带宽、时延变化条件下,固定时延和信遣带宽、误码率变化条件下,固定时延和误码率、信道带宽变化条件下,对TCP协议和XTP协议在卫星链路的传输性能进行了仿真和对比分析,最后得出结论,XTP协议的通信机制比TCP协议更适合于卫星链路数据传输,为基于XTP协议的卫星协议网关设计提供仿真依据.     

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。     

低轨道量子卫星通信时分交换方案及性能分析

为解决低轨道量子卫星覆盖范围下,多个量子用户的接入与信息传输问题,提出了一种多波束时分量子交换方案,并详细给出了时分量子卫星交换机的工作原理。在不同的通信时隙上,为用户分别建立量子纠缠信道并进行量子信息传送。为克服星地链路及星际链路的时延问题,提出了基于量子信道字的交换和传输方法,从而降低单时隙量子比特传输的平均时延。系统性能分析与仿真结果表明,时隙个数、量子信道字长是影响系统的用户数量、吞吐量、呼损指标的关键因素。在一定的信道条件下,通过对这些系统参数进行合理设计,能够满足特定量子卫星系统的服务需求。     

无人机集群联合拓扑控制的智能路由规划方法

针对现有无人机集群路由协议拓扑适变能力弱,易产生包重传、能量空洞和高时延,严重恶化了数据路由性能的问题,针对无人机集群中集群拓扑与路由的耦合特性,提出了一种联合拓扑控制的智能路由规划（IRPJTC）方法。该方法由基于虚拟力的自适应拓扑控制（VFATC）和基于近端策略优化的地理路由规划（PPO-GRP）组成。其中,VFATC使各无人机根据邻居运动状态信息自适应调整与邻居的距离,保证集群中链路的稳定连接;进一步,PPO-GRP引入VFATC中的链路稳定性指标,并结合端到端时延与能耗指标,设计多目标奖励函数,采用深度强化学习中的近端策略优化算法训练路由策略。仿真实验结果表明,IRPJTC相比于现有路由方法,能在保证分组传输成功率的同时,使端到端时延降低12.11%,无人机集群能耗降低4.56%,且具备更强的能耗均衡能力。     

国外激光链路中继卫星系统的发展与启示

激光链路中继卫星系统是指以激光波束为媒介,为低轨信息获取类卫星提供高速数据传输服务的卫星系统。国外已开展了多次星间、星地激光通信实验,已由强度调制/直接探测通信体制过渡到相位调制/相干解调通信体制,通信速率可达5.6 Gbps。卫星激光通信正向更高通信速率、组网应用、终端小型化、轻量化方向发展。在系统分析欧洲、日本、美国等国家典型星间、星地激光通信实验和中继卫星发展计划的基础上,讨论了激光链路中继卫星系统的发展趋势,总结得到对发展我国激光链路中继卫星系统的若干启示。     

星间光通信链路稳定保持时间估算

针对目前星间光通信链路信号传输有效时间较短的问题,提出了双向激光链路跟踪稳定性的概念,分析了多种因素对跟踪稳定性的影响。综合接收信噪比、相对运动角速度和链路性能要求等因素,建立了链路稳定时间的期望公式。利用Simulink建立了双向激光通信链路跟踪仿真模型,通过仿真验证了理论公式的正确性。为实现星间光通信链路保持长时间稳定,提出在不同星间相对运动速度下采用不同控制参数的方法,实现了星间光通信终端控制策略优化,对今后卫星光通信航天工程化应用具有一定的意义。     

有线无线融合的卫星时间敏感网络流调度研究

随着空间通信任务日趋复杂化,尤其是对时间敏感的需求不断提升,一方面要求星内系统的高带宽、可靠性和实时性;另一方面星间无线链路也应具备低时延和高可靠性.但由于卫星内部有线链路与星间无线链路差异大,业务数据经过有线和无线链路联合传输时,容易引发节点拥塞,而无法保障时敏业务的时延有界需求.为了提升数据在空间网络传输的实时性,...     

卫星链路中TCP传输性能改进与仿真

卫星信道与地面有线信道具有不同的特点,当TCP协议直接应用于卫星链路上时,其吞吐量等性能会受到影响。针对卫星链路的特点,分析了现有的卫星链路进行TCP传输的几种解决方案,使用NS 2仿真软件,建立了仿真模型,并在给定的仿真环境下得出了一些卫星链路下TCP传输性能和卫星spoofing技术的仿真结论。卫星链路具有时延大、误码率高等特点,仿真结果说明卫星spoofing技术和PS技术相结合的方案对卫星链路TCP传输性能改善是十分有益的。     

Multiple gateway placement in large‐scale constellation networks with inter‐satellite links

Multiple gateways are required in large satellite constellation networks (LSCNs) with inter‐satellite links (ISLs), and their placement may greatly affect the system performance. Gateway placement can be optimized to achieve better network performance under the non‐uniform ground demand distribution. This paper formulates a gateway placement optimization model for LSCN with ISLs, aiming at achieving an optimal overall performance including delay, traffic peak, and load balance. The constraints of potential gateway location, gateway‐satellite connectivity, and max hop‐count are considered. A genetic algorithm (GA)‐based method is proposed to solve the integer optimization problem with the help of quasi‐evenly distributed reference layout. A Starlink‐like constellation with ISLs is adopted in the simulation. The simulation results show that the optimized layout has better performance than the reference layout. Additionally, the locations with high user demand or at the middle of ocean are preferred by gateways. The network performance is jointly influenced by gateway placement, demand distribution, constellation configuration, node, and link capacities. The abnormally high ISL hop‐count is found in the south Indian Ocean, which is caused by constellation and ISL configuration.     

Satellite constellation of MEO and IGSO network routing with dynamic grouping

Because inter‐satellite links (ISLs) among the distributed satellite nodes can be used to support autonomous control in satellite system operation to reduce dependency on the ground stations, it becomes a popular communication paradigm for the future satellite systems. However, this introduces great technical challenges, particularly for routing protocol to support such space communication system. Facing the challenges, we present out study of routing technology in this paper tailored for satellite network of MEO (Table 1) and IGSO with ISLs in addition to satellite–ground links. The study aims to explore the routing strategies and algorithms of satellite network based on the evolution law of network topology to provide reference design for data exchange in autonomous satellite system. A comprehensive investigation, ranging from the analysis of relevant factors affecting data exchange in satellite networks to the primary application and resource constraints in designing satellite routing strategy, has been conducted. Our main contribution is to propose an on‐demand computing and caching centralized routing strategy and algorithm on the satellite network. The routing strategy and algorithm is designed for satellite network topology dynamic grouping. The route calculation for user data transmission is divided into three phases: direction estimation, direction enhancement, and congestion avoidance. The strategy and algorithm provide significant advantages of high efficiency, low complexity, and flexible configuration, by which the satellite networks can provide the features of flexible configure, efficient transferring, easy management, structural survivability, and great potential in scalability. Copyright © 2013 John Wiley & Sons, Ltd.     

双层卫星网络QoS路由算法研究

具有星际链路的双层通信星座网络可为全球提供宽带实时多媒体通信服务,路由算法设计是其中关键技术之一。本文详细介绍了由低轨卫星与中轨卫星构成的空间信息通信网双层星座系统体系结构,提出了一种新的具有QoS保证的双层卫星网络路由算法。仿真结果表明提出的路由算法可以满足系统的QoS业务要求的延迟、丢包率与抖动等指标。     

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 dynamic even distribution resource scheduling mechanism combined with network coding for inter-LEO satellite networks

Resource scheduling mechanism of LEO satellite networks is the key to determining communication efficiency. Facing the LEO satellite networks with the dynamic topology changes, varying service requirements, and intermittent inter-satellite links (ISLs), the state-of-the-art cannot achieve high resource efficiency under both heavy and burst traffic loads, and the applicability of parameters design is insufficient under intermittent ISLs. Considering this, we propose a dynamic even distribution mechanism combined with network coding DENC. This novel mechanism obtains the service requirements and allocates resources dynamically through the even distribution algorithm to balance network maintenance overhead and resource waste and improves the success probability of transmission based on network coding to balance retransmission and redundancy. In this paper, we establish performance analysis models to optimize the parameters such as maintenance frequency and coding coefficient. Besides, we construct a system-level simulation platform. Mathematical and simulation results indicate that the resource efficiency of EMNC can be improved by more than 48% compared with SAHN-MAC, ICSMA, CSMA-TDMA, and HTM when all nodes have service needs, and the ISL outage rate is 20%. As the outage probability of ISL increases and the proportion of nodes with service requirements decreases, the performance advantage of EMNC becomes more apparent.     

一种低轨卫星通信的定时提前计算方法

低轨(LEO)卫星网络作为地面网络的重要补充,是未来天地一体化网络的重要组成部分。由于LEO卫星的高移动速度以及星地通信的大传播距离造成了高传播时延,因此需要新的针对LEO卫星星地通信背景的上行链路的定时提前量(TA)的计算策略。本文基于LEO卫星的星地通信场景,介绍了TA及其在协议中的规定,并针对LEO卫星的特点,提出一种LEO卫星通信的定时提前计算方法。通过仿真分析验证了所提方案的有效性,为LEO卫星星地通信系统的设计提供了参考。     

SS/TDMA scheduling for satellite clusters

The authors present a novel approach to the optimal time-slot assignment problem for a general satellite-switched time-division multiple-access (SS/TDMA) satellite cluster with intersatellite links (ISLs) interconnection. The proposed allocation algorithm accounts for the following: systems with any number of satellites; each satellite covers an arbitrary number of zones; no onboard buffering at the satellites; and ISLs with arbitrary capacities. They present an analogy between the satellite cluster scheduling problem and the modified openshop scheduling problem. Using this analogy the authors introduce a heuristic algorithm and an optimal branch-and-bound algorithm. They investigate the performance of the proposed heuristic both by theoretical bounds and by comparing the simulation results produced by the heuristic with the optimal results. In all cases the heuristic algorithm results are within 10% of the optimum     

Priority‐based adaptive routing in NGEO satellite networks

In a non‐geostationary satellite constellation with inter satellite links (ISLs), there could be many shortest paths between two satellites in terms of hop count. An efficient routing algorithm should effectively use these paths in order to distribute traffic to ISLs in a balanced way and to improve the performance of the system. This paper presents and evaluates a novel priority‐based adaptive shortest path routing (PAR) scheme in order to achieve this goal. PAR sets the path towards the destination in a distributed manner, using a priority mechanism depending on the past utilization and buffering information of the ISLs. Moreover, to avoid unnecessary splitting of a flow and to achieve better utilization of ISLs, enhanced PAR (ePAR) scheme is proposed. This paper evaluates performance of the proposed techniques by employing an extensive set of simulations. Furthermore, since there are a number of ePAR parameters that should be adjusted depending on the network and traffic characteristics, a detailed analysis of ePAR scheme is provided to form a framework for setting the parameters. This paper also includes a method for adaptation of the proposed algorithms to minimum‐delay path routing. Copyright © 2006 John Wiley & Sons, Ltd.     

A Proposal of Optimal Routing Techniques for non-GEO Satellite Systems

The continuously increasing number of mobile subscribers has generated a strong interest in expanding terrestrial wireless networks and supporting real-time communications regardless of the user location. These targets require a cautious management of available resources since the development of global systems implies a quite high cost. Routing is an important network function and must be very carefully considered. This paper proposes the implementation of optimal routing techniques for connection oriented mode and variable network topology, as non-GEO satellite systems require. In particular a well known optimal routing technique, named Flow Deviation, is modified by adding new procedures that render its applicability to a handover environment feasible and effective. Its performance is investigated through extended real time simulations in terms of delay, throughput, link utilization and also in terms of parameters related to the topology variations and the interruptible operation of ISLs. The pros and cons of the proposed scheme are discussed with respect to the well known shortest path scheme and helpful conclusions for the design of satellite constellations are obtained.     

面向卫星网络的流量工程路由算法

针对卫星网络链路长时延、拓扑时变等特征,将链路传输时延引入并基于MPLS网络中源-目的节点对已知这一先验知识,提出了一种面向卫星网络的MPLS流量工程路由算法。该算法基于卫星网络时变拓扑模型的卫星拓扑快照,定义链路初始权重为链路剩余带宽、传输时延的综合函数,在为当前节点对建路时考虑其余节点对将来建路的可能需求计算链路的关键度,在此基础上通过链路权重的动态调整及延期选用实现流量工程,从而优化卫星网络的链路利用。实验表明,此算法在请求拒绝数、吞吐量、平均跳数及平均时延等方面性能都有较理想的提升。