Propagation measurements and models for wireless communicationschannels

The authors describe the type of signals that occur in various environments and the modeling of the propagation parameters. Models are essentially of two classes. The first class consists of parametric statistical models that on average describe the phenomenon within a given error. They are simple to use, but relatively coarse. In the last few years a second class of environment-specific models has been introduced. These models are of a more deterministic nature, characterizing a specific street, building, etc. They are necessarily more time consuming to use, but are also more revealing concerning physical details and hopefully more accurate. Some key parameters and the measurement of them are discussed and then the different wireless environments are treated. The latter topic is divided into outdoor environments, indoor environments, and radio penetration from outdoor to indoor environments     

MEMS器件在冲击下的可靠性

MEMS器件在制造、运输和使用过程中不可避免地受到不同程度的冲击作用,分析和认识MEMS器件在冲击下的响应和失效模式,对提高器件的耐冲击和可靠性具有一定的指导意义。本文综述了MEMS器件的冲击测试和理论分析方法,对MEMS器件的可靠性设计具有一定参考价值。     

语音增强用于抗噪声的汉语说话人识别

大多数实际应用环境中总是存在各种各样的噪声，由于训练环境与识别环境不匹配，现有的绝大多数说话人识别系统在噪声环境中的性能都不可避免的急剧下降。为了让说话人识别系统在强噪声环境中，有较好的识别效果．研究一个将语音增强器和说话人识别系统级连起来的系统，该系统中将语音增强作为前端处理来提高输入的信噪比。实验证明，该系统具有很好的抗噪声性能。     

Performance analysis of a decision-feedback coherent code tracking loop for pilot-symbol-aided DS/SS systems

In this paper, the performance of a decision-feedback coherent code tracking loop for pilot-symbol-aided (PSA) direct-sequence spread-spectrum systems, considering the effect of both symbol and channel estimation errors, is analyzed. An analytical closed-form expression on the steady-state jitter variance in additive white Gaussian noise (AWGN) environments using the linear analysis model is first derived. Then, the upper and lower bounds of the jitter variance in fading environments are obtained based on the analysis of the loop bandwidth variation according to the input signal level. Finally, a second-order coherent tracking loop is designed, and its performance in both AWGN and fading environments is evaluated, along with verification by computer simulations. It is demonstrated that analytical results are very close to the simulation results in AWGN environments and that the jitter variance in fading environments is located between analytical upper and lower bounds with its position depending on the fading rate.     

云计算环境下计算机网络安全分析

随着云计算技术的发展，越来越多的企业和机构开始采用云计算技术来实现资源共享和灵活部署。然而，云计算环境下的网络安全问题日益凸显。如何保障云计算环境下的网络安全，成为当前亟待解决的问题。文中从多个方面探讨了云计算环境下计算机网络安全管理的保障策略，以期为相关企业和机构提供参考。     

In search of gigabit applications

Applications in existing specialized, metacomputer environments and those yet to be developed for services such as telecommunications, distributed data, and image transfer that will require networks which can handle volumes of data on the order of gigabits per second are discussed. Specific examples are presented from the fields of computational science, data navigation, and collaborative environments and instrument control. It is concluded that distributed computing and collaborative environments that support the interaction of multiple computers, as well as the interaction of computers with humans, are the paradigms that will characterize gigabit applications     

Real traffic-data based evaluation of vehicular traffic environment and state-of-the-art with future issues in location-centric data dissemination for VANETs

Extensive investigation has been performed in location-centric or geocast routing protocols for reliable and efficient dissemination of information in Vehicular Adhoc Networks (VANETs). Various location-centric routing protocols have been suggested in literature for road safety ITS applications considering urban and highway traffic environment. This paper characterizes vehicular environments based on real traffic data and investigates the evolution of location-centric data dissemination. The current study is carried out with three main objectives: (i) to analyze the impact of dynamic traffic environment on the design of data dissemination techniques, (ii) to characterize location-centric data dissemination in terms of functional and qualitative behavior of protocols, properties, and strengths and weaknesses, and (iii) to find some future research directions in information dissemination based on location. Vehicular traffic environments have been classified into three categories based on physical characteristics such as speed, inter-vehicular distance, neighborhood stability, traffic volume, etc. Real traffic data is considered to analyze on-road traffic environments based on the measurement of physical parameters and weather conditions. Design issues are identified in incorporating physical parameters and weather conditions into data dissemination. Functional and qualitative characteristics of location-centric techniques are explored considering urban and highway environments. Comparative analysis of location-centric techniques is carried out for both urban and highway environments individually based on some unique and common characteristics of the environments. Finally, some future research directions are identified in the area based on the detailed investigation of traffic environments and location-centric data dissemination techniques.     

单元筛选后作最小选择的CFAR自适应检测器

为提高雷达自适应检测能力，本文针对多个干扰目标背景提出一种新的CFAR自适应检测方法。在斯威林2型目标的假设下对这种检测方法进行了检测性能分析，理论推导出均匀杂波背景和强干扰目标存在的情况下虚警概率和检测概率的数学模型，并把它同CA、GO、SO(smallest of)等检测方法用MATLAB仿真软件进行了比较。结果表明，这种方法在均匀杂波背景和多个干扰目标背景情况下都有很好的检测性能，尤其是多目标干扰条件下具有更大的优势。     

DS-CDMA systems using q-level m sequences: coding map theory

GF(q) m sequences with complex spreading mapping are considered for DS-CDMA systems by referring to three different environments with increasing synchronicity levels. For all environments, performance evaluation is derived both with a deterministic approach requiring spreading sequence specification, and with a statistical derivation, based on the assumption of spreading sequence ergodicity, in order to give closed-form performance theory. The optimal mapping design criterion, through zero-mean complex code mapping, is computed for all environments and validated through several numerical tests. Performance invariance, with respect to sequence levels, has been demonstrated for low synchronous environments, where the proposed sequence gives better performance     

Assessment of radiation-induced loss for AT&T fiber-optictransmission systems in the terrestrial environment

Environmental radiation dose rate estimates are provided for both outdoor terrestrial and indoor environments. Laboratory radiation sensitivity measurements are reported for the AT&T standard single-mode fiber and standard and radiation-hardened multimode fibers. These are used to estimate typical system losses for long-haul, trunk, feeder, local area network, and optical data environments. It is reported that radiation-induced loss is unusually harsh environments can be minimized by using the radiation hardened 62.5/125-μm multimode fiber, which has sensitivities roughly an order of magnitude lower than the standard product at 0.85 μm and almost two orders of magnitude lower at 1.3 μm     

Sensor data fusion for an indoor and outdoor localization

Geolocation systems are constantly evolving to enhance the integrity, accuracy and availability. Today, the applications are emerging and multiplying which are parts of an overall context of mobility. In outdoor environments, GNSS systems used, such as GPS and Galileo, provide a good accuracy, but in the indoor environments, GNSS signal is deteriorated due to the signal degradation by different obstacles. Many techniques are used to locate users in the indoor environments such as Infrared, Ultrasound or Radiofrequency techniques. The use of these techniques facilitates the exchange and dissemination of information. This paper presents a new design of Indoor-Outdoor positioning system based on the combination of data from UWB and GPS sources.     

Adjusting software failure rates that are estimated from test data

Software test environments are often different from field environments. Using test data exclusively to estimate a field failure rate will not usually give a very accurate estimate. In this paper, we extend an empirical calibration methodology for adjusting the failure rate estimate obtained from analysing test data. In addition to scaling the estimated failure rate of a fault, we propose scaling the estimated number of residual faults as well. We also derive likelihood ratio tests to formally determine (from previous releases of the software) if test, and field environments are significantly different. We illustrate our new results with two telecommunications case studies. The combination of the likelihood ratio test, and the calibration methodology offers a practical way to extend the application of software reliability growth models to less formal test environments.     

Tracking of Frequency-Hopped Spread-Spectrum Signals in Adverse Environments

Tracking requirements for a frequency-hopped spreadspectrum system with a view to application in mobile radio are investigated. Models characterizing Rician fading and multiple access or jamming environments are used to formulate signal detection probabilities. These determine the mean time to loss of lock. Optimized tracking in these environments is then considered.     

ATM everywhere?

The use and deployment of asynchronous transfer mode (ATM) in a target of operating environments and administrative domains are discussed. The operating environments include wide area ATM, regional area ATM, local area ATM, desk area ATM, and local wireless ATM. The challenges of interdomain ATM are reviewed     

Image understanding environments

The organization and the functional components of software environments that have been developed for image understanding (IU) are described. The basic components of general IU environments are detailed with respect to representations, programming constructs, system-specific databases and user interfaces. How these components have been realized in different systems through examples and possible developments in the near future are discussed     

Fast slot synchronization for intercell asynchronous DS/CDMAsystems

Slot synchronization is a critical step for fast and reliable cell search in intercell asynchronous direct sequence-code division multiple access systems. To increase reliability, observations over a number of slots may be combined. In this paper, combining schemes of multiple observations are studied for slot synchronization. The optimal combining rule is determined based on detection theory. It is found that two known combining schemes correspond to special cases of the optimal combining. These schemes may not work well in typical environments, since the schemes are optimized for specific environments. To improve slot synchronization performance in typical environments, a new combining scheme is proposed. The performance of the proposed combining scheme as well as other combining schemes is analyzed for Rayleigh fading channels with frequency offset. Numerical analysis shows that the proposed combining scheme significantly outperforms other combining schemes in typical environments     

软件天线系统中的一种环境识别方法

不同于智能天线，软件天线能够识别所处的电磁环境，并根据所处的环境选择合适的算法，动态地调整波束形状。实现软件天线的关键技术之一就是环境的分类与识别。本文首先结合CDMA系统讨论了环境的分类以及环境识别的准则，并提出了一种基于空间平滑的方法来实现环境的识别。最后给出了几种假设条件下相应的数值模拟结果。     

Service Discovery in Agent-Based Pervasive Computing Environments

Directory based service discovery mechanisms are unsuitable for ad-hoc m-commerce environments. Working towards finding an alternate mechanism, we developed Allia: a peer-to-peer caching based and policy-driven agent-service discovery framework that facilitates cross-platform service discovery in ad-hoc environments. Our approach achieves a high degree of flexibility in adapting itself to changes in ad-hoc environments and is devoid of common problems associated with structured compound formation in mobile commerce environments. Device capabilities and limitations, user preferences regarding device usage, application specifics with respect to mobile commerce are factors that our framework adapts to. We have described our initial implementation of Allia over ThinkPads and iPAQs by extending the LEAP Agent Platform and using Bluetooth as the underlying network protocol. In addition, we evaluated Allia's performance by running simulations of our protocol in Glomosim simulator. We also compared our framework against a structured compound-based architecture.     

一种均温板加速条件下性能试验研究

针对机载电子设备散热应用条件,研究热管均温板在机载加速环境下的传热性能。为提高热管散热稳定性,将热源布置在热管中部,热管两端作为散热端。试验中试验单元安装在离心加速机上,模拟机载加速环境,测试了不同加速度条件下热管传热性能,得到热管均温板当量导热系数变化曲线,分析了加速度对热管当量导热系数的影响。试验结果表明:在0 ~13g加速条件下,热管均温板均能正常工作。结合试验结果给出热管均温板用于机载电子设备散热的设计建议。     

Path-loss prediction model for microcells

Empirical path-loss formulas for microcells in low-rise and high-rise environments are established from measurements conducted in the San Francisco Bay area. Using the 1-km intercepts and slope indexes of the least square fit lines to the measurements at cellular and personal communication services (PCS) frequencies for three base station heights, simple analytic expressions are obtained. Separate formulas are presented for environments of low buildings and for the high-rise urban core. Following the formula development processes for individual test routes, in low-building environments, a single nonline-of-sight (non-LOS) formula that is applicable to all non-LOS routes is derived. Due to the anisotropic property of wave propagation, cell shape of microcells is no longer circular. As examples, cell shape is presented when base stations are on the street in the middle of a block and when they are placed in the backyard