基于并行PO/EEC的ISAR回波生成与成像仿真

为了满足基于模板的逆合成孔径雷达（ISAR）目标识别对海量高分辨模板图像的工程需求,提出了一种基于并行电磁散射特性计算技术的ISAR图像信号级仿真方法。首先,以OpenMP技术为基础采用并行物理光学和等效边缘电磁流对目标的电磁散射特性进行快速计算;其次,以步进频率波形为雷达发射波形结合目标的电磁散射特性生成了宽带雷达回波数据;最后,对使用距离多普勒算法对仿真回波数据进行处理生成ISAR像,并与点阵模型成像结果进行了对比分析。实现了对ISAR图像的信号级快速仿真,对ISAR系统设计与验证、ISAR图像解译和目标识别以及ISAR成像处理等具有重要意义。     

复杂电磁环境仿真在射频辐射特性评估中的应用

针对复杂电磁环境中射频辐射特性的评估,本文给出了分布式仿真系统的设计与实现方法,阐述了系统架构、组成与工作原理。同时,根据常用电波传播模型的特征提出了基于层次分析法的电磁传播模型匹配算法来适配仿真场景中各用频设备的传播路径。最后通过仿真实例结合射频辐射特性评估方法证明采用该匹配算法能有效提高复杂电磁环境下射频辐射特性评估的逼真度。     

一种改进的广义曲线坐标变换的电磁材料设计方法

提出一种改进的基于麦克斯韦Maxwell方程的广义曲线坐标变换的电磁超材料设计方法,首先介绍了该方法的转换方程,然后通过高增益喇叭天线、圆环聚焦和角度旋转的人工电磁超材料这三个例子验证该方法的可行性。将转换公式运用于二维的有限元仿真软件COMSOL Multiphysics中,得到了三种例子的仿真结果,并进行了讨论。仿真结果表明通过广义曲线坐标变换可以得到具有良好场分布特性的人工电磁超材料,具有更广泛的适用性。     

复杂地形条件下电波传播特性预测

电磁环境计算是战场电磁环境预测仿真系统的核心,为了准确预测不同环境下的电波传播特性,从复杂地形条件展开研究,给出一种基于PE模型的电场强度计算方法,仿真比较了辐射源在不同地表类型下的传播损耗,仿真预测了复杂地形条件下电波传播特性,仿真结果表明地表电磁特性对传播损耗的影响较小,相比于地表电磁特性,不规则地形对电波传播影响更为明显。     

背腔双负微带天线的仿真与实验研究

研究了以双负材料为衬底的背腔微带天线的设计方法与电磁特性.采用S参数法提取双负材料异质填充结构的本构电磁参数,基于腔模理论与HFSS仿真相结合的方法设计了背腔双负微带天线,并进行了加工制作和测试.给出了双负材料电磁特性参数的提取结果、背腔双负微带天线的辐射方向图、端口S参数的计算机仿真与实测结果,以及背腔双负微带天线的单站RCS仿真曲线.结果表明:背腔双负微带天线较背腔普通微带天线具有更好的带宽特性和散射特性.     

基于遥感影像中电磁特性的地物提取方法

电磁特性数据是电子信息装备内场仿真试验不可或缺的数据资源,为了克服传统电子信息装备仿真试验中的电磁特性数据获取方法的不足,提出了从遥感影像中大批量获取大区域范围的电磁特性数据的新方法.首先依据不同地物的电磁特性规律对某一地域的地物进行了分类,从多尺度分割概念和基于异质性最小的区域合并算法两个方面.深入研究了针对地物分类的面向对象多尺度分割算法,并结合实践对算法进行了应用.由于遥感影像的真实性.保证了电磁特性数据提取的准确性与可靠性,实践证明此研究为大批量获取电磁特性数据提供了一种有效的方法和思路.     

基于单平面双螺旋谐振单元左手传输线研究

单平面双螺旋谐振单元是一种左手单元,具有不需缺陷地结构和小型化的特点.该文主要对由单平面双螺旋单元组成的对称和非对称两种传输线形式进行了仿真研究.利用电磁仿真工具,仿真分析了两种形式传输线的回波损耗和插入损耗特性.由仿真结果可知,非对称形式传输线的电磁性能较好.该文设计了两组对比仿真实验,即对称和非对称形式传输线结构相位特性对比,一、四单元非对称传输线相位特性对比,对传输线结构的相位特性进行了分析.结果表明,基于单平面双螺旋结构的非对称形式传输线具有左手效应.     

一种无回跳特性TVS的快速建模方法及验证

瞬态抑制二极管是一种常见的电磁防护器件,在静电防护、浪涌防护、强电磁脉冲防护中有着广泛应用,其瞬态行为对于指导电磁防护设计具有重要意义,但市面上一般没有现成可用的模型。文中基于ADS软件建立一种无回跳特性TVS的仿真模型,使用复杂度较低的TVS模型框架。在建模过程中,分析了模型参数对于精度的影响,并利用S参数测试方法和TLP测试方法获取实测数据,最终构建了两款TVS的完整仿真模型。模型验证结果表明,该模型仿真与实测数据在TVS未工作、即将工作和进入工作状态时都较为一致,仿真与实测误差最大不超过10%,说明其精度足够支撑TVS瞬态仿真。所建立的模型可直接用于TVS的瞬态仿真,该方法也可用于其他无回跳特性TVS的模型构建,为电磁防护设计提供支持。     

铁磁性基体与金属线阵列复合体系的双负材料特性

基于铁磁性基体与金属线阵列复合结构等效电磁参数的长波近似模型,设计了一种应用铁磁性基体的二维双负材料。根据带有介质包裹层的金属线的散射特性,采取多重散射方法计算了铁磁性基体与金属线阵列复合结构的传输谱;还通过全波仿真提取了单元结构的等效电磁参数。这些数值结果与长波近似模型的理论结果取得了很好的一致,确认了该模型的正确性。通过仿真周期复合体系中的电磁场分布,在所设计的双负频带内观察到了反向波现象,进一步验证了所设计的复合体系的双负特性。     

一种基于知识推理的电磁目标识别方法

针对基于电磁感知数据进行目标识别的问题，设计了由基本属性和行为属性组成的电磁目标知识模型，在知识模型的基础上提出了基于知识推理的电磁目标识别通用架构及流程。最后，面向典型应用场景，提出了一种基于知识推理的移动目标属性识别方法，介绍了数据预处理方法，给出了轨迹相似度定义并设计了一种基于豪斯多夫距离的轨迹相似度计算方法，开展了仿真实验。仿真结果表明所提算法的有效性，可应用于电磁目标的识别问题。     

Sensor and gateway location optimization in body sensor networks

In body sensor networks (BSNs), energy-constrained sensors monitor the vital signs of human beings in healthcare applications. Energy consumption is a fundamental issue, since BSNs must operate properly and autonomously for long period of time without battery recharge or replacement. In addition, the human exposure to electromagnetic radiation must be limited. For all these reasons, the energy consumption in BSNs should be minimized. In this paper, sensor and gateway location optimization for BSNs has been analyzed. A mathematical model has been proposed to minimize the energy consumption of the BSN and the heating effects on human tissues. We distinguish between ‘in-body’ and ‘on-body’ sensors depending on their location inside or outside the human body, respectively. The theoretical analysis and the numerical results reveal that in in-BSNs the energy consumption can be significantly reduced when the optimal positions of the gateway or the sensors are computed. However, in on-BSNs the energy consumption is not affected by the devices’ location. With power control the interferences are minimized and the human exposure to electromagnetic radiation is reduced.     

基于分层虚拟簇的多信道组网算法

针对无线自组网遭受强电磁干扰造成节点间感知到的可用信道存在差异且组网困难的问题,该文提出一种基于分层虚拟簇的多信道组网方法,以实现网络可靠性提升与干扰控制。首先,基于各相邻节点感知到的公共信道邻居比信息构建相似度指标,并基于该指标对网络模块度函数进行改进,形成以网络模块度最大的分簇网络;其次,通过先控制再连通的方式选举簇头节点和网关节点,并采用生成树方法构建基于R-跳连通控制集(CDS)的虚拟骨干网链路为簇间节点提供路由转发服务;最后,提出受限图着色方法对簇内与簇间信道进行分配,以减小簇内与簇间通信存在的同频干扰。仿真结果表明,所提算法构建的分簇网络模块度更高,且在平均簇规模和干扰控制等方面能够取得更优的性能。     

网关设备H.248协议的实现

通过对H.248协议、软交换技术和数字程控交换机技术的分析,对H.248协议内容进行了详细描述,对网关的软件、硬件体系结构提出了具体的设计思路及方案,针对软件的可扩展性,提出了分层结构的设计思想,并对软硬件各种组成模块的功能进行了详细介绍。提出了H.248协议在网关设备的设计思路及实现方案,基于标准要求,对注册及呼叫流程提出了具体的实现方法,并针对网关在实际应用中的部署环境,提出了网关双归属实现方案,提高了设备的稳定性及可靠性。     

一种智能家庭网关及数据转发方法设计

针对当前智能家居环境中家庭网关所存在的安全隐患问题,文中提出一种智能家庭网关的设计方案以及一种基于该网关的数据转发方法,当所在家庭网关故障时,根据家居设备节点可接入网关的信号强度、节点的数据处理能力、优先级等信息来选择汇聚节点.监控中心根据候选网关的安全等级、带宽情况、当前负载等信息来选择转发网关.仿真实验证明,当网关...     

基于“北斗一代”的Zigbee无线网关设计

为了解决野外多点数据采集无供电、布线复杂和通信困难的问题,提出了一种基于"北斗一代"的Zigbee无线网关设计方案。采用MSP430F6438、CC2341微处理器和一体化的RDSS"北斗"射频芯片完成低功耗、小成本的硬件设计。通过增加SIM卡的数量,将网关转发"北斗"数据的频率降至最低的5 s,提高了网关的通信速率。通过软件设计实现了Zigbee无线传感网络和"北斗一代"系统之间数据的透明交换。该方法已成功应用于野外油气井远程监控系统中。     

Improving broadcast performance by traffic isolation in wireless ad hoc networks

In this paper we propose a new broadcasting algorithm. In the proposed method we significantly reduce the broadcast overhead and also improve the broadcast delivery ratio in mobile networks. A novel traffic isolation method has been used which reduces the control message exchange. The proposed broadcasting method is based on a clustering method called ‘stability‐based clustering algorithm’ which had been proposed before. The broadcasting traffic is divided into internal (flow inside a cluster) and external traffic (flow among the clusters). For internal flooding traffic, cluster‐heads and gateways are responsible for re‐broadcasting but for external type, border nodes may perform the forwarding function as well. This simplifies the gateway selection method through the local selection of gateway nodes by its cluster head. Therefore, a cluster head selects gateway in its own cluster without any knowledge of other clusters. Considering the effect of mobility and node density, simulations have been conducted in a number of wireless environments. Simulation results show the broadcast coverage is close to 100% at different node speeds. Moreover, we study the broadcast parameters in light and dense networks and show improvement of the overhead and the number of forward nodes in comparison to other broadcasting methods. Copyright © 2005 John Wiley & Sons, Ltd.     

A Novel Gateway Selection Technique for Throughput Optimization in Configurable Wireless Mesh Networks

Wireless mesh networks (WMNs) have attracted much attention due to their low up-front cost, easy network deployment, stable topology, robustness, reliable coverage, and so forth. These advantages are suitable for the disaster recovery applications in disaster areas, where WMNs can be advantageously utilized to restore network collapse after the disaster. In this paper, based on a new network infrastructure for WMNs, to guarantee high network performance, we focus on the issue of throughput optimization to improve the performance for WMNs. Owing to selecting different mesh router (MR) as the gateway will lead to different network throughput capacity, we propose a novel gateway selection technique to rapidly select the optimal MR as the gateway, in order to maximize the network throughput. In addition, we take into account the traffic distribution for the MR to eliminate traffic congestion in our method. The performance of our proposed method is evaluated by both numerical and simulated analysis. The simulation results demonstrate that the gateway selection method is effective and efficient to optimize the throughput for WMNs.     

基于GPRS和Socket机制实现多媒体消息传输的研究

文中介绍了一种利用GPRS网络以及Socket通信机制，通过GPRS无线模块实现发送多媒体消息的方法．在多媒体消息发起方的事务处理部分，通过AT命令控制modem登录GPRS，建立网络连接；使用会话管理工具，通过数据报型套接字与WAP网关建立会话；将已封装好的MMS协议数据单元提交至网关，成功实现多媒体消息的发送。     

基于SIP的VOIP系统合法侦听

基于SIP的VOIP属于分布式结构。在提出的模型中,侦听数据的获取涉及到SIP代理服务器和网关。在SIP代理服务器上获取信令数据,从网关上得到通信内容。所以,基于SIP的VOIP系统侦听的实现还涉及到代理服务器和网关的协调工作。     

Gateway load balancing using multiple QoS parameters in a hybrid MANET

A Mobile ad hoc network (MANET) is a self configurable wireless network in which mobile nodes communicate with each other in a multihop fashion without any pre-installed infrastructure. A MANET can be considered to be a standalone network. To enhance the connectivity of a MANET it can be connected to the fixed network, thus forming a heterogeneous network. The integration of MANET and the Internet is called a hybrid MANET which is facilitated by special nodes called Internet gateway nodes. Load balancing among gateways is a challenging task when a MANET is connected to Internet. Gateway nodes with higher loads will lead to disconnected networks and depletes the node’s resources which include their batteries, memory and bandwidth quickly. Gateway selection based on the shortest path may increase traffic concentration on one particular gateway which leads to congestion and increases delay in the network. In this paper a QoS based load balancing mechanism has been proposed among multiple gateway nodes that provide communication between mobile nodes and fixed nodes in the Internet to select lightly loaded gateways so that more packets will be delivered to the fixed host in the Internet. The proposed QoS based scheme selects four QoS parameters that are (1) connecting degree, (2) interface queue length, (3) routing table entries and (4) hop count. A weight based method is used to select the gateway which combines all four QoS metrics. Simulation results demonstrate that when compared with individual parameter, the average ETE delay, queue size and traffic load of gateway generated by proposed algorithm is decreased by 17, 25 and 15 % respectively and when compared with existing schemes, the average ETE delay, queue size and traffic load of gateway is decreased by 25, 25 and 16 % respectively.