DOA estimation of wideband sources without estimating the number of sources

In this paper, we propose a new technique to estimate wideband source directions from the sensor snapshots without requiring to know the number of sources present in the scenario. This work is motivated by the fact that the existing model order estimation (number of sources) techniques for wideband source scenario are either inaccurate or computationally expensive. Direction-of-arrival (DOA) estimation is realized using a beamformer framework which imposes nulls in the spatial spectrum along the source directions. The null width along the frequency axis is widened by introducing a new data dependent term into the optimization problem, thus achieving wideband capability. Furthermore, the temporal processing of the data snapshots drastically reduces the number of snapshots required for wideband DOA estimation. The effectiveness of the proposed formulation is studied with simulated experiments.     

Suppression of cryocooler-induced microphonics in infrared imagers

Sophisticated portable infrared imagers developed for surveillance, reconnaissance, targeting and navigation play a vital role in the modern tactics used for carrying out military and antiterrorist operations. Their superior performance relies on novel optronic technologies and maintaining the infrared focal plane arrays at cryogenic temperatures using close cycle mechanical Stirling cryogenic coolers.Such coolers are well known sources of high-frequency interference contaminating the image signal and causing essential degradation in the overall imagery performance. This phenomenon is generally referred to as microphonics, which mostly manifests itself at the resonant frequencies of sensitive mechanical components of infrared packages.The ruggedizing of these components involves stiffening and dampening which are, evidently, not the best solutions to implement inside, say, an evacuated envelope, where the issues of added heat load, thermal mass, ageing, vacuum contamination due to outgassing are of the primary concern.The paper examines the idea of using externally mounted wideband dynamic absorbers for suppressing the above resonant responses and associated microphonic noise. The suggested analytical model relies on a set of complex frequency response functions experimentally captured on the original infrared package. The optimised dynamic absorber yields about a tenfold suppression of the resonant responses and a threefold attenuation of the overall RMS level of microphonic noise. The results of the analytical prediction are in fair agreement with experimental data.     

西气东输江都-如东线网络架构的优化

针对西气东输江都-如东线频繁出现网络故障的情况,基于江都-如东线现有网络架构,分析了网络系统存在的不足,对网络架构进行了优化,重新划分了局域网,处理了网络环网,禁用了路由器的多余广播,进行了风暴控制,优化了ESD系统参数,提出了在江都-如东线进行网络架构优化的方案。通过对思科交换机、思科路由器、SIXNET交换机和ESD系统的配置进行修改,以及为期1年的试运行,实现了网络故障零发生的目标,提高了网络通讯的质量,保证了系统的可靠性和安全性。     

帧中继业务互扰问题的分析与解决措施

帧中继网络采用比特透明数据业务部件传输同步数据,采用虚拟路由器部件传输IP数据,针对网络运行过程中出现的不同传输链路的IP数据相互影响和IP数据影响同步数据现象,测试发现与带宽利用率有关。分析了优先级相同时用户数据报协议(UDP)数据比传输控制协议(TCP)数据更易受数据流量影响和入口数据流量过大的原因,以及帧中继不同类型业务发送优先级的对应关系,通过接入限速控制数据流量,并根据不同用户数据特点与传输要求设置相应优先级,问题得到有效解决。实际应用表明,基于限速策略和区分发送优先级的解决措施能够有效防止不同业务相互间的影响,确保重要数据稳定可靠地传输,可为解决其他类似问题提供参考。     

基于TD-LTE技术实现企业客户视频传输业务的研究与应用

随着社会安全意识的提高,政府、企业集团客户视频监控传输类需求呈现快速的上升趋势,尽管视频传输业务在有线通信资源满足的条件下已经有较为成熟的解决方案,但是在无法铺设有线管道或现有管线资源无法满足的场景如河坝、山区等仍然面临很大的设计实施困难,尚未形成有效的解决措施。针对以上问题,结合TD-LTE无线通信的传输特点,研究了通过TD-LTE无线通信方式实现集团客户视频传输业务的方法,并结合TD-LTE无线通信的特点给出了相应的解决方案。     

Performance of closed loop transmit diversity in a Rayleigh fading channel

In this paper, the closed loop transmit diversity technology for the Wideband Code Division Multiple Access（WCDMA） systems is investigated in a multipath Rayleigh fading channel. The RAKE receiver model and the weighing vector algorithm are presented. The performance is theoretically analyzed in terms of the average maximal Signal-to-Noise Ratio（SNR） gain available over the Space-Time block coding based Transmit Diversity（STTD） technology. Theoretic analysis and simulation results show that the closed loop transmit diversity can provide a 3dB performance gain over the open loop scheme in a single path fading channel, while the performance gain decreases dramatically with the increasing inherent multipath diversity of the wireless channel.     

Frequency estimation of sinusiode from wideband using sub-Nyquist sampling

A novel frequency estimation algorithm for wideband signal with sub-Nyquist sampling is proposed in this paper. With the aid of information provided by the auxiliary delayed sampling channel and the aliased frequency estimation for wideband signal with sub-Nyquist sampling, the frequency aliasing due to sub-Nyquist sampling can be solved. This method can reduce the complexity of the overall hardware at the cost of an auxiliary sampling channel. Furthermore, in order to alleviate the computation burden for its practicability, a more simplified algorithm is put forward and its validity is proved by our numerical simulation results. The Cramer-Rao Lower Bound （CRLB） of the frequency estimation is also derived at the end of this paper.     

基于校园网中的虚拟路由集群技术

首先讨论了虚拟路由集群中ARRP协议的功能、优点、工作原理以及校园网所需的对应网络拓扑结构。然后讨论和分析了虚拟路由集群技术在校园网中的实现方法。最后通过仿真实验,给出了校园网一种基于虚拟路由集群技术的可靠性方案。     

TendaAX12路由器0-Day栈溢出漏洞挖掘方法

随着 5G 技术对物联网发展的加速, 预计到 2025 年将会有约 250 亿台物联网设备连接到人们的生活。其中承担物联网设备网络管理角色的路由器使用量非常大, 但是路由器存在众多安全问题, 通过路由器设备进行攻击, 可以非法获取用户信息。为了维护网络安全, 提前发现路由器的漏洞具有重要的研究意义。本文以 Tenda AX12 路由器为研究对象, 从固件入手对其进行0-Day 栈溢出漏洞挖掘研究, 并提出了基于危险函数追踪的逆向分析漏洞挖掘方法。首先从危险函数中分析函数所在前端的对应位置, 将前后端对应; 然后对固件中的 Web 服务进行分析, 对其中可能发生栈溢出的 httpd 二进制代码进行危险函数分析, 该方法使用反汇编代码对危险函数的普通形式和展开形式进行定位, 并对危险函数进行参数分析和动态检测; 接着通过搭建仿真模拟机在模拟机上运行该服务的二进制文件, 并在 Web 前端页面对潜在漏洞位置进行数据包捕捉; 最后根据前期分析的危险函数参数情况对包进行改写并发送, 以此来触发漏洞, 验证漏洞的存在性, 同时验证该危险函数是否发生栈溢出。为了更真实地确定漏洞存在, 我们又在真实设备上验证漏洞的真实存在性和可利用性。实验结果表明了该漏洞的挖掘检测方法的有效性, 我们分别在不同型号的路由器上挖掘到 4 个 0-Day 漏洞, 并且经过与 SaTC 工具进行对比实验结果表明该检测方法能够更准确的定位到出现漏洞的函数位置。     

第三层交换技术及其在校园网中的应用

第三层交换技术是将网络层的功能融入交换机,将第二层交换机与第三层路由器两者的优势集成在一起,在各个层次提高网络速度性能的一种网络技术。用三层交换机可取代传统路由器充当局域网路由器的作用,采用三层交换技术还可有效地防止ＩＰ盗用,提高网络的安全性,并使网络管理员对网络管理更加灵活方便。因此,三层交换技术可成为中小型校园网建设的有效解决方案。