IEEE 802.11安全算法WEP

有线等价协议WEP是在IEEE802．1l标准中采用的信息保密机制，它主要用于保障无线局域网络中链路层信息数据的保密。对WEP的工作机理进行了分析，重点对其安全性能进行了研究，并发现WEP不能对无线局域网中的数据提供可靠的保护。最后，提出了对WEP进行改进的建议。     

蓝牙无线测控系统的实现

介绍了蓝牙技术应用于测控领域可设计出无线测控系统,给出了蓝牙无线测控系统的硬件和软件实现方案。     

一种多层胶板雷达吸波材料

依据阻抗匹配原理,设计了具有“陷阱”结构的多层吸波材料.通过方案优化,设计出五层结构的吸波材料,该材料在2～18 GHz频段内具有双吸收峰的宽带吸收特性.改变第五层的厚度,可以调整高频吸收峰的位置,而对低频吸收峰影响不大.应用阻抗圆图,直观显示了三种设计方案的阻抗变换情况.研制的JB-5多层吸波材料,在6 ～ 17 GHz频段内,反射率≤-12 dB,材料厚度小于5.0 mm,并有良好的耐环境性能.该吸波材料可在实验室制作,根据需要裁剪成一定形状,用专用黏结剂粘贴在目标体表面,能有效降低目标对雷达波的反射.     

High Hardware Utilization and Low Memory Block Requirement Decoding of QC-LDPC Codes

This paper presents a simple yet effective decoding for general quasi-cyclic low-density parity-check (QC-LDPC) codes, which not only achieves high hardware utility efficiency (HUE), but also brings about great memory block reduction without any performance degradation. The main idea is to split the check matrix into several row blocks, then to perform the improved message passing computations sequentially block by block. As the decoding algorithm improves, the sequential tie between the two-phase computations is broken, so that the two-phase computations can be overlapped which bring in high HUE. Two overlapping schemes are also presented, each of which suits a different situation. In addition, an efficient memory arrangement scheme is proposed to reduce the great memory block requirement of the LDPC decoder. As an example, for the 0.4 rate LDPC code selected from Chinese Digital TV Terrestrial Broadcasting (DTTB), our decoding saves over 80% memory blocks compared with the conventional decoding, and the decoder achieves 0.97 HUE. Finally, the 0.4 rate LDPC decoder is implemented on an FPGA device EP2S30 (speed grade -5). Using 8 row processing units, the decoder can achieve a maximum net throughput of 28.5 Mbps at 20 iterations.     

可容忍信标误差的三维传感网节点定位方法

针对信标位置存在误差情况下的三维无线传感器网络节点定位问题,提出一种基于正交回归的多跳定位方法.同时考虑到自变量误差和因变量偏差对节点坐标估计的影响,基于约束加权正交回归参数估计准则,建立可容忍信标位置误差的三维多跳定位模型,解决了信标位置和距离估计两方面的误差并存时的节点自定位问题,并给出求解节点坐标最优值的数值方法;推导出相应的坐标估计精度评估标准3D-MCRB (3D Multi-hop Cramér-Rao Bound).仿真结果表明:此方法对信标位置误差和距离估计误差都具有较好的抑制能力,在大多数实验条件下,能将定位精度提高10%以上.     

基于ZigBee的无线网络在航天领域的应用

文章概要介绍基于ZigBee的无线网络的研究现状,结合其应用优势,通过仿真分析指出:在航天器应用环境下,当网络工作在信标使能模式时,若网络中存在多个节点或者网络负载很大,则会造成大量的碰撞和重传,使得网络的吞吐量急剧下降;而当网络工作在非信标使能模式时,不会造成大量的碰撞和重传,网络性能优于信标使能模式。文章还对基于ZigBee的无线网络在多址接入和组网、共存和互联互通、应急通信和机动配置方面的航天应用研究前景进行了展望。     

轴流风扇宽频噪声声功率实验研究

航空发动机降噪研究迫切需要一种叶轮机械管道内宽频噪声测量方法来指导降噪设计。为了研究管道内宽频噪声,利用沿管道内壁面布置的环形麦克风阵列对单级轴流风扇进行了噪声测量,通过测量信号与参考信号互相关以及奇异值分解(SVD)方法成功地得到管道内宽频噪声结果。结果表明:该方法不仅可以计算出管道内主要单音,而且可以计算宽广频率范围内的宽频噪声;并能有效分辨出管道内向前和向后传播的声功率。宽频噪声结果证实该方法可以应用到高背景噪声和硬壁反射下的管道内声场研究。     

Low-Cost Wireless Sensor Network Node Design for Multi-point Bolt Loosening Detection

Bolted connections are commonly used in aerospace structures.Once the bolts on the aircraft are damaged or loose,the consequence will be disastrous.Therefore,monitoring bolt loosening is especially required.However,periodic manual inspection costs much money and time.And it is very difficult to achieve multi-point monitoring for many bolted structures in an aircraft.Therefore,a low-cost,reliable detection method based on wireless sensor networks is presented.The reed switch is selected as a sensor for bolt loosening monitor.The chip PT2262 and PT2272are chosen as hardware codec chip for multi-point placement.A wireless transmitter and receiver circuit is designed on 315 MHz frequency.The codec chip and the wireless transmission are triggered by the reed switches.Bolt loosening is detected by the receiving terminal and indicated by light and sound alarms.The wireless transmitter and the receiver circuit are tested and the monitoring system is verified by experiments.The results show that bolt loosening can be effectively detected within 300 m.The developed sensor network is expected to solve multi-point bolt detection problems and provide a low-cost and reliable monitoring technology.     

基于最小跳数的无线传感器网络跨层设计

传统的严格分层参考模型无法实现对无线传感器网络资源的有效管理和运用,跨层设计是提高网络整体性能的一种有效方法。针对无线传感器网络能量、计算资源、存储资源和带宽资源有限的特点,提出一种基于最小跳数的路由层和MAC层的跨层协议设计方案。MAC层和路由层通过共享sensor节点到sink节点的最小跳数信息,在MAC层建立时间梯度,解决多个节点共享无线信道的问题;并在路由层建立路由表,解决路由选择问题。仿真结果表明,该方案在降低网络能耗的同时,在降低传输延迟,提高数据投递率方面也取得了良好的性能。     

无线传感网的分布式非测距三维定位算法

为解决三维空间无线传感器网络节点定位问题,基于区域立体网格化表示的思想,提出一种分布式非测距三维定位算法3D-DRL(three-Dimensional Distributed Range-free Localization).通过对立体网格投票,选取得票值最高的所有网格的质心作为未知节点的估计位置.3D-DRL无需未知节点间相互通信,具有较小的通信开销,不依赖于锚节点比例,且对网络拓扑结构具有鲁棒性.仿真结果表明,在无线传播环境理想、未知节点通信半径R=50 m、所有节点均随机部署在100 m×100 m×100 m三维区域的情况下,定位误差小于未知节点通信半径的8%,且通过调整VANR,能够实现所有节点的定位.