基于定向天线的导航信号参数估计方法研究

为了实现非合作导航信号的监测,必须估计非合作导航信号的多普勒频率、伪码速率、伪码周期、信号功率和码序列等多个参数。提出一套非合作导航信号盲检测与参数盲估计方法,利用导航信号循环平稳特性估计信号频率、码速率和信号功率,再根据周期信号自相关方法估计伪码周期,最后使用滑动相关和数据累加方法估计信号码序列。仿真结果验证了提出方法的正确性。     

基于概率估计的运动目标检测算法

针对现有智能视频中运动目标检测算法存在的问题,提出一种新的对称差分及背景减除相融合的算法。该算法基于子块操作,首先利用高斯分布的概率特性,分离出运动变化区域和静止区域,对分割阈值的选取进行了改进;然后背景重构;最后通过背景和变化区域相差分得到精确运动目标分割。实验结果表明,该方法能够对监控场景中运动目标进行有效的分割,对光线变化、背景干扰不敏感,具有较好的鲁棒性和实用性。     

一种基于定向天线的邻节点发现算法

为充分利用定向天线的引入而带来的技术上的优势,提出了一种基于定向天线的自组网邻节点发现算法。通过空闲节点定向快扫描侦听信道,发送节点在相同方向上发送6次HELLO信息来减少隐藏终端问题,同时引入节点信息共享机制。仿真结果表明,该发现算法具有发现速度快,对节点密度有较好的适应性等特点。     

Multicast Communication in Ad Hoc Networks with Directional Antennas

This paper investigates the benefits and impacts of using directional antennas for multicast communications in ad hoc networks. In terms of signal reception, directional antennas have shown considerable improvement in the performance of all aspects over omni-directional antennas, especially over dense networks with heavy traffic load. In addition, we have found that transmitting multicast packets directionally to known neighboring group members or forwarders can help reduce the average end-to-end packet delay and increase the overall throughput. However, directional transmission of unacknowledged data transfers may result in lower performance in terms of packet delivery ratio than omni-directional transmission in any carrier sensing MAC protocols under moderate load due to the effect from the hidden terminal problem. Both analytical results and simulation results, as well as an acknowledgment mechanism to improve the successful delivery rate of multicast data packets, are presented. Prepared through collaborative participation in the Communications and Networks Consortium sponsored by the U.S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon.     

定向天线的Ad hoc网络邻居发现

在Ad hoc网络中邻居节点发现（Neighbor Discovery）是网络初始化中的重要步骤之一,节点邻居的信息对于几乎所有的链路选择和路由算法都有着重要的影响,特别是在采用方向性天线时邻居发现不仅难度更大而且其影响作用也更明显。通过分析在采用方向性天线时的Ad hoc网络中的邻居发现算法,总结出了其一般步骤,即首先通过判断网络规模来进行天线收发模式选择算法和扫描图案的选择,然后再设计相应的通信握手协议。     

新型定向超宽带天线

基于圆片单极天线是一种结构简单的超宽带天线,研究了一种新型的超宽带天线,它将4个圆片单极天线垂直交叉放置作为馈源并采用平板反射面,实现定向以及双极化或圆极化特性。分析了2种变形形式:将平板反射器换为抛物面反射器,实现高增益特性;将圆片振子变形,实现更宽的低频端阻抗带宽。通过电磁仿真软件,计算了天线的S参量和辐射方向图随频率的变化规律。分析表明文中的天线对于传统的圆片单极天线有了有效的改进,实现了超宽带、定向辐射、双极化、圆极化、高增益等不同的特性,它们在卫星通信和移动通信中具有良好的应用前景。     

Control of the Directional Pattern of Multielement Plasma Vibrator Antennas

Journal of Communications Technology and Electronics - This paper presents an analysis on the possibilities of controlling the radiation pattern of Yagi-type multielement plasma vibrator antennas....     

Outage Probability in Mobile Telephony with Directive Antennas and Macrodiversity

Signal-to-interference ratio statistics for mobile telephony systems with hexagonal coverage areas, multiple interferers, and threecorner base stations are investigated. Corner base stations simultaneously reduce total interference (because of antenna directivity) and provide macrodiversity against shadow fading. Our results indicate that for 3 or 7 channel sets, with 2 tiers of interferers and typical system parameters (propagation exponent of 3.7 and lognormal spread of 8 dB), the improvement is on the order of 11 dB over a baseline arrangement which employs centrally located omnibase stations without macrodiversity. Additional considerations of blocking probabilities and average voice activity indicate possible further improvements.     

定向天线合成取代全向侦察天线性能分析

分析了在ESM侦察设备中利用不同方位的多个定向天线合成的方法实现全向信号接收的性能,分析表明,这种方法在一定程度上可以取代全向天线或半全向天线,用来提供测频信号。     

椭圆形阵列天线的方向特性研究

对椭圆形阵列天线的方向特性进行了研究,证明了直线阵和圆环阵是椭圆形阵的特例。给出了椭圆形天线阵及在椭圆的中心和两个焦点上分别或同时加上一个阵元的情形下天线阵的方向性函数,并绘制了相应的方向性图,仿真计算结果表明在椭圆的中心和焦点处加上阵元可有效地降低副瓣,同时又不增加阵列的孔径。     

基于全向小波的图像边缘检测算法

 针对现有边缘检测算法难以提取图像任意方向的边缘特征,提出基于全向小波的图像边缘检测算法.首先,定义了全向小波的概念、构造其模型并推导了全向小波的最大值与梯度模值相等的关系.理论分析表明本文算法始终沿小波变换值的最大值方向提取边缘.然后,选择二维高斯函数实例化模型,以8方向和3×3变换窗为例进行算法设计.标准图像对比试验表明本文算法能提取更多方向的边缘特征、边界清晰度也比SADD算法、Canny算子分别高出约2.17%、8.66%.     

中波四塔、八塔定向天线调试方法

本文结合无线局2022台中波四塔、八塔定向天线的调试过程，介绍了中波四塔、八塔定向天线的馈电原理、电气要求和调试方法。     

Receiver-Oriented Multiple Access in Ad Hoc Networks with Directional Antennas

Directional antennas can adaptively select radio signals of interest in specific directions, while filtering out unwanted interference from other directions. A couple of medium access protocols based on random access schemes have been proposed for networks with directional antennas, using the omnidirectional mode for the transmission or reception of control packets in order to establish directional links. We propose a distributed receiver-oriented multiple access (ROMA) scheduling protocol, capable of utilizing multi-beam forming directional antennas in ad hoc networks. Unlike random access schemes that use on-demand handshakes or signal scanning to resolve communication targets, ROMA computes a link activation schedule in each time slot using two-hop topology information. It is shown that significant improvements on network throughput and delay can be achieved by exploiting the multi-beam forming capability of directional antennas in both transmission and reception. The performance of ROMA is studied by simulation, and compared with a well-know static scheduling scheme that is based on global topology information.     

Asymptotic Connectivity in Wireless Ad Hoc Networks Using Directional Antennas

Connectivity is a crucial issue in wireless ad hoc networks (WANETs). Gupta and Kumar have shown that in WANETs using omnidirectional antennas, the critical transmission range to achieve asymptotic connectivity is $O(sqrt{log n/n})$ if $n$ nodes are uniformly and independently distributed in a disk of unit area. In this paper, we investigate the connectivity problem when directional antennas are used. We first assume that each node in the network randomly beamforms in one beam direction. We find that there also exists a critical transmission range for a WANET to achieve asymptotic connectivity, which corresponds to a critical transmission power (CTP). Since CTP is dependent on the directional antenna pattern, the number of beams, and the propagation environment, we then formulate a non-linear programming problem to minimize the CTP. We show that when directional antennas use the optimal antenna pattern, the CTP in a WANET using directional antennas at both transmitter and receiver is smaller than that when either transmitter or receiver uses directional antenna and is further smaller than that when only omnidirectional antennas are used. Moreover, we revisit the connectivity problem assuming that two neighboring nodes using directional antennas can be guaranteed to beamform to each other to carry out the transmission. A smaller critical transmission range than that in the previous case is found, which implies smaller CTP.      

复杂背景下基于贝叶斯-全概率联合估计的前景检测

针对复杂背景下前景提取较为困难或者提取准确率较低等问题,该文提出了基于贝叶斯-全概率联合估计的目标检测模型并引入了背景误差控制变量的概念。通过选择适当的特征向量,在贝叶斯-全概率估计模型下,背景像素将会分为静止与运动两种不同的类型,进而准确提取前景像素点。实验结果表明,该模型是一个较为通用的目标检测模型,在目标提取时,该文算法对各种类型的视频背景环境(包括复杂背景)都具有较好的适用效果。     

基于定向天线的移动自组网路由协议研究

同等功耗下,定向天线能够产生更高的增益,提供更大的传输范围,提高网络的空间复用度和吞吐量,天线选择的方向性又降低了邻近结点之间的相互干扰,采用定向天线能够给移动自组网带来潜在性能的提高。对基于定向天线的移动自组网路由协议进行研究,简单介绍了定向天线,总结了引入定向天线产生的路由问题,对现有的一些典型定向路由协议进行了分类、介绍和比较,最后对引入定向天线带来的好处进行了分析。     

Energy-Efficient Routing Algorithms Using Directional Antennas for Mobile Ad Hoc Networks

Power consumption is an important issue in the wireless ad hoc networking environment. In this paper, we present several energy-efficient routing algorithms using directional antennas for wireless ad hoc networks. These algorithms are simple to implement and are distributed and can be applied to mobile environments. We evaluate how directional antennas improve system throughput. We study the influence of the battery recovery effect and mobility on the network throughput during a network lifetime. We also present an algorithm that exploits the broadcast nature of the wireless communication environment to improve end-to-end bit error performance for a Rayleigh fading channel.     

Cochannel Interference in Cellular Fixed Broadband Access Systems with Directional Antennas

The Cellular Fixed Broadband Access System for LMCS (Local Multipoint Communication Services) is aiming to provide broadband services to fixed subscribers through wireless access. A representative LMCS scenario involves a cellular system design with the entire allocated bandwidth being used in each cell and with a highly directional antenna employed at the subscriber. The LMCS system designs rely on assumed information regarding radio propagation phenomena in the anticipated coverage areas. The research reported here, therefore, has the objective of verifying such information by theoretical modeling and simulation. Simulation and analysis have been used to study the effects of a number of factors on the system performance and interference characteristics of such a LMCS system. The investigated factors include beamwidth and gain ratio of directional antennas, sectorization of hub antennas, propagation exponent, lognormal shadowing, site diversity and transmitter power control. Both models of LOS (line of sight) and NLOS (non-line of sight) have been investigated in this work. The simulation results demonstrate that highly directional antennas at the subscribers can dramatically improve the system performance for both uplink and downlink. The system design with frequency reuse of one is examined, and it is confirmed that an outage of 0.9% for a NLOS system could be achieved by using narrow beam antennas of 3 degrees with site diversity and power control techniques employed. Under the condition of LOS available for the desired links, the outage can be expected to be as low as 0.3%.     

定向Ad hoc网络MAC组网技术研究

定向天线利用数字信号处理技术产生空间定向波束,将发射信号能量集中在某一个或者某些特定的方向上进行辐射,其应用于传统的Ad hoc网络中能够有效减少相邻节点间的互干扰,并能通过增加同时传输的节点对数达到显著提升网络空间复用率和容量的目的。首先简单介绍了定向天线和定向通信特点,然后对定向Ad hoc网络MAC层组网关键技术进行了综述,并对定向邻居发现协议、空分TDMA动态时隙分配机制、定向波束对准与跟踪技术等进行介绍和梳理,最后总结现有研究不足并指出未来重点研究方向。