面向航天器有线无线混合场景的流调度机制研究

随着各国深空探测任务的开展,空间站的建设需求日益增加,而航天器内部大量的数据通信总线在一定程度上影响了航天器的有效载荷。因此,该文将无线通信方式引入到航天器通信系统设计中,但传统无线通信难以保障时敏数据的端到端传输时延,该文提出了一种有线无线融合的时间敏感网络(TSN)流调度方案。设计了一种上下行时隙分离的TDMA时隙分配机制,通过对航天器内部业务类型与有线无线融合传输链路的时延关系进行建模分析,构建了以时敏业务平均端到端时延最小的目标函数,采用粒子群算法对时隙分配方案进行快速求解。最后在Pycharm平台对所提算法进行对比测试,并在EXata网络仿真平台搭建航天传感器采集网络进行验证。实验结果表明,该文所提出的有线无线融合流调度方案能为时敏业务提供稳定、有界的时延保障。     

802.11网络中Eifel算法性能的探讨

相对于有线网络来说,无线局域网的无线链路具有带宽低、误码率高、易受影响和电磁波能量容易被吸收等特点。因此,用户数据分组在无线链路上的传输具有传输时延高、传输时延变化大、链路突发中断的特点。这可能会引起错误的超时,触发TCP重传。分析了传统TCP触发无用重发的原因,介绍了Eifel算法消除错误重传的原理,并在NS-2环境下对Eifel和其他版本的TCP进行了仿真和比较。     

标准化星间激光通信链路接口模型设计方法

在星间数据交换过程中,同时传输不同类型的数据会对系统性能产生较大影响。为统一传输制式,提高数据传输效率,提出星间激光链路接口模型。在星间激光链路接口模型中,针对节点卫星数据处理转发效率低的问题,设计数据帧调整单元整合不同信源的数据;针对空间信道随机错误对系统性能影响较大的问题,添加链路传输处理单元提高激光链路传输的可靠性。研究了星间激光链路接口模型在中继卫星系统与分布式卫星系统中的实现方法。结果表明,采用星间激光链路接口模型后系统传输效率提升了49.93%,纠错性能提升了3.01 dB。     

卫星通信在大数据时代的应用

在信息呈现出爆炸性需求的大数据时代,常规通信技术难以满足海量数据集合的传输要求,卫星通信将不断发展综合化、个人化业务,利用高频段、高功率、多波束及大天线通信卫星支持星间链路、星上处理、星上交换,提供多种虚拟专网,综合传输图文、数据、话音.本文分析了卫星通信在大数据时代中的应用情况,旨在提升通信系统的信息传输能力.     

星地一体化导航系统星问链路仿真及分析

在导航卫星系统中,为了解决星间链路拓扑规划不合理而导致的星地信息传输时延大的问题,提出了一种新的星间链路规划方法。该方法优先考虑星地间的可视覆盖关系,保证卫星与地面站之间实时的信息传输。利用STK仿真软件构建了卫星网络拓扑,进而利用OPNET仿真软件完成了性能仿真验证。仿真结果表明,新的拓扑减小了星地数据传输的跳数和端到端时延,符合星地一体化的需求。     

一种集成无线和有线信号的混合接入系统研究

为了满足不同高带宽业务的需求,提出一种同时传输有线和无线信号的混合接入网系统。在下行链路中,无线信号以相位调制格式在光载波上传输,有线信号以强度调制格式重调制在光载波上,在ONU(光网络单元)采用不同的解调方案进行解调接收;在上行链路中,通过载波重用技术再调制有线基带信号并将其传输至OLT(光线路终端),简化了系统的器件配置。利用光学软件Optisystem验证了系统的可靠性和有效性。仿真结果显示,无线链路信号和有线基带信号经过正交调制传输后,在用户端仍能得到较好效果的眼图,说明它们能被准确地接收。采用载波重用技术的上行基带信号也能被OLT准确地接收。     

动环监控系统无线传输组网方案

随着移动通信行业的迅猛发展,基站覆盖率的提升,动环监控系统所能采用的传输资源环境也更加复杂。在很多基站传输条件下,动环监控系统没有可以使用的固定链路,无线传输成为必然的选择。同时,无线组网相比与2Mbit/s时隙等有线组网而言,有着灵活,可靠,覆盖率广,占用资源少,不会影响无线传输主业务等优势。无线组网在作为固网组网重要补充的同时,也逐渐成为动环监控系统组网的一个发展方向。短信和GPRS链路是两种最为常见的无线链路,不但易于网络组建,而且稳定可靠,能有效满足动环监控组网需求。本文将详细介绍目前动环监控中短信组网,GPRS方式组网,短信+GPRS混合组网等常见的短信和GPRS无线组网方案。     

基于L2TP VPDN技术实现空管核心业务的传输

目前空管核心业务包括雷达、VHF语音、自动转报等,这些核心业务以地面传输链路为主,缺乏有效的无线传输方式做保障,随着运营商4G网络覆盖的普及,稳定性能的提升,可以利用运营商的4G网络传输空管核心业务。本文结合VPDN(Virtual Private Dial-up Networks)技术在互联网上采用L2TP(Layer 2 Tunnel Protocol)建立私有专用通道的特点,设计了一套利用运营商的4g网络传输空管核心业务的方案,以解决缺乏无线传输方式做备份或者部分偏远台站,没有有线链路传输业务的问题。     

基于HDLC协议的数字图像传输链路设计

数字图像传输具有数据量大,实时性要求高的特点,尤其在无线传输中更容易受到外界环境的干扰,为了降低无线传输过程中的误码率,提高传输链路的可靠性,设计了一种基于HDLC协议的传输链路。分析了数字图像的表示形式和HDLC协议的格式,提出了在传输链路中实现数据透明传输的解决方法并给出了部分源代码。最后对本文描述的传输链路进行了仿真测试,仿真结果表明,在无线传输环境下,采用HDLC协议的传输链路可有效降低误码率,传输质量得到明显提高。     

一种用于混合通信网机会式路由选择算法

传统的路由协议都是针对特定的有线或无线网络,仅仅考虑路由的建立过程、路由建立过程中的收敛速度、路由维护的网络开销及路由动态更新时环路的避免等性能。将其用于有线无线混合传输网络会导致较低系统性能。机会式路由选择算法综合分析了无线链路状态和网络时延的影响,得出了各路径优先级的计算表达式,在路由选择时根据各条路径的优先级来选择路由。仿真结果表明,与传统路由算法相比较,该算法能够提高系统吞吐量和减少系统传输时延。     

下一代车载时间敏感网络架构设计与调度评估

智能网联汽车(Intelligent Connected Vehicle, ICV)是未来汽车行业发展的主要方向之一,其对车载网络通信的带宽、延迟出了较高的要求。针对该要求,提出了基于以太网的电子电气架构(Electronic/Electrical Architecture, EEA);在分析基于IEEE802.1Qbv的时间敏感网络(Time-sensitive Networking, TSN)传输调度机制的基础上,实现了控制数据流和传感器数据流的增量式调度。通过评估和对比,TSN拥有更高的带宽、更低的传输时延,有望成为下一代车载网络。     

时间敏感网络流量调度算法研究综述

时间敏感网络（Time-sensitive Networking,TSN）是一种新型确定性网络,具有低时延、低抖动等特点,能够满足现代网络传输控制的要求。流量调度是TSN标准中关键技术之一,用于确保流量传输的服务质量。首先对时间敏感网络的发展背景、重要机制、应用场景进行阐述,着重研究5种时间敏感网络流量调度机制,包括基于时间的整形机制、基于信用值的整形机制、循环队列转发机制、帧抢占机制以及异步流量整形机制;然后,分析了流量调度算法的研究现状,归纳和总结了时间触发（Time-triggered,TT）流和事件触发（Event-triggered,ET）流的调度算法,分析了目前流量调度算法存在的问题;最后,指出了TSN流量调度算法的发展方向和趋势。     

A novel scheduling scheme to share dropping ratio while guaranteeing a delay bound in a MultiCode-CDMA network

A MultiCode-CDMA network that is capable of providing quality-of-service guarantees will find widespread application in future wireless multimedia networks. However, providing delay guarantees to time-sensitive traffic in such a network is challenging because its transmission capacity is variable even in the absence of any channel impairment. We propose and evaluate the performance of a novel transmission scheduling scheme that is capable of providing such a delay guarantee in a MultiCode-CDMA network. The proposed scheme drops packets to ensure that delays for all transmitted packets are within the guaranteed target bounds, but packets are dropped in a controlled manner such that the average dropping ratios of a set of time-sensitive flows can be proportionally differentiated according to the assigned weighting factors or shares. We provide extensive simulation results to show the effectiveness of the proposed scheme as well as to study the effects of various parameters on its performance. In particular, we show that it can simultaneously guarantee a delay upper bound and a proportionally differentiated dropping ratio in a fading wireless channel for different traffic loads, peak transmission rates, and weighting factors of individual flows.     

Empirical evaluation of receiver‐based TCP delay control in CDMA2000 networks

Wide‐area broadband wireless technologies such as CDMA2000 often suffer from variable transfer rate and long latency. In particular, TCP window‐based rate control causes excessive buffering at the base station because of the lower transfer rate of the wireless link than that of the wired backhaul link. This performance characteristic of TCP further increases the end‐to‐end delay, and additional resources are required at the base station. This paper presents a practical mechanism to control the end‐to‐end TCP delay for CDMA2000 networks (or other similar wireless technologies). The key idea is to reduce and stabilize RTT (round‐trip time) by dynamically controlling the TCP advertised window size, based on a runtime measurement of the wireless channel condition at the mobile station. The proposed system has been implemented by modifying the Linux protocol stack. The experiment results, conducted on a commercial CDMA2000 1x network, show that the proposed scheme greatly reduces the TCP delay in non‐congested networks, while not sacrificing the TCP throughput in congested networks. Copyright © 2006 John Wiley & Sons, Ltd.     

Performance Evaluation of Wireless Controller Area Network (WCAN) Using Token Frame Scheme

In this paper, a proposed new wireless protocol so-called wireless controller area network is introduced. WCAN is an adaptation of its wired cousin, controller area network protocol. The proposed WCAN uses token frame scheme in providing channel access to nodes in the system. This token frame method follows the example used in wireless token ring protocol which is a wireless network protocol that reduces the number of retransmissions as a result of collisions. This scheme based on CAN protocol allows nodes to share a common broadcast channel by taking turns in transmitting upon receiving the token frame that circulates around the network for a specified amount of time. The token frame allows nodes to access the network one at a time, giving ‘fair’ chance to all nodes instead of competing against one another. This method provides high throughput in a bounded latency environment. The proposed WCAN protocol has been developed and simulated by means of QualNet simulator. The performances of this proposed protocol are evaluated from the perspective of throughput, end-to-end delay and packet delivery ratio, and are compared against the IEEE 802.11 protocol. Simulation results show that the proposed WCAN outperforms IEEE 802.11 based protocol by 62.5 % in terms of throughput with increasing network size. Also, it shows an improvement of 6 % compared to IEEE 802.11 standard at a higher data interval rate.     

End-to-End Performance Improvement of the Wireless Channel for Video Transmission

Real time video transmission in wireless environment considers various parameters of wireless channel like information rate, error resiliency, security, end-to-end latency, quality of service etc. The available internet protocols are transmission control protocol and user datagram protocol (UDP). But most of the real-time applications uses UDP as their transport protocol. UDP is a fast protocol suitable for delay sensitive applications like video and audio transmission as it does not provide flow control or error recovery and does not require connection management. Due to the tremendous growth in wired and wireless real-time applications, some improvements should be made in the existing systems or protocols. Various techniques to improve end-to-end performance of system for real time video transmission over wireless channel are available in literature. Authors claim that the solution suggested in the paper provide more reliability in wireless video transmission. In the proposed solution, adaptive redundant packets are added in every block (or datagram) transmitted in order to achieve a desired recovery rate at the receiver. The suggested method dose not use any retransmission mechanism. The network simulator NS-2 is used to evaluate the method and the simulation results indicate that the proposed method can guarantee satisfied end-to-end performance by increased packet delivery ratio, reduced end-to-end delay and hence increased network throughput for video transmission in wireless network.     

基于卫星分发链路的地面数字电视单频网关键技术及其应用

本文提出了基于卫星分发链路的地面数字电视单频网的组网方案。该方案利用了卫星链路的转发优势,节目分发链路不受地域差异化条件的限制,不需要单独架设专用有线分发网络,转发延时分布均匀,特别适合于在复杂环境下构建大范围的单频网。本文详细阐述了基于卫星分发链路的地面数字电视单频网的网络结构、特点与关键技术。实验室测试和开路测试结果均表明该方案的可行性和有效性。     

Performance Modelling of TCP Enhancements in Terrestrial–Satellite Hybrid Networks

In this paper, we focus on the performance of TCP enhancements for a hybrid terrestrial–satellite network. While a large body of literature exists regarding modeling TCP performance for the wired Internet, and recently over a single-hop wireless link, the literature is very sparse on TCP analysis over a hybrid wired–wireless (multi-hop) path. We seek to make a contribution to this problem (where the wireless segment is a satellite uplink) by deriving analytical estimates of TCP throughput for two widely deployed approaches: TCP splitting and E2E (End-to-End) TCP with link layer support as a function of key parameters such as terrestrial/satellite propagation delay, segment loss rate and buffer size. Our analysis is supported by simulations; throughput comparisons indicate superiority of TCP splitting over E2E scheme in most cases. However, in situations where end-to-end delay is dominated by terrestrial portion and buffering is very limited at intermediate node, E2E achieves higher throughput than TCP splitting.     

A Distributed Sequential Link Schedule Combined with Routing in Wireless Mesh Networks

This letter proposes a new distributed scheduling scheme combined with routing to support the quality of service of real‐time applications in wireless mesh networks. Next, this letter drives average end‐to‐end delay of the proposed scheduling scheme that sequentially schedules the slots on a path. Finally, this letter simulates the time division multiple access network for performance comparison. From the simulation results, when the average number of hops is 2.02, 2.66, 4.1, 4.75, and 6.3, the proposed sequential scheduling scheme reduces the average end‐to‐end delay by about 28%, 10%, 17%, 27%, and 30%, respectively, compared to the conventional random scheduling scheme.