应用电力仿真软件PSS/E计算网络可用传输能力

可用输电能力(ATC)是指导电力市场交易的重要指标,对系统规划与运行具有重要影响;PSS/E是一种有效的机电暂态分析软件,利用其快速的潮流计算功能及扩展接口可进行ATC指标的计算分析,为电网规划与系统分析人员提供便利。引入ATC指标的定义及主要解算方法,详细分析了PSS/E软件基于直流潮流和交流潮流的ATC计算模型和流程,以及用于N-1故障严重性排序的两种行为性指标。针对IEEE30节点系统算例进行比较分析,计算结果表明了软件ATC指标计算和应用的可行性。     

10G EPON下行传输加密方案的研究

10G EPON是下一代宽带接入网的发展趋势以及重要解决方案,然而,由于PON系统点到多点的通信机制,安全问题是必须解决的关键技术之一.文章根据IEEE 802.3av协议,分析了10G EPON系统中仍然存在的安全问题,介绍了AES(128)加密算法和流程,着重研究了AES加密算法在10G EPON中的应用并给出了对10G EPON下行帧传输的加密解决方案.     

802.16j集中和分布控制模式传输效率分析与仿真

具有中继功能的802.16j协议,是为了增加基于802.16e网络的覆盖能力和容量.新的网络结构在原有网络基础上加入了中继站来进行中继通信,既可以增加本小区网络的覆盖范围,又可以解决非视距传输问题.针对加入新的中继站,带宽资源的控制和管理不再由基站统一管理,IEEE标准制定工作组定义了两种控制方式--集中式和分布式,但没有定义两种控制模式的适用范围.通过分析和仿真说明,集中式适用于拓扑简单的网络,可以提高小区资源利用率.而分布式适用于复杂网络,从而减少信令交互次数和延时.     

基于IEEE802.16e移动宽带无线接入网的切换过程分析与实现

随着WiMAX组织的发展壮大加快了IEEE802.16标准的发展,移动WiMAX ——IEEE802.16e标准的提出更加引人注目.该标准对IEEE802.16标准进行了补充和拓展,定义了一个结合固定和移动宽带无线接入的系统,填补了高速无线局域网和高移动性蜂窝系统之间的空白.对IEEE802.16e标准中规定的移动宽带无线接入系统的切换过程进行了分析,并提出了该过程的软件实现方案.     

Numerical and experimental characterization of antenna positioning in a dual-radio mesh router

This paper investigates the influence of the position of the antennas in a dual-radio mesh router by characterizing the router components from an electromagnetic point of view. Since the behavior of a wireless router equipped with multiple devices and antennas can be affected by mutual coupling among several close conducting bodies, numerical and experimental tests are carried out to provide some suggestions for an accurate positioning of the antennas. A reference configuration is implemented in an electromagnetic Computer-Aided Design (CAD) simulator. The most significant numerical results are validated by performing a campaign of measurements in anechoic chamber and deploying a testbed for the derivation of the experimental values of throughput, return loss, power density, and directivity.     

Phasor measurement based on IEC 61850-9-2 and Kalman–Filtering

This paper proposes a new technique for estimating phasors during the transient phenomena in the electrical power systems. Unlike traditional Phasor Measurement Units (PMUs) that estimates phasors at process level, the proposed technique estimates phasors at bay level. The estimation technique relies on a robust recursive Kalman–Filtering, which is employed for computing the phasors based on the time-critical IEC 61850-9-2 Sampled Measured Values casted by the substation Merging Units (MUs). Many evolution tests of the proposed technique have been carried out for both stationary and transient phenomena in power systems to determine the accuracy of the measurements obtained at various conditions. The proposed estimator can produce phasors at bay level with reporting rate of 100 frames per second, which is encouraged in IEEE Std C37.118 and can satisfy higher accuracies than provided by the traditional Phasor Measurement Units, which are 0.01 degree and 0.01% for phase and magnitude, respectively.     

IEEE 802.11b DCF三维Markov非饱和链路模型

为了准确评估实际网络中IEEE 802.11b分布式协调功能(Distributed Coordination Function,DCF)的系统性能,提出了一种三维Markov链路模型,该模型综合考虑了DCF协议退避计数器冻结状态和有限重传次数,并结合M/M/1/K排队模型给出了在负载有限的情况下DCF系统性能的理论模型。仿真结果表明,该模型能准确地预测IEEE 802.11b DCF协议的系统性能。     

基于FPGA的高精度IEEE1588时间戳的设计与实现

简单介绍了IEEE1588协议的时间同步机制,提出了一种在物理层内部标记时间戳的方案,并采用FPGA设计实现了支持时间戳标记电路的10G Base-R PHY,仿真和测试结果表明这种PHY具有最多一个时钟周期的延迟抖动,极大地降低了网络延时抖动对时间同步精度的影响,满足高精度时间同步的要求.     

A 5-GHz LC VCO with digital AAC and AFBS for 2.4 GHz ZigBee transceiver applications

A 5 GHz LC VCO (voltage-controlled oscillator) with automatic amplitude control (AAC) and automatic frequency-band selection (AFBS) for 2.4 GHz ZigBee transceivers is presented. Instead of continuous feedback loop, an alternative amplitude calibration scheme is proposed in this paper to alleviate the deficiencies inherent in the conventional approach. It helps to keep the VCO at optimum amplitude to avoid saturation of the cross-coupled transistors and therefore stabilizes the phase noise performance over process, voltage and temperature variations. For the ZigBee application with 16 frequency channels, a coarse tuning loop is added in this work to implement the frequency-band selection using the AFBS mechanism. The VCO core and the digital AAC, AFBS modules have been fully integrated in a 2.4 GHz ZigBee transceiver which was fabricated in a 0.18 μm RF-CMOS technology. The current consumption is 4.7 mA at 4.85 GHz with 1.8 V power supply and a chip area of about 0.285 mm² is occupied. The VCO is capable of operating from 4.67 GHz to 5.18 GHz and the measured phase-noise level is –120 dBc/Hz at 1 MHz offset from a 4.85 GHz carrier. The tuning sensitivity K_VCO of the VCO is about 78 MHz/V with 0.9 V control voltage.     

WiMAX MMR网络的军事应用

为进一步提高战术通信网的性能,满足通信保障对网络传输带宽的需求,许多国家的军队使用了3G标准之一的WiMAX技术。WiMAX MMR网络基于IEEE802.16j标准,运用移动多跳接力技术,能有效解决现有WiMAX系统覆盖半径不足、信号传输不佳的问题。介绍WiMAX在军事通信领域的应用情况,结合IEEE802.16j MMR的特点,并就网络安全方面所面临的威胁提出了应对策略。分析表明:WiMAX MMR网络作为一种无线解决方案,具有良好的军事应用前景。