基于定向天线的WSN路由关键技术研究

定向天线相比于全向天线可提高无线传感器网络的吞吐量,减少通信信道之间的干扰,提高网络信噪比,且能有效提升无线传感器网络路由协议DRP的性能,本文针对定向天线技术在无线传感器网络的实现方法,分析其应用优势,并对定向路由中的主要技术进行分析。     

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。     

采用定向天线Ad Hoc网络MAC协议关键问题研究

介绍基于定向天线的MAC协议,阐述使用定向天线所面临的隐藏终端、暴露终端以及聋节点问题。重点分析定向天线的MAC协议造成隐藏终端和暴露终端的原因以及解决这些问题的相应策略,在此基础上提出了新的改进CSMA协议。通过仿真表明,改进CSMA协议能提高基于定向天线Ad Hoc网络的整体性能。     

某型船载移动站天线伺服系统设计和仿真

天线伺服系统是某型船载移动站的关键分系统之一,负责为船载移动站提供信号来源,其性能好坏直接关系到微波链路能否可靠传输;讲述了船载移动站组成及工作原理,设计了移动站的天线及伺服结构,仿真结果表明设计的L波段定向天线和UHF波段全向天线达到了系统指标要求。     

一种新的支持定向天线应用的忙音和功率控制多址接入协议

该文针对移动Ad Hoc网络(MANET),提出了支持定向天线应用的忙音和功率控制多址接入协议(BT-DMACP)。协议充分考虑到定向天线应用中存在的特殊隐藏终端问题和旁瓣干扰,利用RTS/CTS短分组对话机制、定向忙音信号和基于信噪比门限的功率控制策略,对数据分组的定向发送功率进行实时调整。同时为准确估计接收节点处的最大干扰功率,设计了自适应干扰功率估计算法。仿真结果证明,BT-DMACP协议能有效支持定向天线在MANET中的应用,在降低了系统功耗同时,具有很高的信道利用率。     

基于定向天线的移动自组网TDMA协议研究

传统的移动自组网大多采用全向天线组网,为提高传输距离、减少时隙冲突、提高时隙利用率,因此在组网过程中引入定向天线。为解决移动自组网中因引入定向天线带来的时隙冲突问题,论文从研究较为成熟的DTRA协议出发,通过在帧结构中增加随机微时隙的方式来减少时隙冲突。为给网络中各节点提供高效、公平的时隙分配策略,论文改进了DTRA协议中的时隙预留过程,提出了基于节点自身缓存队列数分配不同优先级时隙数目的动态时隙分配算法。通过提出的DTDMA协议与DTRA协议进行的对比仿真,验证了提出的DTDMA协议能够有效减少时隙冲突,且协议在保证高优先级节点可多申请数据时隙的前提下,改善了节点接入信道的公平性。     

多目标无人机跟踪与测控方法

本文给出了多目标捕获、跟踪基本方法。对双向/全向天线、监视雷达/全向天线、单定向天线、多定向天线、相控阵天线以及多波束天线在无人机多目标跟踪与测控应用进行简单叙述。     

基于定向天线的移动自组网TDMA协议研究

传统的移动自组网大多采用全向天线组网,为提高传输距离、减少时隙冲突、提高时隙利用率,因此在组网过程中引入定向天线。为解决移动自组网中因引入定向天线带来的时隙冲突问题,论文从研究较为成熟的DTRA协议出发,通过在帧结构中增加随机微时隙的方式来减少时隙冲突。为给网络中各节点提供高效、公平的时隙分配策略,论文改进了DTRA协议中的时隙预留过程,提出了基于节点自身缓存队列数分配不同优先级时隙数目的动态时隙分配算法。通过提出的DTDMA协议与DTRA协议进行的对比仿真,验证了提出的DTDMA协议能够有效减少时隙冲突,且协议在保证高优先级节点可多申请数据时隙的前提下,改善了节点接入信道的公平性。     

Ad Hoc网中的一种新型MAC协议

在移动Ad Hoc网络中,一个最基本的问题就是如何在避免隐藏终端和暴露终端问题的同时,增加信道利用率．．针对这个问题．在现有的DBTMA协议以及采用定向天线的一些协议的基础上．提出了一种把信道划分与定向天线相结合的新型MAC协议．DC／A协议（Dual Channel／Directional Antennas)一仿真结果表明这种新的MAC协议可以有效改善网络性能.     

毫米波室内传播的场强测量

介绍了毫米波室内传播的场强测量。通过对测量的数据进行处理,可得无论使用全向天线还是定向天线作为接收天线,路径损耗指数都约等于２。慢衰落的累积概率分布符合对数正态分布。快衰落的累积概率分布在没有直达波的民政部下符合瑞利分布,而在有直达波的情况下,如果使用全向天线则趋向瑞利分布,使定向天线符合莱斯分布。     

Detection Probability Estimation of Directional Antennas and Omni-Directional Antennas

This paper studies the problem of detection of directional antennas and omni-directional antennas by hostile detection systems. We present a model for calculating the probability of detecting a transmitter at arbitrary location around the transmitter. Our study shows that, if a directional antenna employs the same transmit power as an omni-directional antenna, the directional antenna can not decrease the probability of being detected. In some scenarios, a directional antenna is more likely to be detected than an omni-directional antenna. However, if a directional antenna provides the same Effective Isotropic Radiated Power in the direction of the receiver as an omni-directional antenna, the transmit power needed by a directional antenna to send data is much less than that of an omni-directional antenna. In this scenario, the probability of detecting a directional antenna is reduced by over 90%. This reveals that directional antennas can be used to build a secure path to send data at low probability of being detected by adversaries.     

一种基于多天线的动态TDMA协议仿真研究

提出一种用于Ad Hoc网络MAC层的多天线、多信道动态TDMA协议,它采用一个全向天线和多个方向性的扇区天线.该协议通过空分复用控制,可提高网络的吞吐量,通过基于动态时隙分配算法和相应的邻居发现策略,以减少时隙空闲,提高信道利用率.利用NS-2平台进行的仿真研究表明,与单一全向天线的MAC协议相比,所提出的协议在吞吐量和时延方面有明显的提高.     

宽带无线Mesh网络中的多扇区天线阵列设计

在宽带无线Mesh网络中,为了扩展传输距离和提升链路速率,天线的性能至关重要。提出了一种多扇区天线阵列,每个扇区天线为带反射板的微带偶极子阵列天线,工作频段为5.1～5.9 GHz,其水平主瓣张角为45°,增益为18 dbi。多扇区天线阵列共包括8个扇区,信号在各扇区天线间进行动态切换,从而实现水平360°全向覆盖。通过采用HFSS三维电磁场仿真工具进行仿真及实际生产并在微波暗室中进行测试,结果表明和传统无线Mesh网络所采用的全向天线相比,在满足全向覆盖的同时,天线的方向性有了很大的改善。     

On Busy-Tone Based MAC Protocol for Wireless Networks with Directional Antennas

The application of directional antennas in wireless ad hoc networks offers numerous benefits, such as the extended communication range, the increased spatial reuse, the improved capacity and the suppressed interference. However, directional antennas can cause new location-dependent carrier sensing problems, such as new hidden terminal and deafness problems, which can severely degrade the network performance. Recently, a few schemes have been proposed to address these problems. However, most of these existing methods can only partially solve the hidden terminal and deafness problems. Some of them even bring significant performance overhead. In this paper, we propose a novel MAC protocol, in terms of the busy-tone based directional medium access control (BT-DMAC) protocol. In BT-DMAC, when the transmission is in progress, the sender and the receiver will turn on their omni-directional busy tones to protect the on-going transmission. Integrating with the directional network allocation vector (DNAV), the scheme can almost mitigate the hidden terminal problem and the deafness problem completely. We then propose an analytical model to investigate the throughput performance of BT-DMAC. The numerical results show that BT-DMAC outperforms other existing directional MAC schemes. We next evaluate the performance of BT-DMAC through extensive simulation experiments. The results show that our proposed BT-DMAC scheme has superior performance to other existing solutions, in terms of higher throughput.     

Exploiting Macrodiversity with Distributed Antennas in Micro-Cellular CDMA Systems

We consider the use of distributed antennas to increase the capacity and peak data rate achievable in a microcellular CDMA system with limited bandwidth. In additon to the diversity against Rayleigh fading achievable by use of microdiversity among nearly co-located transmit or receive antennas, we exploit macrodiversity against shadow fading that more widely separated antennas permit. We report on antenna configurations for both directional and omni-directional antennas that provide the most uniform signal-to-interference ratio coverage, averaged over a large number of position vectors drawn from a spatially uniform distribution of mobiles. Call capacities and peak transmission rates are determined for an integrated system carrying traffic at different constant rates, where processing gain and the transmission rate are selected to satisfy a common chip rate. For the downlink a 5.5 dB capacity gain can be achieved for 64 kb/s calls using four antennas located on the diagonals of each square cell. A bandwidth of 5 MHz allows two or more calls to be simultaneously supported at data rates up to 512 kb/s, as opposed to only 128 kb/s for three co-located antennas. On the uplink we distinguish between the computationally simpler equal-gain combining of the antenna signals and the possibly more complex maximum-ratio combining. With equal gain combining we achieve a peak data rate of 128 kb/s and a capacity gain of 2.5 dB relative to equal gain combining of three nearly co-located antenna signals. With maximum ratio combining the peak uplink rate can be as high as 512 kb/s and the capacity is increased by 2.0 dB relative to the maximum-ratio combining of three co-located antennas.     

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.     

A compact flush-mounting antenna with direction finding and steerable cardioid pattern capability

A flush-mounting antenna is described which could be used, in lieu of present antennas, to provide direction finding and steerable directional pattern capability in airborne beacon transponder systems. The antenna is comparable in size to the existing, omni-directional antennas presently used for air-traffic control and military identification, friend or foe (IFF) functions. The design and performance of an experimental model of the antenna are discussed.     

机载共形的双环微带缝隙全向天线

机载全向天线不但要满足水平面全向的指标要求,而且要与机体表面共形设计,常规的单极子天线和微带天线均无法满足要求。提出一种双环微带缝隙天线,可以实现机载共形的全向天线。分析了系统对机载天线的要求、双环微带缝隙天线的展宽带宽的方法,并给出了该天线的设计参数和实测结果,实测结果与仿真结果一致,验证了设计方法的正确性。     

Performance Analysis of Directional CSMA/CA for IEEE 802.15.3c under Saturation Environments

In this paper, the directional carrier sense multiple access/collision avoidance (CSMA/CA) protocol in the immediate acknowledgement mode for IEEE 802.15.3c is analyzed under saturation environments. For the analysis, a sensing region and an exclusive region with a directional antenna are computed probabilistically and a Markov chain model in which the features of IEEE 802.15.3c and the effects of using directional antennas are incorporated is analyzed. An algorithm to find the maximal number of concurrently transmittable frames is proposed. The system throughput and the average transmission delay are obtained in closed forms. The numerical results show the impact of directional antennas on the CSMA/CA media access control (MAC) protocol. For instance, the throughput with a small beamwidth of antenna is more than ten times larger than that for an omnidirectional antenna. The overall analysis is verified by a simulation. The obtained results will be helpful in developing an MAC protocol for enhancing the performance of mmWave wireless personal area networks.