Traveling-wave tube efficiency improvement with textured pyrolytic graphite multistage depressed collector electrodes

The improved efficiency of a multistage depressed collector (MDC) with ion-beam textured pyrolytic graphite electrode surfaces is demonstrated by comparison with the performance of other MDC's tested with the same microwave rf amplifier traveling-wave tube (TWT). Because of the sensitivity of overall TWT efficiency to collector efficiency, significant improvements in TWT performance are possible with the use of textured pyrolytic graphite MDC's.     

Development of information collection scheme in internet of things environment for intelligent radiation monitoring systems

The new revolution in computing and wireless communications technologies led to Internet of Things (IoT). Information collection scheme performs an important role for energy efficient utilization and latency awareness in IoT environments. The enhancement of an effectual information collection scheme is crucial to improve the overall performance of the internet of things applications. In this paper, the proposed information collection scheme aimed to enhance the confidence regarding any captured measurements under IoT environment. The scheme can verify the selection of optimal information collection routes through using the Dijkstra algorithm. It depends on selecting the preferable IoT devices (collectors) with optimal paths in efficient energy utilization. The IoT devices (sources) have to elect whichever a preferable collector can deliver the captured information with an endeavour to sense the latest contextual information. They elect the optimal collectors through implicit and explicit solutions. Also, it considers different failure conditions to specify the optimal collection time for furtherance scalability of IoT environment. The simulation results show the ability of our scheme to improve the performance in terms of network lifetime, energy consumption, and reliability.

     

汽车无线传感器的研究与设计

汽车在定型前要对其各部分检测数据进行分析。目前,汽车中的很多传感器都是用导线直接连接数据采集器和汽车电瓶,大量的导线将直接影响测试环境。基于此,研究设计了一种新的稳压电源和通信子系统来替代导线,尽量减少这些导线对测验环境的影响,提高汽车环境监测数据的真实性,以改善驾驶的安全性和舒适感。     

微型多级降压收集极的电、热及动力学优化设计

介绍一种对行波管中使用的微型多级降压收集极进行电、热及动力学优化设计的系统方法,同时期望这样一种方法能够移植到行波管其他部分的设计优化中。优化所得的收集极在全频带上的仿真效率达到79.5%以上,其散热能力满足环境要求,热裕量充分,并且结构强度远超环境需要。     

Three-dimensional simulation of multistage depressed collectors onmicro-computers

A three-dimensional (3-D) package for simulation of asymmetric and crossed-field multistage depressed collectors for microwave tubes has been developed. This package is based upon the 3-D finite-difference code KOBRA3-INP. The main features of the package are a user-friendly input interface, post-processors for collector analysis and calculation of secondary electron trajectories, and versatile output graphics. Both PC and mainframe versions of the package have been developed. The results of simple benchmark tests and those of simulation and analysis of asymmetric and crossed-field collectors including the effects of secondary electrons are presented. It is found that the asymmetric hyperbolic electric field collector shows very low backstreaming. It is shown that the representation of trajectories in energy space gives a better insight into the behavior of individual trajectories than plotting in coordinate space. The package will be useful for designing novel types of depressed collector     

Design and extensive hardware performance analysis of an efficient pairwise key generation scheme for Smart Grid

Generating pairwise shared keys among different entities of Smart Grid is of great significance because it provides the possibility of subsequent fast and secure communications by means of symmetric key algorithms. Due to the constrained resources of the measurement devices or the smart meters, the shared key generation scheme must not only provide the security features but also put the least possible burden on the measurement devices. Several key generation schemes have been presented thus far. However, many require time and resource consuming operations, some are not suitable for hierarchical data collection in the honest‐but‐curious model, some rely on a third trusted party, and last but not least, most of them have not considered suitable hardware that can be employed for each entity of Smart Grid. Therefore, in this paper, we propose a key generation scheme that not only is free from the aforementioned issues but is also efficient in both communication and computational costs. Additionally, and more importantly, we have implemented the cryptographic elements on (a) an ARM Cortex‐M3 microcontroller, which is a proper candidate for the measurement devices; (b) an Intel Core i7‐4702MQ processor, which can be employed for either the data collectors or the power operator; and (c) 4 ARM processors, three 32‐bit and one 64‐bit. Eventually, we have evaluated the feasibility of using the ARM processors to be employed for the data collectors. We hope that the achieved results be useful for other researches in this field.     

COCA: a novel 3-D FE simulator for the design of TWT's multistagecollectors

In this paper, the simulator COCA, a novel fully three-dimensional (3-D) finite-element (FE) tool for the design of multistage depressed TWTs collectors is illustrated. COCA has been developed at the University of Catania under an ESA/ESTEC project. The complete simulator consists of three main modules: a fully 3-D deterministic/neural FE mesh generator, an FE Vlasov solver coupled with an electron trajectory tracer taking into account also external magnetic fields, and a postprocessing module for result restitution, including secondary electron emission effects. All the functions are interactively managed and executed by means of an especially developed user-friendly graphical user interface which controls all the various aspects of a simulation session. The results of a simulation test performed on an asymmetric collector are also reported showing excellent agreement with available measured data. The COCA simulator provides the user with flexible and effective tools to design, test, optimize, and verify innovative asymmetrical geometries for TWT collectors     

Land mobile satellite channel measurements and modeling

This paper, tutorial in nature, describes the effort of many investigators who have and still are conducting channel measurements and modeling for land mobile satellite communications. Various channel measurement results, ranging from ultrahigh frequency to Ka-band, are given. Many statistical channel models and simplified models that have been developed are referred to. Some of the models are applicable to geostationary and nongeostationary communications satellites. A statistical model developed by Loo (1985) is described in detail, as well as its extension to modeling land mobile satellite communications at Ka-band. This was accomplished by including a Gaussian probability density function to account for weather conditions. Also, practical computer-generated statistical channel models are given. These computer models should facilitate the estimation of performance of satellite communications systems     

Performance of DTN protocols in space communications

Delay/disruption tolerant networking (DTN) was developed to enable automated network communications despite the long link delay and frequent link disruptions that generally characterize space communications. The performance of DTN convergence layer adapter (CLA) protocols over asymmetric space communication channels has not yet been comprehensively characterized. In this paper, we present an experimental performance evaluation of DTN CLA protocols for reliable data transport over a space communication infrastructure involving asymmetric channel rates, with particular attention to the recently developed Licklider transmission protocol (LTP) CLA (i.e., LTPCL). The performance of LTPCL is evaluated in comparison with other two reliable CLAs, TCP CLA and a hybrid of TCP CLA and LTPCL, for long-delay cislunar communications in the presence of highly asymmetric channel rates. LTPCL is also evaluated and analyzed in a deep-space communication scenario characterized by a very long link delay and lengthy link disruptions.     

Densely Functionalized Cyanographene Bypasses Aqueous Electrolytes and Synthetic Limitations Toward Seamless Graphene/β‐FeOOH Hybrids for Supercapacitors

Supercapacitors are a promising energy storage technology owing to their unparalleled power and lifetime. However, to meet the continuously rising demands of energy storage, they must be equipped with higher energy densities. For this purpose, the seamless integration of metal oxides on carbon matrices, such as iron oxides/oxyhydroxides, has been pursued through hydrothermal, atomic layer and electro‐deposition methods directly on current collectors. Nevertheless, such methods present limited compatibility with commercial paste‐coating processes on the current collectors. Furthermore, iron oxides/oxyhydroxides lack conductivity and are hydrophilic, operating with low‐voltage aqueous electrolytes, limiting their power and energy and requiring corrosion‐resistant H₂O current collectors. To mitigate these challenges, a seamless and paste‐ready material is successfully developed through a 15 min wet‐chemical method, via the coordination of ultrasmall β‐FeOOH (akaganéite) nanoparticles to the nitrile groups of a covalent graphene derivative. Endowed with graphene‐like impedance response and very high wettability in organic electrolytes, combined high power and energy densities are obtained, with respect to the total mass of both electrode materials and current collectors, overcoming the identified challenges. This offers future prospects for the exploration of alternative molecular handles for improved interfaces and their application in different energy‐storage chemistries.     

Design of an Optical Photon Counting Array Receiver System for Deep-Space Communications

Demand for increased capacity in deep-space to Earth communications systems continues to rise as sensor data rates climb and mission requirements expand. Optical free-space laser communications systems offer the potential for operating at data rates 10 to 1000 times that of current radio-frequency systems. A key element in an optical communications system is the Earth receiver. This paper reviews the design of a distributed photon-counting receiver array composed of four meter-class telescopes, developed as a part of the mars laser communications demonstration (MLCD) project. This design offers a cost-effective and adaptable alternative approach to traditional large, single-aperture receive elements while preserving the expected improvement in data rates enabled by free-space laser communications systems. Key challenges in developing distributed receivers and details of the MLCD design are discussed.     

A New Time Independent Asynchronous Protocol and Its Applications

Communications to, or between, low-end microprocessors within a product always comes at a cost. This paper develops a new, economic solution that will be useful in a variety of cost-sensitive applications. This paper starts by identifying the properties of an inter-microprocessor communications system that adds minimal cost to a product and enables the use of lower price microprocessors. This leads us to introduce a new category of communications called time independent asynchronous (TIA) communications. An economic 2-wire TIA communications protocol is developed and described using timing diagrams. The protocol is modeled using signal transition graphs (STGs), which are found to have some limitations, and so a modification is developed called STG for threads (STG-FT). Two-wire TIA is simulated to confirm livelock and deadlock properties. An implementation is created that verifies the simulation results, and the performance is reported. Finally, a novel application of 2-wire TIA is discussed.     

Ad Hoc网络的发展及其应用前景

无线自组织网络（Ad Hoc）是当前无线通信领域一种新的、正在发展的网络技术，它正在迅速地从军事通信渗透到相关的民用通信领域。它的特点：无需常规的基础设施的支持，组网灵活方便，这种技术拓宽了移动通信的应用领域，具有广阔的发展前景。着重对Ad Hoc网络的发展历程进行了介绍，同时对Ad Hoc网络的应用前景进行了简单预测。     

Super‐Aligned Carbon Nanotube Films as Current Collectors for Lightweight and Flexible Lithium Ion Batteries

Carbon nanotube (CNT) current collectors with excellent flexibility, extremely low density (0.04 mg cm^?2), and tunable thickness are fabricated by cross‐stacking continuous CNT films drawn from super‐aligned CNT arrays. Compared with metal current collectors, better wetting, stronger adhesion, greater mechanical durability, and lower contact resistance are demonstrated at the electrode/CNT interface. Electrodes with CNT current collectors show improvements in cycling stability, rate capability, and gravimetric energy density over those with metal current collectors. These results suggest that CNT films can function as a promising type of current collector for lightweight and flexible lithium ion batteries with high energy density.     

DDC-OMDC: Deadline-based data collection using optimal mobile data collectors in Internet of Things

Mobile data collectors (MDCs) are very efficient for data collection in internet of things (IoT) sensor networks. These data collectors collect data at rendezvous points to reduce data collection latency. It is paramount to determine these points in an IoT network to collect data in real time. It is important to consider IoT network characteristics to collect data on a specific deadline. First, the disconnected IoT sensor network is a real challenge in IoT applications. Second, it is essential to determine optimal data collection points (DCPs) and MDCs simultaneously to collect data in real time. In this study, Deadline-based Data Collection using Optimal Mobile Data Collectors (DDC-OMDC) scheme is proposed that aims to collect data in a disconnected network with the optimal number of mobile data collectors in a specific deadline for delay-intolerant applications. DDC-OMDC works in two phases. In the first phase, the optimal number of MDCs is determined to collect data at the optimal data collection points to guarantee one-hop data collection from each cluster. The optimal mobile data collectors are determined using optimal DCPs, data collection stopping time, and a specific deadline. In the second phase, the optimal data collection trajectory is determined for each MDC using the nearest neighbor heuristic algorithm to collect data in real time. The simulation results show that the proposed scheme outperforms in collecting data in real time and determines optimal mobile data collectors and optimal data collection trajectory to collect data in a specific deadline for delay-intolerant applications.     

An underwater acoustic communication scheme exploiting biological sounds

Underwater acoustic (UWA) communications have attracted a lot of interest in recent years motivated by a wide range of applications including offshore oil field exploration and monitoring, oceanographic data collection, environmental monitoring, disaster prevention, and port security. Different signaling solutions have been developed to date including non‐coherent communications, phase coherent systems, multi‐input and multi‐output solutions, time‐reversal‐based communication systems, and multi‐carrier transmission approaches. This paper deviates from the traditional approaches to UWA communications and develops a scheme that exploits biomimetic signals. In the proposed scheme, a transmitter maps the information bits to the parameters of a biomimetic signal, which is transmitted over the channel. The receiver estimates the parameters of the received signal and demaps them back to bits to estimate the message. As exemplary biomimetic signals, analytical signal models with nonlinear instantaneous frequency are developed that match mammal sound signatures in the time‐frequency plane are developed. Suitable receiver structures as well as performance analysis are provided for the proposed transmission scheme, and some results using data recorded during the Kauai Acomms MURI 2011 UWA communications experiment are presented. Copyright © 2016 John Wiley & Sons, Ltd.     

Grey systems theory applications to wireless communications

This paper discusses grey systems theory (GST) applications in wireless communications and highlights its potential to cognitive radio. GST consists of information theory concepts and practical algorithms developed to address situations where information is incomplete and affected by random uncertainties. Two GST concepts, grey relational analysis (GRA) and grey model (GM) prediction theory are discussed. GRA provides a method to quantify the similarity between a reference data series and set of data while GM is used for modeling time series data and enables prediction of future values with limited data points and unknown probability distributions. These two techniques are surveyed with respect to their applications to wireless communications. Their application to predictive Cognitive Radio and as a similarity measure for case based reasoning cognitive engines is highlighted. A GRA based Automatic Modulation Classification (AMC) algorithm is applied to digital communications signals with preliminary results shown in simulation.     

Demand assignment in the ACTS LBR system

The advanced communications technology satellite (ACTS) is an experimental communications satellite being developed by NASA's Lewis Research Center. Low burst rate (LBR) traffic stations will access the ACTS multibeam communications package (MCP) through two hopping beams that can be directed at certain cities and areas in the continental United States. An onboard baseband processor (BBP) demodulates uplink traffic received via two up-link (30 GHz) hopping beams, switches the traffic between uplink and downlink beams at baseband, and then remodulates the traffic for retransmission at 20 GHz via two downlink hopping beams. This study concentrates on the demand assigned operation of the ACTS LBR system where the onboard switch is remote from both the traffic stations and the centralized master control station (MCS). Network control uses inbound and outbound orderwire channels and a BBP control channel thereby allowing the MCS to coordinate assignment of individual 64-kb/s channels in the spacecraft. Models are developed to simulate the dynamics of the demand assignment process in order to verify call blocking behavior, to predict control channel loads, and to evaluate alternative algorithms for burst time plan rearrangement that becomes necessary to minimize blocking under conditions of high-traffic intensity     

HDPE-POF的选材与制作

光纤通信已经成为现代通信网络的主要方式.与传统通信方式相比,塑料光纤(POF)具有很多无可比拟的优点,因而,在很多领域都得到了广泛的应用.但是POF本身也有很多缺陷,为此研发了新的原材料以及新的光纤结构,使POF得到更广阔的发展空间.同时,还对制备光纤的一些实验设备进行了改进和更新,以利于研究的顺利进行.     

NTT all-optical switch for ultra-fast processing

Nippon Telegraph and Telephone Corporation (NTT) has developed a surface reflection all-optical switch that uses a semiconductor super-lattice-structure for achieving an ultra-fast switching speed of 250 femtoseconds during which light can move only 0.075 mm in vacuum.The optical switch creates the world's fastest processing speed among semiconductor AND gate devices and features a high on/off ratio (extinction ratio) by large optical non-linearity. Since both signal and control light can be used in a wide range around 1.55-micron band for optical communications, the device can be used for time-division-multiplexing and wavelength-division-multiplexing communications.