TCP-ATCA： Improved Transmission Control Algorithm in Satellite Network

An adaptive transmission control algorithm based on TCP （TCP-ATCA） is proposed to reduce the effects of long propagation delay and high link error rate of the satellite network on the performances. The flow control and the error recovery are differentiated by combined dynamic random early detection-explicit congestion notification （DRED-ECN） algorithm, and, moreover, the pertaining congestion control methods are used in TCP-ATCA to improve the throughput. By introducing the entire recovery algorithm, the unnecessary congestion window decrease is reduced, and the throughput and fairness are improved. Simulation results show that, compared with TCP-Reno, TCP-ATCA provides a better throughput performance when the link capacity is higher （ ≥600 packet/s）, and roughly the same when it is lower. At the same time, TCP-ATCA also increases fairness and reduces transmission delay.     

A high-capacity aeronautical mobile satellite system

A conceptual system design is described for a satellite-based aeronautical safety communications system capable of serving both general aviation (GA) aircraft and commercial aviation (CA) aircraft in the contiguous US (CONUS) in the mid-1990s. It is shown how the large system capacity that is required can be obtained using a 15-m deployable antenna onboard a high-power commercial communications satellite expected to be available in the mid-1990s     

TP-Satellite: A New Transport Protocol for Satellite IP Networks

As a result of the exponential growth of the worldwide Internet, satellite systems are used to support broadband Internet access. Existing TCP protocols perform very well for Internet access on wired networks. However, in the case of satellite channels, due to the effects of high bandwidth asymmetry, long propagation delay, high sporadic bit error rate (BER) and burst errors, TCP performance degrades significantly. In this paper, a new end-to-end transport protocol, TP-Satellite, is proposed for satellite IP networks. TP-Satellite replaces the traditional slow start algorithm with a novel super start algorithm. In order to distinguish congestion events from link errors, a new scheme is introduced, which is based on alternate transmission of different class priority packets. Bandwidth asymmetry problems are addressed by the adoption of a modified negative acknowledgement (M-NACK) strategy, which periodically sends M-NACK packets. Simulation results show that TP-Satellite enhances the throughput performance on the forward path, reduces the bandwidth used in the reverse path, and offers a fair share of network resources.     

Core-based Shared Tree Multicast Routing Algorithms for LEO Satellite IP Networks

A new core-based shared tree algorithm, viz core-cluster combination-based shared tree （CCST） algorithm and the weighted version （i.e. w-CCST algorithm） are proposed in order to resolve the channel resources waste problem in typical source-based multicast routing algorithms in low earth orbit （LEO） satellite IP networks. The CCST algorithm includes the dynamic approximate center （DAC） core selection method and the core-cluster combination multicast route construction scheme. Without complicated onboard computation, the DAC method is uniquely developed for highly dynamic networks of periodical and regular movement. The core-cluster combination method takes core node as the initial core-cluster, and expands it stepwise to construct an entire multicast tree at the lowest tree cost by a shortest path scheme between the newly-generated core-cluster and surplus group members, which results in great bandwidth utilization. Moreover, the w-CCST algorithm is able to strike a balance between performance of tree cost and that of end-to-end propagation delay by adjusting the weighted factor to meet strict end-to-end delay requirements of some real-time multicast services at the expense of a slight increase in tree cost. Finally, performance comparison is conducted between the proposed algorithms and typical algorithms in LEO satellite IP networks. Simulation results show that the CCST algorithm significantly decreases the average tree cost against to the others, and also the average end-to-end propagation delay ofw-CCST algorithm is lower than that of the CCST algorithm.     

AeroMTP: A fountain code-based multipath transport protocol for airborne networks

Airborne networks(ANs) are special types of ad hoc networks that can be used to enhance situational awareness, flight coordination and flight efficiency in civil and military aviation.Compared to ground networks, ANs have some unique attributes including high node mobility, frequent topology changes, mechanical and aerodynamic constrains, strict safety requirements and harsh communication environment.Thus, the performance of conventional transmission control protocol(TCP) will be dramatically degraded in ANs.Aircraft commonly have two or more heterogeneous network interfaces which offer an opportunity to form multiple communication paths between any two nodes in ANs.To satisfy the communication requirements in ANs, we propose aeronautical multipath transport protocol(Aero MTP) for ANs, which effectively utilizes the available bandwidth and diversity provided by heterogeneous wireless paths.Aero MTP uses fountain codes as forward error correction(FEC) codes to recover from data loss and deploys a TCP-friendly rate-based congestion control mechanism for each path.Moreover, we design a packet allocation algorithm based on optimization to minimize the delivery time of blocks.The performance of Aero MTP is evaluated through OMNe T++ simulations under a variety of test scenarios.Simulations demonstrate that Aero MTP is of great potential to be applied to ANs.     

Experiments on aeronautical satellite communications using ETS-Vsatellite

The world's first aeronautical satellite communication experiments, conducted at L-band frequencies using a commercial aircraft, are described. An airborne antenna with electronically steerable beam and communication equipment was installed in a B-747F freighter flying over transoceanic flight routes. The satellite used in these experiments is the Engineering Test Satellite-Five (ETS-V). During the test period, various experiments, such as antenna pattern measurements, transmission performances, and voice quality evaluation were conducted. As the airborne antenna is the key component for the aeronautical satellite communication system, emphasis has been placed on antenna characteristics. Its performance is found to be closely related to the fading characteristics in low-elevation areas and to transmission error performance     

适于低轨卫星IP网络的单核共享树组播算法(英文)

为了解决低轨卫星IP网络中现有典型源组播算法的信道资源浪费问题,本文提出了一套单核共享树组播算法,即核心群合并共享树(CCST)和加权核心群合并共享树(w-CCST)算法。CCST 算法包括动态近似中心(DAC)选核方法和核心群合并组播路径构建方法。DAC方法专为周期、规律运动的低轨卫星网络提出,不需要复杂的星上计算。在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的带宽利用率和组播传输效率。w-CCST 算法中所提出的加权因子可以调整树代价和端到端传播时延之间的折衷程度,因此,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以支持某些端到端时延要求苛刻的实时组播业务。最后,与低轨卫星 IP 网络中典型算法进行了性能比较,仿真结果说明,CCST 算法的平均树代价比其它算法显著降低,w-CCST 算法的平均端到端传播时延小于 CCST 算法。     

High gain airborne antenna for satellite communications

The performance of an airborne phased-array antenna, which was developed and evaluated onboard a commercial aircraft using the Engineering Test Satellite V (ETS-V), is reported. The system requirements and the antenna configuration that satisfies them are described. The radiation pattern, gain and axial ratio, noise temperature and ratio of gain to noise temperature, and environmental characteristics are presented. The results obtained by the flight experiments demonstrate that the performance of the antenna is the same as that on the ground, so that the antenna is suitable for installation in an aircraft for satellite communications     

Wavelength dimensioning for wavelength-routed WDM satellite network

Internet and broadband applications driven by data traffic demand have become key dri-vers for satellite constellations. The key technology to satisfy the high capacity requirements between satellites is optical satellite networks by means of wavelength division multiplexing inter-satellite links (ISLs) with wavelength routing (WDM-OSN). Due to the limited optical amplifier bandwidth onboard the satellite, it is important to minimize the wavelength requirements to provi-sion requests. However, ISLs should be dynamically established and deleted for each satellite according to its visible satellites. Furthermore, different link assignments will result in different topologies, hence yielding different routings and wavelength assignments. Thus, a perfect match model-based link assignment scheme (LAS-PMM) is proposed to design an appropriate topology such that shorter path could be routed and less wavelengths could be assigned for each ISL along the path. Finally, simulation results show that in comparison to the regular Manhattan street net-work (MSN) topology, wavelength requirements and average end-to-end delay based on the topol-ogy generated by LAS-PMM could be reduced by 24.8%and 12.4%, respectively.     

国外航空疲劳研究现状及展望

航空疲劳问题是影响在研/在役飞机性能的关键因素之一。以航空疲劳事故为线索,本文论述了航空结构强度设计理念的变革历程以及相应各时期的航空疲劳发展现状,并围绕21世纪以来国际航空疲劳界的关注热点,从结构长寿命设计、疲劳分析方法及工具、全尺寸结构疲劳试验技术、结构健康监测技术、老龄飞机延寿技术等五个方面阐述了航空疲劳工程领域的重大研究进展及方向。考虑目前航空疲劳工程中的问题及未来航空器的发展方向,从航空疲劳评定基础问题、长寿命设计应用问题、试验评估及数字化新技术等方面指出航空疲劳研究所面临的挑战,以满足现代飞机长寿命、轻质和高可靠性设计要求,为航空疲劳未来发展提供技术参考。     

Ad-hoc网络中数据包大小对通信性能的影响

本绍Ad-hoc网络的特点以及常用的TCP协议版本(Tahoe,Reno和Vegas),分析数据包大小对移动无线网络通信性能的影响,利用NS2网络模拟软件对此做出检验,发现数据包有限增大时通信性能大幅提高,在此基础上提出一种提高网络吞吐量的有效方法,该方法适用于通信链路频繁中断的无线网络环境。     

自动相关监视系统信息传输性能分析方法及测试平台构建

本研究目的在于提出一种在民用飞机机载自动相关监视系统(Automatic Dependent Surveillance,简称ADS)系统设计和试验过程中实时/非实时检测该系统端到端信息传输性能的分析方法,并进行相应的地面测试平台搭建设计。对口于飞机的机载系统,ADS监视系统信息传输性能分析平台能够快速准确定位ADS系统的试验故障,实现有效的排故和分析,直观地评估自相关监视系统的工作状态。这项研究的结果有助于推动机载合同式自动相关监视系统(Automatic Dependent Surveillance-Contract,简称ADS-C)和广播式自动相关监视系统(Automatic Dependent Surveillance-Broadcast,简称ADS-B)机上地面功能试验、民机机上地面试验、民机飞行试验等各项工作的开展。该平台在飞机交付以后,也有利于维护工作与客户支持工作的进行。     

一种新的星间链路切换保护算法

 星间链路切换将严重影响卫星网络的通信性能，需要对切换链路加以保护，这方面的研究目前还很欠缺。为此,给出一种新颖的星间链路切换保护(ISLHP)算法，该算法可同时生成业务路径和备份路径，且具有最小的综合费用（包括备份费用和业务费用）。算法采用本地链路保护，为星间链路切换提供快速恢复，并利用星间链路切换的可预测性和备份资源的可共用性，通过降低需要保护的链路数，减少闲置的备份资源，来提高网络资源的利用率。仿真结果表明:该算法具有切换恢复时间短，网络资源利用率高等优点。     

面向高轨空间的北斗导航性能增强星座选型研究

由于高轨空间超出北斗卫星导航系统的正常服务区域,导航信号微弱、可见性差,难以实现高轨飞行器全程稳定可靠的导航定位服务。提出了以空间卫星为时空基准传递平台,向高轨空间区域发射导航信号,从而提高高轨飞行器导航性能的方法,并展开面向高轨空间的北斗导航性能增强星座选型研究。基于卫星可见性、精度衰减因子（DOP）、信号接收门限和所需增强卫星数目等评估指标,仿真分析了基于LEO星座、MEO星座和HEO星座的北斗导航增强性能。     

中国拟建航空卫星移动通信地面地球站（GES）的技术方案

中国民航正在计划实施航空卫星移动业务通信。ＡＭＳＳ系统有三个主要组成部分：空间段，地面地球站和机载地球站。中国国际航空公司已居其两架波音７４７型飞机上装有ＡＥＳ。不久将有更多飞国际航线的飞机安装ＡＥＳ。     

40G以太网在航电系统中的应用初探

随着飞机整体性能的提升，航电系统的发展日新月异，对总线网络提出了越来越高的要求。基于远端内存直接访问技术传输机制的以太网以其高带宽、低延时以及生态开放性的特点，在航电系统总线中逐渐得到推广。本文介绍了航电总线网络的发展，对典型的航电总线进行了对比分析，开展了10G/40GE交换工程样机的研制和测试工作，为下一代航电系统总线网络的选型提供了参考。     

Analytic study of Doppler-based handover management in LEO satellite systems

The problem of dynamic handover management in low Earth orbit (LEO) satellite systems is addressed. Particularly, an analytical study of a newly proposed method for handover management, called dynamic Doppler-based handover prioritization scheme (DDBHP), is presented. DDBHP utilizes Doppler shift monitoring of each communicating user terminal onboard the satellite and geometric characteristics to accurately predict the handover load. As a result, handover requests are more effectively managed, resulting in an improved performance in terms of blocking and forced termination probabilities. Moreover, by supporting guaranteed handovers, DDBHP can be used to provide QoS to users of future broadband satellite networks. An extensive mathematical model that justifies Doppler shift monitoring is presented along with a detailed queueing model used not only to evaluate DDBHP performance but also to provide a methodology for associating DDBHP operational parameters with desired performance. Comparison of analytical and simulation results validate the proposed model.     

A TCP Driven CAC Scheme: Efficient Resource Utilization in a Leaky HAP-Satellite Integrated Scenario

An integrated high altitude platform (HAP)-satellite communication system appears to be very suitable for a large set of scenarios including emergency situations, exceptional events, etc. In fact, the satellite capability to provide a broadband and ubiquitous access can be enhanced by the deployment of HAP that allows the use of low-power consuming, cost-efficient, and portable terminals. To obtain an optimum utilization of radio resource, without renouncing to QoS satisfaction, a suitable call admission control scheme must be implemented. Nevertheless, transmission control protocol (TCP) behavior, mainly affected by the high latency and shadowing events, can impact call admission control (CAC) performance. Therefore, it would be desirable that the CAC scheme takes into account also the TCP congestion window real evolution. We present an innovative CAC scheme that uses TCP statistics as one of its inputs and is able to manage different classes of users. Results show that CAC performance is significantly improved by introducing TCP statistics about network congestion as an input parameter.     

TCP／IP下的Socket及Winsock通信机制

Socket接口是TCP/IP网络的API(应用程序接口),WindowsSockets(Winsock)是一个基于Socket模型的API,本文通过论述Unix及Windows环境下的实现计算机数据传输服务的机制,提供了一种网络环境下实现计算机通信的手段,并给出了编制通信应用接口程序的具体实现方法。