一种有效提高无标度网络负载容量的管理策略

现有研究表明明显的社团结构会显著降低网络的传输性能. 本文基于网络邻接矩阵的特征谱定义了链路对网络社团特性的贡献度, 提出一种通过逻辑关闭或删除对网络社团特性贡献度大的链路以提高网络传输性能的拓扑管理策略, 即社团弱化控制策略(CWCS 策略). 在具有社团结构的无标度网络上分别进行了基于全局最短路径路由和局部路由的仿真实验, 并与关闭连接度大的节点之间链路的HDF 策略进行了比较. 仿真实验结果显示, 在全局最短路径路由策略下, CWCS策略能更有效地提高网络负载容量, 并且网络的平均传输时间增加的幅度变小. 在局部路由策略下, 当调控参数0<α<2, 对网络负载容量的提升优于HDF策略. 关键词： 复杂网络 社团特性 负载容量 拓扑管理     

无人机数据链信道编码方法研究

信道编码是提高通信可靠性的重要途径,针对无人机数据链传输遥控/遥测指令时的高可靠性要求,研究了无人机数据链不同码率的卷积码、Turbo码和LDPC码三种信道编码方法,结合无人机信道的特点,仿真验证了无人机数据链的三种信道编码与解码方案;三种编码方式都带来了较大增益,其中LDPC码的性能略优于Turbo码,卷积码性能相比最差,但三种编码方式都可以使数据链的误码率达到了10-5以下,满足了无人机数据链高可靠性要求。     

无人机数据链电磁干扰机理和防护研究

针对无人机在飞行过程中其数据链系统容易受到外界电磁干扰而导致链路中断的问题,以某型无人机数据链系统为研究对象,提出了一种基于前门耦合的电磁敏感度注入效应试验方法。基于该方法开展了某型无人机数据链系统电磁敏感度效应试验,得到了该数据链系统的敏感度阈值曲线,确定了其电磁敏感度阈值,分析了机载数据链接收机射频前端的工作原理和电磁干扰作用下接收机的信号传输过程,揭示了组合频率干扰和带外饱和干扰对无人机机载数据链的作用机理,最后进行了试验验证。在实验研究的基础上,从电磁兼容设计层面和自适应控制策略方面分别有针对性地提出了相应的防护方法。     

长距离和多模接入网络中低密度奇偶校验-正交频分复用的性能研究

研究了低密度奇偶校验编码与正交频分复用相结合的编码调制技术,从理论上分析了光纤链路中色散和频率选择性衰落的影响,并通过数值模拟仿真,比较了不同编码码率的编码调制信号在长距离单模光纤传输和多模光纤接入网络中的传输性能.仿真结果表明,采用码率为0.75的长码型非规则的低密度奇偶校验编码与正交频分复用相结合的编码调制技术更适合光纤通信系统中的长距离传输和多模接入网络.     

基于OPNET的星地光网络性能测试仿真平台研究

为了测试星地光网络的性能,设计了一种基于OPNET的星地光网络性能测试仿真平台。介绍了平台的总体技术架构,探讨了星间链路建立的条件。采用最大接入仰角与最长服务时间加权的方式,完成星地链路的卫星接入服务;按照切换呼叫优先的策略完成业务传输中的卫星切换服务,确保星地链路不间断的通信能力。根据最小链路代价和首次命中原则,实现星地光网络的路由与波长的动态分配。最后,利用平台的OPNET软件测试了三种星座下的星地光网络性能,测试结果表明：在LEO、MEO和GEO星座下,星地光网络的网络阻塞率分别为10%、40%和54%,平均网络时延分别为0.1s、0.07s和0.054s。测试结果对星地光网络的工程应用具有一定的指导意义。     

多跳噪声量子纠缠信道特性及最佳中继协议

在量子通信网络中, 最佳中继路径的计算与选择策略是影响网络性能的关键因素. 针对噪声背景下量子隐形传态网络中的中继路径选择问题, 本文首先研究了相位阻尼信道及振幅阻尼信道上的纠缠交换过程, 通过理论推导给出了两种多跳纠缠交换信道上的纠缠保真度与路径等效阻尼系数. 在此基础上提出以路径等效阻尼系数为准则的隐形传态网络最佳中继协议, 并给出了邻居发现、量子链路噪声参数测量、量子链路状态信息传递、中继路径计算与纠缠资源预留等工作的具体过程. 理论分析与性能仿真结果表明, 相比于现有的量子网络路径选择策略, 本文方法能获得更小的路径平均等效阻尼系数及更高的隐形传态保真度. 此外, 通过分析链路纠缠资源数量对协议性能的影响, 说明在进行量子通信网设计时, 可以根据网络的规模及用户的需求合理配置链路纠缠资源.     

长距离和多模接入网络中低密度奇偶校验-正交频分复用的性能研究

研究了低密度奇偶校验编码与正交频分复用相结合的编码调制技术,从理论上分析了光纤链路中色散和频率选择性衰落的影响,并通过数值模拟仿真,比较了不同编码码率的编码调制信号在长距离单模光纤传输和多模光纤接入网络中的传榆性能.仿真结果表明,采用码率为0.75的长码型非规则的低密度奇偶校验编码与正交频分复用相结合的编码调制技术更适...     

一种基于分层的量子分组传输方案及性能分析

大规模量子通信网络中,采用量子分组传输技术能有效提升发送节点的吞吐量,提高网络中链路的利用率,增强通信的抗干扰性能.然而量子分组的快速传输与路由器性能息息相关.路由器性能瓶颈将严重影响网络的可扩展性和链路的传输效率.本文提出一种量子通信网络分层结构,并根据量子密集编码和量子隐形传态理论,给出一种基于分层的量子分组信息传输方案,实现端到端的量子信息传输.该方案先将量子分组按照目的地址进行聚类,再按聚类后的地址进行传输.仿真结果表明,基于分层的量子分组信息传输方案能够有效减少量子分组信息在量子通信网络中的传输时间,并且所减少的时间与量子路由器性能与发送的量子分组数量有关.因此,本文提出的量子分组信息传输方案适用于大规模量子通信网络的构建.     

基于最短路径长度的空间网络路由

以通信网、电力网、交通网为代表的很多复杂网络以传输负载为基本功能.在这些网络中,网络的吞吐量是衡量网络传输性能的重要指标,如何提升网络的吞吐量是研究热点之一.不少研究人员提出了不同的路由算法,通过调节传输路径来提高网络吞吐量.但之前的研究很少考虑网络中节点的空间位置.本文针对空间网络提出了一种高效的路由策略,通过节点位置得到路径长度;采用该算法,负载从源节点沿着最短长度的路径传输到目标节点.为了检验算法的有效性,采用网络从自由流状态转变成拥塞状态的相变点Rc来衡量网络的吞吐量.在匀质和异质空间网络上的仿真表明,与传统的最少跳数路由策略相比,本文提出的基于最短路径长度的路由算法能有效提高空间网络的吞吐量.     

基于多核点共享树的多源光组播路由方法

通过网络编码方法优化多核点选择和组播信息传输,本文提出一种基于多核点共享树和网络编码的光组播路由构造和波长分配方法、减少波长资源消耗和提高网络的负载平衡性能.首先,删除产生源点迂回回路的网络编码备选核点集合,采用启发式矩阵运算方法确定多源共享树的网络编码核点,实现多源共享树以最少的核点覆盖最多的源节点;然后,为减少波长信道消耗数目,在确定的核点到目的节点间加入网络编码方法传输信息;最后,讨论了多核点共享树的波长分配方法和目的节点成功解码的边分离路径方法.仿真结果表明:与单核共享树、基于网络编码的单核共享树相比,基于网络编码的多核点共享树组播路由方法需求最少的波长数目和获得最好的网络负载平衡性能.     

飞控系统的光传网络的可靠性及实时性

调研了传统光传(FBL)网络的几种拓扑结构, 就可靠性和实时性两方面对它们进行了分析和比较。选择采用一个包含256个节点的mesh光交换网络, 它具有冗余拓扑结构能承受3处链路故障, 保证了网络的可靠性。以网络中发生链路故障的数目, 及多个故障同时发生时故障的邻近程度来衡量网络故障的严重性。对所有链路故障情形进行仿真, 测试端到端的通信延迟。仿真结果表明, 采用这种网络拓扑结构的光传网络, 即使在发生较为严重的故障的情况下, 端到端通信路由的跳数增加不大, 仍能满足实时通信的要求。     

二元决策图和故障树相融合的无线传感器网络可靠性分析

为了提高无线传感器分析网络可靠性,提出一种基于二元决策图和故障树相融合的无线传感器网络可靠分析方法;首先根据无线传感器网络拓扑结构建立了故障树模型,然后将无线传感器网络故障树转化为二元决策图结构,最后采用仿真实验分析了不同节点冗余度、不同跳数条件下无线传感器网络的可靠性;仿真结果表明,文章方法的分析结果可以帮助无线传感器网络性能的优化,可以提高无线传感器网络的可靠性。     

A survey on UAV placement optimization for UAV-assisted communication in 5G and beyond networks

With the increase in capacity demands and the requirement of ubiquitous coverage in the fifth generation and beyond wireless communications networks, unmanned aerial vehicles (UAVs) have acquired a great attention owing to their outstanding characteristics over traditional base stations and relays. UAVs can be deployed faster and with much lower expenditure than ground base stations. In addition, UAVs can enhance the network performance thanks to their strong line-of-sight link conditions with their associated users and their dynamic nature that adapts to varying network conditions. Optimization of the UAV 3D locations in a UAV-assisted wireless communication network was considered in a large body of research as it is a critical design issue that greatly affects communication performance. Although the topic of UAV placement optimization was considered in few surveys, these surveys reviewed only a small part of the growing literature. In addition, the surveys were brief and did not discuss many important design issues such as the objectives of the optimization problem, the adopted solution techniques, the air-to-ground channel models, the transmission media for access and backhaul links, the limited energy nature of the UAV on-board batteries, co-channel interference and spectrum sharing, the interference management, etc. Motivated by the importance of the topic of UAV placement optimization as well as the need for a detailed review of its recent literature, we survey 100 of the recent research papers and provide in-depth discussion to fill the gaps found in the previous survey papers. The considered research papers are summarized and categorized to highlight the differences in the deployment scenario and system model, the optimization objectives and parameters, the proposed solution techniques, and the decision-making strategies and many other points. We also point to some of the existing challenges and potential research directions that have been considered in the surveyed literature and that requires to be considered     

Assessing the impact of physical layer techniques on ad hoc network performance

This article provides an overview on the topic of ad hoc network performance analysis, mainly from a physical layer standpoint. The emphasis of the paper is on how the individual link and network performance can be evaluated in an analytically tractable manner, such that design insights can be obtained and optimization over key parameters is possible. Our model is that of a large random network, where the wireless channel comprises path-loss and fading. Various physical layer factors are taken into account: the multiple-access (MA) scheme, such as direct-sequence (DS) CDMA and frequency-hopping (FH) CDMA; error correction coding such as Reed–Solomon (RS) or convolutional coding; coherent or noncoherent detection; the use of multiple-input, multiple-output (MIMO) techniques to enhance error protection or to increase the transmission rate. The performance of the network is evaluated and optimized in terms of useful metrics such as the network throughput, the information efficiency and the transmission capacity.     

Secured data transmissions in corporeal unmanned device to device using machine learning algorithm

Cyber–physical systems (CPS) for device-to-device (D2D) communications are gaining prominence in today’s sophisticated data transmission infrastructures. This research intends to develop a new model for UAV transmissions across distinct network nodes, which is necessary since an automatic monitoring system is required to enhance the current D2D application infrastructure. The real time significance of proposed UAV for D2D communications can be observed during data transmission state where individual data will have huge impact on maximizing the D2D security. Additionally, through the use of simulation, an exploratory persistence tool is offered for CPS networks with fully characterized energy issues. This UAV CPS paradigm is based on mobility nodes, which host concurrent systems and control algorithms. In sixth-generation networks, when there are no barriers and the collision rate is low and the connectivity is fast, the method is also feasible. Unmanned aerial vehicles (UAVs) can now cover great distances, even while encountering hazardous obstacles. When compared to the preexisting models, the simulated values for autonomous, collision, and parametric reliability are much better by an average of 87%. The proposed model, however, is shown to be highly independent and exhibits stable perceptual behaviour. The proposed UAV approach is optimal for real-time applications due to its potential for more secure operation via a variety of different communication modules.     

Analysis of fluctuations of antenna pattern in U-V2X communications

The third-generation partnership project (3GPP) defined several scenarios of vehicle-to-everything (V2X) networks such as vehicle-to-vehicle, vehicle-to-pedestrian, and vehicle-to-infrastructure. Unmanned aerial vehicles (UAVs) exploiting such scenarios for vehicular applications like vehicular-platooning, autonomous driving, and traffic management have shown improved networks’ performance in UAV-V2X (U-V2X) communications. This promising performance is typically obtained by considering high directional UAV antennas. However, the UAV vibration makes UAV antennas’ beam-width sensitive to UAV fluctuations which results in degrading the networks’ performance. Thus, in this paper, the performance of a U-V2X network in the presence of UAV fluctuations is investigated. The UAVs are modeled using an independent homogeneous Poisson Point Process and the vehicular-nodes are modeled using an independent Poisson Line Process. To this end, the association probability and success probability of various links such as vehicular-node connected to a UAV link, vehicular-node connected to a near-by vehicular-node link, and the overall U-V2X link are derived. In addition, the effect of different network settings such as the number of vehicular-nodes, UAVs, roads, and antennas is quantified. Moreover, the spectral efficiency of a U-V2X network is evaluated. Extensive simulations revealed that V2X networks facilitate UAVs and that for less dense areas with fewer roads, buildings, and crowds; UAVs provide more reliable links for connectivity than vehicular-nodes. Furthermore, it is also revealed that UAVs provide less reliable connection for V2X networks with larger UAV antenna fluctuations.     

Optimal dynamic bandwidth allocation for complex networks

Traffic capacity of one network strongly depends on the link’s bandwidth allocation strategy. In previous bandwidth allocation mechanisms, once one link’s bandwidth is allocated, it will be fixed throughout the overall traffic transmission process. However, the traffic load of every link changes from time to time. In this paper, with finite total bandwidth resource of the network, we propose to dynamically allocate the total bandwidth resource in which each link’s bandwidth is proportional to the queue length of the output buffer of the link per time step. With plenty of data packets in the network, the traffic handling ability of all links of the network achieves full utilization. The theoretical analysis and the extensive simulation results on complex networks are consistent. This work is valuable for network service providers to improve network performance or to do reasonable network design efficiently.     

无人机姿态控制器设计及仿真

由于无人机模型的非线性和参数的时变性,传统PID方法设计的控制器动静态性能可能会变得很差,针对这种问题,设计了适合于某型无人机的模糊自适应姿态控制器。对于模糊控制器的隶属函数选择中盲目性的问题,利用粒子群优化算法对隶属函数进行智能寻优,降低设计过程中专家主观意向对控制器性能不确定性的影响。仿真结果表明,本文设计的控制器相对传统PID有更好的动静态性能,并且对于模型参数的时变性具有一定的鲁棒性。