High performance K-band active mixer using BiCMOS SiGe process

A SiGe BiCMOS double-balanced down-converter is reported. As a consequence of its highly balanced configuration, this design achieves outstanding port-to-port isolation and results in a spurious-free IF output spectrum. Original RF/LO baluns, a simplified Gilbert mixer and 3D interconnections have been implemented on a compact single chip. Measurements confirm the suitability of this design for future millimetre-wave multimedia circuits     

一种K波段电磁超材料的设计及其在微带天线中的应用

根据电磁材料的相关理论,设计出一种由新型谐振器和金属线组成的电磁双负超材料,即介电常数和磁导率同时为负的电磁材料。新型谐振器通过较小谐振腔并联的方式,在较大的单元尺寸下提高了谐振频率,既使该电磁超材料在K波段实现了双负特性,又保证了材料的辐射面积,克服了高频段超材料由于尺寸太小而难以应用的困难。设计出一种K波段的微带天线,将新型谐振器加载在天线上,并用HFSS软件对未加载谐振器和加载谐振器的天线进行仿真对比。仿真结果表明,相比普通天线,加载新型谐振器的微带天线性能得到明显提升,驻波比2 d B以下的带宽增加了58.3%,增益变大,并且由于谐振器对天线副瓣的抑制,提高了天线的方向性。     

Improved multi-fractal network traffic model and its performance analysis

This paper demonstrates the limitation of the traditional multi-fractal wavelet model(MWM).Through analyzing the multi-resolution behaviors of the real video traffic,we propose an improved MWM model.It synthesizes the traffic traces using another wavelet basis,and can adjust wavelet coefficients and multiplicative coefficients at each time scale,based on the network measurement.Subsequently,multifractal spectra and queue performances of the new model have been analyzed.The simulation proves it can capture the multifractal behaviors of network traces.     

适合大规模网络的一种新型智能网管模型及性能分析

提出了一种适合大规模网络的新型智能网管模型——MADINM(multi-agent based distributed intelligent network management)模型。该模型采用基于域的管理策略,在管理功能的实现上集移动agent和智能agent的优点于一身,既能够对网络管理提供更多的智能支持,又能够解决系统的性能瓶颈问题。理论分析和实验结果均表明,在管理大规模网络时,MADINM模型在性能上优于基于SNMP的网管模型和基于移动agent的网管模型。     

A construction of locality-aware overlay network: mOverlay and its performance

There are many research interests in peer-to-peer (P2P) overlay architectures. Most widely used unstructured P2P networks rely on central directory servers or massive message flooding, clearly not scalable. Structured overlay networks based on distributed hash tables (DHT) are expected to eliminate flooding and central servers, but can require many long-haul message deliveries. An important aspect of constructing an efficient overlay network is how to exploit network locality in the underlying network. We propose a novel mechanism, mOverlay, for constructing an overlay network that takes account of the locality of network hosts. The constructed overlay network can significantly decrease the communication cost between end hosts by ensuring that a message reaches its destination with small overhead and very efficient forwarding. To construct the locality-aware overlay network, dynamic landmark technology is introduced. We present an effective locating algorithm for a new host joining the overlay network. We then present a theoretical analysis and simulation results to evaluate the network performance. Our analysis shows that the overhead of our locating algorithm is O(logN), where N is the number of overlay network hosts. Our simulation results show that the average distance between a pair of hosts in the constructed overlay network is only about 11% of the one in a traditional, randomly connected overlay network. Network design guidelines are also provided. Many large-scale network applications, such as media streaming, application-level multicasting, and media distribution, can leverage mOverlay to enhance their performance.     

BGP收敛性及其对网络性能影响的定量分析

从Internet的结构特征入手，分析了BGP的收敛特性与域间路由系统的幂律特性与层次性之间的关系。根据域间路由系统的幂律特性以及AS间商业关系的层次性特点建立了三层幂律一层次模型，剖析了不同层次上的不同收敛事件的收敛参数与网络结构本质的联系。在此基础上，提出了“Best Up”的收敛模式，取得了显著效果。     

强耦合阵列中匹配网络设计及对天线性能影响

为研究强耦合阵列匹配网络对收发状态下性能影响以及评估该匹配网络在两种状态下的通用性,以网络散射理论为基础,分别在发射和接收耦合天线框架内讨论了该网络参数对阵列性能的影响,并给出了网络不同端接负载条件下的相关函数。理论和计算表明:对于强耦合组成的发射阵列,其匹配网络在收发状态下具有一定通用性;网络负载对天线分集性能具有明显的作用。文章中的理论和方法为研究强耦合阵列特性提供了便利和条件,也为工程实施和应用提供了较强的指导意义。     

Control protocol and its performance analysis for distributed ATMvirtual path self-healing network

A restorable network comprised of a mesh of ATM virtual paths (AVPs) is expected to be superior to distributed SONET digital cross-connect self-healing networks in terms of restoration time. The paper presents a reliable protocol and evaluation of its performance for control information transfer in distributed AVP self-healing networks. Two error-recovery technologies for the data-link level (selective retransmission and go-back-N) in AVP networks are reviewed, and a model for evaluating the delay of the go-back-N method that has been used in existing terrestrial systems is derived analytically. The proposed analytic model is combined with a self-healing simulator for AVP mesh networks to evaluate the restoration time characteristics. Case study results for the worst-case scenario show that the total restoration time, including link-by-link error control for self-healing control messages, is expected to be less than 2 s, which is the time objective for complete restoration for a metropolitan LATA network. The results also show that the estimated average delay penalty for adding the link-by-link error recovery process is 7.5 ms for complete service restoration     

分层多描述视频编码及其在差错网络环境下的仿真研究

提出了一种适用于差错网络视频传输的联合编码结构。首先从理论上分析了这种编码结构的特点、应用环境及其优势,然后以两种不同的具体实现方法和不同的分层比例实现了这一编码结构。通过对该编码结构在差错网络环境中的数值仿真,给出了具体的性能评估和分析,证明了这一编码结构的有效性,且其有效性不依赖于具体实现手法和分层比例。     

Analysis and performance of some basic space-time architectures

In this paper, we discuss some of the most basic architectural superstructures for wireless links with multiple antennas: M at the transmit site and N at the receive site. Toward leveraging the gains of the last half century of coding theory, we emphasize those structures that can be composed using spatially one dimensional coders and decoders. These structures are investigated primarily under a probability of outage constraint. The random matrix channel is assumed to hold steady for such a large number of M-dimensional vector symbol transmission times, that an infinite time horizon Shannon analysis provides useful insights. The resulting extraordinary capacities are contrasted for architectures that differ in the way that they manage self-interference in the presence of additive receiver noise. A universally optimal architecture with a diagonal space-time layering is treated, as is an architecture with horizontal space-time layering and an architecture with a single outer code. Some capacity asymptotes for large numbers of antennas are also included. Some results for frequency selective channels are presented: It is only necessary to feedback M rates, one per transmit antenna, to attain capacity. Also, capacity of an (M,N) link is, in a certain sense, invariant with respect to signaling format.     

Realisation of basic 2-terminal network elements

The concept of basic 2-terminal network elements, which include resistors, inductors, capacitors and memristors as special cases, is introduced. It is shown that every basic 2-terminal network element can be realised by linear capacitors, linear inductors, linear algebraic controlled sources and one nonlinear resistor.     

小型化K波段下变频组件的设计

介绍了一种K波段下变频组件的集成设计,主要研究了有源二倍频器、增益放大器、混频器和带通滤波器等部件。利用ADS设计软件,在分别对上述部件进行设计、仿真的基础上,完成了对下变频组件的集成仿真计算,计算结果较好地满足了组件的电性能要求,组件版图尺寸为47．5mm×28mm,达到小型化设计要求。     

超低噪声K波段放大器仿真设计

介绍了一种超低噪声K波段放大器的设计方法,以高电子迁移率晶体管为基础,采用3级放大拓扑结构,提出了一种改进型的负反馈网络,较好地改善了电路的增益平坦度。利用Agilent公司的微波电路CAD（计算机辅助设计）软件ADS2006对电路原理图及版图进行了仿真设计,最终实现了在工作频段19．5GHz～21．5GHz内,噪声系数小于1．5dB、增益大于30dB的优异电性能。     

联合网络编码和中继选择的协作传输方案及其性能分析

研究了Nakagami信道中联合网络编码和双向协作中继选择的中断与平均误码率的性能,基于3个时隙的网络编码方案提出了一种最小化较差用户误码率的协作中继选择策略。在Nakagami信道下,从双向通信的角度,通过理论分析得出其中断概率和平均误码率的解析式和渐近式,同时推导了无协作中继选择时网络编码的中断概率和平均误码率解析式。通过理论分析发现,当Nakagami信道衰落参数降低时,联合网络编码的协作中继选择方案相对于无协作中继选择时的性能增益将逐渐升高。数值仿真实验结果表明,所提策略的平均误码率性能要显著高于无协作中继选择时的网络编码性能。     

基于K波段的FSS天线罩设计技术

主要针对工作在K波段的天线罩开展了相关设计验证工作,根据设计目标开展了频率选择表面结构天线罩的设计优化工作,应用局部平面近似技术和有限元与物理光学相结合的方法对天线罩设计结果进行了数值仿真,通过对制造的典型样件进行测试,测试结果验证了设计的正确性。     

IP校园网网络性能与方法研究

随着高校校园网规模的逐步扩大和网络功能的不断完善,建成安全、可靠、高效的校园网络已经成为衡量院校办学综合实力的重要指标之一。目前,校园网在不断的应用和发展中面临网络安全性、健壮性、可靠性等多重指标的复合评估。在这种新要求下,校园网必须采用新思路、新方法和新的网络模型进行研究。文章通过研究传统的IP网络性能指标和方法,说明了传统的排队论、马尔科夫链、ON/OFF模型已不适用于分组网的研究,并介绍了IP网络的度分布、IP网络流量概率分布特性、IP网络流量H分布、长程依赖性、自相似性等特点,对武威职业学院校园网性能提升和网络优化提供有力的理论和数据支持。     

Circuit design and transmission performance of ISDN basic interface

An LSI-based user-network interface circuit, applicable to a network terminal (NT) for the integrated services digital network (ISDN) basic interface is developed. Adaptive timing extraction, with a simplified polyphase phase-locked oscillator, is introduced into the circuit for application to both point-to-point and passive bus configurations. This circuit does not require any manual adjustment. In addition to the primitives defined by CCITT between layers one and two, a new primitive is adopted for controlling the transmission of information. This primitive avoids premature transmission due to processing delays in the exchange terminal (ET). The above functions are fabricated on a CMOS gate-array LSI chip with 4000 gates. The performance of the interface circuit is confirmed with special attention to transmission and electrical characteristics     

宽带网络监控技术性能优化的研究与实践

叙述了网络监控系统的实现原理,分析了宽带网络环境网络监控所面临的问题。详细阐述了宽带网络监控技术性能优化的方案和测试结果,指出在百兆网络下,发掘应用程序和数据获取软件结构间的关系将显著提高系统性能;在吉比特网络下提出了CCDP结构,以合理利用现有的计算资源处理快速连接和海量数据。最后文中指出应该基于新出现的网络处理器等先进硬件技术,结合分布式处理和并行计算等传统技术来实现更高速率下的网络监控。     

基于随机网络编码的无线广播重传方案及性能分析

针对自动重复重传(ARQ)机制在无线广播系统中吞吐量性能不佳的缺陷,提出一种基于随机网络编码的广播重传方案RNC-ARQ.对于广播节点,采用随机线性码对所有丢失包进行编码组合重传.对于接收节点,当接收的编码包累积到一定数量后可通过解码操作恢复出原始数据.该方案可有效减少重传次数,改善无线广播的吞吐量性能.基于Gilbert-Elliott模型描述的突发错误信道,建立了信道状态和节点接收处理流程合并的多状态马尔可夫模型,并以此为基础推导了RNC-ARQ方案的吞吐量闭合解.最后,使用NS-2模拟器评估RNC-ARQ方案的性能,结果表明在突发差错信道下,基于随机网络编码重传方案的吞吐量优于传统的选择承传ARQ方案和基于异或编码的重传方案.     

K波段推-推介质振荡器设计

为了满足现代通信系统对于高频率与高稳定性信号源的需求,提出一种K波段介质振荡器。该振荡器通过推-推结构将两路子振荡器合二为一,使其能够在一个电路中同时实现振荡器和倍频器。在介质谐振器的两条耦合微带线上增加变容二极管模块,通过改变变容二极管的偏置电压调整谐振器中传输信号的相位。变容二极管模块的加入能够有效降低有源器件不一致性对电路的影响,减少两个子振荡器在基频处对输出信号的干扰,同时让振荡器获得200 MHz左右的输出信号频率可调范围。测试结果表明:在输出频率为20.96 GHz时,输出功率约为-4.59 dBm,在10 kHz时达到-66.50 dBc/Hz的相位噪声,在100 kHz时达到-94.31 dBc/Hz的相位噪声,基波抑制度达到-25.42 dBc。