扫描型红外探测系统指向精度的测量

描述和分析了扫描型红外探测系统指向精度测量的必要性,并提出了一种扫描型红外探测系统指向精度的测量方法.该方法综合了内场测量和外场测量的优点,降低了系统在整个测量过程中由于检测设备的误差和检测方法不当所引起的偏差.并对误差产生的原因以及造成的结果进行了分析.有利于扫描型红外探测系统指向精度的高精度测量和校正.     

混合激励线性预测低速率语音编码研究

为了满足数字通信及其他商业应用的需求,语音压缩编码技术得到迅速发展。近年来主流的低速率语音编码方案主要基于LPC-10,混合激励线性预测（MELP）,多带激励编码（MBE）,正弦变换编码（SCI）,波形内插编码（WI）。大多都工作在2．4kb／s速率下。作为一种重要的低速率语音编码算法。MELP算法对LPC-10编码方案进行大量改进,引入混合激励,非周期脉冲,残差付氏幅度谱,脉冲散布和自适应谱滤波5个特征。实验结果表明,该混合激励线性预测编码在2．4kb／s上得到了更好的合成语音,并使得合成语音能更好地拟合自然语音。     

用于白癜风治疗的308nm XeCl准分子激光系统

研制了一台用于白癜风治疗的308nm XeCl准分子激光系统。根据准分子激光器脉冲式放电的特点,设计了推挽式脉冲开关电源。实验研究了激光器脉冲重复频率、工作电压、气体寿命对激光输出能量的影响,并检测了激光输出脉冲能量的稳定性。通过自动反馈控制系统调整激光头放电工作电压实现输出激光能量的稳定。激光采用扩展型紫外液芯光纤传导,得到均匀性良好的治疗光斑,液芯光纤对308nm激光的传输效率约为70%。激光器脉冲重复频率1～200Hz,工作电压18～25kV,输出能量不稳定度小于4%。经光纤输出用于治疗的有效光斑直径22mm,脉冲能量密度2～3mJ/cm2。     

1.5 m垂直状态真空平行光管主镜支撑结构设计与分析

针对平行光管主镜应用真空垂直状态的特点,从主镜的支撑方式入手,推导了适用于whiffle tree 结构的支撑点的位置公式,设计了空间曲线切口式柔性铰链,分析了不同结构形式的主镜室的变形.建立主镜室支撑系统的有限元模型,分析计算了系统的静力学变形和谐振频率,分析的结果表明在支撑结构的作用下,主镜镜面的面形RMS优于0.05λ,一阶谐振频率达到65.9 Hz,完全达到了设计要求.     

FTTx系统的IPv6解决方案简介

在介绍IPv6发展演进趋势的基础上,从业务透传、业务感知、IPv6协议栈支持等方面介绍了FTTx系统的IPv6改造阶段,最后给出了烽火通信FTTx系统IPv6的解决方案。     

Opportunistic media access control and routing for delay-tolerant mobile ad hoc networks

In delay-tolerant mobile ad hoc networks, motion of network nodes, network sparsity and sporadic density can cause a lack of guaranteed connectivity. These networks experience significant link delay and their routing protocols must take a store-and-forward approach. In this paper, an opportunistic routing protocol is proposed, along with its compatible media access control, for non-real-time services in delay-tolerant networks. The scheme is mobility-aware such that each network node needs to know its own position and velocity. The media access control employs a four-fold handshake procedure to probe the wireless channel and cooperatively prioritize candidate nodes for packet replication. It exploits the broadcast characteristic of the wireless medium to utilize long-range but unreliable links. The routing process seizes opportunities of node contacts for data delivery. It takes a multiple-copy approach that is adaptive with node movements. Numerical results in mobile ad hoc networks and vehicular ad hoc networks show superior performance of the proposed protocol compared with other routing protocols. The mobility-aware media access control and routing scheme exhibits relatively small packet delivery delay and requires a modest amount of total packet replications/transmissions.     

Quantitative spectrum occupancy evaluation in China: based on a large scale concurrent spectrum measurement

Due to the usable frequency becomes more and more crowed,dynamic spectrum access (DSA) is a new hope to solve this problem.However,DSA in China requires a quantitative analysis of the current spectrum ...     

Performance analysis of covert wireless communication based on beam forming with noise uncertainty

In order to establish covert wireless communication in Rayleigh fading environment with noise uncertainty,a scheme of downlink covert wireless communication based on complex Gaussian random coding and beam forming was adopted,and more importantly,the performance of covert wireless communication was analysed.Firstly,the covert probability of communication was analyzed by using the hypothesis test theory.Secondly,the optimal detection threshold of the illegal detection party was given and proved,and the closed expressions of the average covert probability,connection interruption probability and covert throughput of the system were further obtained.Finally,by jointly designing the transmission power and target covert rate,the optimal goal of the maximum covert throughput of the system was achieved,and the corresponding algorithm based on step search was given.The simulation results show that the beam forming technology could provide some gain for covert wireless communication.Compared with the ideal case in which the legitimate receiver is not affected by the noise uncertainty,the covert throughput in non-ideal case is significantly reduced and almost not affected by the basic noise level of the environment.     

Ad hoc wireless network traffic-self-similarity and forecasting

Lots of works have been carried out to discuss the self-similarity of Ethernet and World Wide Web traffic. In this letter, we study the ad hoc wireless network traffic collected in an ad hoc network (AHN) testbed and show that the ad hoc wireless network traffic is self-similar, which validates that AHN traffic is forecastable because self-similar time-series can be forecasted. We apply a fuzzy logic system to ad hoc wireless network traffic forecasting and simulation results show that it performs much better than does an LMS adaptive filter. All these studies are very important for evaluating network capacity and determining the battery power mode based on the forecasted traffic workload     

雷电波对通信设备的危害研究

科学技术不断发展使得通信设备的应用已越来越广泛,无线通信技术也已普及,但通信系统的计算和传输部分还是离不开精密设备,因此对通信设备的保护仍需受到重视。文章研究雷电波对通信设备造成危害的原理及其对目前通信设备造成的威胁和损害,探索科学、有效的防雷技术应用,以期对通信设备的正常工作和安全运转提供保障。