A New Exposed-terminal-free MAC Protocol for Multi-hop Wireless Networks

This article presents a new multichannel medium access control (MAC) protocol to solve the exposed-terminal (ET) problem for efficient channel sharing in multi-hop wireless networks. It uses request-to-send and clear-to-send (RTS/CTS) dialogue on a common channel and flexibly opts for conflict-free traffic channels to carry out the data packet transmission on the basis of a new channel selection scheme. The acknowledgment (ACK) packet for the data packet transmission is sent back to the sender over another common channel thus completely eliminating the exposed-terminal effects. Any adjacent communication pair can take full advantage of multiple traffic channels without collision and the spatial reuse of the same channel is extended to other communication pairs which are even within 2 hops from them. In addition, the hidden-terminal effect is also considerably reduced because most of possible packet collisions on a single channel are avoided due to traffic load balance on multichannels. Finally, a performance comparison is made between the proposed protocol and other typical MAC protocols. Simulation results evidence its obvious superiority to the MAC protocols associated with other channel selection schemes and traditional ACK transmission scheme as well as cooperative asynchronous multichannel MAC (CAM-MAC) protocol in terms of four performance indices: total channel utilization, average channel utilization, average packet delay, and packet dropping rate.     

基于冗余连接机制的SLE网络协议体系模型

CCSDS(Consultative Committee for Space Data Systems,空间数据系统咨询委员会)SLE(Space Link Extension,空间链路拓展)网络协议体系模型中,一个服务实例只支持建立一个物理通信链路,造成上层应用与下层链路耦合过强,存在一定的安全隐患。针对此问题,设计了基于冗余连接机制的SLE网络协议体系模型,该模型在现有的SLE网络协议体系模型中增加了逻辑连接层,支持单一服务实例同时使用多个物理链路进行空间数据传输,可根据多连接状态重新设计TML(Transport Mapping Layer,传输映射层)状态变换关系以及数据传输模式。该模型能够兼容现有的SLE网络传输体系模型,提高SLE服务的可靠性。     

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.     

Optimal acknowledgment frequency over asymmetric space-internet links

The acknowledgement (ACK) strategy of transmission control protocol (TCP) has been modified to delay the ACKs for a configurable period of time that is related to the round-trip time (RTT) to improve its performance in asymmetric links such as space communications. A general relationship between the asymmetric channel ratio and the optimal ACK frequency to achieve maximum throughput is not available. This paper studies the optimal ACK frequency with respect to the channel RTT to achieve the maximum throughput over various asymmetric, geo-stationary earth orbit (GEO)-satellite links using a test-bed. It is found that when the asymmetric channel ratio is as high as about 100/1, the optimal ACK frequency must be increased with an increase in asymmetric ratio to complement the impact of the reduction of ACK channel rate. As a rule of thumb, every two-fold increase in asymmetric ratio requires the optimal ACK frequency to be increased by one ACK per RTT. A regression model was built to reflect the relationship between the optimal ACK frequency and the asymmetric channel ratio and has been validated     

空地数据链自适应编码调制方法研究

针对空地数据链高效可靠的传输要求,本文研究了空地数据链自适应编码调制方法。该方法基于码率可变的Turbo码,传输信道模型解算与加栽,最大似然信道估计,自适应判决门限的确定等技术,在微波暗室环境内模拟了空地数据链的通信。仿真结果表明：在误码率为10^-5时,自适应编码调制方法能够根据信道状况自适应调整编码与调制模式,较大...     

频率选择性衰落信道DS-CDMA无人机中继通信系统航迹规划

无人机中继通信是实现远距离无线通信的一种重要技术手段，无人机的飞行航迹对无人机中继通信系统的链路传输可靠性存在显著的影响，在频率选择性衰落信道环境下研究了基于直序列码分多址（DS-CDMA）的无人机中继通信系统的航迹优化的问题。首先，给出了基于DS-CDMA的译码转发无人机中继通信系统的模型，并理论分析给出无人机中继通信系统的链路中断概率及平均误码率计算公式，以此为基础，基于链路中断概率最小化准则提出了中继无人机的航迹规划方法，最后通过仿真验证了所提出方法的正确性与有效性。研究表明：最大比值合并DS-CDMA无人机中继通信系统可充分获取频率选择性衰落信道提供的分集增益，显著改善链路传输的可靠性。     

TCP协议在空间网络中的传输时延分析

探讨了为适应空间网络环境对TCP协议机制进行的一些改进,通过模拟实验,对协议改进方案的性能进行了分析和比较。实验结果表明：协议改进后能够减小时延,避免不必要的重传,提高了信道的利用率。     

空时分组编码的无人机中继通信航迹规划方法

无人机(UAV)中继通信是实现远距离点对点无线通信的一种重要技术手段。为提高无人机中继通信系统链路传输的可靠性,提出基于空时分组编码的无人机放大转发中继通信传输方案,并基于双跳链路遍历容量最大化的准则给出了无人机最佳航迹规划方法,并进一步利用FM-EM算法给出了基于空时分组编码无人机中继通信系统的中断概率及遍历信道容量计算公式。计算机仿真表明:提出的方法显著优于传统的单发单收(SISO)无人机中继通信系统。     

全球卫星导航星座网络协议体系与运行模式

针对全球卫星导航星座网络建设初期或论证阶段所涉及的网络体系结构、协议体系及相关组网等技术问题,开展了基于导航星座星间链路构建空间信息网络的技术研究,分别提出了由子网、接入网、骨干网等节点及其相互之间星间、星地无线链路构成的分层网络系统结构,设计了兼容遥控、遥测、测量与网络交互支持等业务的基于IP over CCSDS(基于空间数据系统咨询委员会标准的空间链路承载互联网协议业务)的协议体系,给出了全系统基本通信业务运行模式等。与传统高轨卫星通信系统相比,该星座网络具有高覆盖、低时延、随遇接入等优点,可实现星座导航性能与中低轨及地面用户通信性能的全方位提升,相关结果对我国全球卫星导航星座网络技术研究具有一定的参考意义。     

移动Ad Hoc网络中一种有效多址协议的性能仿真

基于有效竞争预约接入、无冲突轮询传输的思想,本文提出了支持节点移动性和多跳网络结构的依据用户妥善安排的多址接入(UPMA)协议,并使用网络仿真工具OPNET评估了它的多址性能。仿真结果表明,该协议显著提高了多跳网络的业务传输效率。     

基于CRC校验的航电网络传输通道安全性分析

完整性概率是民用飞机与系统安全性的评价指标之一。循环冗余校验(CRC)是航空电子系统通信网络中广泛应用的完整性设计措施。针对缺乏CRC校验定量安全性分析的现状,基于标准CRC校验的性能,研究了业务数据在航空电子系统通信网络传输过程中出现错误且被CRC漏检的概率。结合案例分析了CRC校验对航电网络传输通道完整性需求的影响。分析结果表明通过在应用层采取CRC校验等设计措施,并确保业务数据在网络传输过程中发生错误且被CRC漏检的概率满足顶层分配的完整性需求,则网络传输通道或链路层可无需考虑针对特定业务数据的完整性需求,进而缓解对网络传输通道的安全性需求。分析思路为航电网络CRC校验设计及安全性分析提供参考。     

基于跨层信道感知的SPMA 协议自适应阈值算法

基于统计优先级的多址接入协议（SPMA, Statistical Priority-based Multiple Access protocol）应用于机     

采用丝杠传动的电动舵机运动学分析

为了改善旋转电动舵机的控制输出中存在的系统振荡问题,针对电动舵机中连杆及摇臂等传动结构导致的非线性不确定特性,文章通过建立传动机构的数学模型,根据其位置变化量及速度变化量关系,确立了控制输出与实际输出在传动过程中的正逆运动学方程,分析了传动机构运动时所引入的非线性环节,并提出了通过修正传动参数来补偿非线性的影响,为伺服系统的分析及控制器设计提供参考,对提高舵机系统的控制性能与控制精度有重要作用。     

星间链路数量受限的导航卫星网络链路分配问题

对星间链路数量非常有限、需要同时满足星间测距和星间通信需求的导航卫星网络的链路分配问题进行了研究。首先,分析了导航卫星网络的特点,并设计了一种基于有限状态自动机(FSA)的拓扑处理机制。然后,将星间测距需求作为一个约束,以星间通信的延时性能为优化目标,将导航卫星网络的链路分配问题建模为一个多目标优化问题。最后,针对建立的多目标优化问题,分别提出一种基于首次改善(FI)的本地搜索算法和基于模拟退火(SA)的启发式优化算法以对链路分配问题进行求解,并提出一种基于分支交换策略的新链路分配生成方法。仿真结果表明,通过FI算法和SA算法获得的优化链路分配的网络延时性能均得到了改进,且SA算法的性能要优于FI算法;同时,FSA的状态持续时间的减小有利于获得网络延时性能好的链路分配。     

针对TCP/IP漏洞的航天测控通信网安全防护

航天测控通信网自建成以来,整体运行较为稳定,但在网络安全方面也暴露出了一些问题,为研究和解决目前航天测控通信网中存在的网络安全问题, 在分析TCP/IP (Transmission ControlProtocol/Internet Protocol,传输控制协议/互联网协议)分层协议基本原理的基础上,研究了IP网数据链路层、网络层和传输层的协议漏洞及常见攻击方法,详细介绍了当前航天测控通信网的网络安全部署情况,根据网络现状分别对航天测控通信网上数据链路层、网络层和传输层存在的安全问题进行了纵向分析,针对分析出的各类安全问题,进一步给出了有效的防御措施和防护方法。最后,探讨提出了一套航天测控通信网配置维护管理系统的设计方案,通过建立设备配置信息库、检查信息记录库及网络故障库等,实现了对航天测控通信网安全稳定运行的有效管理。     

无人机自组网络多媒体数据传输路由算法研究

针对无人机自组网络多媒体数据传输中链路不稳定问题,提出了一种无人机自组网络多媒体数据传输路由算法。该算法在GPSR路由算法基础上,结合无人机多媒体通信的特点,充分考虑了位置、速度、运动方向这三个因素对选择下一跳节点的影响,从而达到同时兼顾三者和提高链路性能的目的。提出的算法具有开销小、可靠性高等优点,有效提高了分组交付率以及降低了平均端到端延迟,从而提高了无人机自组网络多媒体数据传输的性能。     

连续时变信道对协作通信性能影响的研究

协作通信能够抵抗无线信道衰落,是提高无线通信系统性能的有效手段。但是,其性能优势的发挥受信道时变的影响。文章研究了连续时变信道下协作通信系统的性能,为了准确反映信道连续时变情况,采用内插滤波高斯噪声法构建连续时变信道模型,选取误包率作为性能指标。仿真结果表明,连续时变信道下,随数据传输逐渐加重程度的过时信道状态信息将导致协作通信误包率性能大幅恶化。     

A feedback-retransmission based asynchronous frequency hopping MAC protocol for military aeronautical ad hoc networks

Attacking time-sensitive targets has rigid demands for the timeliness and reliability of information transmission, while typical Media Access Control (MAC) designed for this application works well only in very light-load scenarios; as a consequence, the performances of system throughput and channel utilization are degraded. For this problem, a feedback-retransmission based asynchronous FRequency hopping Media Access (FRMA) control protocol is proposed. Burst communication, asynchronous Frequency Hopping (FH), channel coding, and feedback retransmission are utilized in FRMA. With the mechanism of asynchronous FH, immediate packet transmission and multi-packet reception can be realized, and thus the timeliness is improved. Furthermore, reliability can be achieved via channel coding and feedback retransmission. With theories of queuing theory, Markov model, packets collision model, and discrete Laplace transformation, the formulas of packet success probability, system throughput, average packet end-to-end delay, and delay distribution are obtained. The approximation accuracy of theoretical derivation is verified by experimental results. Within a light-load network, the proposed FRMA has the ability of millisecond delay and 99% reliability as well as outperforms the non-feedback-retransmission based asynchronous frequency hopping media access control protocol.     

适于长传播时延无线网络的快速预约按需发送MAC协议

为解决无线网络中长传播时延所带来的信道资源利用率低的问题,提出一种基于快速预约按需发送(FRODT)的媒质接入控制(MAC)协议.该协议利用中心控制节点(CCN),在两个信道上安排各节点的分组预约和发送,保证了各节点可以在一帧中无碰撞地发送一个或多个业务分组,并且各节点通过一次握手预约即可完成整个通信会晤的业务分组发送...     

Synchronization of QAM Signals in the Presence of ISI

A data-aided carrier reconstruction method is described for quadrature amplitude modulation (QAM) data communications over narrow-band transmission channels. Previous analyses of this problem have assumed an "infinite" bandwidth of the communication link, so that negligible intersymbol interference (ISI) resulted. On the contrary, when ISI takes place, a different structure must be used which operates on sampled data. The performance of this structure is expressed analytically as a function of 1) the statistics of the message symbols, 2) the characteristics of the channel, and 3) the parameters of the tracking system. Excellent agreement has been found between the theory and the results of a computer simulation.