Iterative receivers for space-time block-coded OFDM systems indispersive fading channels

We consider the design of iterative receivers for space-time block-coded orthogonal frequency-division multiplexing (STBC-OFDM) systems in unknown wireless dispersive fading channels, with or without outer channel coding. First, we propose a maximum-likelihood (ML) receiver for STBC-OFDM systems based on the expectation-maximization (EM) algorithm. By assuming that the fading processes remain constant over the duration of one STBC code word and by exploiting the orthogonality property of the STBC as well as the OFDM modulation, we show that the EM-based receiver has a very low computational complexity and that the initialization of the EM receiver is based on the linear minimum mean square error (MMSE) channel estimate for both the pilot and the data transmission. Since the actual fading processes may vary within one STBC code word, we also analyze the effect of a modeling mismatch on the receiver performance and show both analytically and through simulations that the performance degradation due to such a mismatch is negligible for practical Doppler frequencies. We further propose a turbo receiver based on the maximum a posteriori-EM algorithm for STBC-OFDM systems with outer channel coding. Compared with the previous noniterative receiver employing a decision-directed linear channel estimator, the iterative receivers proposed here significantly improve the receiver performance and can approach the ML performance in typical wireless channels with very fast fading, at a reasonable computational complexity well suited for real-time implementations     

一种简易可靠的射频激光调制器

采用ＰＩＮ电调衰减器、ＴＬ４９４等元件组成了射频（ＲＦ）大功率ＣＯ２激光调制器，调制频率、占空比和调制度单独可调。给出了电路的工作原理和测试结果。     

自适应相位制中波同步广播及现场试验

在本试验中，采用智能同步广播激励器和ＣＣＴＶ传输的１ＭＨｚ标频，实现了中波同步广播同频保护率趋于０ｄＢ．并提出了自适应相位跟踪同步的概念。     

OSEK/VDX——汽车电子系统的开放式平台

介绍了当前在国际汽车工业界日益占据主导地位的汽车电子系统开放式平台--OSEK/VDX体系.详细地论述了这种体系的由来、运行机制和最新的发展动向,以及它对汽车电子技术发展的深远影响.     

回火处理对高碳冷拔钢丝强度和塑性的影响

研究了６５钢冷拔钢丝在５００℃不同时间回火时的抗拉强度和延伸率的变化。试验结果发现，在回火初期，抗拉强度首先增长，然后随口火时间的延长连续降低，而延伸率始终在增长，增长速度是先快后慢。这种行为可归因于第一内应力的消除和ε－碳化物在形变铁素体中的析出以及后来再结晶的发生。     

HfOxNy的场发射特性

用直流溅射和高温退火相结合的方法制备了HfOxNy薄膜并测试了其场发射性能,发现其具有较低的开启电场、较大的发射电流密度以及很好的发射稳定性.高压"锻炼"对提高HfOxNy场发射性能起着关键作用,这与高压"锻炼"下薄膜内部结构和表面性质的改变有关.对场发射机理的研究表明,HfOxNy的场发射符合经典的FN隧穿理论.     

Efficient 3-d capacitance extraction considering lossy substrate with multilayered green's function

An efficient algorithm for extraction of three-dimensional (3-D) capacitance on multilayered and lossy substrates is presented. The new algorithm presents a major improvement over the quasi-3-D approach used in a Green's function-based solver and takes into consideration the sidewalls of 3-D conductors. To improve the efficiency of the computation and the transformation of the Green's function, a nonuniform grid is adopted. The most computationally intensive part in the transformation of the Green's function is computed separately as technology-independent matrices Tk foremost. Once computed, Tk can be stored and used for any technology, thus the storage requirement and computational complexity are reduced from O (S/sup 2/) and O (S/sup 2/ log S/sup 2/), respectively, to just O [(log S/sub max/)/sup 2/]. Extensive tests have been performed to verify the new algorithm, and its accuracy has been established by comparing with other programs.     

YAG：Ce Phosphors for WLED via Nano-Pesudoboehmite Sol-Gel Route

The sub-micron sized YAG ： Ce phosphors were synthesized via a modified sol-gel method by peptizing nano-pesudoboehmite particulate. It is found that YAG phase from the dried gel powders appears at 1000 ℃ then the pure YAG phase exists at a relatively lower sintering temperature of 1400 ℃. The smaller sizes of phosphors in the ranges of 1 - 3 μm are obtained due to the contribution of seeding effects of nano-sized alumina particles to strengthen each step of the processes. Both the excitation and emission spectra of photoluminescence of the phosphor obtained at 1400 ℃ meet well with the spectroscopic requirements of the WLED phosphors.     

两种网络安全协议分析与比较

对SSL／TLS和IPSec两种网络安全协议进行了研究，分析了协议的目的、特点，比较了性能、实用性和应用，并给出可能的优化途径。