大气激光通信PPM调制解调系统设计与仿真研究

脉冲位置调制(PPM)是大气激光通信的关键技术之一,可以减少激光器的发射功率,增加通信距离。从实际出发,采用高速数字信号处理器(DSP)设计出PPM调制解调系统;同时介绍了PPM解调时对时隙同步和帧同步的处理方法。仿真结果表明,该调制解调系统具有较好的抗干扰能力,可以满足通信系统的要求。     

Slot Routing as a Solution for Optically Transparent Scalable WDM Wide Area Networks*

All-optical Wavelength Division Multiplexing (WDM) backbones are believed to be a fundamental component in future high speed networks. Currently, the most pursued approach for Wide Area Networks (WANs) is wavelength routing, in which communication circuits are established between node pairs by means of lightpaths (paths of light) spanning one or more fiber-optic links. This approach has, however, two drawbacks. Since the number of wavelengths and links in a network is finite, not all node pairs can be connected via a dedicated lightpath directly. Consequently, some node pairs will communicate using a concatenation of lightpaths, which requires electronic switching of in transit information, loosing the advantages of optical transparency. Secondly, typically some form of (electronic) traffic grooming will be necessary to make efficient use of the fixed lightpath capacity. This paper proposes to design all-optical WANs using a novel approach, called photonic slot routing. With photonic slot routing, entire slots, each carrying multiple packets on distinct wavelengths, are switched transparently and individually, using available fast and wavelength non-sensitive devices. The advantage of using photonic slot routing is threefold. All node pairs in the network communicate all-optically. Traffic aggregation necessary to efficiently use the capacity of the wavelength channels is optically achieved. The solution is practical as it is based on proven optical technologies. In addition, through the use of wavelength non-sensitive devices the proposed WAN design yields intrinsic scalability in the number of wavelengths.     

一种新型的超宽带锥削缝隙天线设计

提出了一种微带线-槽线馈电形式的指数锥削缝隙天线,在辐射臂的外边缘引入半椭圆形缝隙来进一步提高天线低频段的定向性,获得了高增益和超宽带性能。利用HFSS12软件进行仿真,天线的极化方式为垂直极化,在2~13 GHz的工作频段内电压驻波比＜2,增益最高达11 dB,具备良好的定向性,仿真与实测结果基本吻合,表明该设计是有效、可行的。     

小型化北斗导航圆极化天线研究

结合多种贴片开槽方案,采用正交馈电圆极化激励方式,实现了一款北斗B3(1 268.52±10)MHz频点导航天线的小型化设计。通过电磁仿真软件HFSS对其结构参数进行优化仿真分析,数值结果表明:小型化天线在B3处的顶空增益为3.69 dB,低仰角增益≥-1.5 dB(≤±70°),反射损耗小于-10 dB的带宽为20 MHz,带内轴比≤2 dB。该小型化天线贴片尺寸相比同介电常数基板的同频点未开槽天线缩小72.8%,具有一定的应用前景。     

Concurrent Blind Channel Equalization in Impulsive Noise Environments

In some communication systems the trans- mitted signal is contaminated by impulsive noise with a non-Gaussian distribution. Non-Gaussian noise caused significant performance degradation to communication re- ceivers. The new constant modulus blind equalizer based on Fractional lower-order statistics of the equalizer input, which is defined as FLOS_CMA, is able to mitigate impul- sive channel noise while restoring the constant modulus character of the transmitted communication signal. How- ever, like the Constant modulus algorithm （CMA）, the steady-state Mean square error （]VISE） of the FLOS_CMA algorithm may not be sufficient low for the system to ob- tain adequate performance. This paper proposes a con- current equalizer, in which a Decision-directed least mean p norm （DD_LMP） equalizer operates cooperatively with a FLOS_CMA equalizer, controlled through a non-linear link. Simulation results using M-QAM and 8-PSK signal- ing have shown that besides the capability of compensating the phase offset, the proposed concurrent FLOS_CMA and DD_LMP blind equalizer has faster convergence rate and lower steady-state MSE than the FLOS_CMA approach.     

基于多普勒频偏估计的单帧图像低速运动目标检测方法

常用的图像域运动目标检测跟踪方法对虚警率较敏感,当虚警率较高时,目标检测跟踪的实时性受限。为了降低目标初始检测的虚警率,进而提高目标检测跟踪的实时性,该文提出一种基于多普勒频偏估计的单帧图像低速运动目标检测算法,通过发射多普勒不敏感的LFM脉冲对,忽略多普勒效应对成像结果的影响,但在图像域检测的同时,利用目标回波的多普勒频偏信息进行静目标和杂波亮点的剔除,基于单帧数据,减小运动目标检测的虚警率,实现单帧图像的运动目标检测,从而为目标跟踪奠定良好基础。该算法首先进行图像域的恒虚警检测,再利用宽带时域波束形成和复相关频率测量法,对检测亮点处的波束输出信号进行多普勒测频,仅通过单帧图像就可有效剔除静目标和杂波亮点。同时为了改善宽带时域波束形成的性能,利用2阶锥规划设计滤波器的系数,用9阶FIR滤波器实现了0.01倍采样点的小数时延,提高了多普勒频偏的估计精度。最后通过计算机仿真和水池试验验证了所提算法的有效性。     

正交矩形波导复合耦合槽特性分析

两个正交矩形波导公共宽边上偏离中心线的耦合斜槽称为复合耦合槽。考虑波导壁的厚度，根据等效原理和缝隙口面切向磁场的连续条件建立一对耦合积分方程，利用矩量法进行求解，给出复合耦合槽的谐振长度、散射参量随缝隙的倾角、偏离波导中心线距离的关系曲线     

基于HFC-CATV网的媒体访问控制协议

通过引入“组群 (cluster)”的概念 ,提出一种适用于HFC CATV网络的媒体访问控制 (MAC)协议的新结构模型 ,并分析该协议的工作原理和实现机制。     

新型宽带圆极化毫米波平面缝隙天线

研究了一种新型共面波导馈电的宽带圆极化毫米波平面缝隙天线.通过新型的短路微扰法实现了平面圆环形缝隙天线的单馈宽带圆极化,回波损耗(RL)≤-10dB时的实测阻抗带宽达到约20%,AR≤3时的实测轴比带宽约为21.2%,实测最大增益约为5.2dB.实测结果与ANSOFT HFSS软件仿真结果基本吻合,表明了设计的合理性.     

机载雷达平板裂缝天线的结构设计

介绍了机载雷达平板裂缝天线的基本原理、结构设计方法、材料的选择以及公差的确定等，并提出了今后的努力方向。