以改进影像逼真度为约束条件的变换域水印嵌入强度

在改进影像逼真度透明性指标约束下，对变换域数字水印各AC系数嵌入强度的上限进行了讨论，给出了满足改进影像逼真度约束的嵌入强度上限估计式．该结论及其推论可作为影像逼真度透明性指标的充分条件，用于确定数字水印的嵌入强度(max)的值对值△Fuv及嵌入版本数r等具体参数．实验结果证明了该结论的有效性．     

Dual-band CPW-fed folded-slot monopole antenna for RFID application

A folded slot with open end is introduced to achieve a dual-band coplanar waveguide (CPW)-fed monopole antenna for radio frequency identification (RFID) applications. The designed antenna, which, including the substrate, is only 32 mm in height and 20 mm in width, can operate simultaneously at the 2.45 and 5.8 GHz bands with -1.8 and 2.3 dBi gains, respectively. Its properties make the antenna suitable for RFID tags     

Improved LUT Technique for HPA Nonlinear Pre-Distortion in OFDM Systems

In this paper, we focus on the Look-up Table (LUT) technique for the compensation of HPA nonlinear distortion. An improved LUT method is proposed with better performance compared with conventional LUT technique in terms of convergence speeds, BER and total degradation (TD). It can get over 8 dB gain in out-of-band spectrum re-growth suppression and about 0.3 dB BER performance gain than conventional LUT technique with the same iteration times. Also, we propose an actual application of HPA with pre-distorter in OFDM transmitter. Ai Bo was born in Shannxi Province in China on February 7, 1974. He received a BSc. Degree from Engineering Institute of Armed Police Force in 1997, a Master and Dr. degree from Xidian University in 2002 and 2004 in China respectively, and now working as a post dr. in Dept. of E&E, state of key lab. on microwave and digital communications in Tsinghua University in China. He has once participated in the key research project on HDTV in TEEG (Team of Engineering Expert Group) of China. He is an editorial committee member of journal of “Computer Simulations”, “Information and Electronic Engineering”, an IEEE member and a senior member of Electronics Institute of China (CIE). He has published over 60 scientific papers in his research area till now. His current interests are the research and applications of OFDM techniques with emphasis on synchronization and HPA linearization techniques. Yang Zhi-Xing graduated from Tsinghua University, P.R. China in 1970. He is now a Professor and Deputy Director of State Key Lab. on Microwave and Digital Communication at the Department of Electronic Engineering and the Director of the DTV R&D Center in Tsinghua University. As a DTV technical expert for the Chinese government, Professor Yang has also been a member of the DTV standardization Committee of China and a leader of the DTV Standardization Harmonizing Group in Ministry of Information Industry of China. His major research interests include broadband information transmission technologies and DTV broadcasting systems. Pan Chang-Yong received the B.S. and M.S. degrees from the Department of Electronic Engineering in Tsinghua University, P.R. China, in 1996 and 1999, respectively. He is now an associate professor in the Department of Electronic Engineering and a member of the DTV R&D Center in Tsinghua University. His research interests are in the areas of broadband wireless transmission systems and satellite communications. Zhang Tao-Tao was born in Shandong Province in China in 1982, he received BSc. degree from Tsinghua University in 2004 and now pursing his Master degree in Dept. of E&E, state of key lab. on microwave and digital communications in Tsinghua University in China. His research interests is the power amplifier linearization techniques. Wang Yong was born in Shannxi Province in China in 1976. He received a BSc., a Master and a Dr. Degree from Xidian University in China in 1997, 2002 and 2005, respectively, and now is an associate professor in Xidian University. He has once participated in the key research project on HDTV in TEEG (Team of Engineering Expert Group) in China and is an IEEE Member. His interests are broadband multimedia communications. Ge Jian-Hua was born in September, 1961 in JiangSu Province in China. He received the B.Sc., Master and Ph.D. degree from Xidian University in 1982, 1985 and 1989, respectively. He is now the professor in both Xidian University in Xi’an and Shanghai Jiaotong University in Shanghai. He is the senior member of Chinese Electronics Institute. He has won lots of scientific and technical prizes in China and published many papers. His interests are transmission communications and web security.     

An improved method of MCXO

To improve the MCXO performance and simplify its structure, a new MCXO design method has been developed. Through deleting pulses of clock signal of a microcomputer and shifting its phase, the frequency-temperature stability of MCXO can be made satisfactory, and the DDS chip, which is often used in high performance MCXO, can be eliminated. Several different MCXOs have been made with this method and different performance specifications can be obtained. According to the simplicity, in a wide temperature range from -40 to +80 degrees C, the frequency-temperature stability of the MCXOs can be from +/-3x10(-8) to +/-2x10(-7).     

Correlation between 1/f noise and hFElong-term instability in silicon bipolar devices

Accelerated life tests with high-temperature storage and electric aging for n⁺-p-n silicon planar transistors were carried out. Current gain h_FE increases monotonously with time during the tests, and the h_FE drift is correlated with initial measured 1/f noise in the transistors, i.e. the drift amount significantly increases with the increase of noise level. The correlation coefficient of relative drift Δh_FE /h_FE and 1/f noise spectral density S_iB(f) is far larger than that of Δ h_FE/h_FE and initial DC parameters of the transistors. A quantitative theory model for the h _FE drift has been developed and explains the h _FE drift behavior in the tests, which suggests that the h _FE drift and 1/f noise can be attributed to the same physical origin, and both are caused by the modulation of the oxide traps near the Si-SiO₂ interface to Si surface recombination. 1/f noise measurement, therefore, may be used as a fast and nondestructive means to predict the long-term instability in bipolar transistors     

基于Java的VRML网络通信功能的实现

VRML是应用于Internet上的虚拟现实建模语言，本身不具有通信功能。该文扩展了其Script节点的功能，能够支持网络通信，使得VRML节点能够通过网络接收数据并能实时进行场景的渲染。由于VRML和Java都不依赖于平台，因此利用该方法搭建的应用系统也具有跨平台性。在不考虑速度的情况下，它可以将整个Internet改造成一个大的多用户应用系统。应用实例说明了该方案的可行性。     

Multiple models track algorithm for radar with high pulse-repetition frequency in frequency-modulated ranging mode

When the airborne fire control radar operates with the high pulse-repetition frequency (PRF) in the frequency-modulated ranging mode, the range measurement is ambiguous. Here, the problem of target range estimation and ambiguity resolving is converted to the problem of static multiple models estimation and decision. Frequency and pseudo-range measurements are used to update each model of the target with the probabilistic data association and tracking filter. The method to select the PRF used to detect the target is also suggested according to the state estimates of the survived models. Simulation results demonstrate the improved accuracy and convergence when compared with the conventional methods     

辅助激励源区域分解算法在电磁散射问题中的应用

针对电大问题，提出了一种基于辅助激励源的区域分解算法．首先把原求解区域划分成若干个子区域，显著地降低了原问题的规模和复杂度．在子区域分界面上引入虚拟的辅助激励源以交换信息，建立了相应的矩阵方程及其快速求解算法．一旦获得了辅助激励源，即可并行地计算各子区域内部的场．与传统算法相比，该算法有效地提高了计算效率和计算精度，降低了存储量；此外，它特别适合于求解具有几何重复性特征的结构，如栅格、光子带隙／电磁带隙、频率选择表面等．     

6H-SiC NMOS与PMOS温度特性分析

考虑界面态电荷高斯分布模型以及Poole-Frenkel效应,对SiC MOSFET补偿电流源模型进行了修正,分析了造成6H-SiC NMOS与PMOS器件补偿电流源变化的原因.结果表明:界面态电荷的非均匀分布造成由阈值电压漂移引起的输出漏电流改变量随温度的升高逐渐减小;漏衬界面缺陷是造成体漏电流较大(达到微安量级)的主要因素,且缺陷密度越大,该值随温度增长的速度越快.     

基于局部频谱连续细化的高精度频率估计算法

针对噪声环境下多普勒频率的快速、精确估计问题，提出了一种基于局部频谱连续细化的高精度频率估计算法．该算法先采用快速傅里叶变换对信号进行粗略的频谱估计，获取到感兴趣的窄带频谱范围后，再进行频域细化分析．由于在细化过程中采取时、频域两次加窗技术，将噪声抑制与频谱分析有机地结合在一起，提高了估计精度和频域稳定性，降低了计算量．