Wide-band packet radio technology

Advances in signal processing and architectural design for high-performance packet radio are described. The scope of the work roughly encompasses the data-link and physical levels of standardized layered-network architectures. A hardware-function layering approach is used, including the purposeful design of an interface to provide a structured control environment for a demonstration packet radio. The advanced signal processing provides a robust, flexible data link to service demanding network environments, and uses 100-MHz-bandwidth surface-acoustic-wave (SAW) convolvers as large time-bandwidth product matched filters for communication with nonrepeating pseudonoise waveforms. The convolvers are combined with a binary-quantized postprocessor to implement a hybrid correlator which provides high processing gain for detection, demodulation, and ranging measurements. Data rates can be selected, in response to varying channel conditions, over a range from 1.45 Mbits/s down to 44 bits/s with an almost ideal tradeoff in processing gain for interference rejection and privacy ranging from 18 dB up to 61 dB. Future enhancements are proposed that will advance both the signal processing and the architecture.     

Advances in photonic packet switching: an overview

The current fast-growing Internet traffic is demanding more and more network capacity every day. The concept of wavelength-division multiplexing has provided us an opportunity to multiply network capacity. Current optical switching technologies allow us to rapidly deliver the enormous bandwidth of WDM networks. Photonic packet switching offers high-speed, data rate/format transparency, and configurability, which are some of the important characteristics needed in future networks supporting different forms of data. In this article we present some of the critical issues involved in designing and implementing all-optical packet-switched networks     

Jointly optimal routing and scheduling in packet ratio networks

A multihop packet radio network is considered with a single traffic class and given end-to-end transmission requirements. A transmission schedule specifies at each time instant the set of links which are allowed to transmit. The purpose of a schedule is to prevent interference among transmissions from neighboring links. Given amounts of information are residing initially at a subset of the network nodes and must be delivered to a prespecified set of destination nodes. The transmission schedule that evacuates the network in minimum time is specified. The decomposition of the problem into a pure routing and a pure scheduling problem is crucial for the characterization of the optimal transmission schedule     

WPAN/WLAN应用环境下基于PER的链路自适应算法

本文重点研究基于包错误率测量的链路自适应算法，分析了包错误率与信道参数的关系，提出了一种有别于固定门限值方案的优化门限值方案。仿真结果表明，优化门限值方案的网络吞吐量要大于固定门限值方案和基于信干比估计的链路自适应算法，最大增幅可达12Mbit/s。在系统引入重传机制后，网络吞吐量将有所损失，但最大不超过1Mbit/s，相比较服务质量的提高是值得的。需指出的是，虽然分析和仿真均以HIPERLAN／2为例，但不失一般性，它们同样适合于WPAN/WLAN等类似系统。     

CDMA2000 分组域核心网移动IP技术

移动IP技术为CDMA2000 系统中的一种基本接入技术.分析了移动IP技术网络架构,介绍了移动IP网络部署下的几种关键技术.为了使只支持简单IP的终端使用移动IP业务,引入了代理移动IP技术.内容计费业务作为一种灵活的计费方式,同样也可以应用在CDMA2000分组网络中.     

光分组交换技术在未来通信网中的应用

随着带宽需求的日益增长,电信工业不得不把重心从传统的电话业务转向IP数据业务。在这种情形下,SDH/SONET的作用大大地减小了,而OTN（光传输网）将为IP数据业务提供一个全球的基础传输设施。采用了DWDM和OXC的光网络为传输IP业务提供了许多新的机会与挑战。该网络不仅可以在网络之间快速自动建立和拆除路由,而且还可以在路由上支持多种用户信号。因此,今天的光网络发展计划关键在于核心网络可以提供一个以快速OXC和适当的管理控制机制为基础的可重构的光传输层。在不久的将来,光传输网将能够支持大量的高容量的光信道,这…     

移动城域网中分组传送技术的应用

分组化和宽带化是下一代城域网络发展的趋势,但在向IP城域网络发展的过程中,时分复用(TDM)和IP业务将长期共存.文章介绍了移动城域传送网的定位和需求,分析了目前常见的运营商骨干网桥接(PBB)、运营商骨干网传输(PBT)和传送多协议标签交换(TMPLS)等分组传送网(PTN)技术,在此基础上探讨了PTN设备的组网方案和时分同步码分多址(TD-SCDMA)基站同步的解决方案.     

无线分组通信网精确定时技术的研究

IEEE 1588标准的基本功能是使分布式网络内的各个时钟与最精确的时钟保持同步,目前主要用于以太网中,无线分组网中尚未移植该协议.本文旨在研究无线分组通信网精确定时技术,分析IEEE 1588定义的PTP(Precision Time Protocol)体系结构和时钟同步原理,提出能在无线分组网络中通过IEEE 15...     

国外高变焦比中波红外镜头的研究进展

与红外定焦镜头和红外两档变焦镜头相比,红外连续变焦镜头具有连续可变的视场,可对目标进行连续的跟踪,是未来红外成像技术的发展方向.随着光学冷加工、精密机械加工、镀膜技术等工艺水平的不断进步,以及现代科技的发展要求,红外变焦镜头向高变焦比方向发展,同时还须保持良好的成像和消热差性能.概述了国外各种高变焦比中波红外镜头的结构和设计方法,包括20高变焦比中波红外镜头、30高变焦比中波红外镜头、300高变焦比中波红外镜头,总结了一套高变焦比中波红外镜头设计经验,对国内高变焦比中波红外镜头的应用发展研究有借鉴价值.     

40 Gbit/s packet bit error ratio and loss real-time measurement for ultrahigh-speed packet switched network

A novel packet bit error rate (BER) and loss measurement method and system is proposed. A proposed 40 Gbit/s packet BER and loss measurement system is expressed in detail. A 40 Gbit/s BER and loss measurement with various conditions is demonstrated experimentally. In real time, only the payload part of a packet and burst stream with fluctuated guard time is evaluated. The BER and packet loss of a randomly received packet sequence due to routing and buffering can be also evaluated by the measurement system. A 10 Gbit/s packet BER and loss measurement with optical label switching, buffering, and preamble-free optical packet 3R are demonstrated experimentally.     

接入层分组交换设备技术探讨

指出了接入层设备的向分组化演进的趋势和接入层分组交换设备接口需求,简要介绍了接入层的设备原理及采用的QoS技术,然后提出了一种实现接入层的分组化方案,对方案的OAM模块实现和采用的降低功耗措施进行了说明.     

弹性分组环技术及其带宽公平分配机制

弹性分组环是一种新的城域网技术,根据2004年6月正式推出的IEEE 802.17协议[1],文章简单介绍了RPR的主要技术特点,然后重点分析了带宽公平分配原理和公平算法的实现,最后简单分析了公平算法中两种速率调整模式的优缺点以及低通滤波器参数lpCoef设置值对各自的影响.     

Advances in SiC power MOSFET technology

In recent years, SiC has received increased attention because of its potential for a wide variety of high temperature, high power, high frequency, and/or radiation hardened applications under which conventional semiconductors cannot adequately perform. For semiconductor devices designed to operate in these harsh conditions, SiC offers an unmatched combination of electronic and physical properties. The availability of SiC wafers on a commercial basis has led to the demonstration of many types of metal-oxide semiconductor (MOS)-gated devices that exploit its unique properties. To which extent the potential of SiC power MOSFET can be utilized is a question of appropriate SiC polytype, device structure, MOS interface quality and maturity of the technology. This paper reviews the present status of the SiC power MOSFETs technology that is approaching commercialization. Emphasis is placed upon the impact of SiO₂–SiC interface quality on the performance of SiC MOSFETs.     

Iptables包过滤技术及其在机载网络上的实现

针对机载无线信息系统可能由地面网络技术引入网络安全威胁,因此机载网络需要对数据包进行过滤,根据规则限制数据传输。阐述了Iptables的工作原理,分析数据包过滤的规则操作及数据包的传输过程,及其在机载网络上的应用环境。对用Iptables在Linux上实现丢弃某IP数据包和阻止相关网页访问请求进行实验,在此基础上对基于Iptables的包过滤技术进行研究。     

同步无线Mesh网络数据包连发技术研究

现有的基于多方向天线阵列的同步无线Mesh网络在一个数据时隙内只发送一个数据包,这在发送节点采用高调制速率发送数据包时会造成时隙利用率的下降。针对该问题,对该网络下的数据包连发技术进行了研究,给出了最多可连发的数据包个数与计算时机、序列号与确认机制、涉及到的参量、父子节点处理流程的详细设计方案。理论性能对比结果表明,在发送节点采用高调制速率发送数据包时,在该网络下采用数据包连发技术能够大幅度提高时隙利用率,网络性能明显提升。     

基于TCAM的深部包检测技术研究与实现

深度包检测技术(DPI)已成为网络信息安全的研究重点。基于硬件实现模式匹配的DPI技术凭借其更强的处理能力受到广泛关注。本文提出一种基于TCAM模式匹配的方法实现DPI,规则表项按字节分别存储在TCAM(三态内容寻址存储器)中,输入字符按不同字节与TCAM中内容进行匹配,提高了DPI中模式匹配的处理速度。针对该技术功耗大的缺点,提出BF(Bloom Filter)和TCAM相结合的两级模式匹配技术,BF可将较少可疑包转发给TCAM处理模块,从而降低了系统功耗,大大提高了系统处理速度。     

Analysis of multipath Routing-Part I: the effect on the packet delivery ratio

In this paper, we develop an analytical framework for evaluating multipath routing in mobile ad hoc networks. The instability of the topology (e.g., failure of links) in this type of network due to nodal mobility and changes in wireless propagation conditions makes transmission of time-sensitive information a challenging problem. To combat the inherent unreliability of these networks, we propose a routing scheme that uses multiple paths simultaneously by splitting the information between a multitude of paths, so as to increase the probability that the essential portion of the information is received at the destination without incurring excessive delay. Our scheme works by adding an overhead to each packet, which is calculated as a linear function of the original packet bits. The resulting packet (information and overhead) is fragmented into smaller blocks and distributed over the available paths. The probability of reconstructing the original information at the destination is derived in an analytical form and its behavior is studied for some special cases. It is shown that, under certain constraints, the packet dropping probability decreases as the number of used paths is increased.     

能量存储技术的发展为无线设备提供动力

能量采集依赖于间歇的能源,并且需要能量存储设备,如电容或电池。这些部件新的进步都是为了获得更小、更长寿命的无线传感器节点,但长寿命的初级电池可能是最简单的能源选择。